effect of shoulder presentation

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• Prenatal Care

Shoulder Presentation – All You Should Be Aware Of

When Does the Fetus Move in Birthing Position?

What is shoulder presentation, what is transverse lie, what is the frequency of shoulder presentation, what causes shoulder presentation, how is shoulder presentation diagnosed, complications of shoulder presentation, how is shoulder presentation managed.

Most doctors and midwives will recommend that you have a natural vaginal birth if you have a choice. However, there are certain complications that can sometimes present themselves and stop this from happening. Shoulder presentation is one such complication.

A baby will most likely begin to move into the birthing position latest by week 30 . She will have her head down and facing your spine, her body and face more inclined to one side and arms will be folded across the chest. Any other position is not normal.

This is an abnormal fetus position where the baby is in a transverse lie , causing the baby’s shoulder to be positioned to come out first if vaginal delivery is attempted. However, since this is very easy to diagnose, doctors will always recommend a C-Section and never even suggest attempting to deliver the child through normal vaginal delivery.

A transverse lie is a position where your baby is lying sideways with her head to one of your sides and her bottom at your other side. This position is considered normal before 26 gestational weeks.

Shoulder presentation takes place in 1 out of every 300 births and is commonly seen in premature and macerated babies. It is five times more likely to happen in a woman who has had children before than it is to occur in a first-time mother. Mothers carrying twins are also 40% more likely to have at least one baby in shoulder position.

Here are some reasons why a shoulder presentation can take place:

1. Contracted Pelvis

A very narrow pelvis in the mother can cause a shoulder presentation to occur.

2. Placenta Previa

A condition where the placenta covers the uterus opening, either completely or partially. This makes it difficult for your baby’s head to enter the pelvic brim.

3. Intra-Uterine Fetal Death

There are times when the fetus dies inside the womb, and when this happens, the muscle tone starts to degenerate, which results in the fetus falling lower into the uterus.

4. Lax Abnormal Musculature

Women who have had multiple pregnancies may have more relaxed uterine and abdominal muscles. This will make their ability to keep the baby in a normal position very difficult.

5. Uterine Over Distension

There are many reasons why a uterus can become enlarged. Some of these include a large baby, polyhydramnios , multiple pregnancies and others. A uterus that is too large very often leads to shoulder presentation.

6. Polyhydramnios

A very large amount of amniotic fluid that is present in the uterus is known as polyhydramnios. This causes the fetus to be able to move very freely in the uterus and will lead to shoulder presentation.

7. Uterine Abnormalities

There are different abnormalities in the uterus that can cause your baby to move into shoulder presentation. Some of these are the bicornuate uterus, a sub-septate uterus and even a large fibroid  uterus .

Here is how Shoulder presentation diagnosed:

• The top of the mother’s uterus to the top of the pelvic bone is called a fundus. The height of the fundus is an indicator of whether or not the baby is in the shoulder presentation.
• The uterus becomes broader.
• The mother can feel the baby’s head on one abdominal side.
• If shoulder presentation takes place, arms prolapse will cause the baby’s arm to be seen outside the vagina.
• During a vaginal examination, the doctor will be able to feel the babies ribs.

If your doctor identifies that you have shoulder presentation before you go into labour, he will opt for a C-Section instead. If there is a case of neglected shoulder presentation and it is only identified after you go into labour, it becomes very dangerous, and you face many complications. Here are some of the complications that can occur:

1. Cord Prolapse

When the umbilical cord comes out before the fetus does, it is called a cord prolapse and is very dangerous as it can cause the baby’s heart rate to drop, cause changes in blood pressure and even result in brain damage or death of the baby.

2. Ruptured Uterus

The myometrial wall is the middle layer of the wall of the uterine. The breach of this layer during childbirth is a rupture in the uterus, and it is very dangerous for both mother and child.

3. Fetal Hypoxia

When your baby doesn’t get enough oxygen, it will lead to suffocation, and if the necessary measures are not taken, it will result in death.

4. Obstructed Labour

Though contractions are taking place, the baby is not able to come through the birth canal as there is something blocking the way. Failure to diagnose and remedy this condition is a major reason why both mother and child die during childbirth.

5. Trauma to Prolapsed Arm

If there is a prolapsed arm, there is a higher chance that it will be injured or damaged. This injury may be severe and could last for a lifetime.

Here is how Shoulder presentation is managed:

1. C-Section

The first choice for doctors who have a case of shoulder presentation is a C-Section. This is the safest method that ensures the safety of both mother and child.

2. External Cephalic Version

In this procedure, your baby’s heartbeat will be monitored, and you will be given medication through an IV to ensure a relaxed uterus. Your doctor will then place her hands on the outside of your stomach and attempt to turn your baby into the correct position. This is done only before labour starts.

3. Internal Podalic Version

This is only used in the case of twins, where the second twin will need to be moved into a breech position and then extracted.

Though it sounds scary, if you keep a careful track of your baby’s position in the weeks before delivery, you will be able to identify and rectify the problem before it becomes serious. Exercising throughout your pregnancy will be very helpful in ensuring that your baby gets into the correct position for labour.

Also Read:  When Does a Baby Turn Head Down During Pregnancy?

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Shoulder Presentation (Transverse or Oblique lie)

• The longitudinal axis of the foetus does not coincide with that of the mother.
• These are the most hazardous malpresentations due to mechanical difficulties that occur during labour .
• The oblique lie which is deviation of the head or the breech to one iliac fossa, is less hazardous as correction to a longitudinal lie is more feasible.

3-4% during the last quarter of pregnancy but 0.5% by the time labour commences.

Factors that

• change the shape of pelvis, uterus or foetus,
• allow free mobility of the foetus or
• Contracted pelvis.           
• Lax abdominal wall.
• Uterine causes as bicornuate, subseptate and fibroid uterus.
• Pelvic masses as ovarian tumours.
• Multiple pregnancy.     
• Polyhydramnios.    
• Placenta praevia.           
• Prematurity.
• Intrauterine foetal death.

The scapula is the denominator

• Left scapulo-anterior.
• Right scapulo-anterior.
• Right scapulo-posterior.
• Left scapulo-posterior.

Scapulo-anterior are more common than scapulo-posterior as the concavity of the front of the foetus tends to fit with the convexity of the maternal spines.

During pregnancy

• The abdomen is broader from side to side.
• Fundal level: lower than that corresponds to the period of amenorrhoea.
• Fundal grip: The fundus feels empty.
• Umbilical grip: The head is felt on one side while the breech one the other. In transverse lie, they are at the same level, while in oblique lie one pole, usually the head as it is heavier, is in a lower level i.e. in the iliac fossa.
• First pelvic grip: Empty lower uterine segment.
• FHS are best heard on one side of the umbilicus towards the foetal head.
• Confirms the diagnosis and may identify the cause as multiple pregnancy or placenta praevia.

During labour

In addition to the previous findings, vaginal examination reveals:

• The presenting part is high.
• Membranes are bulging.
• Premature rupture of membranes with prolapsed arm or cord is common. The dorsum of the supinated hand points to the foetal back and the thumb towards the head. The right hand of the foetus can be shacked, correctly by the right hand of the obstetrician and the left hand by the left one.
• When the cervix is sufficiently dilated particularly after rupture of the membranes, the scapula, acromion, clavicle, ribs and axilla can be felt.

Mechanism of Labour

As a rule no mechanism of labour should be anticipated in transverse lie and labour is obstructed.

If a patient is allowed to progress in labour with a neglected or unrecognized transverse lie, one of the following may occur:

• This is the usual and most common outcome.
• The lower uterine segment thins and ultimately ruptures.
• The foetus becomes hyperflexed, placental circulation is impaired, cord is prolapsed and compressed leading to foetal asphyxia and death.
• Rarely the foetal lie may be corrected by the splinting effect of the contracted uterine muscles so that the head presents.
• Rarely, by similar process the breech may come to present.
• Very rarely, if the foetus is very small or dead and macerated, the shoulder may be forced through the pelvis followed by the head and trunk.
• Very rarely, the head is retained above the pelvic brim, the neck greatly elongates, the breech descends followed by the trunk and the after -coming head, i.e. spontaneous version occurs in the pelvic cavity.

External cephalic version

Can be done in late pregnancy or even early in labour if the membranes are intact and vaginal delivery is feasible. In early labour, if version succeeded apply abdominal binder and rupture the membranes as if there are uterine contractions.

Internal podalic version

It is mainly indicated in 2nd twin of transverse lie and followed by breech extraction.

Prerequisites:

• General or epidural anaesthesia.
• Fully dilated cervix.
• Intact membranes or just ruptured.

Caesarean section

• It is the best and safest method of management in nearly all cases of persistent transverse or oblique lie even if the baby is dead.
• As rupture of membranes carries the risk of cord prolapse, an elective caesarean section should be planned before labour commences.

Neglected (Impacted) shoulder

Clinical picture (impending rupture uterus)

• Exhaustion and distress of the mother.
• Shoulder is impacted may be with prolapsed arm and / or cord.
• Membranes are ruptured since a time.
• Liquor is drained.
• The uterus is tonically contracted.
• The foetus is severely distressed or dead.
• Caesarean section is the safest procedure even if the baby is dead. A classical or low vertical incision in the uterus facilitates extraction of the foetus as a breech in such a condition.
• Any other manipulations will lead eventually to rupture uterus so they are contraindicated.

UNSTABLE LIE

A foetus which changes its lie frequently from transverse to oblique to longitudinal.

• Polyhydramnios.
• Prematurity and IUFD.
• Contracted pelvis.
• Placenta praevia.
• Pelvic tumours. 
• Multiparae with a lax uterus and abdominal wall.
• Can be done whenever the woman is examined but in majority of cases it will recur so it is better to defer it until full term (37-40 weeks).
• After correcting the foetal lie to longitudinal, apply an abdominal binder, start oxytocin infusion and do amniotomy when the uterine contractions started and the presenting part is well settled into the pelvic brim.
• Failure of external version .
• Some do it selectively in cases discovered after 40 weeks’ gestation.
• Shoulder dystocia : Guidelines, reviews

7.6 Transverse lie and shoulder presentation

A transverse lie constitutes an absolute foeto-pelvic disproportion, and vaginal delivery is impossible.

This is an obstetric emergency, because labour is obstructed and there is a risk of uterine rupture and foetal distress.

7.6.1 Diagnosis

• The uterus is very wide: the transverse axis is virtually equivalent to the longitudinal axis; fundal height is less than 30 cm near term.
• On examination: head in one side, breech in the other (Figures 7.1a and 7.1b). Vaginal examination reveals a nearly empty true pelvis or a shoulder with—sometimes—an arm prolapsing from the vagina (Figure 7.1c).

Figures 7.1 - Transverse lie and shoulder presentation

7.6.2 Possible causes

• Grand multiparity (5 deliveries or more)
• Uterine malformation

Twin pregnancy

• Prematurity
• Placenta praevia
• Foeto-pelvic disproportion

7.6.3 Management

This diagnosis should be made before labour begins, at the last prenatal visit before the birth.

At the end of pregnancy

Singleton pregnancy.

• External version 4 to 6 weeks before delivery, in a CEmONC facility ( Section 7.7 ).
• If this fails, delivery should be carried out by caesarean section, either planned or at the beginning of labour (Chapter 6, Section 6.4.1 ).
• External version is contra-indicated.
• If the first twin is in a transverse lie (unusual): schedule a caesarean section.
• If the second twin is in a transverse lie: there is no indication for caesarean section, but plan delivery in a CEmONC facility so that it can be performed if necessary. Deliver the first twin and then, assess the foetal position and give a few minutes for the second twin to adopt a longitudinal lie. If the second twin stays in a transverse lie, and depending on the experience of the operator, perform external version ( Section 7.7 ) and/or internal version ( Section 7.8 ) on the second twin.

During labour, in a CEmONC facility

Foetus alive and membranes intact.

• Gentle external version, between two contractions, as early as possible, then proceed as with normal delivery.
• If this fails: caesarean section.

Foetus alive and membranes ruptured

• Multipara with relaxed uterus and mobile foetus, and an experienced operator: internal version and total breech extraction.
• Primipara, or tight uterus, or immobile foetus, or engaged arm, or scarred uterus or insufficiently-experienced operator: caesarean section.
• Incomplete dilation: caesarean section.

Caesarean section can be difficult due to uterine retraction. Vertical hysterotomy is preferable. To perform extraction, grasp a foot in the fundus (equivalent to a total breech extraction, but by caesarean section).

Foetus dead

Embryotomy for transverse lie (Chapter 9, Section 9.7.7 ).

During labour, in remote settings where surgery is not available

Try to refer the patient to a CEmONC facility. If not feasible:

• Attempt external version as early as possible.
• If this fails, wait for complete dilation.
• Perform an external version ( Section 7.7 ) combined with an internal version ( Section 7.8 ), possibly placing the woman in various positions (Trendelenburg or knee-chest).
• Put the woman into the knee-chest position.
• Between contractions, push the foetus back and try to engage his head.
• Vacuum extraction (Chapter 5, Section 5.6.1 ) and symphysiotomy (Chapter 5, Section 5.7 ) at the slightest difficulty.
• Incomplete dilation: Trendelenburg position and watchful waiting until complete dilation.

Try to refer the patient, even if referral takes some time. If not feasible, embryotomy for transverse lie (Chapter 9, Section 9.7.7 ).

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• Rotator cuff injury

Types of rotator cuff injuries

Rotator cuff injuries can range in severity from simple inflammation to complete tendon tears.

The rotator cuff is a group of muscles and tendons that surround the shoulder joint, keeping the head of the upper arm bone firmly within the shallow socket of the shoulder. A rotator cuff injury can cause a dull ache in the shoulder that worsens at night.

Rotator cuff injuries are common and increase with age. These injuries may occur earlier in people who have jobs that require repeatedly performing overhead motions, such as painters and carpenters.

Physical therapy exercises can improve flexibility and strength of the muscles surrounding the shoulder joint. For many people with rotator cuff problems, these exercises are all that's needed to manage their symptoms.

Sometimes, rotator cuff tears may occur from a single injury. In those circumstances, people should seek medical advice quickly because they might need surgery.

Video: Rotator cuff damage

The rotator cuff is a group of muscles and tendons that hold the shoulder joint in place and allow you to move your arm and shoulder. Problems occur when part of the rotator cuff becomes irritated or damaged. This can result in pain, weakness and reduced range of motion.

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The pain associated with a rotator cuff injury may:

• Be described as a dull ache deep in the shoulder
• Disturb sleep
• Make it difficult to comb your hair or reach behind your back
• Be accompanied by arm weakness

Some rotator cuff injuries don't cause pain.

When to see a doctor

Your family doctor can evaluate short-term shoulder pain. See your doctor right away if you have immediate weakness in your arm after an injury.

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Rotator cuff injuries are most often caused by progressive wear and tear of the tendon tissue over time. Repetitive overhead activity or prolonged bouts of heavy lifting can irritate or damage the tendon. The rotator cuff can also be injured in a single incident during falls or accidents.

Risk factors

The following factors may increase the risk of having a rotator cuff injury:

• Age. The risk of a rotator cuff injury increases with age. Rotator cuff tears are most common in people older than 60.
• Some occupations. Jobs that require repetitive overhead arm motions, such as carpentry or house painting, can damage the rotator cuff over time.
• Certain sports. Some types of rotator cuff injuries are more common in people who participate in sports like baseball, tennis and weight-lifting.
• Family history. There may be a genetic component involved with rotator cuff injuries as they appear to occur more commonly in certain families.

Complications

Without treatment, rotator cuff problems may lead to permanent loss of motion or weakness of the shoulder joint.

Rotator cuff injury care at Mayo Clinic

• Giangarra CE, et al., eds. Rotator cuff repair. In: Clinical Orthopaedic Rehabilitation: A Team Approach. 4th ed. Elsevier; 2018. https://www.clinicalkey.com. Accessed Jan. 4, 2022.
• Rotator cuff tears. American Academy of Orthopaedic Surgeons. https://orthoinfo.aaos.org/en/diseases--conditions/rotator-cuff-tears. Accessed Jan. 4, 2022.
• Ferri FF. Rotator cuff disease. In: Ferri's Clinical Advisor 2022. Elsevier; 2022. https://www.clinicalkey.com. Accessed Jan. 4, 2022.
• Simons SM, et al. Presentation and diagnosis of rotator cuff tears. https://www.uptodate.com/contents/search. Accessed Jan. 4, 2022.
• Martin SD, et al. Management of rotator cuff tears. https://www.uptodate.com/contents/search. Accessed Jan. 4, 2022.
• AskMayoExpert. Rotator cuff surgery. Mayo Clinic; 2020.
• Azar FM, et al. Campbell's Operative Orthopaedics. 14th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed Jan. 4, 2022.
• Krych AJ (expert opinion). Mayo Clinic. Jan. 12, 2022.
• Stewart RK, et al. Outcomes of subacromial balloon spacer implantation for massive and irreparable rotator cuff tears: A systematic review. The Orthopaedic Journal of Sports Medicine. 2019; doi:10.1177/2325967119875717.
• Braswell-Pickering EA. Allscripts EPSi. Mayo Clinic. Nov. 3, 2021.
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• Cortisone shots
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Malpresentation, Malposition, Cephalopelvic Disproportion and Obstetric Procedures

26 Malpresentation, Malposition, Cephalopelvic Disproportion and Obstetric Procedures Kim Hinshaw 1,2 and Sabaratnam Arulkumaran 3 1 Sunderland Royal Hospital, Sunderland, UK 2 University of Sunderland, Sunderland, UK 3 St George’s University of London, London, UK Malpresentation, malposition and cephalopelvic disproportion Definitions The vertex is a diamond‐shaped area on the fetal skull bounded by the anterior and posterior fontanelles and laterally by the parietal eminences. Vertex presentation is found in 95% of labours at term and is associated with flexion of the fetal head. Breech, brow, face and shoulder presentations constitute the remaining 5% and are collectively known as malpresentations . Their aetiology is usually unknown, but associations include macrosomia, multiparity, polyhydramnios, multiple pregnancy, placenta praevia, preterm labour, and anomalies of the uterus or pelvis (congenital or acquired, e.g. lower segment fibroids) and more rarely the fetus. The denominator is a laterally sited bony eminence on the presenting part (‘occiput’ for vertex presentation, ‘mentum’ for face, ‘acromium’ for shoulder and ‘sacrum’ for breech). The position of the presenting part is defined by the relationship of the denominator to the maternal bony pelvis. The vertex enters the pelvis in the occipito‐transverse (OT) position and during descent rotates to an occipito‐anterior (OA) position in 90% of cases. This position is associated with a well‐flexed head, allowing the smallest anteroposterior (suboccipito‐bregmatic) and lateral (biparietal) diameters to pass through the pelvis (both 9.5 cm). Malposition occurs when the occiput remains in a tranverse or posterior position as labour progresses. Persistent malposition results in deflexion with a larger anteroposterior diameter presenting (occipito‐frontal 11.5 cm). It is associated with increasing degrees of anterior or posterior asynclitism , with one of the parietal bones preceding the sagittal suture (in posterior asynclitism, the posterior parietal bone leads; Fig. 26.1 ). Significant degrees of asynclitism can result in labour dystocia and a higher risk of operative delivery [1] . Fig. 26.1 Posterior asynclitism of the vertex: posterior parietal bone presenting below the sagittal suture. In most cases, flexion occurs as the vertex descends onto the pelvic floor, leading to correction of the malposition and a high chance of spontaneous delivery. The level of the presenting part should be critically assessed as labour progresses. On abdominal examination, the head should descend until it is no more than 1/5 palpable in the late first stage. On vaginal examination the presenting part is assessed relative to the level of the ischial spines. Care must be taken to assess the level using the lowest bony part . Malposition is associated with increased moulding of the fetal skull and a large caput succedaneum, which may give false reassurance about the true degree of descent. In modern obstetric practice, operative vaginal delivery is not attempted if the leading edge of the skull is above the ischial spines (i.e. above ‘0’ station; Fig. 26.2 ). Fig. 26.2 Level of the presenting part relative to the ischial spines. Malpresentations Breech presentation The incidence of breech presentation varies according to gestation: 20% at 30 weeks falling to 4% by term. The aetiology of most breech presentations at term is unclear but known factors to consider include placenta praevia, polyhydramnios, bicornuate uterus, fibroids and, rarely, spina bifida or hydrocephaly. Types of breech presentation Between 50 and 70% of breech presentations manifest with hips flexed and knees extended (extended breech) Complete (or flexed) breech is more common in multiparous women and constitutes 5–10% at term (hips and knees flexed; Fig. 26.3 ). Incomplete or footling breech (10–30%) presents with one or both hips extended, or one or both feet presenting and is most strongly assoiated with cord prolapse (5–10%). Knee presentation is rare. Fig. 26.3 The common types of breech presentation. Clinical diagnosis may miss up to 20% of breech presentations, relying on identifying the head as a distinct hard spherical hard mass to one or other side under the hypochondrium which distinctly ‘ballots’. In such cases the breech is said to feel broader and an old adage reminds us: ‘Beware the deeply engaged head – it is probably a breech!’ Auscultation may locate the fetal heart above the maternal umbilicus and ultrasound confirmation should be considered. Antenatal management If breech presentation is suspected at 36 weeks, ultrasound assessment is recommended as it allows a comprehensive assessment of the type of breech, placental site, estimated fetal weight, confirmation of normality and exclusion of nuchal cord or hyperextension of the fetal neck. External cephalic version (ECV) is encouraged after 36 or more weeks as the chance of spontaneous version to cephalic presentation after 37 weeks is only 8%. Absolute contraindications are relatively few but include placenta praevia, bleeding within the last 7 days, abnormal cardiotocography (CTG), major uterine anomaly, ruptured membranes and multiple pregnancy [2] . Couples should receive counselling about the procedure and its success rates and complications, and the subsequent management of persistent breech presentation. Tocolysis increases the likelihood of success, with average rates of 50% (range 30–80%). Women should be made aware that even with a cephalic presentation following ECV, labour is still associated with a higher rate of obstetric intervention than when ECV has not been required. ECV should be performed in a setting where urgent caesarean section (CS) is available in case of fetal compromise during or soon after ECV. CTG for 30–40 min prior to and after ECV should provide confirmation of fetal health. The chance of success is greater with multiparity, flexed breech presentation and an adequate liquor volume. The use of moxibustion at 33–35 weeks, in combination with acupuncture, may reduce the numbers of births by CS. Training specialist midwives is potentially cost‐efficient with success rates comparable to consultant‐led services (51–66%) [3] . The first step in ECV involves disengaging the breech by moving the fetus up and away from the pelvis, shifting it to a sideways position, followed by a forward somersault to move the head to the lower pole; if this fails a backward somersault can be tried. The need for emergency delivery by CS because of suspected fetal compromise is estimated to be 0.5%. Mothers who are rhesus‐negative should have a Kleihauer–Betke test after the procedure and receive anti‐D. If ECV is unsuccessful, women who are keen to avoid CS may be offered a repeat attempt under neuraxial blockade. This increases the chances of success (58.4% vs. 43.1%; relative risk, RR 1.44, 95% CI 1.27–1.64) and reduces the incidence of CS (46.0% vs. 55.3%; RR 0.83, 95% CI 0.71–0.97) [4] . Otherwise appropriate counselling about the options of elective CS or assisted vaginal breech delivery should be offered. Deciding mode of delivery Despite increasing evidence supporting elective CS for breech delivery at term, controversy and debate continue among professional groups. Breech presentation at term diagnosed antenatally . The Term Breech Trial is the largest published randomized controlled trial where the primary outcome (serious perinatal morbidity and mortality) favoured planned CS over planned vaginal birth: 17/1039 (1.6%) versus 50/1039 (5.0%; RR 0.33, 95% CI 0.19–0.56; P <0.0001) [5] . The trial concluded that ‘planned CS is better than planned VB for the term fetus in the breech presentation; serious maternal complications are similar between the groups’. This has significantly changed practice in many countries despite continuing debate and criticism about the trial design and intepretation of outcomes. However, the latest systematic review has confirmed a significant increased perinatal risk associated with planned vaginal birth [6] . Breech at term diagnosed in labour and preterm breech delivery . Observational trials of term breech ‘undiagnosed’ until presentation in labour confirm that this group has a high vaginal delivery rate with relatively low perinatal morbidity. In a similar vein, the evidence to guide best practice for delivery of the preterm breech remains equivocal, decisions often being based on individual interpretation of the data and local custom and practice. Conducting a vaginal breech delivery For women who wish to deliver vaginally, antenatal selection aims to ensure optimal outcome for mother and baby but remains relatively subjective. Women with frank and complete breech presentations (fetal weight <4000 g) encounter minimal problems, while those with footling breech are advised elective CS because of the increased risk of cord prolapse. CT or X‐ray pelvimetry do not appear to improve outcome. Spontaneous onset of labour is preferred and labour management is similar to vertex presentation. Successful outcome depends on a normal rate of cervical dilatation, descent of the breech and a normal fetal heart rate (FHR) pattern. Where progress of labour is poor and uterine contractions are inadequate, oxytocin augmentation can be used juidiciously with early resort to emergency CS if progress remains slow (<0.5 cm/hour), particularly in the late first stage. Epidural anaesthesia prevents bearing down before the cervix is fully dilated and is particularly important for labour with a preterm breech, when there is a real risk of head entrapment in the incompletely dilated cervix if pushing commences too early. For all breech labours, the mother should be encouraged to avoid bearing down for as long as possible. It is best to wait until the anterior buttock and anus of the baby are in view over the mother’s perineum, with no retraction between contractions. Classically, the mother’s legs are supported in the lithotomy position (the alternative upright breech technique is described later). Primigravidae will usually require an episiotomy with appropriate analgesia, although multigravidae can be assessed as the perineum stretches up. The buttocks deliver in the sacro‐tranverse position. The mother should be encouraged to push with contractions, aiming for an unassisted delivery up to and beyond the level of the umbilicus. There is no need to pull down a loop of cord. The accoucheur should sit with hands ready, but resting on their own legs. Assistance is only required if the legs do not deliver. Gentle abduction of the fetal thigh whilst hyperflexing the hip, followed by flexing the lower leg at the knee will release the foot and leg ( Fig. 26.4 ). Fig. 26.4 Delivery of extended legs by gentle abduction of the thigh with hyperflexion at the hip, followed by flexion at the knee: (a) right leg; (b) left leg. When the scapulae are visible with the arms flexed in front of the chest, sweep each arm around the side of the fetal chest to deliver using a finger placed along the length of the humerus. If the scapulae are not easily seen or if the arms are not easily reached, they may be extended above the shoulders. This can be resolved using the Løvset manoeuvre. Hold the baby by wrapping both hands around the bony pelvis, taking care not to apply pressure to the soft fetal abdomen. Rotate the baby 180° to bring the posterior shoulder to the front, i.e. to lie anteriorly ( Fig. 26.5 a). Complete delivery of the anterior arm by gently flexing the baby laterally downwards towards the floor; the arm will deliver easily from under the pubic ramus ( Fig. 26.5 b). Repeat the 180° rotation in the opposite direction, bringing the posterior shoulder to the front, then flex the baby laterally downwards to deliver the second arm. Fig. 26.5 Løvset’s manoeuvre for extended arms: (a) rotation to bring the posterior (left) arm to the front followed by (b) delivery of the left arm (now anterior) from under the pubic ramus. Nuchal displacement (an arm trapped behind the fetal neck) is rare. If the left arm is trapped, the baby will need to be rotated in a clockwise direction to ‘unwrap’ the arm so that it can be reached. If the right arm is involved, anticlockwise rotation is needed. Allow the head to descend into the pelvis, assisted by the weight of the fetus until the nape of the neck is visible under the symphysis pubis. Ensure slow controlled delivery of the head using one of four methods. Mauriceau–Smellie–Veit manoeuvre: two fingers are placed on the maxilla, lying the baby along the forearm. Hook index and fourth fingers of the other hand over the shoulders with the middle finger on the occiput to aid flexion. Apply traction to the shoulders with an assistant applying suprapubic pressure if needed ( Fig. 26.6 ). Burns–Marshall method: grasp the feet, apply gentle traction and swing the baby gently up and over the maternal abdomen until the mouth and nose appear. Forceps are applied to the head from below, with an assistant supporting the baby’s body in the horizontal plane avoiding hyperextension. Kielland’s forceps can be useful as they lack a pelvic curve. Apply traction, bringing the forceps upwards as the mouth and nose appear. The upright breech technique is increasingly popular in midwifery deliveries. Mobility is encouraged with delivery on all fours, sitting (on a birth stool), kneeling, standing or lying in a lateral position. Delivery is spontaneous with no manual assistance in 70% of cases and a reduced incidence of perineal trauma (14.9%). Fig. 26.6 Delivery of the head using the Mauriceau–Smellie–Veit manoeuvre assisted by suprapubic pressure. Entrapment of the aftercoming head This rare complication occurs in two situations. If the fetal back is allowed to rotate posteriorly, the chin may be trapped behind the symphysis pubis. Correction requires difficult internal manipulation to free the chin by pushing it laterally. McRoberts’ manoeuvre and suprapubic pressure may help. Symphysiotomy is a last resort that can increase the available pelvic diameters. In preterm delivery, the body can slip through an incompletely dilated cervix, with resulting head entrapment. If the cervix cannot be ‘stretched up’ digitally, surgical incisions are made in the cervical ring at 2, 6 and 10 o’clock (Dührssen incisions). Head entrapment in the contractile upper segment can occur at CS. Acute tocolysis and/or extension of the uterine incision may be required to release the head. Women should be intimately involved in decisions about mode of breech delivery and the available evidence presented appropriately. A senior midwife or a doctor experienced in assisted breech delivery must be present. As vaginal breech deliveries decline, developing expertise in breech delivery now relies on simulation training and experience of breech delivery at CS. Summary box 26.1 ECV has a high success rate (51–66%) and should be encouraged. Ensure the fetal back does not rotate posteriorly during breech delivery. The most experienced accoucheur available should directly supervise vaginal breech delivery. Brow presentation Brow presentation occurs in 1 in 1500–3000 deliveries. The head is partially deflexed (extended), with the largest diameter of the head presenting (mento‐vertical, 13.5 cm). The forehead is the lowest presenting part but diagnosis relies on identifying the prominent orbital ridges lying laterally. The eyeballs and nasal bridge may just be palpated lateral to the orbital ridges. Position is defined using the frontal bone as the denominator (i.e. ‘fronto‐‘). Persistent brow presentation results in true disproportion, but when diagnosed in early labour careful assessment of progress is appropriate. Flexion to vertex or further extension to face presentation occurs in 50% and vaginal delivery is possible. Cautious augmentation with oxytocin should only be considered in nulliparous patients for delay in the early active phase of labour. If brow presentation persists, emergency CS is recommended. Vaginal delivery of a brow presentation is possible in extreme prematurity. Preterm labour is best managed in the same way as term labour, with delivery by CS if progress slows or arrests. Cord prolapse is more common and, though rare, uterine rupture can occur in neglected labour or with injudicious use of oxytocin. For this reason labour should not be augmented in multigravid patients with a confirmed brow presentation if progress is inadequate. Face presentation Face presentation occurs in 1 in 500–800 labours. The general causes of malpresentation apply for face presentation, but fetal anomalies (neck or thyroid masses, hydrocephalus and anencephaly) should be excluded. The fetal head is hyperextended and the occiput may be felt higher and more prominently on the same side as the fetal spine. However, face presentation is rarely diagnosed antenatally. On vaginal examination in labour, diagnosis relies on feeling the mouth, malar bones, nose and orbital ridges. Position is defined using the chin or mentum as the denominator. The mouth and malar bones form a triangle which can help differentiate face presentation from breech, where the anus lies in a straight line between the prominent ischial tuberosities. Face presentation is often first diagnosed in late labour. The submento‐bregmatic diameter (9.5 cm) is compatible with normal delivery but only with the fetus in a mento‐anterior position (60%) ( Fig. 26.7 ). The same diameter presents with a persistent mento‐posterior position (25%) but this cannot deliver vaginally as the fetal neck is maximally extended. Fetal scalp clips, blood sampling and vacuum extraction are absolutely contraindicated. Forceps delivery from low cavity can be undertaken for mento‐anterior or mento‐lateral positions by an experienced accoucheur but CS may still be required when descent is poor. Fig. 26.7 The anteroposterior submento‐bregmatic diameter of face presentation. Shoulder presentation The incidence of shoulder presentation at term is 1 in 200 and is found with a transverse or oblique lie. Multiparity (uterine laxity) and prematurity are common associations and placenta praevia must be excluded. The lie will usually correct spontaneously before labour as uterine tone increases, although prolapse of the cord or arm is a significant risk if membranes rupture early. For this reason, hospital admission from 38 weeks is recommended for persistent transverse lie. External version can be offered (and may also be considered for transverse lie presenting in very early labour). On vaginal examination, the denominator is the acromium but defining position can be difficult. If membrane rupture occurs at term with the uterus actively contracting, delivery by CS should be undertaken promptly to avoid an impacted transverse lie. If the uterus is found to be moulded around the fetus, a classical CS is recommended to avoid both fetal and maternal trauma. In cases of intrauterine death with a transverse lie, spontaneous vaginal delivery is possible for early preterm fetuses by extreme flexion of the body (spontaneous evolution). However, CS will usually be required beyond mid‐trimester, although a lower segment approach may be used. Malposition and cephalopelvic disproportion In higher‐income countries, cephalopelvic disproportion is usually ‘relative’ and due to persistent malposition or relative fetal size (macrosomia). Classically we consider these problems with regard to the passage, the passenger or the powers, either alone or in combination. The passage Absolute disproportion due to a contracted pelvis is now rare in higher‐income countries unless caused by severe pelvic trauma and this should be known before the onset of labour. Caldwell and Moloy described four types of pelvis: gynaecoid (ovoid inlet, widest transversely, 50%), anthropoid (ovoid inlet, widest anteroposterior, 25%), android (heart‐shaped inlet, funnel‐shaped, 20%) and platypelloid (flattened gynaecoid, 3%). These can influence labour outcome but as pelvimetry is rarely used and clinical assessment of pelvic shape is inaccurate, this rarely influences clinical mangement in labour. The anthropoid pelvis is associated with a higher risk of persistent occipito‐posterior (OP) position and relative disproportion. The passenger and OP malposition Fetal anomalies (e.g. hydrocephalus, ascites) where disproportion may be a problem in labour are usually assessed antenatally and delivery by elective CS considered. Fetal macrosomia is increasing, related to the rising body mass index (BMI) in many pregnant populations. The evidence for inducing non‐diabetic women with an estimated fetal weight above the 90th centile (or >4000 g) in order to reduce cephalopelvic disproportion remains equivocal. Malposition is an increasingly common cause of disproportion and may be related to a sedentary lifestyle. OP position is associated with deflexion and/or asynclitism with a larger diameter presenting. Optimal uterine activity will correct the malposition in 75% of cases. Flexion occurs as the occiput reaches the pelvic floor with long rotation through 135° to an OA position and a high chance of normal delivery. Moulding of the fetal skull and pelvic elasticity (related to changes at the symphysis pubis) are dynamic changes that facilitate progress in labour and delivery. Short rotation through 45° to direct OP can result in spontaneous ‘face to pubes’ delivery, although episiotomy may be required to allow the occiput to deliver. Persistent OP position occurs in up to 25% of cases and is associated with further deflexion. The risk of assisted delivery is high because of relative disproportion as the presenting skull diameters increase. Delivery in the OP position from mid‐cavity (0 to +2 station) requires critical assessment to decide whether delivery should be attempted vaginally or abdominally and is discussed in later sections. The powers Disproportion is intimately related to dystocia and failure to progress in labour. National Institute for Health and Care Excellence (NICE) guidelines recommend that first stage delay is suspected with cervical dilatation of less than 2 cm in 4 hours when forewater amniotomy should be offered. Delay is confirmed if progress is less than 1 cm 2 hours later and oxytocin augmentation should be offered [6] . This shortens labour but does not affect operative delivery rates. High‐dose oxytocin may reduce CS rates but larger trials are required before these regimens are used routinely. The decision to use oxytocin in labour arrest in multigravid patients must only be made by the most senior obstetrician and should always be approached with extreme caution as uterine rupture is a possible consequence. In the second stage, particularly with epidural analgesia, passive descent for at least 1 hour is recommended, and possibly longer if the woman wishes, before encouraging active pushing. With regional analgesia and a normal FHR pattern, birth should occur within 4 hours of full dilatation regardless of parity [7] . Oxytocin may be commenced in nulliparous patients in the passive phase if contractions are felt to be inadequate and particularly with the persistent OP position. Failure of second‐stage descent combined with excessive caput or moulding suggests disproportion and requires critical assessment to decide the appropriate mode of delivery. Summary box 26.2 OP position with deflexion of the head and asynclitism results in relative disproportion compounded by inadequate uterine activity. With epidural analgesia in place, passive descent should be encouraged for at least 1 hour. Augmentation with oxytocin should be used with extreme caution in multigravid patients with labour arrest. Instrumental vaginal deliveries Background The incidence of instrumental vaginal delivery (IVD) varies widely and in Europe ranges from 0.5% (Romania) to 16.4% (Ireland), although there is no direct relationship with CS rates [ 8 , 9 ]. Epidural analgesia is associated with higher IVD rates. Allowing a longer passive second stage for descent results in less rotational deliveries and possibly a reduction in second‐stage CS [ 10 , 11 ]. Common indications for IVD include delay in the second stage of labour due to inadequate uterine activity, malposition with relative disproportion, maternal exhaustion and fetal compromise. Women with severe cardiac, respiratory or hypertensive disease or intracranial pathology may require IVD to shorten the second stage (when forceps may be preferred). Assessment and preparation for IVD The condition of the mother and fetus and the progress of labour should be assessed prior to performing IVD. Personal introductions to the woman and her partner are essential, explaining the reason for IVD and ensuring a chaperone and enough support are available. The findings, plan of action and the procedure itself should be explained and the discussions carefully recorded. Verbal or written consent is obtained. The mother and her partner may be physically and emotionally exhausted and great care should be exercised in terms of behaviour, communication and medical action. On abdominal examination, the fetal head should be no more than 1/5 palpable (preferably 0/5). A scaphoid shape to the lower abdomen may indicate an OP position. The FHR pattern should be assessed, noting any clinical signs of fetal compromise (e.g. fresh meconium). With acute fetal compromise (e.g. profound bradycardia, cord prolapse) delivery must be expedited urgently and this may only allow a brief explanation to be given to the patient and her partner at the time. If contractions are felt to be infrequent or short‐lasting, an oxytocin infusion should be considered in the absence of signs of fetal compromise. Both vacuum and forceps deliveries are associated with an almost threefold increased risk of shoulder dystocia compared with spontaneous delivery and this should be anticipated. However, it remains unclear whether this increased incidence is a cause or effect phenomenon [12] . On vaginal examination the cervix should be fully dilated with membranes absent. The colour and amount of amniotic fluid is recorded. Excessive caput or moulding may suggest the possibility of disproportion. Inability to reduce overlapping skull bones with gentle pressure is designated ‘moulding +++’; overlapping that reduces by gentle digital pressure is ‘moulding ++’, and meeting of the bones without overlap is ‘moulding +’. Identification of position, station, degree of deflexion and asynclitism will help decide whether IVD is appropriate, where it should be undertaken and who should undertake the procedure. Successful IVD is associated with station below the spines and progressive descent with pushing. If the head is 1/5 palpable abdominally, the leading bony part of the head is at the level of the ischial spines (mid‐cavity). When the head is more than 1/5 palpable and/or when station is above the spines, delivery by CS is recommended. Position is determined by identification of suture lines and fontanelles. The small posterior fontanelle (PF) lies at the Y‐shaped junction of the sagittal and lambdoidal sutures but may be difficult to feel when there is marked caput. The anterior fontanelle (AF) is a larger diamond‐shaped depression at the junction of the two parietal and two frontal bones. It can be differentiated from the PF by identifying the four sutures leading into the fontanelle. In deflexion (particularly OP positions) the AF lies centrally and is easily felt. Position can be confirmed by reaching for the pinna of the fetal ear, which can be flicked forwards indicating that the occiput lies in the opposite direction. Reaching the ear suggests descent below the mid‐pelvic strait. The degree of asynclitism should be assessed (see Fig. 26.1 ), with increasing degrees suggesting disproportion and a potentially more difficult IVD. Assessment of level and position can be difficult with OP position and in obesity. If there is any doubt after careful clinical examination, ultrasound assessment is recommended. The fetal orbits are sought and the position of the spine is noted. This is simple to do and can reduce the incorrect diagnosis of fetal position without delaying delivery, although on its own may not reduce morbidity associated with IVD [13] . IVD is normally performed with the mother in the dorsal semi‐upright position with legs flexed and abducted, supported by lithotomy poles or similar. The procedure is performed with good light and ideally aseptic conditions. The vulva and perineum should be cleansed and the bladder catheterized if the woman is unable to void. Adequate analgesia is essential and requires careful individualized assessment. Epidural anaesthesia is advisable for mid‐cavity IVD (i.e. station 0 to +2 cm below the ischial spines; see Fig. 26.2 ). In the absence of a pre‐existing epidural, spinal anaesthesia may be considered. IVD at station +2 cm or below is termed ‘low‐cavity’ and regional or pudendal block with local perineal infiltration (20 mL 1% plain lidocaine) can be used. Outlet IVD is performed when the head is on or near the perineum with the scalp visible without separating the labia. Descent to this level is associated with an OA position requiring minimal or no rotation and perineal infiltration with pudendal anaesthesia is effective. When the vertex is below the spines, IVD is carried out with different types of forceps or vacuum equipment, depending on the position and station of the vertex and the familiarity and experience of the doctor. Overall, comparing outcomes is easier if designation is by station and position at the time of instrumentation (e.g. left OP at +3) rather than simply mid, low or outlet IVD [ 11 , 14 ]. Choice of instruments: forceps or ventouse The choice of instrument depends on the operator’s experience, familiarity with the instrument, station and position of the vertex. Therefore, knowledge of the station and the position of the vertex is essential. The fetus in an OA position in the mid/low cavity can be delivered using non‐rotational, long or short‐handled forceps or a vacuum device: silicone, plastic or anterior metal cups (with suction tubing arising from the dorsum of the cup) are all suitable. For the fetus lying OT at mid‐ or low‐cavity, or lying OP position mid‐cavity, Kielland’s forceps or vacuum devices can be used to correct the malposition. Manual rotation is another technique to consider. Low‐cavity direct OP positions can be delivered ‘face to pubis’ but this may cause signifcant perineal trauma as the occiput delivers. For this reason, an OP vacuum cup (with the suction tubing arising from the edge of the cup) may be preferred. The cup will promote flexion and late rotation to OA often occurs on the perineum just prior to delivery. The Kiwi OmniCup® is an all‐purpose disposable vacuum delivery system with a plastic cup and in‐built PalmPump™ suitable for use in all positions of the vertex. Later models also display force traction to help the accoucheur avoid cup slippage ( http://clinicalinnovations.com/portfolio‐items/kiwi‐complete‐vacuum‐delivery‐system/ ) Forceps delivery Forceps come in pairs and most have fenestrated blades with a cephalic and pelvic curve between the heel and toe (distal end) of each blade. The heel continues as a shank which ends in the handle. The handles of the two blades sit together and meet at the lock. The cephalic curve fits along either side of the fetal head with the blades lying on the maxilla or malar eminences in the line of the mento‐vertical diameter ( Fig. 26.8 a). When correctly attached, uniform pressure is applied to the head, with the main traction force applied over the malar eminences. The shanks are over the flexion point, allowing effective traction in the correct direction. Non‐rotational forceps (the longer‐handled Neville Barnes or Simpson, and the shorter‐handled Wrigley’s) have a distinct pelvic curve that allows the blades to lie in the line of the pelvic axis whilst the handles remain horizontal. Kielland’s forceps have a minimal pelvic curve to allow rotation within the pelvis to correct malposition. Fig. 26.8 (a) Malar forceps application showing mento‐vertical diameter; (b) forceps traction (Pajot’s manoeuvre). Prior to applying forceps, the blades should be assembled to check whether they fit together as a pair. All forceps have matching numbers imprinted on the handles or shanks and these should also be checked. Non‐rotational forceps can be applied when the vertex is no more than 45° either side of the direct OA position (i.e. right OA to left OA). Application and delivery in a direct OP position is also possible but not routinely recommended because of increased perineal trauma. The left blade is inserted first using a light ‘pencil grip’, negotiating the pelvic and cephalic curves with a curved movement of the blade between the fetal head and the operator’s right hand, which is kept along the left vaginal wall for protection. Hands are swapped to insert the right blade using the same technique. Correct application results in the handles lying horizontally, right on top of left, and locking should be easy. Before applying traction, correct application must be confirmed: (i) the sagittal suture is lying midline, equidistant from and parallel to the blades; (ii) the occiput is no more than 2–3 cm above the level of the shanks (i.e. head well‐flexed); and (iii) no more than a fingertip passes into the fenestration at the heel of the blade. From mid‐ and low‐cavity, Pajot’s maneouvre should be used, balancing outward traction with one hand with downward pressure on the shanks with the other ( Fig. 26.8 b, white arrow). The handles are kept horizontal to avoid trauma to the anterior vaginal wall from the toes of the blades. Traction is synchronized with contractions and maternal effort, and the resultant movement is outwards down the line of the pelvic axis until the head is crowning. An episiotomy is usually needed as the perineum stretches up. The direction of traction is now upwards once the biparietal eminences emerge under the pubic arch and the head is born by extension. The mother will usually ask to have her baby handed to her immediately (unless active resuscitation is required). After completing the third stage, any perineal trauma is repaired and a full surgical count completed. The procedure, including plans for analgesia and bladder care, should be fully documented. Rotational forceps Kielland’s forceps have a minimal pelvic curve allowing rotation of the head at mid‐cavity. They are powerful forceps requiring a skilled accoucheur who is willing to abandon the procedure if progress is not as expected. The number of units able to teach use of Kielland’s forceps to the point of independent practice is declining in the UK. The forceps should match and are applied so that the knobs on the handles face the fetal occiput. Kielland’s are used to correct both OT and OP positions using two methods of application. Direct application involves sliding each blade along the side of the head if space permits, and is more easily achieved with OP positions. Wandering application is useful in OT positions. The first blade is applied in front of the fetal face, from where it is gently ‘wandered’ around to lie in the usual position alongside the malar bone. The posterior blade is applied directly using the space in the pelvic sacral curve. If application is difficult or the blades do not easily lock, the procedure should be abandoned. Correct application should be confirmed. Once locked, it is essential to hold the handles at a relatively steep angle downwards in the line of the mid‐pelvic axis in order to achieve easy rotation. Asynclitism is corrected using the sliding lock, moving the shanks over each other until the knobs are aligned. Rotation should take place between contractions, using only gentle force. Rotation may require the fetal head to be gently disimpacted, either upwards or downwards but no more than 1‐cm displacement is needed. Correct application should be checked again after rotation. Traction should result in progressive descent and an episiotomy is usually required. At the point of delivery, the handles of Kielland’s are only just above the horizontal because of the lack of pelvic curve. If there is no descent with traction during three contractions with maternal effort, the procedure should be abandoned. Whether Kielland’s delivery takes place in the delivery room or in obstetric theatre requires careful assessment of fetal and maternal condition, analgesia and labour progress. If there is any doubt, a formal trial of forceps should be arranged. Vacuum delivery Ventouse or vacuum delivery is increasingly favoured over forceps delivery for similar indications in the second stage of labour. The prerequisites to be satisfied before vacuum delivery are the same as for all forms of IVD. Vacuum delivery is contraindicated below 34 +0 weeks and should be used with caution between 34 +0 to 36 +0 weeks [11] . Overall it is contraindicated for fetuses with possible haemorrhagic tendencies (risk of subgaleal haemorrhage) and before full dilatation [11] . Experienced practitioners may consider vacuum after 8 cm in a multigravid patient in some circumstances. There are many types of vacuum cup in regular use, made of different materials and of differing shapes. Whichever cup is used, the aim is to ensure that the centre of the cup is directly over the flexion point. The flexion point is 3 cm in front of the occiput in the midline and is the point where the mento‐vertical diameter exits the fetal skull [15] . Traction on this point promotes flexion, presenting the smallest diameters for descent through the pelvis: this is the optimum flexing median application ( Fig. 26.9 a). Other applications increase the risk of cup detachment, failed vacuum delivery and scalp trauma. In decreasing order of effectiveness, these are the flexing paramedian application ( Fig. 26.9 b), the deflexing median application ( Fig. 26.9 c) and the deflexing paramedian application ( Fig. 26.9 d). Fig. 26.9 Placement of the vacuum cup, from most favourable (a) to unfavourable (d). (a) Flexing median; (b) flexing paramedian; (c) deflexing median; (d) deflexing paramedian. It is vitally important to select the correct cup and this will vary depending on both the position and attitude of the fetus. The soft Silc, Silastic or anterior metal cups (where the tubing is attached on the dorsum of the cup) are not suitable for OT or OP positions, as their shape and configuration do not allow application over the flexion point. They are suitable for OA positions where the flexion point is accessible in the midline. Metal cups come in different sizes, usually 4, 5 or 6 cm in diameter. In a systematic review they were more likely to result in successful vaginal birth than soft cups (RR 1.63, 95% CI 1.17–2.28), but with more cases of scalp injury (RR 0.67, 95% CI 0.53–0.86) and cephalhaematoma (RR 0.61, 95% CI 0.39–0.95) [16] . A specially designed cup should be used for OT and OP positions: metal OP cups have tubing emerging from the lateral aspect of the cup and the Kiwi OmniCup has a groove in the dorsum of the cup to accommodate the flexible stem. These cups can be manoeuvred more laterally or posteriorly to reach the flexion point. Hand‐held vacuum is associated with more failures than metal ventouse [16] , although a larger study suggested that the OmniCup has an overall failure rate of 12.9% [11] . Aldo Vacca (1941–2014) was the doyen of vacuum delivery and (with reference to the flexion point and cup application) his favourite quote was ‘It’s always more posterior than you think’. After ensuring flexion point application, the cup must be held firmly on the fetal scalp, and a finger should be run around the rim to ensure that no maternal tissue is entrapped. A vacuum of 0.2 bar (150 mmHg or 0.2 kg/cm 2 negative pressure) is created using a hand‐held or mechanical pump, before rechecking the position over the flexion point and confirming maternal tissue is not trapped. The vacuum is increased to 0.7–0.8 bar (500–600 mmHg or 0.8 kg/cm 2 ) in one step, waiting 2 min where possible to develop the ‘chignon’ within the cup. Axial traction in the line of the pelvic axis should be timed with uterine contractions and maternal pushing. A thumb should be placed on the cup, with the index finger on the scalp at the edge of the cup allowing the operator to feel any potential detachment before it is heard (by which point it is often too late to prevent detachment). Descent promotes auto‐rotation of the head to the OA position and episiotomy is often not required. Parents should be reassured that the ‘chignon’ will settle over 2–3 days. Manual rotation Manual rotation for persistent OP position is an alternative to IVD. The procedure requires insertion of one hand into the posterior vagina to encourage flexion and rotation. Careful patient selection is essential and the operator must ensure that effective analgesia is in place. The right hand is inserted for a left OP position (insert left hand for right OP). Four fingers are placed behind the fetal occiput to act as the ‘gutter’ on which the head will rotate, with the thumb placed alongside the anterior fontanelle. When the mother pushes with a contraction, the thumb applies pressure to flex the head and rotation to an OA position should occur with minimal effort. In a series ( N  = 61) where OP position was managed in two groups, the spontaneous delivery rate increased from 27% to 77% in the group offered digital rotation ( P <0.0001) [17] . Complications of IVD In a Cochrane review of 32 studies ( N  = 6597), forceps were less likely to fail to achieve a vaginal birth compared with ventouse (RR 0.65, 95% CI 0.45–0.94) [16] . Vaginal and perineal lacerations, including third‐ and fourth‐degree tears, are more common with forceps than with vacuum. Infra‐levator haematomas may occur occasionally and these should be drained if large or symptomatic. The risk of flatus incontinence or altered continence is also higher. Follow‐up of women who have had low or outlet IVD confirms normal physical and neourological outcomes for the vast majority of the newborn. In terms of neonatal outcome, cephalhaematoma is more common with vacuum but risk of facial injury is less. Facial and scalp abrasions are usually minor and heal in a few days. Unilateral facial nerve palsy is rare and resolves within days or weeks and is not usually related to poor technique. Skull fracture is rare and most need no treatment unless depressed, when surgical elevation may be indicated. Vacuum delivery may result in retinal haemorrhages, haematoma confined to one of the skull bones and neonatal jaundice. Severe scalp lacerations imply poor technique and are fortunately rare. Subgaleal haemorrhage may cause minor or severe morbidity and rarely mortality [18] . In reviewing morbidity associated with IVD, it is important to remember that the alternative option of second‐stage CS is also associated with increased morbidity for both mother and baby. Safe practice: sequential intrumentation and trial of instrumental delivery For all IVDs, the procedure should be abandoned if there is ‘no evidence of progressive descent with moderate traction during each contraction, or where delivery is not imminent following three contractions of a correctly applied instrument by an experienced operator’ [11] . Sequential instrumentation is associated with increased neonatal morbidity and the decision to proceed must take into account the relative risks of delivery by second‐stage CS from deep in the pelvis. It can be difficult to judge whether to proceed with IVD, especially in cases with mid‐cavity malposition at the level of the ischial spines. In such cases a trial of instrumental delivery should be undertaken in theatre under regional anaesthesia, with the full theatre team and neonatal practitioner present. The estimated incidence of trial of instrumental delivery is 2–5%. It is vital to maintain awareness of the situation, with a clear willingness to abandon the attempt if progress is not as expected, proceeding immediately to CS. The couple should be advised of this strategy and appropriate consent obtained prior to the procedure, which should be undertaken by the most senior obstetrician available. In the presence of fetal compromise, it is prudent to consider delivery by emergency CS, rather than proceeding with a potentially difficult IVD. Paired cord blood samples should be taken and results recorded after every attempted IVD. Contemporary developments in IVD New methods are being developed to achieve IVD and include disposable plastic forceps with the ability to measure traction force (see http://www.medipex.co.uk/success‐stories/pro‐nata‐yorkshire‐obstetric‐forceps/ and Fig. 26.10 ) and the Odon device where traction is applied using a plastic bag placed around the fetal head and neck. This device is undergoing trials led by the World Health Organization (see http://www.who.int/reproductivehealth/topics/maternal_perinatal/odon_device/en/ ). Fig. 26.10 Pro‐Nata Yorkshire obstetric forceps. Reproduced with permission of Mark Jessup.

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D. ASHLEY HILL, MD, JORGE LENSE, MD, AND FAY ROEPCKE, MD, MPH

Am Fam Physician. 2020;102(2):84-90

Author disclosure: No relevant financial affiliations.

Shoulder dystocia is an obstetric emergency in which normal traction on the fetal head does not lead to delivery of the shoulders. This can cause neonatal brachial plexus injuries, hypoxia, and maternal trauma, including damage to the bladder, anal sphincter, and rectum, and postpartum hemorrhage. Although fetal macrosomia, prior shoulder dystocia, and preexisting or gestational diabetes mellitus increases the risk of shoulder dystocia, most cases occur without warning. Labor and delivery teams should always be prepared to recognize and treat this emergency. Training and simulation exercises improve physician and team performance when shoulder dystocia occurs. Unequivocally announcing that dystocia is happening, summoning extra assistance, keeping track of the time from delivery of the head to full delivery of the neonate, and communicating with the patient and health care team are helpful. Calm and thoughtful use of release maneuvers such as knee to chest (McRoberts maneuver), suprapubic pressure, posterior arm or shoulder delivery, and internal rotational maneuvers will almost always result in successful delivery. When these are unsuccessful, additional maneuvers, including intentional clavicular fracture or cephalic replacement, may lead to delivery. Each institution should consider the length of time it will take to prepare the operating room for general inhalational anesthesia and abdominal rescue and practice this during simulation exercises.

Shoulder dystocia is an obstetric emergency in which gentle downward traction of the fetal head does not lead to delivery and additional maneuvers are required to deliver the fetal shoulders. 1 Shoulder dystocia is usually attributed to impaction of the anterior shoulder against the maternal symphysis after delivery of the fetal head; less commonly, it is caused by impaction of the posterior shoulder against the sacral promontory. 2

Shoulder dystocia complicates 0.3% to 3% of all vaginal deliveries. 3 , 4 The exact incidence can be difficult to determine because the diagnosis is subjective and there are no agreed upon diagnostic criteria for shoulder dystocia. Objective criteria of a head-to-body delivery interval of 60 seconds or the need for additional delivery maneuvers are proposed based on the incidence of significantly more birth injuries and lower Apgar scores during these deliveries. 5

Risk Factors and Prevention

Risk factors for shoulder dystocia include fetal macrosomia (odds ratio = 16.1), prior shoulder dystocia (odds ratio = 8.25), and preexisting or gestational diabetes mellitus (odds ratio = 1.8). 6 – 8 Other risk factors include maternal obesity, excessive maternal weight gain during pregnancy, oxytocin (Pitocin) use, prolonged first or second stage labor, and operative vaginal delivery (forceps or vacuum); however, these are poorly predictive of shoulder dystocia. 9 There are no accurate models to predict or prevent shoulder dystocia. 10 , 11

Fetal macrosomia is difficult to accurately predict. At term, fetal sonography has at least a 10% margin of error for diagnosis of macrosomia. 11 Although the incidence of shoulder dystocia increases with increasing fetal weight and maternal diabetes, one study of pregnancies complicated by shoulder dystocia found that half of the neonates weighed less than 4,000 g (8 lb, 13 oz) and that only 20% of the patients had diabetes. 12 Results from studies evaluating labor induction for suspected macrosomia are inconsistent, and induction is not recommended to prevent shoulder dystocia. 13 Given the increased risk of shoulder dystocia with increasing fetal weights, the American College of Obstetricians and Gynecologists (ACOG) recommends consideration of cesarean delivery for a patient who does not have diabetes and is carrying a fetus with an estimated fetal weight of 5,000 g (11 lb). ACOG also recommends consideration of cesarean delivery for a patient who has diabetes and is carrying a fetus with an estimated fetal weight of 4,500 g (9 lb, 15 oz). 10

ACOG and the Advanced Life Support in Obstetrics program recommend that labor and delivery teams conduct regular team training drills that include identification and management of shoulder dystocia. 10 , 14

Complications

Shoulder dystocia can cause several maternal and neonatal complications ( Table 1 ) . 10 The most common maternal complications are postpartum hemorrhage (11%) and obstetric anal sphincter injuries (3.8%). 15 The most common neonatal injuries are brachial plexus injuries and clavicular or humeral fractures. 16 Transient brachial plexus injuries may occur in up to 20% of deliveries complicated by shoulder dystocia. 3 Most resolve without permanent disability, although approximately 10% may result in permanent neurologic injury. 17 The head-to-body delivery interval does not predict fetal asphyxia or death. 10 However, due to the potential for serious maternal or neonatal harm, a systematic approach to expeditious delivery is necessary. 10 , 15

Initial Response

Physicians should announce delivery of the fetal head so that an assistant can start a timer. If the fetus fails to deliver using normal traction or if retraction of the fetal head against the perineum (turtle sign) occurs, the physician should announce that there is a shoulder dystocia, and the delivery team should call for additional team members to assist. A longitudinal study of a shoulder dystocia simulation program found a significant reduction in neonatal brachial plexus injuries at discharge (7.6% to 1.3%) when the delivery team performed specified actions during shoulder dystocia deliveries . 18 These included an unequivocal announcement of the shoulder dystocia, calling for additional assistance from qualified personnel, and having an assistant announce the time from delivery of the fetal head every 30 seconds.

Physicians should also obtain assistance from a physician qualified to perform cesarean delivery and someone to resuscitate the neonate. Additional helpful actions that have not been studied include communicating with the patient so that she knows when to push, lowering the bed, using a stool for the assistant applying suprapubic pressure, and having someone record events for precise documentation.

Delivery Maneuvers

If the fetus does not deliver using gentle traction, release maneuvers can be used in a thoughtful and sequential manner to deliver the impacted shoulder ( Figure 1 ) . Aggressive lateral or downward traction on the fetal head and neck should be avoided because it can injure the brachial plexus. 4 There are no randomized trials comparing the various maneuvers used to release an impacted shoulder 10 ( Table 2 10 , 18 , 19 ) . ACOG, the Royal College of Obstetricians and Gynaecologists, and the Advanced Life Support in Obstetrics program recommend using the McRoberts maneuver first, followed by suprapubic pressure if necessary. 10 , 14 , 19 The McRoberts maneuver, performed by flexing the hips and bringing both knees toward the chest, rotates the symphysis pubis cephalad and further opens the pelvic outlet  ( Figure 2 ) . This is a simple and proven method to manage shoulder dystocia, with a success rate of up to 42% as the sole maneuver. 10 , 15

If delivery does not occur, firm, steady suprapubic pressure should be performed concurrently with the McRoberts maneuver. An assistant should apply firm downward or oblique pressure just above the symphysis pubis toward the side the infant is facing. This decreases the distance between the infant's shoulders (bisacromial distance), potentially assisting anterior shoulder dislodgement ( Figure 3 ) . Fundal pressure increases the risk of uterine rupture. 20

If the McRoberts maneuver and suprapubic pressure are unsuccessful, delivery of the posterior arm should be considered 10 , 14 , 21 ( Figure 4 ) . A retrospective review revealed that the combination of the McRoberts maneuver, suprapubic pressure, and posterior arm delivery resulted in successful delivery within four minutes in 95% of cases. 21 Computer modeling suggests that delivery of the posterior arm results in the least amount of brachial plexus stretch compared with other maneuvers. 22 Delivery of the posterior arm requires patience and communication to keep the patient calm. Training with a birth simulator will likely improve operator confidence and performance of this procedure.

An episiotomy may help depending on the size of the physician's hands and ability to enter the posterior vagina, but it is not mandatory for this or any release maneuver. 23 The physician should apply lubricant, compress all five fingers from the appropriate hand into a “duck-bill” shape, and gently maneuver the hand into the posterior vagina, under the baby (see a video of a posterior arm release ). The physician should then slide the hand along the fetal chest, not the back, up to the fetal hip, or until the posterior hand is identified. Grasping the wrist by forming an OK sign with the physician's thumb and index finger ( Figure 4 ) , he or she should flex the fetal elbow and slide the arm along the fetal chest to deliver from the posterior vagina. Using the operator's fifth finger as a fulcrum by placing it along the fetal elbow may help.

Posterior Arm Release

If the posterior arm is tight against the vaginal sidewall and cannot be delivered, other methods of delivering the posterior shoulder can be used. The Menticoglou maneuver involves placing one finger from each hand under the posterior axilla and applying gentle traction along the curve of the pelvis to deliver the posterior shoulder. 24 After the shoulder delivers, it should be easier to deliver the entire posterior arm. The posterior axilla sling traction maneuver uses a suction catheter or urinary catheter placed under the posterior shoulder axilla to apply downward traction to deliver the posterior shoulder. 25 Alternatively, the physician can use the sling to rotate the posterior shoulder 180 degrees to anterior, similar to the Woods maneuver. A description and video of this technique  is available.

Additional maneuvers include rotational methods (e.g., Rubin II, the Woods or reverse Woods [corkscrew] maneuvers) and rolling the patient to her hands and knees (Gaskin all-fours maneuver). To perform the Rubin II maneuver, the physician places two fingers into the vagina to push the scapula of the anterior fetal shoulder toward the fetal face to attempt to rotate the fetus 30 degrees ( Figure 5 ; see a video of the Rubin II maneuver ).

Rubin II Maneuver

The Woods maneuver combines the hand placement for the Rubin II maneuver with two fingers on the anterior aspect of the posterior fetal shoulder with the intent of rotating the fetus 180 degrees ( Figure 5 ; see a video of the Woods maneuver ). For the reverse Woods maneuver, fingers or hands are placed on the front side of the anterior shoulder and back side of the posterior shoulder to rotate the fetus 180 degrees. An episiotomy may be helpful for the Woods maneuvers to be able to gain access with two hands. The Gaskin all-fours maneuver requires the patient to roll onto her hands and knees. This had an 83% success rate as the sole maneuver used in one series. 26 This maneuver may be more difficult if the patient is fatigued or has neuraxial anesthesia.

Woods Maneuver

Maneuvers for catastrophic shoulder dystocia.

If these maneuvers do not result in delivery, options include performing the maneuvers again ( Figure 1 ) or enlisting assistance from another experienced physician who might try the previously attempted maneuvers again or who can collaborate to attempt less proven maneuvers, such as abdominal rescue, cephalic replacement (Zavanelli maneuver), and intentional clavicular fracture ( Table 3 ) . 10 , 27 , 28 Each institution should consider the length of time it will take to prepare the operating room for general inhalational anesthesia and abdominal rescue and practice this during simulation exercises.

Documentation

Precise documentation is extremely important after a shoulder dystocia to inform the clinical team of the delivery events, including the head-to-body delivery interval and maneuvers used. ACOG has provided a checklist for documenting the occurrence of shoulder dystocia . 29

This article updates a previous article by Baxley and Gobbo . 30

Data Sources: A PubMed search was completed in Clinical Queries using the key terms shoulder dystocia, shoulder, brachial plexus, and abnormal labor. The search included meta-analyses, randomized controlled trials, clinical trials, and reviews. We also searched Ovid, Clinical Key, Cochrane Library, Web of Science, the Agency for Healthcare Research and Quality evidence reports, and Essential Evidence Plus. Search dates: September 5, 2019, and April 13, 2020.

Resnik R. Management of shoulder girdle dystocia. Clin Obstet Gynecol. 1980;23(2):559-564.

Hankins GD, Clark SL. Brachial plexus palsy involving the posterior shoulder at spontaneous vaginal delivery. Am J Perinatol. 1995;12(1):44-45.

Gherman RB, Chauhan S, Ouzounian JG, et al. Shoulder dystocia: the unpreventable obstetric emergency with empiric management guidelines. Am J Obstet Gynecol. 2006;195(3):657-672.

American College of Obstetricians and Gynecologists; Task Force on Neonatal Brachial Plexus Palsy. Neonatal Brachial Plexus Palsy . American College of Obstetricians and Gynecologists; 2014.

Beall MH, Spong C, McKay J, et al. Objective definition of shoulder dystocia: a prospective evaluation. Am J Obstet Gynecol. 1998;179(4):934-937.

Tsur A, Sergienko R, Wiznitzer A, et al. Critical analysis of risk factors for shoulder dystocia. Arch Gynecol Obstet. 2012;285(5):1225-1229.

Bingham J, Chauhan SP, Hayes E, et al. Recurrent shoulder dystocia: a review. Obstet Gynecol Surv. 2010;65(3):183-188.

Zhang C, Wu Y, Li S, et al. Maternal prepregnancy obesity and the risk of shoulder dystocia: a meta-analysis. BJOG. 2018;125(4):407-413.

Ouzounian JG, Gherman RB. Shoulder dystocia: are historic risk factors reliable predictors?. Am J Obstet Gynecol. 2005;192(6):1933-1935.

Committee on Practice Bulletins—Obstetrics. Practice bulletin no. 178: shoulder dystocia. Obstet Gynecol. 2017;129(5):e123-e133.

Gupta M, Hockley C, Quigley MA, et al. Antenatal and intrapartum prediction of shoulder dystocia. Eur J Obstet Gynecol Reprod Biol. 2010;151(2):134-139.

Ouzounian JG, Korst LM, Miller DA, et al. Brachial plexus palsy and shoulder dystocia: obstetric risk factors remain elusive. Am J Perinatol. 2013;30(4):303-307.

American College of Obstetricians and Gynecologists; Committee on Practice Bulletins—Obstetrics. Practice bulletin number 173: fetal macrosomia. Obstet Gynecol. 2016;128(5):e195-e209.

Shields SG, Ratcliffe S. Chapter F: labor dystocia. In: Leeman L, Quinlan JD, Dresang LT, et al. Advanced Life Support in Obstetrics Provider Manual . 8th edition. American Academy of Family Physicians; 2017:1–14.

Gherman RB, Goodwin TM, Souter I, et al. The McRoberts' maneuver for the alleviation of shoulder dystocia: how successful is it?. Am J Obstet Gynecol. 1997;176(3):656-661.

Gherman RB, Ouzounian JG, Goodwin TM. Obstetric maneuvers for shoulder dystocia and associated fetal morbidity. Am J Obstet Gynecol. 1998;178(6):1126-1130.

Gherman RB, Ouzounian JG, Miller DA, et al. Spontaneous vaginal delivery: a risk factor for Erb's palsy?. Am J Obstet Gynecol. 1998;178(3):423-427.

Grobman WA, Miller D, Burke C, et al. Outcomes associated with introduction of a shoulder dystocia protocol. Am J Obstet Gynecol. 2011;205(6):513-517.

Royal College of Obstetricians and Gynaecologists. Shoulder dystocia (green-top guideline No. 42). March 28, 2012. Updated February 2017. Accessed March 11, 2020. https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg42/

Sturzenegger K, Schäffer L, Zimmermann R, et al. Risk factors of uterine rupture with a special interest to uterine fundal pressure. J Perinat Med. 2017;45(3):309-313.

Leung TY, Stuart O, Suen SS, et al. Comparison of perinatal outcomes of shoulder dystocia alleviated by different type and sequence of manoeuvres: a retrospective review. BJOG. 2011;118(8):985-990.

Grimm MJ, Costello RE, Gonik B. Effect of clinician-applied maneuvers on brachial plexus stretch during a shoulder dystocia event: investigation using a computer simulation model. Am J Obstet Gynecol. 2010;203(4):339.e1-339.e5.

Sagi-Dain L, Sagi S. The role of episiotomy in prevention and management of shoulder dystocia: a systematic review. Obstet Gynecol Surv. 2015;70(5):354-362.

Menticoglou SM. A modified technique to deliver the posterior arm in severe shoulder dystocia. Obstet Gynecol. 2006;108(3 pt 2):755-757.

Cluver CA, Hofmeyr GJ. Posterior axilla sling traction for shoulder dystocia: case review and a new method of shoulder rotation with the sling. Am J Obstet Gynecol. 2015;212(6):784.e1-784.e7.

Bruner JP, Drummond SB, Meenan AL, et al. All-fours maneuver for reducing shoulder dystocia during labor. J Reprod Med. 1998;43(5):439-443.

O'Shaughnessy MJ. Hysterotomy facilitation of the vaginal delivery of the posterior arm in a case of severe shoulder dystocia. Obstet Gynecol. 1998;92(4 pt 2):693-695.

Sandberg EC. The Zavanelli maneuver: 12 years of recorded experience. Obstet Gynecol. 1999;93(2):312-317.

American College of Obstetricians and Gynecologists. Patient safety checklist no. 6: documenting shoulder dystocia. Obstet Gynecol. 2012;120(2 pt 1):430-431.

Baxley EG, Gobbo RW. Shoulder dystocia. Am Fam Physician. 2004;69(7):1707-1714. Accessed March 11, 2020. https://www.aafp.org/afp/2004/0401/p1707.html

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Shoulder impingement syndrome.

Julie A. Creech ; Sabrina Silver .

Affiliations

Last Update: April 17, 2023 .

• Continuing Education Activity

Shoulder impingement syndrome is a painful condition of the upper extremity resulting from a structural narrowing of the subacromial space. It is primarily diagnosed by history and physical examination. The mainstay of treatment involves identification early before the onset of degenerative changes, physical therapy exercises to strengthen the shoulder girdle, and pharmacologic interventions to decrease inflammation. This activity describes the evaluation and management of shoulder impingement syndrome and highlights the role of an interprofessional team in the care of patients with this condition.

• Identify the etiology of shoulder impingement syndrome.
• Outline the evaluation of shoulder impingement syndrome.
• Review the management options available for shoulder impingement syndrome.
• Describe the interprofessional team strategies for improving care coordination and communication to enhance the care patients with shoulder impingement syndrome and improve outcomes.
• Introduction

Shoulder pain is a common indication for visits to primary care or orthopedic clinic worldwide. The estimated prevalence of shoulder complaints is 7% to 34%, often with shoulder impingement syndrome as the underlying etiology. [1]  Since it was first described in 1852, shoulder impingement syndrome is believed to be the most common cause of shoulder pain, accounting for 44% to 65% of all shoulder complaints. [2]  Similarly, of the 20% to 50% of people within the United Kingdom who seek shoulder pain treatment from a general practitioner, 25% of these individuals are then diagnosed with shoulder impingement syndrome. Not only is shoulder pain common, but it is often a chronic and/or relapsing complaint, with 54% of patients affected by shoulder pain reporting persistent symptoms after 3 years. [3]

Shoulder external impingement should be recognized as a clinical entity that is separate from internal impingement. The most basic clinical differentiation between the former and the latter is defined by the rotator cuff as the anatomic boundary of the external and internal forms. The latter occurs secondary to a repetitive impingement in overhead throwers or manual laborers and constitutes articular-sided rotator cuff pathology, glenohumeral internal rotation deficit (GIRD), and superior labrum anterior posterior (SLAP) tears. [4] [5] [6] [7] [8]

External impingement, often commonly referred to by clinicians and providers as shoulder impingement, is best described as a painful condition of the shoulder that results from the inflammation, irritation, and degradation of the anatomic structures within the subacromial space. [2] [9]  Previously, shoulder impingement syndrome was thought to be a sole diagnosis itself but is now considered to be a cluster of symptoms and anatomic characteristics. [10]

Its anatomic borders define the subacromial space. The acromion and coracoacromial ligament provide the anterior border, the acromioclavicular (AC) joint acts as the superior border, and the humeral head serves as the inferior border. [2]  The acromion shape is thought to play a role in the development of external, or "outlet-based" impingement syndrome. Bigliani and Morrison classified the shape of the acromion by its three most common morphologies: [6]

• Class I: Flat acromion
• Class II: Curved acromion
• Class III: Hooked acromion

During the actions of shoulder abduction, forward flexion, and internal rotation, normal shoulder girdle movement results in narrowing of the subacromial space. This subacromial space, which is normally 1.0 to 1.5 cm in width, narrows with the superior migration of the humeral head, allowing it to approach the anteroinferior edge of the acromion. [11]  The symptom of pain associated with shoulder impingement results with this movement due to the humeral head applying a compressive force to either the rotator cuff, the subacromial bursa, or both structures. [2]

Repetitive pathologic compression, degeneration, and fraying of the rotator cuff tendons are known to contribute to the narrowing of the subacromial space, but it is unknown whether or not the inflamed and damaged tendons cause impingement, or if the narrowed subacromial space causes the tendon inflammation. [2]

Shoulder impingement syndrome can be described according to either the location of the impingement, characterized as external or internal, and/or the underlying cause of the impingement, referred to as primary or secondary impingement. [10] [12] [13] External, or subacromial impingement, results from a mechanical or physical encroachment of the soft tissue located within the subacromial space. Conversely, internal impingement results when the tendons of the rotator cuff encroach between the humeral head and glenoid rim. Internal impingement is most commonly associated with the supraspinatus and infraspinatus tendons. [10]

In primary impingement, there is a structural narrowing of the subacromial space. Examples of primary shoulder impingement syndrome include those attributable to abnormal acromion anatomy, such as a hooked class III acromion, or swelling of the soft tissues. Secondary shoulder impingement syndrome is characterized by normal anatomy at rest and onset of impingement during shoulder motion, likely secondary to rotator cuff weakness, permitting uncontrolled cranial translation of the humeral head. [10] [12] [13] Another potential cause of secondary impingement syndrome is a weakness of the trapezius and serratus anterior muscles, limiting the external rotation and rise of the scapula with the abduction of the upper extremity, further narrowing the subacromial space. [2]

Neer classified shoulder impingement in three categories or stages of severity. In stage I, impingement primarily results from edema, hemorrhage, or both and is classically seen with overuse-type mechanisms. Stage II is characterized by greater fibrosis and irreversible tendon changes. A rupture or tear of the tendon may result from chronic, longstanding fibrosis and is seen in stage III shoulder impingement syndrome. [14] [15]

• Epidemiology

Shoulder impingement syndrome is most commonly seen in individuals who participate in sports and activities that require repetitive overhead activities, including but not limited to handball, volleyball, swimming, carpenters, painters, and hairdressers. [4] Other extrinsic risk factors that may predispose to the development of impingement syndrome include bearing heavy loads, infection, smoking, and fluoroquinolone antibiotics. [2]  The incidence of shoulder impingement syndrome rises with age, with peak incidence occurring in the sixth decade of life. [12]

• History and Physical

A thorough history and physical examination are key to the diagnosis of shoulder impingement syndrome. Individuals will often present with complaints of pain upon lifting the arm or with lying on the affected side.  They may report loss of motion as the primary reason they come in to be evaluated, or that nighttime pain prevents them from sleeping. Weakness and stiffness often result secondary to the pain. [16] Onset is usually gradual or insidious, typically developing over weeks to months, and patients are often unable to describe a direct trauma or inciting event that resulted in the pain. [12] [17] Pain is commonly described as being located over the lateral acromion, frequently with radiation to the lateral mid-humerus. Clinicians should attempt to obtain details regarding the nature of the shoulder pain, such as onset, quality, exacerbating, and remitting factors, and interventions attempted thus far with clinical response and history of prior injuries to the affected extremity. Special attention should be made by the clinician to inquire about overhead activities and repetitive activities. Relief may be noted with rest, anti-inflammatory medications, and ice, but symptoms often recur upon return to activity.

Physical examination should consist of inspection, palpation, passive, and active range of motion, and strength testing of the neck and shoulder, all of which are compared bilaterally. Often, patients will have weakness of abduction and/or external rotation of the affected side. [10] [12] Scapular dyskinesis can be seen with forward elevation of the arm. Tenderness to palpation is usually present over the coracoid process of the affected arm.

Special tests are key components of the physical examination. [8] Those tests specific to shoulder impingement syndrome include the Hawkins test, Neer sign, Jobe test, and a painful arc of motion. Individually, these tests have low sensitivity and specificity, but when combined, they can help complete the picture of shoulder impingement syndrome. [10]

Hawkins test: The Hawkins test is performed when the patient's arm is passively internally rotated with the shoulder in 90 degrees of shoulder forward flexion and elbow flexion. Pain over the acromion indicates subacromial impingement but may be negative in internal impingement. [10]

Neer sign: With the scapula fixed into a depressed position, this test is performed by the examiner maximally forward flexing the patient's arm (passive range of motion testing). Localized pain on the anterior shoulder suggests subacromial impingement, whereas posterior shoulder pain suggests internal impingement.

Jobe test: Also known as the empty can test, this test is performed by placing the patient's arms at 90 degrees of abduction within the scapular plane, maximally internally rotating the arms and resisting further abduction by the patient. A positive test occurs with localized pain to the affected arm. [10]

Painful arc of motion: The painful arc is a physical exam finding in which pain is appreciated with abduction of the arm between 70 and 120 degrees and forced overhead movement. [12]

Special tests to evaluate for shoulder instability include the sulcus sign, anterior apprehension, and relocation. Classically, these tests are negative in shoulder impingement syndrome.

Sulcus sign: With the patient sitting upright with arm resting at their side, the clinician stabilizes the shoulder proximally and applies an inferiorly-directed force at the elbow. A positive test is noted based on the inferior displacement of the humeral head. [18]

Anterior apprehension: With the patient lying supine, this test is performed by placing the patient's shoulder in 90 degrees of abduction and 90 degrees of external rotation. While supporting the proximal shoulder, the clinician then applies greater gentle external rotation movement. The exam is considered positive when the patient reports a subjective feeling of impending subluxation or near dislocation. [18]

Relocation test: This test for shoulder instability requires a positive anterior apprehension test. After the patient reports the prodrome of dislocation or subluxation described above, the clinician applies a posteriorly directed force on the anterior humeral head, which relieves the patient's symptoms. [18]

While the overall diagnostic sensitivity of the physical exam is reportedly as high as 90%, imaging studies are often performed to confirm the diagnosis and rule out other pathologies. [12]  If the decision to obtain radiographs is made, they should be obtained bilaterally, rather than only on the affected side, to evaluate potential anatomic differences and to rule out other pathologies such as calcific tendinitis or arthritic changes.

Plain radiograph standard shoulder films include 2 views (AP and lateral/scapular Y) The AP view of the shoulder can be used to determine the critical shoulder angle (CSA), which involves the extent of lateral coverage by the acromion and the inclination of the glenoid. At CSAs greater than 35 degrees, there is an increased likelihood that a rotator cuff is contributing to impingement syndrome. Similarly, measurements such as the acromiohumeral distance (AHD) can help to detect rotator cuff pathologies and defects. The AHD is measured from the inferior edge of the acromion to the humeral head. The normal range is approximately 7 to 14 mm in men and 7 to 12 mm in women. A lower AHD suggests rotator cuff pathology. The scapular Y view allows for the assessment of the humeral head on the glenoid. Additional plain radiographs featuring the outlet view will best visualize and evaluate the shape of the acromion. [12]

Other imaging modalities to consider include ultrasound and magnetic resonance imaging (MRI). Consideration for advanced imaging with MRI is recommended after 6 weeks of therapy without clinical improvement. [19]  MRI allows for a detailed evaluation of bony and soft tissue structures within the shoulder girdle. Ultrasound is a bedside imaging option that primarily enables assessment of the soft tissue contributing factors such as bursitis, tendinopathy, and/or tendon ruptures. [12] [20]

• Treatment / Management

Classically, the foundation of management for shoulder impingement syndrome has been rehabilitative exercise programs with subsequent surgical intervention if indicated by underlying anatomy, pathology, or failure of response to physiotherapy. Without known structural damage, non-operative therapies with a controlled exercise program, nonsteroidal anti-inflammatory drugs (NSAIDs), and subacromial injections are considered the treatment of choice for the first 3 to 6 months of treatment. [2]

In one study, exercise therapy was found to have better results when compared to a control/placebo in the sub-acute injury phase. [21]  Physiotherapy for shoulder impingement syndrome should consist of exercises that focus on rotator cuff strengthening, with a special focus on the supraspinatus and infraspinatus rotator cuff muscles, the trapezius, and serratus anterior strengthening and retraining exercises to minimize scapular dyskinesia, and other exercises to correct strength imbalances of the upper extremities. The combination of exercise with other conservative therapy lead to greater improvements in pain score compared to either treatment alone. Physiotherapy plus localized injection resulted in a maximized treatment effect compared to solitary localized injection. [15]  Further, moderate strength evidence supports the effective addition of hyperthermia to physical therapy, though symptom relief was only noted to be short-term. [21]

Numerous methodologies and approaches for corticosteroid injections exist, but the commonly used posterior subacromial approach requires less precision and is often viewed as most straightforward. [22] A 1.5 inch, 21, or 22 gauge needle with lidocaine and corticosteroid is commonly used. In this approach, the clinician locates the posterior shoulder portal, located 1 cm medial and inferior to the posterior corner of the acromion. While angling the needle in the direction of the underside of the acromion, the clinician advances the needle toward the acromion in an anterosuperior direction. Injection flow should be easy, without resistance, otherwise, the needle should be redirected slightly inferiorly to avoid directly injecting a rotator cuff tendon. While landmark-based approaches provide clinical benefit, ultrasound-guided injections may be superior in symptom relief. [23]

A systematic review of randomized controlled trials comparing surgical intervention versus conservative therapy yielded moderate evidence that surgical intervention was not more effective for reducing pain than impingement-directed physical therapy. [24]  Arthroscopic subacromial decompression (ASD) consists of acromioplasty at the anterolateral edge, bursal debridement, and resection of the coracoacromial ligament. [2]  The ASD or other similar procedure is recommended when a patient has severe, persistent subacromial shoulder pain with functional impairments that have not improved despite conservative therapy. [1] [12] [17]   Combined ASD and treatments such as radiofrequency ablation and arthroscopic bursectomy have more beneficial effects than open subacromial decompression (OSD) plus platelet-leukocyte gel injection. [15]   However, a 2018 systematic review found there was no additional benefit in pain reduction when comparing the results of ASD surgery to placebo surgery at 12 months. [25]  Alternative surgical options include acromioplasty or bursectomy alone, though, like ASD, these surgical interventions appear to provide minimal benefit to patients. [26]  

When comparing surgical intervention with physiotherapy to that of surgery alone, no statistically significant or clinically significant difference between the two arms was observed with respect to pain at 3 months, 6 months, 5 years, and 10 years. Further, no statistical or clinically significant difference in function was noted at 3 months, 6 months, and 1 year follow-up between the groups. [1]

• Differential Diagnosis
• Adhesive capsulitis
• Rotator cuff tear
• Acromioclavicular joint arthritis
• Acromioclavicular joint sprain
• Trapezius muscle spasm
• Biceps tendonitis
• Biceps tendon rupture
• Calcific tendonitis
• Glenohumeral arthritis
• Distal clavicle osteolysis
• Cervical radiculopathy
• Thoracic outlet syndrome

In 60% of patients, physical therapy, NSAIDs, corticosteroid injections, and other means of conservative therapy yield satisfactory results within two years. [2] [12]

• Complications

Due to the underlying etiology of shoulder impingement syndrome, complications that may arise predominantly result from structural damage within the subacromial space, altered biomechanics, or avoidance of use with subsequent atrophy. Potential pathologies that may result include rotator cuff tendonitis or tear, bicipital tendonitis or tear, or adhesive capsulitis.

• Deterrence and Patient Education

Patient education should focus on the importance of not only adherence to physical therapy and a home exercise program but also activity modifications, such as discontinuing overhead activities until the pain improves. Lifestyle modification such as “living within the window,” wherein movements are restricted to the anterior portion of one’s body in an approximate 2 to 3 feet rectangle, with attempts to minimize reaching overhead or behind the back is benefical. [12] [17]

• Enhancing Healthcare Team Outcomes

Treatment and recovery from shoulder impingement syndrome rely heavily on interprofessional healthcare interaction. This includes the primary clinician providing pain relief modalities such as NSAIDs or corticosteroid injections and providing education and referral for physiotherapy. Physiotherapy, as lead by a physical therapist, should involve office-based exercises in addition to a home exercise program. Communication between the physical therapist and primary care clinician should occur on a routine basis to guide further imaging and treatment. If the patient is a candidate for surgical intervention, the primary care clinician should refer to an orthopedic surgeon. Orthopedic nurses assist in assessment, provide patient education, and communicate changes in patient status to the orthopedist. [Level 5]

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Disclosure: Julie Creech declares no relevant financial relationships with ineligible companies.

Disclosure: Sabrina Silver declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Creech JA, Silver S. Shoulder Impingement Syndrome. [Updated 2023 Apr 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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• Physiotherapy for patients with shoulder pain in primary care: a descriptive study of diagnostic- and therapeutic management. [Physiotherapy. 2017] Physiotherapy for patients with shoulder pain in primary care: a descriptive study of diagnostic- and therapeutic management. Karel YHJM, Scholten-Peeters GGM, Thoomes-de Graaf M, Duijn E, van Broekhoven JB, Koes BW, Verhagen AP. Physiotherapy. 2017 Dec; 103(4):369-378. Epub 2016 Nov 28.
• Incidence, prevalence, and consultation rates of shoulder complaints in general practice. [Scand J Rheumatol. 2012] Incidence, prevalence, and consultation rates of shoulder complaints in general practice. Greving K, Dorrestijn O, Winters JC, Groenhof F, van der Meer K, Stevens M, Diercks RL. Scand J Rheumatol. 2012 Mar; 41(2):150-5. Epub 2011 Sep 21.
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Fetal Presentation, Position, and Lie (Including Breech Presentation)

• Variations in Fetal Position and Presentation |

During pregnancy, the fetus can be positioned in many different ways inside the mother's uterus. The fetus may be head up or down or facing the mother's back or front. At first, the fetus can move around easily or shift position as the mother moves. Toward the end of the pregnancy the fetus is larger, has less room to move, and stays in one position. How the fetus is positioned has an important effect on delivery and, for certain positions, a cesarean delivery is necessary. There are medical terms that describe precisely how the fetus is positioned, and identifying the fetal position helps doctors to anticipate potential difficulties during labor and delivery.

Presentation refers to the part of the fetus’s body that leads the way out through the birth canal (called the presenting part). Usually, the head leads the way, but sometimes the buttocks (breech presentation), shoulder, or face leads the way.

Position refers to whether the fetus is facing backward (occiput anterior) or forward (occiput posterior). The occiput is a bone at the back of the baby's head. Therefore, facing backward is called occiput anterior (facing the mother’s back and facing down when the mother lies on her back). Facing forward is called occiput posterior (facing toward the mother's pubic bone and facing up when the mother lies on her back).

Lie refers to the angle of the fetus in relation to the mother and the uterus. Up-and-down (with the baby's spine parallel to mother's spine, called longitudinal) is normal, but sometimes the lie is sideways (transverse) or at an angle (oblique).

For these aspects of fetal positioning, the combination that is the most common, safest, and easiest for the mother to deliver is the following:

Head first (called vertex or cephalic presentation)

Facing backward (occiput anterior position)

Spine parallel to mother's spine (longitudinal lie)

Neck bent forward with chin tucked

Arms folded across the chest

If the fetus is in a different position, lie, or presentation, labor may be more difficult, and a normal vaginal delivery may not be possible.

Variations in fetal presentation, position, or lie may occur when

The fetus is too large for the mother's pelvis (fetopelvic disproportion).

The uterus is abnormally shaped or contains growths such as fibroids .

The fetus has a birth defect .

There is more than one fetus (multiple gestation).

Position and Presentation of the Fetus

Variations in fetal position and presentation.

Some variations in position and presentation that make delivery difficult occur frequently.

Occiput posterior position

In occiput posterior position (sometimes called sunny-side up), the fetus is head first (vertex presentation) but is facing forward (toward the mother's pubic bone—that is, facing up when the mother lies on her back). This is a very common position that is not abnormal, but it makes delivery more difficult than when the fetus is in the occiput anterior position (facing toward the mother's spine—that is facing down when the mother lies on her back).

When a fetus faces up, the neck is often straightened rather than bent,which requires more room for the head to pass through the birth canal. Delivery assisted by a vacuum device or forceps or cesarean delivery may be necessary.

Breech presentation

In breech presentation, the baby's buttocks or sometimes the feet are positioned to deliver first (before the head).

When delivered vaginally, babies that present buttocks first are more at risk of injury or even death than those that present head first.

The reason for the risks to babies in breech presentation is that the baby's hips and buttocks are not as wide as the head. Therefore, when the hips and buttocks pass through the cervix first, the passageway may not be wide enough for the head to pass through. In addition, when the head follows the buttocks, the neck may be bent slightly backwards. The neck being bent backward increases the width required for delivery as compared to when the head is angled forward with the chin tucked, which is the position that is easiest for delivery. Thus, the baby’s body may be delivered and then the head may get caught and not be able to pass through the birth canal. When the baby’s head is caught, this puts pressure on the umbilical cord in the birth canal, so that very little oxygen can reach the baby. Brain damage due to lack of oxygen is more common among breech babies than among those presenting head first.

In a first delivery, these problems may occur more frequently because a woman’s tissues have not been stretched by previous deliveries. Because of risk of injury or even death to the baby, cesarean delivery is preferred when the fetus is in breech presentation, unless the doctor is very experienced with and skilled at delivering breech babies or there is not an adequate facility or equipment to safely perform a cesarean delivery.

Breech presentation is more likely to occur in the following circumstances:

Labor starts too soon (preterm labor).

The uterus is abnormally shaped or contains abnormal growths such as fibroids .

Other presentations

In face presentation, the baby's neck arches back so that the face presents first rather than the top of the head.

In brow presentation, the neck is moderately arched so that the brow presents first.

Usually, fetuses do not stay in a face or brow presentation. These presentations often change to a vertex (top of the head) presentation before or during labor. If they do not, a cesarean delivery is usually recommended.

In transverse lie, the fetus lies horizontally across the birth canal and presents shoulder first. A cesarean delivery is done, unless the fetus is the second in a set of twins. In such a case, the fetus may be turned to be delivered through the vagina.

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Biomechanics of the Shoulder

CHAPTER 6 Biomechanics of the Shoulder Eiji Itoi, MD, PhD, Bernard F. Morrey, MD, Kai-Nan An, PhD Because of its component parts, a description of the biomechanics of the shoulder complex is rather involved. To make the subject at once comprehensive and relevant to the clinician, the structure and function of the sternoclavicular and acromioclavicular joints are dealt with first. The anatomy and biomechanics of the glenohumeral joint are then discussed in three parts according to an outline familiar to clinicians: motion, constraints, and forces across the joint ( Table 6-1 ). By way of classification, we have adopted the increasingly accepted phrase of arm elevation rather than abduction or flexion, when possible. Although this organization is somewhat arbitrary and has some overlap, it does allow a reasonably simple and logical approach to understanding the entire shoulder complex. TABLE 6-1 Relationship of Joint Function and Biomechanical Measurements Clinical Function Biomechanical Description Motion Kinematics Stability Constraints Strength Force transmission SHOULDER COMPLEX The function of the shoulder girdle requires the integrated motion of the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints. This motion is created by the delicate interaction of almost 30 muscles that control the total system complex. Discussion of the biomechanics of this complex focuses first on the sternoclavicular and acromioclavicular joints and then on the glenohumeral and scapulothoracic joints. Sternoclavicular Joint According to Dempster, six actions occur at the sternoclavicular joint: elevation, depression, protrusion, retraction, and upward and downward rotation. 1 The amount of potential motion present at this articulation has been studied by disarticulating the scapula. Anteroposterior rotation exceeds superoinferior motion by about 2 : 1. 2 In an intact and functioning extremity, the actual amount of displacement is of course limited by the attachment to the scapula; this motion is described later. At the extremes, motion is limited by tension developed in the ligamentous complex on the opposite side of the joint. This constraint occurs in concert with increased contact pressure at the articulation and the intra-articular disk ligament ( Fig. 6-1 ). Approximately 35 degrees of upward rotation occurs at the sternoclavicular joint. 3, 4 A similar 35 degrees of anterior and posterior rotation and up to 45 to 50 degrees of axial rotation also occur at this joint. FIGURE 6-1 Superior ( A ), inferior ( B ), anterior ( C ), and posterior ( D ) ligaments stabilize the sternoclavicular joint by enhancing the contact force at certain joint positions. (Redrawn from Dempster WT: Mechanisms of shoulder movement. Arch Phys Med Rehabil 46A:49-70, 1965.) Anterior displacement of the distal end of the clavicle is not affected by release of the interclavicular or costoclavicular ligaments or by the intra-articular disk. 5 Release of the capsular ligament is followed by downward displacement of the lateral aspect of the clavicle. Inferior displacement of the clavicle at the sternum is resisted by articular contact at the inferior aspect of the joint and by tautness developed in the interclavicular ligament and the posterior expansion of the capsular ligament. 1 Superior translation of the joint is resisted by tension developed in the entire costoclavicular complex. Little, if any, articular constraint assists in resisting this displacement. Protrusion or anterior displacement of the clavicle is resisted not only by the anterior capsule but also by the posterior portion of the interclavicular ligament and the posterior sternoclavicular ligament. Conversely, posterior displacement or retraction of the medial aspect of the clavicle generates tension in the anterior portion of the inferior capsular ligaments and in the anterior sternoclavicular ligament, as well as in the anterior portion of the costoclavicular ligament. Only a limited amount of articular contact resists such displacement; this contact is on the posterior vertical ridge of the sternal articulation and the posterior portion of the clavicle. Spencer and colleagues demonstrated that the posterior capsule was the most important stabilizer for both the anterior and posterior translations of the medial end of the clavicle, whereas the anterior capsule was also important for anterior translation. 6 According to them, the costoclavicular and interclavicular ligaments had little effect on the anterior-to-posterior stability of this joint. Clavicular rotation causes twisting of the capsular ligaments. Only about 10 degrees of downward (forward) rotation occurs before the ligaments become taut and limit further motion. With upward (backward) rotation of the clavicle, up to 45 degrees of rotation occurs before the entire complex again becomes taut and resists further rotatory displacement. 7 Both these actions increase compression across the sternoclavicular joint. The costoclavicular ligament is thought to be the most important single constraint in limiting motion at this joint. 8 Acromioclavicular Joint Motion and Constraint The amount of possible acromioclavicular motion that is independent of the sternoclavicular link has been found to be limited by the complex arrangement of the coracoclavicular and acromioclavicular ligaments. According to most investigators, rotation of the acromioclavicular joint takes place about three axes. 1, 3, 8, 9 These motions are variously described but can simply be termed anteroposterior rotation of the clavicle on the scapula, superoinferior rotation , and anterior (inferior) and posterior (superior) axial rotation . Of these three, anteroposterior rotation of the clavicle with respect to the acromion is approximately three times as great as superoinferior rotation of an intact specimen. 10 Sahara and colleagues quantified anterior-to-posterior and superior-to-inferior translations of the distal end of the clavicle on the acromion using open MRI. They reported that the distal end of the clavicle translated most posteriorly (average 1.9 mm) at 90 degrees of abduction and most anteriorly (average 1.6 mm) at maximum abduction. The superior-to-inferior translation was much smaller, with the distal end of the clavicle shifted slightly superiorly (average 0.9 mm) during arm elevation. Regarding the constraints of the acromioclavicular joint, Dempster noted that the conoid and trapezoid became taut with anteroposterior scapular rotation, thus serving as the constraint of this motion. 1 In a subsequent study by Fukuda and coworkers, however, the acromioclavicular ligament was noted to be taut in its anterior component with posterior rotation and taught in its posterior component with anterior rotation. 9 Anterior rotation of the clavicle with regard to the scapula was also found to cause some tightness in the conoid and trapezoid ligaments, but this tightness was of a magnitude approximately equal to the stretch observed in the posterior acromioclavicular ligament. Thus, the limiting factor to this motion is the posterior component of the acromioclavicular ligament. On the other hand, posterior rotation of the clavicle is restrained only by the anterior fibers of the acromioclavicular ligament, with virtually no contribution from the other structures. Superoinferior rotation of the clavicle is quite limited at the acromioclavicular joint. Both Dempster and Kapandji noted virtually no ligamentous contribution to resisting inferior displacement ( Fig. 6-2 ). 1, 8 However, superior rotation of the clavicle with respect to the acromion is limited primarily by the medial aspect of the conoid ligament, with subsequent tightening of the lateral portion of this structure ( Fig. 6-3 ). The trapezoid provides approximately the same degree of constraint as do the anterior and posterior portions of the acromioclavicular ligament complex. Once again, the magnitude of this displacement is not reported by either investigator but is said to be limited. FIGURE 6-2 Superior orientation ( A ) and anterior orientation ( B ) of the acromioclavicular joint. It is considered a plane type of joint. FIGURE 6-3 The coracoclavicular ligament complex consists of the larger and heavier trapezoid ligament, which is oriented laterally, and the smaller conoid ligament, which is situated more medially. (Modified from Hollinshead WH: Anatomy for Surgeons, vol 3. New York: Harper & Row, 1969.) Anterior and posterior axial rotation (inferior to superior) was reported by Dempster to be about 60 degrees in cadaveric shoulders without the thorax. 1 In live shoulders, Rockwood and Green demonstrated only 5 to 8 degrees of motion at the acromioclavicular joint using two Kirschner wires inserted into the acromion and the clavicle. 7 According to the recent three-dimensional kinematic analysis using open MRI, Sahara and colleagues demonstrated in volunteer shoulders that the anterior axial rotation of the clavicle at the acromioclavicular joint increased linearly with abduction and reached 35 degrees on average at maximum abduction of the arm. 11 Both anterior and posterior axial rotations are limited by the conoid ligament. Posterior axial rotation is accompanied by tightening of the trapezoid ligament, with some contribution from the medial and anterior conoid as well as from the acromioclavicular ligament complex. 9 Dempster, however, indicates that the acromioclavicular ligament is taut in the extreme of anterior and posterior axial rotation and is a limiting factor of this motion. 1 Fukuda and colleagues have quantified the displacement as a function of the ligamentous constraints. 9 Slight displacement is limited by the acromioclavicular ligament, but large displacements are resisted by the coracoclavicular ligaments ( Fig. 6-4 ). FIGURE 6-4 All displacements are resisted by the force generated in the acromioclavicular ligament, and large displacements are also resisted by the conoid and trapezoid structures. A-C, acromioclavicular. (Redrawn from Fukuda K, Craig EV, An K-N, et al: Biomechanical study of the ligamentous system of the acromioclavicular joint. J Bone Joint Surg Am 68:434-440, 1986.) Relative contributions of the individual capsular ligaments (anterior, posterior, superior, and inferior) were studied by Klimkiewicz and colleagues, who demonstrated that the superior and posterior acromioclavicular ligaments were the most important contributors to the acromioclavicular restraint against posterior translation of the distal end of the clavicle (56% and 25%, respectively). 12 Debski and coworkers also investigated the capsular contribution to stability of the acromioclavicular joint. When the capsule was released, significant anterior-to-posterior instability was observed but not superior-to-inferior instability. 13 Capsular release increased loading on the coracoclavicular ligaments: Anterior load increased tension in the conoid ligament, and posterior load increased tension in the trapezoid ligament. Thus, the trapezoid and conoid ligaments have different functions. Motion of the Clavicle The potential motion present at the sternoclavicular and acromioclavicular joints exceeds that actually attained during active motion of the shoulder complex. Current data indicate that accurate demonstration of the phasic three-dimensional motion of the sternoclavicular and acromioclavicular joints that occurs with arm elevation is a complex problem. 14 During elevation of the extremity, clavicular elevation of about 30 degrees occurs, with the maximum at about 130 degrees of elevation ( Fig. 6-5 ). 3 The clavicle also rotates forward approximately 10 degrees during the first 40 degrees of elevation. No change takes place during the next 90 degrees of elevation, but an additional 15 to 20 degrees of forward rotation subsequently occurs during the terminal arc. Forward elevation (flexion) demonstrates virtually an identical pattern of clavicular motion. FIGURE 6-5 Clavicular elevation during abduction and forward flexion of the arm. (Redrawn from Inman VT, Saunders JR, Abbott LC: Observations on the function of the shoulder joint. J Bone Joint Surg 26:1-30, 1944.) Axial rotation of the clavicle is reported by Inman and coworkers to be an essential and fundamental feature of shoulder motion, particularly arm elevation ( Fig. 6-6 ). If the clavicle is not allowed to rotate, elevation of only about 110 degrees is said to be possible. 3 Superior (posterior) rotation of the clavicle begins after the arm has attained an arc of about 90 degrees of elevation and then progresses in a rather linear fashion, with approximately 40 degrees of rotation attained at full elevation (see Fig. 6-6 ). 3 These findings have been challenged by Rockwood and Green. Placement of pins in the clavicle and acromion shows less than 10 degrees of rotation with full arm elevation. 7 This discrepancy suggests that more than 30 degrees of axial rotation occurs at the sternoclavicular joint. FIGURE 6-6 Axial rotation of the clavicle during arm elevation. (Redrawn from Inman VT, Saunders JR, Abbott LC: Observations on the function of the shoulder joint. J Bone Joint Surg 26:1-30, 1944.) Sahara and coworkers, in contrast, reported that 35 degrees of axial rotation occurred at the acromioclavicular joint, indicating that less rotation occurred at the sternoclavicular joint. 11 Clinically, fixation of the clavicle to the coracoid by a screw does not greatly limit shoulder elevation and ankylosis caused by ectopic bone also causes minimal loss of arm elevation ( Fig. 6-7 ). The patient shown in Figure 6-7 could elevate his arm to about 160 degrees. On the other hand, ankylosis of the sternoclavicular joint allows only 90 degrees of shoulder elevation. 7 Thus, loss of motion at the acromioclavicular joint appears to be better tolerated than loss of motion at the sternoclavicular joint. FIGURE 6-7 Extensive ectopic ossification of the coracoclavicular ligaments. By limiting clavicular motion, only a small portion of the full range of motion of the shoulder complex is limited. Clinical Relevance Acromioclavicular instability is one of the most important and controversial topics clinically relevant to the shoulder. The acromioclavicular capsular ligament complex is the primary constraint for small rotational displacements at this joint. Downward force applied to the end of the scapula causes inferior displacement of the acromion (grade III injury) and thus violates the constraint provided by the conoid and trapezoid ligaments. Lesser degrees of ligamentous disruption, such as occur with grade I or II acromioclavicular sprains, demonstrate minimal or no inferior migration of the acromion. Biomechanical data have explained this finding by showing that the conoid ligament must be intact to prevent even slight displacement. Resection of the distal clavicle is commonly performed in patients with osteoarthritis of the acromioclavicular joint. Debski and colleagues reported that acromioplasty did not affect kinematics of this joint, but acromioplasty together with distal clavicle resection increased posterior translation by 30% during posterior loading and increased the in situ force in the trapezoid and conoid ligaments almost three times greater than in the intact shoulder during anterior loading. 15 Corteen and Teitge also reported that resection of the distal clavicle increased posterior translation by 32%. 16 Reconstruction using the coracoacromial ligament significantly stabilized the acromioclavicular joint. Thus, the significant effect of distal clavicle resection on motion and ligament forces should be taken into consideration when this procedure is to be used. GLENOHUMERAL AND SCAPULOTHORACIC JOINT MOTION The motion of the shoulder complex is probably greater than that of any other joint in the body. The arm can move through an angle of approximately 0 to 180 degrees in elevation, internal and external rotation of approximately 150 degrees is possible, and flexion and extension—or anterior and posterior rotation in the horizontal plane—is approximately 170 degrees. 17 This motion, which represents the composite motion of several joints, occurs primarily in the glenohumeral and scapulothoracic joints; extreme positions require rotation at the sternoclavicular and acromioclavicular joints. Motion of the shoulder complex has been a topic of concern and controversy for more than 100 years. Reasons for this debate are numerous and include imperfect devices or means of measurement because the soft tissue envelope makes it difficult to actually observe the skeletal motion, confusion with respect to terminology, inconsistency in defining the reference system, and an early lack of understanding of the concept of sequence-dependent serial rotation. Early investigations focused on arm motion about the sagittal, coronal, and transverse planes. However, because the sequence-dependent nature of rotation about orthogonal axes was not appreciated, years of debate and discussion centered on understanding and explaining Codman’s paradox. Codman’s Paradox Codman’s paradox may be demonstrated easily ( Fig. 6-8 ). From the resting position in the anatomic posture with the medial epicondyle pointing toward the midline of the body, the arm is brought forward to 90 degrees of flexion and abducted 90 degrees. The epicondyle is now pointing perpendicular to the coronal plane. The arm is then brought back to the side to its apparent initial position, but the medial epicondyle is now observed to be rotated anteriorly away from the body instead of medially toward the midline of the body. The humerus, however, was never axially rotated. 18 FIGURE 6-8 Codman’s paradox. Top , The humerus is flexed to a right angle (B) and swung backward to the plane of the scapula (C) . Bottom, It is then brought back to the vertical. An axial rotation position change has occurred without actual axial rotation taking place. (From Johnston TB: The movements of the shoulder joint. A plea for the use of the “plane of the scapula” as the plane of reference for movements occurring at the humero-scapular joint. Br J Surg 25:252-260, 1937.) The difficulty in understanding this phenomenon has prompted numerous discussions. 18 – 21 The simplest explanation is that serial angular rotations are not additive but are sequence dependent, which means that 90 degrees of rotation about the z-axis and then the x-axis results in a different final position than does rotation about the x-axis and then the z-axis ( Fig. 6-9 ). Multiple rotations about orthogonal axes must therefore be defined by the sequence of the rotation. In aerospace terms, these rotations are called the Eulerian angles: yaw, pitch, and roll. FIGURE 6-9 Final orientation depends on the sequence of serial rotations around the orthogonal axes. The confusion is significantly resolved by the use of two reference systems. First, scapular motion is best defined in reference to the classic anatomic system of the trunk. Second, humeral motion is described in reference to the scapula. This issue is discussed in detail later. Techniques to Observe and Describe Motion of the Shoulder Complex Because of the complexity of this issue and the conflicting results, it is appropriate to describe various techniques that have been used to measure upper extremity motion. Methods of observing and describing motion of the upper extremities may be broadly categorized into research and clinical effort. The early research effort to describe shoulder joint (complex) motion consisted of simple (but careful) observation of cadaveric material and thus often included observation of the ligamentous constraints. 18, 22 – 24 A gross description of motion and displacement has proved to be accurate even today because of the careful nature of these early observations. With the advent of the roentgenogram, uniplanar 25 and biplanar cineradiographic studies are the more common techniques used today for active and passive investigations. These techniques are particularly attractive because they can be used in vivo. By implanting metal markers, very accurate three-dimensional rotation may be measured from these radiographs. 26 With the advent of computer data manipulation, replication of motion by using a complex system involving an interactive microcomputer for analyzing images with real-time graphic display has been developed. This method and other modeling techniques are much too complex for routine use but can serve as valuable research tools. 27, 28 Clinical measurement techniques include simple and complex goniometers. Doody and associates designed a goniometer to be used in vivo that measures glenohumeral and scapulothoracic motion simultaneously. 24, 29 Electrogoniometers have not been of routine clinical value but have been used extensively for basic science investigations. Unfortunately, the anatomy constraints at the shoulder limit the value of electrogoniometers. A stereometric method has also been used for three-dimensional kinematic analysis. Basically, when three non-colinear points fixed to a rigid body are defined within an inertial reference frame, the position and orientation of that rigid body can be specified and the relative rotation and translation occurring at a joint can be determined. Numerous commercial systems using light-emitting diodes, reflecting dots, and ultrasonic transducer techniques are available for such an application. Aerospace technology has provided a device that uses three mutually orthogonal magnetic fields 30 ; it has proved useful as both a research and a clinical tool. This instrument has been applied to in vivo and in vitro studies and measures simultaneous three-dimensional rotational motion. 31, 32 In addition, translation displacement has also been calculated, thus allowing determination of the screw axis, which defines the complete displacement characteristics of the system. More recently, Sahara and colleagues used magnetic resonance images to measure three-dimensional kinematics of the glenohumeral joint. 33 Magnetic resonance images were obtained with volunteers in a seated position and in seven static positions of the arm from 0 degrees to maximum abduction using vertically open magnetic resonance imaging. Three-dimensional surface models were created and three-dimensional movements of each bone in the glenohumeral joint were calculated using a computer algorithm. This is a noninvasive method, and in vivo kinematics of the bony structures can be precisely measured. Description of Joint Motion The aforementioned techniques permit joint motion to be described with varying degrees of sophistication. In general, joint kinematics may be divided into two-dimensional planar motion and three-dimensional spatial motion. With planar motion, the moving segment both translates and rotates around the fixed segment. A more distinctive description of planar motion, however, can be based on rotation around a point or axis, which is defined as the instantaneous center of rotation (ICR). Theoretically, the ICR could be determined accurately if the velocities of points on the rigid body are measurable. In practice, an alternative technique based on the method of Rouleaux is commonly adopted. In this method, the instantaneous locations of two points on the moving segment are identified from two consecutive positions within a short period of time, and the intersection of the bisectors of the lines joining the same points at the two positions defines the ICR ( Fig. 6-10 ). FIGURE 6-10 Measurement of the center of rotation of the humeral head as defined by the Rouleaux technique. MAX, maximum. (From Walker PS: Human Joints and Their Artificial Replacements. Springfield, Ill: Charles C Thomas, 1977.) Occasionally it is useful to describe the planar joint articulating motion. 34 For general planar or gliding motion of the articular surface, the terms sliding, spinning, and rolling are commonly used ( Fig. 6-11 ). FIGURE 6-11 All three types of motion (spinning, rolling, and sliding) occur at the glenohumeral articulation. Sliding motion is defined as pure translation of a moving segment against the surface of a fixed segment. The contact point of the moving segment does not change, but its mating surface has a constantly changing contact point. If the surface of the fixed segment is flat, the ICR is located at infinity; otherwise, it is at the center of the curvature of the fixed surface. Spinning motion is the exact opposite of sliding motion; the moving segment rotates and the contact point on the fixed surface does not change. The ICR, in this case, is located at the center of curvature of the spinning body that is undergoing pure rotation. Rolling motion is motion between moving and fixed segments in which the contact points on each surface are constantly changing. However, the arc length of the moving surface matches the path on the fixed surface so that the two surfaces have point-to-point contact without slippage. The relative motion of rolling is a combination of translation and rotation. The ICR is located at the contact point. Most planar articulating motion can be described by using a combination of any two of these three basic types of motion. Three-Dimensional Glenohumeral Joint Motion Three-dimensional analysis of motion of a rigid body requires three linear and three angular coordinates to specify the location and orientation of a rigid body in space. In other words, any rigid body with unconstrained motion has six degrees of freedom in space. Numerous methods are available to describe spatial rigid body motion, two of the most commonly used of which are description of the Eulerian angle and the screw displacement axis. If the glenohumeral joint is stable and the motion can be assumed to be that of a ball-and-socket joint, it is sufficient to consider only rotation of the joint and neglect small amounts of translation. In this case, description of three-dimensional rotation by using the Eulerian angle system is most appropriate ( Fig. 6-12 ). It should be remembered, as emphasized earlier, that general three-dimensional rotation is sequence dependent. In other words, with the same specified amount of rotation around three axes, the final result will be different if the sequence of the axes of rotation is different, which is one of the explanations for Codman’s paradox. FIGURE 6-12 Three-dimensional rotation around each of the orthogonal axes is most accurately described by using the Eulerian angle system. Glenohumeral motion is defined by the sequence-dependent Eulerian angles. PA, posteroanterior. With the arm hanging at the side of the body, the z-axis is defined to be perpendicular to the scapular plane. The y-axis points out laterally and the x-axis points distally along the humeral shaft axis. The rotational sequence for the Eulerian description of glenohumeral joint rotation or the orientation of the humerus relative to the scapula is as follows: First rotate the humerus around the x-axis by an amount f to define the plane of elevation. Then rotate the arm around the rotated z (z′)-axis by an amount q to define the arm elevation. Finally, axial rotation of the humerus around the rotated x (x″)-axis by an amount ψ completes the process. During circumduction motion of the humerus, for example, the corresponding Eulerian angle could be measured as shown in Figure 6-12 . This description could be used clinically to describe the range of joint motion as well as the specification of joint position at which any abnormality or pathologic process should be documented. In instances in which a more general description of glenohumeral joint displacement is required, the screw displacement axis (SDA) description is most appropriate. The rotation and translation components of displacement of the humerus relative to the glenoid or scapula are defined by rotation around and translation along a unique screw axis ( Fig. 6-13 ). In addition to incorporating a description of translation, the advantage of using the SDA method is that the orientation of the SDA remains invariant regardless of the reference coordinate axes used. The SDA can be determined experimentally with various methods. With a rotational matrix describing the orientation and a positional vector from a reference point known for the rigid body, the SDA can be calculated. 35 If the coordinates of at least three reference points on the rigid body are measured, the SDA can also be calculated. 36 FIGURE 6-13 Both rotational (Φ) and translational ( tn ) components of displacement of a rigid body may be expressed by the concept of the screw axis ( n ), which represents the shortest path from position a to position q around or along which the displacement can be described. s, shortest distance from the center of coordinate system to the screw axis. SHOULDER MOTION Resting Posture Scapula The resting position of the scapula relative to the trunk is anteriorly rotated about 30 degrees with respect to the frontal plane as viewed from above ( Fig. 6-14 ). The scapula is also rotated upward about 3 degrees with respect to the sagittal plane as viewed from the back ( Fig. 6-15 ). 17, 37 Finally, it is tilted forward (anteflexed) about 20 degrees with respect to the frontal plane when viewed from the side. 14 This posture of the scapula is not influenced by an external load (up to 20 kg) applied to the extremity. 14 FIGURE 6-14 The resting position of the scapula is about 30 degrees forward with respect to the coronal plane as viewed in the transverse plane. FIGURE 6-15 The resting position of the scapula is rotated about 3 degrees superior as viewed in the frontal plane. McClure and colleagues measured the three-dimensional kinematics of the scapula during dynamic movement of the shoulder. A three-dimensional motion sensor was firmly fixed to the scapula with a Kirschner wire. 38 During arm elevation in the scapular plane, the scapula upwardly rotated (average of 50 degrees), tilted posteriorly around a medial-lateral axis (30 degrees), and externally rotated around a vertical axis (24 degrees). Lowering of the arm resulted in reversal of these motions in a slightly different pattern. The mean ratio of glenohumeral to scapulothoracic motion was 1.7:1. The researchers concluded that normal scapular motion consists of substantial rotation around three axes, not simply upward rotation. Using the same method, Bourne and colleagues reported similar results. 39 Fung and associates measured scapular and clavicular kinematics during passive humeral motion. 40 Scapular and clavicular rotation was relatively small until the humerus reached approximately 90 degrees of elevation. The glenohumeral-to-scapulothoracic ratio was approximately 2 for the entire range of elevation for each elevation plane, but it was dramatically larger during early elevation than during late elevation. Humerus The humeral head rests in the center of the glenoid when viewed in the plane of the glenoid surface. 18, 41 Fick referred to this relationship as Nullmeridianebene, or dead meridian plane. 41 The humeral head and shaft are thought to lie in the plane of the scapula. The 30-degree retroversion of the articular orientation is complemented by the 30-degree anterior rotation of the scapula on the trunk. Articular Surface and Orientation Humerus The articular surface of the humerus constitutes approximately one third the surface of a sphere with an arc of about 120 degrees. This articular surface is oriented with an upward tilt of approximately 45 degrees and is retroverted approximately 30 degrees with respect to the condylar line of the distal end of the humerus ( Fig. 6-16 ). 1, 17, 41, 42 Retroversion of the humerus is much greater in children. 43 The average retroversion is 65 degrees between 4 months and 4 years of age and 38 degrees between 10 and 12 years of age. Most of the derotation process takes place by the age of 8 years, with the remainder developing gradually until adulthood. This derotation process seems to be restricted in young throwing athletes, 44 resulting in increased retroversion in dominant arms. 45, 46 FIGURE 6-16 Two-dimensional orientation of the articular surface of the humerus with respect to the bicondylar axis. (Modified from Mayo Clinic © 1984.) Glenoid In the coronal plane, the articular surface of the glenoid comprises an arc of approximately 75 degrees. The shape of the articulation is that of an inverted comma. The typical long-axis dimension is about 3.5 to 4 cm. In the transverse plane, the arc of curvature of the glenoid is only about 50 degrees, with a linear dimension of approximately 2.5 to 3 cm. 41 The relationship of the articular surface to the body of the scapula is difficult to define precisely because of the difficulty in defining a frame of reference. Typically, it is accepted that the glenoid has a slight upward tilt of about 5 degrees 47 with respect to the medial border of the scapula and is retroverted a mean of approximately 7 degrees, although individual variation in these measurements is considerable ( Fig. 6-17 ). 48 FIGURE 6-17 The glenoid faces slightly superior and posterior (retroverted) with respect to the body of the scapula. (Modified from Mayo Clinic © 1984.) Saha has defined the relationship of the dimensions of the humeral head and the glenoid as the glenohumeral ratio . This relationship is approximately 0.8 in the coronal plane and 0.6 in the horizontal or transverse plane. 48 These values are consistent with several observations that have estimated that only about one third of the surface of the humeral head is in contact with the glenoid at any given time. 17 Hertz 49 measured the surface area of the glenoid with and without the labrum and compared it with that of the humeral head. The surface ratio of the glenoid and humeral head was 1:4.3 without the labrum and 1:2.8 with the labrum. In other words, the glenoid surface with the labrum attached is approximately one third the humeral head surface, and it is approximately one fourth the humeral head surface without the labrum. Arm Elevation The most important function of the shoulder—arm elevation—has been extensively studied to determine the relationship and contribution of the glenohu-meral and scapulothoracic joints, the scapulohumeral rhythm . 3, 24, 25, 42, 48, 50 – 55 Although early descriptions of scapulohumeral rhythm were based on motion with respect to the coronal (frontal) plane, recent discussion has defined this motion with respect to the scapular plane. Neither reference system is completely adequate to fully describe the complex rotational sequences involved in elevation of the arm because the changes in scapular position during elevation usually have not been considered. Early descriptions of this motion defined the glenohumeral contribution as the first 90 degrees, followed by scapulothoracic rotation. 17 Subsequent discussions place the overall glenohumeral-to-scapulothoracic motion ratio at 2:1. 3, 14 This ratio is inconsistent during the first 30 degrees of elevation, with variation by person and even by sex. 21, 29, 52 Poppen and Walker reported a 4:1 glenohumeral-to-scapulothoracic motion ratio during the first 25 degrees of arm elevation. 25 Thereafter, an almost equal 5:4 rotation ratio occurs during subsequent elevation. The average overall ratio is about 2:1. The lack of linearity of this motion complex has also been observed by Doody and coworkers, who showed a 7:1 ratio of scapulothoracic-to-glenohumeral motion during the first 30 degrees of elevation and an approximately 1:1 ratio from 90 to 150 degrees of arm elevation. 29 Others have also shown nonlinear variation during elevation. 55 Further evaluation of the arm against resistance elicits scapulothoracic motion earlier than with passive motion alone. 29 The various studies have been simply summarized by Bergmann. 56 During the first 30 degrees of elevation, variably greater motion occurs at the glenohumeral joint. The last 60 degrees occurs with about an equal contribution of glenohumeral and scapulothoracic motion. The overall ratio throughout the entire arc of elevation is about 2:1 ( Fig. 6-18 ). FIGURE 6-18 A, The classic study by Inman and colleagues shows the relationship between glenohumeral and scapulothoracic motion. The blue line indicates the regression line. The red lines indicate the range of ±2 SD. B, Angular changes of the glenohumeral joint with respect to arm elevation were determined by several investigators. 1, Nobuhara K: The Shoulder: Its Function and Clinical Aspects. Tokyo: Igaku-Shoin, 1987. 2, Poppen NK, Walker PS: Normal and abnormal motion of the shoulder. J Bone Joint Surg Am 58:195-201, 1976. 3, Inman VT, Saunders JR, Abbott LC: Observations on the function of the shoulder joint. J Bone Joint Surg 26:1-30, 1944. 4, Freedman L, Munro RH: Abduction of the arm in scapular plane: Scapular and glenohumeral movements. J Bone Joint Surg Am 18:1503-1510, 1966. 5, Reeves B, Jobbins B, Flowers M: Biomechanical problems in the development of a total shoulder endoprosthesis. (Proc Br Orthop Res Soc) J Bone Joint Surg [Br] 54:193, 1972. ( A, Redrawn from Inman VT, Saunders JR, Abbott LC: Observations on the function of the shoulder joint. J Bone Joint Surg 26:1-30, 1944. B, Redrawn from Bergmann G: Biomechanics and pathomechanics of the shoulder joint with reference to prosthetic joint replacement. In Koelbel R, Helbig B, Blauth W [eds]: Shoulder Replacement. Berlin: Springer-Verlag, 1987, pp 33-43.) Harryman and associates confirmed this ratio for planes other than the scapular or coronal plane. 57 After measuring the three-dimensional kinematics of the glenohumeral and scapulothoracic joints in various planes of elevation, they concluded that the relative contribution of glenohumeral and scapulothoracic motion to the total arc of elevation was consistent and essentially 2:1. The scapulohumeral rhythm is affected by the speed of arm elevation. 58 At high speed, glenohumeral motion is more dominant at the beginning of motion. The rhythm remains the same, although the total range of motion is reduced with age. 59 With upward movement of the arm, a complex rotational motion of the scapula occurs ( Fig. 6-19 ). In addition to the upward rotation described earlier, about 6 degrees of anterior rotation with respect to the thorax occurs during the first 90 degrees of arm elevation. Posterior rotation of about 16 degrees occurs next, with the scapula coming to rest about 10 degrees posteriorly rotated in comparison to the original resting position. 50 Thus, an arc of about 15 degrees of anteroposterior rotation of the scapula occurs with elevation of the arm; about 20 degrees of forward tilt with respect to the thorax also occurs during elevation. 14 Scapulohumeral rhythm is affected by various pathologic conditions of the shoulder. In stiff shoulders with anterior capsular tightness, a more excessive scapular upward rotation is observed. 60 On the other hand, shoulders with instability show delay in retraction and posterior tilt of the scapula during arm elevation, which can contribute to shoulder instability. 61 Scapulohumeral rhythm changes after total shoulder arthroplasty, with the 2:1 ratio changed to 1:2 after nonconstrained total shoulder arthroplasty. 62 FIGURE 6-19 Complex three-dimensional rotation and translation of the scapula during arm elevation from 0 to 180 degrees in the frontal plane (F) and sagittal plane (S). α, scapular rotation in the frontal plane; β, scapular rotation in the sagittal plane; γ, scapular rotation in the horizontal plane; Dist, distance between the vertical at C7 and the medial border of the scapular spine. (Modified from Laumann U: Kinesiology of the shoulder joint. In Koelbel R, Helbig B, Blauth W [eds]: Shoulder Replacement. Berlin: Springer-Verlag, 1987, pp 23-31.) External Rotation of the Humerus Early observers noted that “obligatory” external rotation of the humerus was necessary for maximal elevation. 18 Impingement of the tuberosity on the coracoacromial arch was assumed to be the mechanical constraint. External rotation clears the tuberosity posteriorly, thereby allowing full arm elevation ( Fig. 6-20 ). 18 We have observed in our laboratory that external rotation of the humerus also loosens the inferior ligaments of the glenohumeral joint. This mechanism thus releases the inferior checkrein effect and allows full elevation of the arm. Full elevation with maximal external rotation has also been shown to be a position of greater stability of the shoulder than the elevated position. 51 FIGURE 6-20 Upward elevation of the arm requires obligatory external rotation to avoid impingement of the tuberosity under the acromial process. A, Neutral position. B, Internal rotation. C, External rotation. Browne and associates 63 quantified the relationship between elevation and rotation of the humerus with respect to the fixed scapula by using a three-dimensional magnetic tracking device. The plane of maximal arm elevation was shown to occur 23 degrees anterior to the plane of the scapula. Elevation in any plane anterior to the scapular plane required external rotation of the humerus, and maximal elevation was associated with approximately 35 degrees of external rotation. Conversely, maximal glenohumeral elevation with the arm in full internal rotation occurs in a plane about 20 to 30 degrees posterior to that of the scapula and is limited to only about 115 degrees. 63 They reported that the observed effects of this rotation were to clear the humeral tuberosity from abutting beneath the acromion and to relax the inferior capsuloligamentous constraints. Gagey and Boisrenoult also reported that the inferior capsule determines the maximum abduction angle. 64 On the other hand, Jobe and Iannotti reported that obligatory external rotation occurs not because of abutment between the greater tuberosity and the acromion but because of abutment between the greater tuberosity and the superior posterior glenoid rim. 65 This concept was first described by Walch and colleagues as posterosuperior impingement 66 and was later known as internal impingement . In vivo measurements of maximal elevation by Pearl and colleagues 67 revealed a slight difference from these cadaver studies. According to them, maximal elevation was achieved with the humerus just behind the scapular plane (−4 degrees). A difference in definition of the scapular plane and a difference between in vivo behavior and that of the cadaver might explain the discrepancy. The complex sequence of events in combined motion of the glenohumeral and scapulothoracic joints has been divided into four stages. Glenohumeral motion occurs first; next, sternoclavicular and then acromioclavicular rotation is observed with elevation of the scapula; and finally, the scapula pivots upward around the acromioclavicular joint. This simplified analytic description is, in general, consistent with the observations of Laumann, Nobuhara, and others. 14, 55 Center of Rotation An accurate calculation of the ICR of the humeral head is a complex problem that is much simplified if the motion is limited to a single plane. 68, 69 Such has been the assumption of most analyses. Hence, the center of rotation of the glenohumeral joint has been defined as a locus of points situated within 6 ± 2 mm of the geometric center of the humeral head (see Fig. 6-10 ). 25 This definition, generated by the Rouleaux technique, is considered reasonably accurate. 70 However, this particular technique for defining the center of rotation is accurate only for pure spinning motion, is subject to input-type error, 71 and is not accurate in pathologic conditions in which translation is a significant component of the displacement or in which a significant amount of nonplanar motion is present. These limitations might explain why other authors have found the center to lie 8 mm behind and 6 mm below the intersection of the shaft and head axes. 72 Still others have reported that multiple centers of rotation occur during abduction. 73 The relatively small dimension of this locus as well as the relative consistency of its definition as lying in the geometric center of the humeral head reflects the small amount of translation that normally occurs at this joint and is consistent with the aforementioned observations. A small amount (∼3 mm) of upward translation has been reported in the intact shoulder during the first 30 degrees of elevation; only about 1 mm of additional excursion occurs with elevation measured at greater than 30 degrees. 25 A small amount of translation has also been confirmed in cadaver models. During passive elevation without force to the muscles, the humeral head shifted superiorly by 0.35 to 1.2 mm. 31, 74 By using simulated muscle force to the deltoid and rotator cuff muscles, greater superior-to-inferior translation of the humeral head was recorded (2.0-9.0 mm). 75, 76 Furthermore, an increase in translation occurs with certain pathologic processes such as rotator cuff deficiency 25 and tendon rupture of the long head of the biceps (LHB). 77 The center of rotation of the scapula for arm elevation is situated at the tip of the acromion as viewed edge on ( Fig. 6-21 ). 78 FIGURE 6-21 The center of rotation of the scapula for arm elevation is focused in the tip of the acromion. Left, Anterposterior view. Right, Lateral view. Os, reference point of the scapula (center of the glenoid). (Redrawn from Poppen NK, Walker PS: Normal and abnormal motion of the shoulder. J Bone Joint Surg Am 58:195-201, 1976.) Screw Axis Application of the SDA for glenohumeral joint motion has one specific advantage. By using the concept of the intersection or the middle point of the common perpendicular between two instantaneous screw axes as the measurement of the three-dimensional ICR, the stability or laxity of the joint can be described. If the joint is tight and stable, the points of intersection of all the screw axes will be confined within a small sphere ( Fig. 6-22 ). On the other hand, when the joint is becoming unstable because of disease of either the capsuloligamentous structures or the rotator cuff, the points of intersection of the screw axes will be more dispersed and confined in a larger sphere. Stokdijk and colleagues compared different methods in determining the glenohumeral joint rotation center in vivo, and they prefer the screw axes method as a reliable and valid method in movement registration. 79 The concept had also been used to measure the anterior instability of the shoulder at the end of the late preparatory phase of throwing. 80 FIGURE 6-22 The common intersection of the screw axes creates a perfect ball-and-socket joint ( left ). When significant translation occurs, the axes do not intersect at a single point ( right ). Clinical Relevance Understanding of the biomechanical features discussed earlier has several clinically relevant applications. The orientation of the scapula and humerus with respect to the thorax and to each other has been important in designing the optimal radiographic studies to best visualize the scapulohumeral relationship. Thus, the true anteroposterior radiograph of the glenohumeral joint is taken 30 degrees oblique to the sagittal plane. Some think that this orientation is closer to 45 degrees because this angle produces a better true anteroposterior radiographic study. 7 The scapular view is taken at a 30-degree angle to the frontal plane; thus, the anteroposterior radiograph ( Fig. 6-23 ) that is perpendicular to this view is taken at an angle of about 60 degrees to the thorax. 81 FIGURE 6-23 The anterior ( left ) and lateral ( right ) views of the glenohumeral joint were defined by Neer based on knowledge of the scapulothoracic orientation. (Modified from Neer CS II: Displaced proximal humeral fractures. I. Classification and evaluation. J Bone Joint Surg Am 52:1077-1089, 1970.) The relationship of coupled external rotation with maximal arm elevation helps explain, to some extent, the limitation in elevation that is seen with a frozen shoulder. To the extent that this condition results in limitation of external rotation, an even more severe restriction of arm elevation is likely to occur. In fact, any simple movement of the glenohumeral joint results in coupled motion in two additional planes. By using a universal full-circle goniometer to determine the relationship between flexion and rotation at the glenohumeral joint it was found that flexion was accomplished by internal rotation. 82 It has also been demonstrated that certain passive motions of the glenohumeral joint were reproducibly accompanied by translation of the humeral head on the glenoid. 31 Knowledge of this coupling effect is also important with respect to prescribing the appropriate physical therapy after certain surgical procedures or pathologic states. Arthrodesis of the shoulder is an effective procedure but is most efficacious if the fusion is performed in the appropriate position. 83 Although the optimal position is debated, the basis of the selection depends on normal scapulothoracic motion ( Fig. 6-24 ). This knowledge, combined with an understanding of the motion required for activities of daily living, dictates the position of the fusion. FIGURE 6-24 Arthrodesis of the glenohumeral joint in the optimal position ( left ) allows arm elevation to and above the horizontal by scapulothoracic motion ( center ) as well as by tilting the trunk ( right ). The potential for scapulothoracic motion provides an explanation for the remaining motion of the shoulder girdle present with a frozen shoulder and after arthrodesis. In addition, rotation of the scapula may be viewed as a means of providing a glenohumeral relationship that allows the deltoid muscle to remain effective even with the arm fully elevated ( Fig. 6-25 ). FIGURE 6-25 Scapulothoracic motion allows the deltoid to remain in the optimal position for effective contraction throughout the arc of arm elevation. (From Lucas DB: Biomechanics of the shoulder joint. Arch Surg 107:425-432, 1973. © 1973, American Medical Association.) Understanding the axis of rotation is important for prosthetic replacement of the glenohumeral joint. The relative lack of translation in an intact shoulder justifies the design of an unconstrained glenoid surface. Karduna and associates 84 reported a significant increase in superoinferior and anteroposterior translation with increased radial mismatch of the prosthesis. The mean translation for natural joints was best reproduced by implant joints with a 3- to 4-mm radial mismatch. To the extent that the cuff musculature is deficient, a greater amount of translation is anticipated, which places additional requirements on the optimal glenoid design to accommodate the increased translation. 85 As is discussed later, probably more important is that the initiation of shoulder abduction results in forces directed toward the superior rim of the glenoid; this has implications regarding the stability, force, and optimal prosthetic design and surgical implantation technique. Finally, the well-recognized superior translation of the humeral head in a rotator cuff–deficient shoulder is explained in part by the superiorly directed resultant vector that occurs with initiation of abduction by the intact deltoid, the lack of soft tissue interposition of the rotator cuff ( Fig. 6-26 ), 86 and the lack of centralizing force to the humeral head against the glenoid socket produced by the rotator cuff. Yamaguchi and colleagues measured the kinematics of the glenohumeral joint with symptomatic and asymptomatic rotator cuff tears. 87 They found similar superior migration of the humeral head during arm elevation in both symptomatic and asymptomatic rotator cuff tears. Symptoms in shoulders with a rotator cuff tear may be related to factors other than superior migration of the humeral head. In addition to the size of the tear and the duration of symptoms, the important factor that influences superior migration of the humeral head is fatty degeneration of the infraspinatus muscle. 88 FIGURE 6-26 Superior migration of the humeral head in a rotator cuff–deficient shoulder is due in part to pull of the deltoid muscle. Thus, knowledge of the motion of the glenohumeral and scapulothoracic joints has numerous current clinical applications. A clear understanding of these factors is important for proper diagnosis and management of many shoulder conditions. SHOULDER CONSTRAINTS It is convenient to consider the constraints of any joint as consisting of static and dynamic elements. The static contribution may be further subdivided into articular and capsuloligamentous components ( Box 6-1 ). Knowledge of the shoulder constraints is of particular clinical interest because it pertains to anterior dislocation as well as to posterior and multidirectional instability of the shoulder. 23, 89 BOX 6-1 Static and Dynamic Contributions to Shoulder Stability Static Soft Tissue Coracohumeral ligament Glenohumeral ligaments Labrum Capsule Articular Surface Joint contact Scapular inclination Intra-articular pressure Dynamic Rotator cuff muscles Biceps Deltoid Early investigators focused on one element or the other. Hence, Saha emphasized the articular component of shoulder stability, 48, 90 Moseley and Overgaard 91 and Townley 70 focused on the capsuloligamentous complex, and DePalma and others emphasized the dynamic contribution of the interrelationship between the dynamic and the static capsuloligamentous constraints. 92 – 94 Since the 1990s, the static and dynamic components have been extensively investigated. In addition, the interrelationship between these components has become clarified in both experimental and clinical settings. The shoulder stability is easy to understand if we think about it in two different conditions: the mid range of motion and the end range of motion. The mid range of motion is the position of the arm when the capsuloligamentous structures are all lax, for example, with the arm in the hanging position or at 60 degrees of abduction. The end range of motion is defined as the position of the arm when the capsuloligamentous structures become tight, such as at 90 degrees of abduction and maximum external rotation or at 90 degrees of flexion and maximum horizontal adduction. In the mid range of motion, the capsuloligamentous structures are lax and the humeral head is movable anteriorly, posteriorly, or inferiorly by applying force. This mobility is called laxity . There is a great variety in the midrange laxity: Some patients are very stiff, but others can dislocate their shoulders voluntarily without any symptoms. The midrange stabilizers are the intra-articular pressure when all the muscles are relaxed; when the muscles are in contraction, the midrange stabilizer is the concavity of the glenoid. On the other hand, translation of the humeral head at the end range of motion is quite limited because the capsuloligamentous structures are tight and prevent further movement of the arm. At this limit of motion, an excessive force can cause failure of the capsuloligamentous structures, which results in traumatic dislocation of the shoulder. The end-range stabilizers are the capsuloligamentous structures. The midrange stabilizers and the end-range stabilizers are independent. For example, a shoulder with hyperlaxity can reveal an inferior dislocation of the shoulder with the arm in hanging position (midrange laxity), but it might not be dislocated with the arm in an apprehension position of abduction and maximum external rotation (end-range stability). Conversely, a shoulder with recurrent anterior dislocation does not show inferior subluxation or dislocation with the arm in hanging position because the end-range stabilizers are not intact but the midrange stabilizers are intact. Static Constraints Articular Contribution to Glenohumeral Stability The humeral articular surface is not inherently stable. The 30-degree retroversion is obviously necessary for proper balance of the soft tissues and normal kinematics. Most studies of the articular contribution to shoulder stability have focused on the glenoid. The glenoid articulation demonstrates a slight, but definite posterior or retroverted orientation averaging about 7 degrees with regard to the body of the scapula (see Fig. 6-17 ). Saha has emphasized that this orientation is an important contribution to stability of the joint. 48 Recent biomechanical studies have revealed that an anteverted glenoid component results in increased anterior translation of the humeral head and a retroverted glenoid component increases posterior translation of the humeral head, 95 whereas compensatory anteversion of the humeral component does not increase shoulder stability. 96 Theoretically, version of the glenoid could be a predisposing factor for instability. In the clinical setting, however, anterior shoulder instability often observed as a result of traumatic dislocation is not associated with anteversion of the glenoid, 97 whereas posterior shoulder instability often observed as a symptom of atraumatic multidirectional instability is associated with increased retroversion of the glenoid. 98 Only 25% to 30% of the humeral head is covered by the glenoid surface in any given anatomic position. 17, 42, 49, 92 The dimensional relationship between the humeral head and the glenoid reflects the inherent instability of the joint and has been referred to as the glenohumeral index, which is calculated as the maximal diameter of the glenoid divided by the maximal diameter of the humeral head. Saha reported this ratio to be approximately 0.75 in the sagittal plane and approximately 0.6 in the more critical transverse plane. 48 Later, this relationship was redetermined, with similar values of 0.86 and 0.58, respectively. 99 Developmental hypoplasia of the glenoid can alter this ratio and might play some role in recurrent dislocation of the shoulder, but such observations have been rather limited in the clinical literature. 100, 101 Subtle variation in articular anatomy of the glenoid has also been described and has been advocated as an explanation for inherent instability of the joint ( Fig. 6-27 ). FIGURE 6-27 Articular stability of the glenohumeral joint is enhanced or lessened according to the variation in articular congruence. A, Shallow glenoid surface. B, Conforming surfaces. C, Excessively deepened glenoid surface. (Modified from Saha AK: Dynamic stability of the glenohumeral joint. Acta Orthop Scand 42:491-505, 1971.) The glenoid labrum has three layers of collagen fibers. 102 The thin superficial layer (articular side) is composed of reticulated collagen fibers, the second layer is composed of stratified collagen fibers, and the third is composed of dense collagen fibers running parallel to each other and oblique to the glenoid rim. The glenoid labrum increases the area and depth of the glenoid cavity. The area of the glenoid with the labrum attached is approximately one third the humeral articular surface, and it is one quarter without the labrum. 49 The area of the labrum decreases with age, but the area of the osseous glenoid does not change ( Fig. 6-28 ). The depth of the glenoid is also functionally deepened by the presence of the glenoid labrum. FIGURE 6-28 The labral area decreases with age, but the osseous glenoid area remains unchanged. (Redrawn from Hertz H: Hertz H: Die Bedeutung des Limbus glenoidalis für die Stabilität des Schultergelenks. Wien Klin Wochenschr Suppl 152:1-23, 1984.) The early literature placed little emphasis on this anatomic structure as increasing the stability offered by the glenoid articular surface. Townley 70 removed the labrum of cadaveric shoulders through a posterior approach but could not create anterior dislocation until he resected the anterior capsule. Moseley and Overgaard demonstrated that the labrum was a specialized portion of the anterior capsule. 91 With external rotation, this structure flattens and thus serves only as a source of attachment for the inferior glenohumeral ligament (IGHL); hence, they concluded that the labrum itself seems to offer little to the inherent stability of the joint. However, other studies have attributed additional importance to the labrum. 94 Howell and coworkers measured an average depth of 9 mm in the superior-to-inferior direction of the glenoid. 103 This depth is equivalent to approximately 40% of the radius of a typical 44-mm humeral replacement prosthesis. The anteroposterior depth of the glenoid measured an average of only 2.5 mm. However, these investigators thought that the anterior and posterior glenoid labrum added an additional 2.5 mm of depth. These data suggest that the labrum may be effective in increasing the depth of the glenoid and therefore has some contribution to articular stability. The humeral head needs to override the rim of the glenoid to dislocate. In other words, midrange stability depends on the depth of the glenoid to some extent. A cadaveric study revealed that removal of the entire anterior labrum without damaging the capsule resulted in increased translation of the humeral head in adduction (midrange instability) but did not alter the degree of stability in the anterior apprehension position (end-range stability). 104 Fukuda and associates 105 were the first to evaluate the relationship between the glenoid depth and stability in various kinds of shoulder prostheses. They used a ratio of a force necessary to dislocate the humeral component out of the glenoid socket to a force compressing the humeral component against the glenoid component to assess the inherent stability of the shoulder prosthesis. This ratio was constant in each type of prosthesis, and the deeper the glenoid socket, the greater the ratio. Later, Lippitt and associates 106 termed this ratio the stability ratio . In normal shoulders, the stability ratio is 50% to 60% in the superior-to-inferior direction and 30% to 35% in the anterior-to-posterior direction. The stability ratio increases with an increase in glenoid depth. After the labrum is removed, the stability ratio decreases by approximately 20%. The stability ratio further decreases after creating a chondrolabral defect. 37 According to Halder and colleagues, 107 the stability ratio was greatest in the inferior direction ( Fig. 6-29 ), and it was greater with the arm in adduction than in abduction. In shoulders with multidirectional instability, the stability ratio is decreased due to glenoid dysplasia. In surgical procedures, the stability ratio can be increased by 25% with use of capsulolabral augmentation 78 and by 34% with use of glenoid osteotomy. 108 FIGURE 6-29 The average stability ratios of the shoulders, with and without the labrum, in eight tested directions. The ratios are defined as the peak translational force divided by the applied compressive force. The values are given as the average (and standard deviation). (From Halder AM, Kuhl SG, Zobitz ME, et al: Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavity-compression: An in vitro study. J Bone Joint Surg Am 7:1062-1069, 2001.) Detachment of the s uperior aspect of the l abrum from a nterior and p osterior is called a type II SLAP lesion. The pathogenesis of this lesion has been studied in the literature. Grauer and coworkers applied a 20-N force to the LHB and measured the strain in the anterior and posterior portions of the labrum. 109 They found that strain was the greatest with the arm in full abduction and the smallest in adduction. Bey and colleagues applied a failure load to the LHB with the shoulder reduced and subluxated inferiorly. 110 In reduced shoulders, the load created a type II SLAP lesion in two of eight shoulders, whereas in subluxated shoulders, the lesion developed in seven of eight shoulders. Pradhan and associates simulated a throwing motion and measured strain on the anterosuperior and posterosuperior portions of the labrum in cadaveric shoulders. 111 They found that the strain was greatest at the posterosuperior portion of the labrum when the arm was in abduction and external rotation (late cocking phase). Repetitive throwing motion can bring the superior labrum under constant strain and various degrees of shear force created by the cuff tendons during internal impingement, which can eventually result in detachment of the superior labrum from the glenoid. Once a type II SLAP lesion is created, a cadaveric study has shown that range of motion increases and the translation of the humeral head also increases. 112, 113 The joint contact area and position change during various glenohumeral motions are difficult to accurately measure by direct techniques. The contact point moves forward and inferior during internal rotation. 14, 48 With external rotation, the contact is just posteroinferior ( Fig. 6-30 ). Saha reported that with elevation, the contact area moves superiorly. If elevation is combined with internal and external rotation, however, the humeral head remains centered in the glenoid as viewed in the axillary plane. 53 The joint surface geometry and contact area have been measured with either stereophotogrammetry 114 or electromagnetic tracking devices. 115 In one study, the maximal contact area was obtained at 120 degrees of elevation. With an increase in arm elevation, the contact area shifted from an inferior region to a superocentral-posterior region, whereas the glenoid contact area shifted posteriorly ( Fig. 6-31 ). 114 Glenohumeral contact is maximal at functional positions (60-120 degrees of elevation) that provide stability to this joint. FIGURE 6-30 Humeral contact positions as a function of glenohumeral motion and positions. BG, bicipital groove; GT, greater tuberosity; LT, lesser tuberosity. (Colorized from Nobuhara K: The Shoulder: Its Function and Clinical Aspects. Tokyo: Igaku-Shoin, 1987.) FIGURE 6-31 The contact area of the humeral head shifts from the inferior to the superocentral-posterior region with an increase in arm elevation, whereas the glenoid contact area shifts posteriorly. (From Soslowsky LJ, Flatow EL, Bigliani LU, et al: Quantitation of in situ contact areas at the glenohumeral joint: A biomechanical study. J Orthop Res 10:524-534, 1992.) Warner and colleagues measured the contact area by using Fuji prescale film. In adduction, the contact area of the humeral head on the glenoid was limited to the anatomic region of the central glenoid known as the bare area , whereas in abduction, the contact area as well as the congruity increased. 116 They concluded that there was a slight articular mismatch in adduction but that it became more congruent and stable in abduction. Sahara and colleagues used open MRI to describe three-dimensional motion of the glenoid on the articular surface of the humeral head ( Fig. 6-32 ). 11 The glenoid was initially located at the inferior portion of the humeral head at 0 degrees of abduction. The glenoid shifted posteriorly from 0 to 60 degrees of abduction, moved up to the posterior-superior part of the humeral head from 60 to 120 degrees of abduction, and then moved anteriorly close to the bicipital groove at maximum abduction. FIGURE 6-32 The glenoid movement relative to the humeral head. The semitransparent gray ellipse is the glenoid at 0 degrees, 60 degrees, and maximum abduction. The black dots are the centers of the glenoid at each abducted position. The bars indicate the superior directions of the long axis of the glenoid. Ant, anterior; BG, bicipital groove; Inf, inferior; Post, posterior; Sup, superior. (From Sahara W, Sugamoto K, Murai M, Tanaka H: Yoshikawa H: The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI. Clin Biomech 22:304-312, 2007.) The slight 5-degree superior tilt of the articular surface has been offered by Basmajian and Bazant as a factor in preventing inferior subluxation of the humerus when combined with the effect of the superior capsule and superior glenohumeral ligament (SGHL) ( Fig. 6-33 ). 47 Clinically, glenoid dysplasia with the glenoid facing downward is related to multidirectional instability of the shoulder. 117 Glenoid osteotomy or pectoralis major transfer can be performed in shoulders with multidirectional instability to increase scapular inclination. 55 A biomechanical study by Itoi and associates 118 has clarified the relationship between scapular inclination and inferior stability of the shoulder. As the scapula was adducted (glenoid facing downward), all the vented shoulders dislocated inferiorly, whereas they were reduced with an increase in scapular abduction ( Fig. 6-34 ). They further studied the bulk effect of the rotator cuff muscles on the stability provided by scapular inclination. 119 After removal of the cuff muscles, the stability provided by scapular inclination did not change. Thus, the mechanism of scapular inclination seems to be a cam effect determined by the geometry of the glenoid and humerus and also by the length and orientation of the superior capsuloligamentous structures. Later, Metcalf and colleagues demonstrated that glenoid osteotomy and a 5-mm bone graft increased the stability ratio from 0.47 to 0.81 in the posteroinferior direction. 108 FIGURE 6-33 The upward tilt of the glenoid, coupled with the superior glenohumeral ligament and the coracohumeral ligament, resists passive downward displacement of the humeral head. A, Plane geometric diagram. B, Anatomic diagram. (Modified from Basmajian JV, Bazant FJ: Factors preventing downward dislocation of the adducted shoulder joint. J Bone Joint Surg Am 41:1182-1186, 1959.)

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• Antenatal Care Module: Ethiopian Federal Ministry of Health
• Labour and Delivery Care Module: Acknowledgements
• Labour and Delivery Care Module: Introduction
• Labour Delivery and Care Module: 1. Recognition of Normal Labour
• Labour and Delivery Care Module: 2. Assessing the Woman in Labour
• Labour Delivery and Care Module: 3. Care of the Woman in Labour
• Labour and Delivery Care Module: 4. Using the Partograph
• Labour and Delivery Care Module: 5. Conducting a Normal Delivery
• Labour and Delivery Care Module: 6. Active Management of the Third Stage of Labour
• Labour and Delivery Care Module: 7. Neonatal Resuscitation
• Introduction
• Learning Outcomes for Study Session 8
• 8.1.1  Vertex presentation
• 8.1.2  Malpresentations
• 8.1.3  Malposition
• 8.2  Causes and consequences of malpresentations and malpositions
• 8.3.1  Causes of breech presentation
• 8.3.2  Diagnosis of breech presentation
• 8.3.3  Types of breech presentation
• 8.3.4  Risks of breech presentation
• 8.4.1  Causes of face presentation
• 8.4.2  Diagnosis of face presentation
• 8.4.3  Complications of face presentation
• 8.5.1  Possible causes of brow presentation
• 8.5.2  Diagnosis of brow presentation
• 8.5.3  Complications of brow presentation
• 8.6.1  Causes of shoulder presentation

8.6.2  Diagnosis of shoulder presentation

8.6.3  Complications of shoulder presentation

• 8.7.1  Types of twin pregnancy
• 8.7.2  Diagnosis of twin pregnancy
• 8.7.3  Consequences of twin pregnancy
• 8.8  Management of women with malpresentation or multiple pregnancy
• Summary of Study Session 8
• Self-Assessment Questions (SAQs) for Study Session 8
• Labour and Delivery Care Module: 9. Obstructed Labour
• Labour and Delivery Care Module: 10. Ruptured Uterus
• Labour and Delivery Care Module: 11. Postpartum Haemorrhage
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Labour and Delivery Care

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Complications include:

• Cord prolapse
• Trauma to a prolapsed arm
• Obstructed labour and ruptured uterus
• Fetal hypoxia and death.

Remember that a shoulder presentation means the baby cannot be born through the vagina; if you detect it in a woman who is already in labour, refer her urgently to a higher health facility.

8.7  Multiple pregnancy

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What the New Overtime Rule Means for Workers

One of the basic principles of the American workplace is that a hard day’s work deserves a fair day’s pay. Simply put, every worker’s time has value. A cornerstone of that promise is the  Fair Labor Standards Act ’s (FLSA) requirement that when most workers work more than 40 hours in a week, they get paid more. The  Department of Labor ’s new overtime regulation is restoring and extending this promise for millions more lower-paid salaried workers in the U.S.

Overtime protections have been a critical part of the FLSA since 1938 and were established to protect workers from exploitation and to benefit workers, their families and our communities. Strong overtime protections help build America’s middle class and ensure that workers are not overworked and underpaid.

Some workers are specifically exempt from the FLSA’s minimum wage and overtime protections, including bona fide executive, administrative or professional employees. This exemption, typically referred to as the “EAP” exemption, applies when: 

1. An employee is paid a salary,  

2. The salary is not less than a minimum salary threshold amount, and 

3. The employee primarily performs executive, administrative or professional duties.

While the department increased the minimum salary required for the EAP exemption from overtime pay every 5 to 9 years between 1938 and 1975, long periods between increases to the salary requirement after 1975 have caused an erosion of the real value of the salary threshold, lessening its effectiveness in helping to identify exempt EAP employees.

The department’s new overtime rule was developed based on almost 30 listening sessions across the country and the final rule was issued after reviewing over 33,000 written comments. We heard from a wide variety of members of the public who shared valuable insights to help us develop this Administration’s overtime rule, including from workers who told us: “I would love the opportunity to...be compensated for time worked beyond 40 hours, or alternately be given a raise,” and “I make around $40,000 a year and most week[s] work well over 40 hours (likely in the 45-50 range). This rule change would benefit me greatly and ensure that my time is paid for!” and “Please, I would love to be paid for the extra hours I work!”

The department’s final rule, which will go into effect on July 1, 2024, will increase the standard salary level that helps define and delimit which salaried workers are entitled to overtime pay protections under the FLSA. 

Starting July 1, most salaried workers who earn less than $844 per week will become eligible for overtime pay under the final rule. And on Jan. 1, 2025, most salaried workers who make less than $1,128 per week will become eligible for overtime pay. As these changes occur, job duties will continue to determine overtime exemption status for most salaried employees.

The rule will also increase the total annual compensation requirement for highly compensated employees (who are not entitled to overtime pay under the FLSA if certain requirements are met) from $107,432 per year to $132,964 per year on July 1, 2024, and then set it equal to $151,164 per year on Jan. 1, 2025.

Starting July 1, 2027, these earnings thresholds will be updated every three years so they keep pace with changes in worker salaries, ensuring that employers can adapt more easily because they’ll know when salary updates will happen and how they’ll be calculated.

The final rule will restore and extend the right to overtime pay to many salaried workers, including workers who historically were entitled to overtime pay under the FLSA because of their lower pay or the type of work they performed. 

We urge workers and employers to visit  our website to learn more about the final rule.

Jessica Looman is the administrator for the U.S. Department of Labor’s Wage and Hour Division. Follow the Wage and Hour Division on Twitter at  @WHD_DOL  and  LinkedIn .  Editor's note: This blog was edited to correct a typo (changing "administrator" to "administrative.")

• Wage and Hour Division (WHD)
• Fair Labor Standards Act
• overtime rule

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What caused Dubai floods? Experts cite climate change, not cloud seeding

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The French industry minister Roland Lescure on Friday launched a call for interest for carbon capture at various sites to help carbon-intense industries abate emissions.

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Gaza protest in Paris sees tense standoff with Israel supporters

Tensions flared in front of Paris' prestigious Sciences Po university over the war in Gaza on Friday as pro-Israeli protesters came to challenge pro-Palestinian students occupying the building.