Mathematic modeling of forces associated with shoulder dystocia: a comparison of endogenous and exogenous sources

Risk factors for neonatal brachial plexus palsy attributed to anatomy, physiology, and evolution

The inherent variable anatomy of the neonate and the uniquely-shaped maternal birth canal that is associated with the evolution of human bipedalism constitute risk factors for neonatal brachial plexus palsy (NBPP). For example, those neonates with a prefixed brachial plexus (BP) are at greater risk of trauma due to lateral neck traction during delivery than those with a normal or postfixed BP. Compared to adults, neonates also have extremely large and heavy heads (high head: body ratio) set upon necks with muscles and ligaments that are weak and poorly developed. Accordingly, insufficient cranial stability can place large torques on the cervical spinal nerves. In addition, the pelvic changes necessary for habitual bipedal posture resulted in a uniquely-shaped, obstruction-filled, sinusoidal birth canal, requiring the human fetus to complete a complicated series of rotations to successfully traverse it. Furthermore, although there are many risk factors that are known to contribute to NBPP, the specific anatomy and physiology of the neonate, except for macrosomia, is not considered to be one of them. In fact, currently, the amount of lateral traction applied to the neck during delivery is the overwhelming legal factor that is used to evaluate whether a birth attendant is liable in cases of permanent NBPP. Here, we suggest that the specific anatomy and physiology of the neonate and mother, which are clearly not within the control of the birth attendant, should also be considered when assessing liability in cases of NBPP.

Pathophysiologic Origins of Brachial Plexus Injury

OBJECTIVE

To analyze the origins and consequences of cases of brachial plexus injuries and their relationship to shoulder dystocia.

METHODS

We conducted a retrospective cohort study and identified all neonates with brachial plexus injury delivered at our institution between March 2012 and July 2019. A review was performed of the maternal and neonatal records of each neonate to identify obstetric antecedents, including the occurrence of shoulder dystocia and persistence of the injury. Experience of the delivering clinician was also examined. Statistical analysis was performed with the Fisher exact test, χ test for trends, and two-tailed t tests.

RESULTS

Thirty-three cases of brachial plexus injury were identified in 41,525 deliveries (0.08%). Fourteen (42%) of these cases were not associated with shoulder dystocia; three (9%) followed cesarean delivery. Brachial plexus injury without shoulder dystocia was related to the absence of maternal diabetes, lower birth weights, and a longer second stage of labor. Persistent brachial plexus injury at the time of discharge was seen with equal frequency among neonates with (17/19, 89%, 95% CI 0.52-100%) and without shoulder dystocia (10/14, 71%, 95% CI 34-100%), P=.36). Whether brachial plexus injury was transient or persistent after shoulder dystocia was unrelated to the years of experience of the delivering clinician. Despite ongoing training and simulation, the already low incidence of brachial plexus injury did not decrease over time at our institution.

CONCLUSION

Brachial plexus injury and shoulder dystocia represent two complications of uterine forces driving a fetus through the maternal pelvis in the presence of disproportion between the passage and the shoulder girdle of the passenger. Either or both of these complications may occur, but often are not causally related.

Risk Factors for Brachial Plexus Birth Injury

Over the course of decades, the incidence of brachial plexus birth injury (BPBI) has increased despite advances in healthcare which would seem to assist in decreasing the rate. The aim of this study is to identify previously unknown risk factors for BPBI and the risk factors with potential to guide preventative measures. A case control study of 52 mothers who had delivered a child with a BPBI injury and 132 mothers who had delivered without BPBI injury was conducted. Univariate, multivariable and logistic regressions identified risk factors and their combinations. The odds of BPBI were 2.5 times higher when oxytocin was used and 3.7 times higher when tachysystole occurred. The odds of BPBI injury are increased when tachysystole and oxytocin occur during the mother's labor. Logistic regression identified a higher risk for BPBI when more than three of the following variables (>30 lbs gained during the pregnancy, stage 2 labor >61.5 min, mother's age >26.4 years, tachysystole, or fetal malpresentation) were present in any combination.

Birth fracture of the clavicle

Birth fracture of the clavicle occurs in approximately 0.4% to 10% of vaginal births. The most common symptom is decreased movement of the ipsilateral arm. A high index of suspicion is necessary in infants presenting without any symptoms. Although displaced clavicular fractures are relatively easily diagnosed clinically, nondisplaced fractures may be apparent only after callus formation, or if all neonates are subjected to radiography or ultrasonography, or multiple physical examinations by trained examiners. We present a case of an infant delivered with vaginal labor with a fracture of the right clavicle diagnosed after apparent callus formation and discuss the current evidence of associated factors and obstetrical care.

Shoulder Dystocia: Etiology, Common Risk Factors, and Management

Shoulder dystocia and brachial plexus injury occur in 0.5% to 1.5% of all births. Risk factors for both include maternal obesity, excessive prenatal weight gain, maternal diabetes, protracted labor, and fetal macrosomia. These factors are involved in only about 50% of births complicated by shoulder dystocia or brachial plexus injury. Shoulder dystocia has a low recurrence rate (9.8%-16.7%), although history of previous shoulder dystocia is the most reliable predictor of occurrence. Brachial plexus injury is the most common morbidity associated with shoulder dystocia, but 50% of newborns who present with this injury were not subject to shoulder dystocia at birth. Most brachial plexus injuries are transient, although 5% to 22% become permanent. Shoulder dystocia followed by permanent brachial plexus injury or mental impairment is one of the leading causes of malpractice allegations. Prompt assessment and management of shoulder dystocia and preparation to maximize the efficiency of shoulder dystocia maneuvers are critical. Documentation of the appropriate use of maneuvers to relieve shoulder dystocia demonstrates standard of care practice, thereby decreasing the potential for successful malpractice allegations.

Contemporary Management of Shoulder Dystocia

Shoulder dystocia is an uncommon but potentially catastrophic intrapartum event. Although risk factors such as maternal diabetes, obesity and macrosomia can be identified, shoulder dystocia most frequently occurs in patients who lack risk factors. Many maneuvers have been described to assist the operator in the safe release of the shoulder and subsequent delivery; however, no prospective trials have compared these maneuvers in such a way to suggest that one maneuver is superior to another. This article describes the identification of patients at risk for shoulder dystocia, clinical management of the shoulder dystocia, event documentation and the contemporary use of drills and simulation training to improve team preparedness for this unpredictable and usually unavoidable event.

Is it possible to reduce obstetrical brachial plexus palsy by optimal management of shoulder dystocia?

Obstetrical brachial plexus palsies (OBPP) have been historically attributed to the impaction of the fetal shoulder behind the symphysis pubis and to excessive lateral traction of the fetal head during maneuvers to deliver the fetal shoulders in shoulder dystocia. Shoulder dystocia is indeed a major risk factor as it increases the risk for OBPP 100-fold. The incidence of OBPP following shoulder dystocia varies widely from 4% to 40%. However, a significant proportion of OBPPs are secondary to in utero injury. The propulsive forces of labor, intrauterine maladaptation, and compression of the posterior shoulder against the sacral promontory as well as uterine anomalies are possible intrauterine causes of OBPP. Many risk factors for OBPP may be unpredictable. Early identification of risk factors for shoulder dystocia, as well as appropriate management when it occurs, may improve our ability to prevent the occurrence of OBPP in those cases that are caused by shoulder dystocia.

Shoulder dystocia without versus with brachial plexus injury: A case–control study

OBJECTIVE

To delineate factors that differentiate shoulder dystocia with and without brachial plexus injury (BPI).

STUDY DESIGN

A case-control study culled from an established shoulder dystocia database. Cases of shoulder dystocia-related BPI were identified and matched (1:1) with a control group of shoulder dystocia in which BPI did not result. Odds ratios (OR) and 95% confidence intervals (CI) were calculated.

RESULTS

From 1980 to 2002, there were 89 978 deliveries with 46 cases of dystocia and BPI. The rate of dystocia with BPI was 0.5 per 1000 births and of permanent BPI, 0.9/10 000 deliveries. The two groups were similar for maternal demographics, diabetes, gestational age, induction, use of epidural, the duration of labor, operative vaginal delivery, rate of macrosomia, and maneuvers used to relieve the dystocia. Fracture of the clavicle occurred significantly less often among those without (2%) vs. with BPI (17%; OR 0.10, 95% CI 0.01, 0.88).

CONCLUSIONS

Neither antepartum nor intrapartum factors can differentiate the patient who will have shoulder dystocia with vs. without BPI.

Primiparity: A risk factor for brachial plexus injury in the presence of shoulder dystocia?

The objective of the study was to assess the risk factors associated with obstetric brachial plexus injury. It was a retrospective analysis over a 7-year period, of women whose labours were either complicated by shoulder dystocia or had neonates who sustained brachial plexus injury. The 133 women included were divided into two groups: (1) Non-brachial plexus injury (Non-BPI) group: 106 women with labours complicated by shoulder dystocia. (2) Brachial plexus injury (BPI) group: 27 women whose neonates sustained BPI. Comparison of ante-partum, intra-partum and post-partum factors was done. In the BPI group, there were significantly more nulliparous women, with more use of oxytocin. The neonatal variables were similar in both groups. Mean birth weight was more than 4 kg in both groups. In the presence of similar neonatal variables, brachial plexus injury is more likely to occur in neonates of primiparous women in the presence of shoulder dystocia, if labour is accelerated.

Obstetric brachial plexus palsy: treatment strategy, long-term results, and prognosis

BACKGROUND

Obstetric brachial plexus palsy is rare, but the limb impairments are manifold and often long-lasting. Physiotherapy, microsurgical nerve reconstruction, secondary joint corrections, and muscle transpositions are employed with success. The role of conservative and operative treatment options should be regularly reviewed.

METHODS

Selective literature review (evidence levels 3 and 4) and analysis of personal clinical operative and scientific experience over the past 15 years.

RESULTS

Children with upper and total plexus palsy displaying nerve root avulsions and/or -ruptures are treated today by early primary nerve reconstruction in the first few months of life followed by secondary corrections, with good functional results. The late complications, with muscle weakness, impaired motion patterns, and joint dysplasia, are often underrated.

CONCLUSIONS

The potential for scientific analysis is limited, due to the rarity and interindividual variability of the lesions and the varying effects on function and growth. Expectations and compliance are different in every patient. Surgical techniques are not yet standardized. Knowledge of the consequences for joint growth and congruence is inadequate. Today, functional improvement can be achieved by surgery in most clinical manifestations of obstetric brachial plexus palsy, within the framework of an interdisciplinary treatment concept.

Lyme disease--current state of knowledge

BACKGROUND

Lyme disease is the most frequent tick-borne infectious disease in Europe. The discovery of the causative pathogen Borrelia burgdorferi in 1982 opened the way for the firm diagnosis of diseases in several clinical disciplines and for causal antibiotic therapy. At the same time, speculation regarding links between Borrelia infection and a variety of nonspecific symptoms and disorders resulted in overdiagnosis and overtreatment of suspected Lyme disease.

METHOD

The authors conducted a selective review of the literature, including various national and international guidelines.

RESULTS

The spirochete Borrelia burgdorferi sensu lato is present in approximately 5% to 35% of sheep ticks (Ixodes ricinus) in Germany, depending on the region. In contrast to North America, different genospecies are found in Europe. The most frequent clinical manifestation of Borrelia infection is erythema migrans, followed by neuroborreliosis, arthritis, acrodermatitis chronica atrophicans, and lymphocytosis benigna cutis. Diagnosis is made on the basis of the clinical symptoms, and in stages II and III by detection of Borrelia-specific antibodies. In adults erythema migrans is treated with doxycycline, in children with amoxicillin. The standard treatment of neuroborreliosis is third-generation cephalosporins.

CONCLUSIONS

After appropriate antibiotic therapy, the outcome is favorable. In approximately 95% of cases neuroborreliosis is cured without long-term sequelae. When chronic borreliosis is suspected, other potential causes of the clinical syndrome must be painstakingly excluded.

Obstetrical brachial plexus palsy

Obstetrical brachial plexus palsy, one of the most complex peripheral nerve injuries, presents as an injury during the neonatal period. The majority of the children recover with either no deficit or a minor functional deficit, but it is almost certain that some will not regain adequate limb function. These few cases must be managed in an optimal way. Considerable medical and legal debate has surrounded the etiologic factors of this traumatic lesion, and obstetricians are often considered responsible for the injury. According to recent studies, spontaneous endogenous forces may contribute substantially to this type of neonatal trauma. All obstetric circumstances that predispose to brachial plexus damage and that could be anticipated should be assessed. Correct diagnosis is necessary for the accurate estimation of prognosis and treatment. The most important aspect of therapy is timely recognition and referral, to prevent the various possible sequelae affecting the shoulder, elbow, or forearm. Since the early 1990s, research has increased the understanding of obstetrical brachial plexus palsy. Further research is needed, focused on developing strategies to predict brachial injury. This review focuses on emerging data relating to obstetrical brachial plexus palsy and discusses the present controversies regarding natural history, prognosis, and treatment in infants with brachial plexus birth palsies.

Permanent brachial plexus injury following vaginal delivery without physician traction or shoulder dystocia

A vaginal delivery that resulted in a permanent brachial plexus injury unassociated with shoulder dystocia or physician traction is reported by the delivering physician. This case demonstrates unequivocally that not all permanent brachial plexus injury at vaginal birth is due to physician traction.

[Effects of Buthus occitanus tunetanus envenomation on an experimental murine model of gestation]

Scorpion envenoming is less studied in pregnant victims. In this work, the effect of Buthus occitanus tunetanus on parturition in late pregnancy was studied in an animal model. Four groups of six primigravid female rats, each one at the 22nd day of pregnancy, were used. The first two groups had received an intra-peritoneal injection of 500 microg/kg of Buthus occitanus tunetanus crude venom or a physiological saline solution and left until foetal delivery. Then, the time elapsed until the first pup delivery and that separating the first and latest ones were measured. The other two groups served for the uterine electrophysiological activity exploration. Rats were anaesthetized, artificially ventilated and had received an intraperitoneal injection of 500 microg/kg of Buthus occitanus tunetanus crude venom or a physiological saline solution. Our results showed a significant increase of the latency to foetal delivery, labour time, and uterine contractile activity in envenomed rats compared to controls. Such signs are usually seen in dynamic dystocia. It was concluded that Buthus occitanus tunetanus envenoming might induce a dynamic dystocia, when it occurred in late pregnancy.

On the Mechanical Aspects of Shoulder Dystocia and Birth Injury

This article presents objective evidence about shoulder dystocia and its associated mechanical injuries, namely clavicle fractures, and brachial plexus injuries. Specifically, the review focuses on the mechanical response of the fetus to forces applied to it or its anatomic components, including possible force thresholds for injury. This is followed by presenting the medical and engineering literature on the mechanical aspects of shoulder dystocia with emphasis on kinematics, the forces associated with labor and with traction forces associated with delivery. Finally, the paper discusses the mechanical characteristics of maternal and fetal maneuvers for shoulder dystocia and demonstrates how shoulder dystocia models can be used to train clinicians in the performance of maneuvers that stress the fetus the least. From a mechanical point of view, there are obstetric methods and training that can be employed to reduce the stresses induced by the fetus while alleviating shoulder dystocia, thereby reducing, but not eliminating, the risk of mechanical injury.

Shoulder dystocia

Using an evidence-based, medical approach, the strengths and pitfalls of the causation- and standard-of-care-based arguments proffered by plaintiff and defense counsel in shoulder dystocia- associated birth injury litigation are reviewed based on medical plausibility. The role of the expert witness as arbiter of the relationship between medical care rendered and the untoward outcome of such care is distinguished from that of other court members. Proposed solutions to the medical malpractice litigation crisis are also examined in light of relevant differences in the pathogenetic bases for birth injuries of various types.

Labour characteristics and neonatal Erb's palsy

OBJECTIVE

To determine risk factors for Erb's palsy, with a focus on graphic labour patterns.

DESIGN

A case-control study.

SETTING

New York City.

SAMPLE

A total of 45 consecutive cases of Erb's palsy and 90 controls.

METHODS

Pregnancies and labours of neonatal Erb's palsy cases were compared with 90 controls using univariate and multiple logistic regression analysis.

MAIN OUTCOME MEASURES

Erb's palsy and shoulder dystocia.

RESULTS

Mothers of children with Erb's palsy had a higher term body mass index and more gestational diabetes than those of controls. Even cases without diabetes had higher blood glucose values after a 50-g glucose challenge than did controls. Cases had a higher birthweight and a lower ratio of head-to-thoracic circumference than controls. Shoulder dystocia occurred in 67% of cases and in 2% of controls (P = 0.001). Only 46% of labours had a completely normal dilatation pattern. In a multiple logistic regression model, variables independently associated with brachial plexus injury were long deceleration phase of labour, long second stage, high birthweight, black race, and high neonatal or maternal body mass.

CONCLUSIONS

Erb's palsy was frequently preceded by abnormal labour and shoulder dystocia; however, a substantial proportion of cases occurred after normal labour and delivery. Predictive models will be necessary to determine to what extent careful monitoring of the terminal portion of dilatation and of fetal descent and incorporation of maternal body mass and race (all independent risk factors in this study) will help identify fetuses at risk for brachial plexus palsy.

Shoulder dystocia: the unpreventable obstetric emergency with empiric management guidelines

OBJECTIVE

Much of our understanding and knowledge of shoulder dystocia has been blurred by inconsistent and scientific studies that are of limited scientific quality. In an evidence-based format, we sought to answer the following questions: (1) Is shoulder dystocia predictable? (2) Can shoulder dystocia be prevented? (3) When shoulder dystocia does occur, what maneuvers should be performed? and (4) What are the sequelae of shoulder dystocia?

STUDY DESIGN

Electronic databases, including PUBMED and the Cochrane Database, were searched using the key word "shoulder dystocia." We also performed a manual review of articles included in the bibliographies of these selected articles to further define articles for review. Only those articles published in the English language were eligible for inclusion.

RESULTS

There is a significantly increased risk of shoulder dystocia as birth weight linearly increases. From a prospective point of view, however, prepregnancy and antepartum risk factors have exceedingly poor predictive value for the prediction of shoulder dystocia. Late pregnancy ultrasound likewise displays low sensitivity, decreasing accuracy with increasing birth weight, and an overall tendency to overestimate the birth weight. Induction of labor for suspected fetal macrosomia has not been shown to alter the incidence of shoulder dystocia among nondiabetic patients. The concept of prophylactic cesarean delivery as a means to prevent shoulder dystocia and therefore avoid brachial plexus injury has not been supported by either clinical or theoretic data. Although many maneuvers have been described for the successful alleviation of shoulder dystocia, there have been no randomized controlled trials or laboratory experiments that have directly compared these techniques. Despite the introduction of ancillary obstetric maneuvers, such as McRoberts maneuver and a generalized trend towards the avoidance of fundal pressure, it has been shown that the rate of shoulder-dystocia associated brachial plexus palsy has not decreased. The simple occurrence of a shoulder dystocia event before any iatrogenic intervention may be associated with brachial plexus injury.

CONCLUSION

For many years, long-standing opinions based solely on empiric reasoning have dictated our understanding of the detailed aspects of shoulder dystocia prevention and management. Despite its infrequent occurrence, all healthcare providers attending pregnancies must be prepared to handle vaginal deliveries complicated by shoulder dystocia.

What factors are associated with neonatal injury following shoulder dystocia?

OBJECTIVE

To identify factors associated with the development of neonatal injury in the setting of shoulder dystocia.

STUDY DESIGN

Medical record ICD-9 codes and a computerized perinatal database were reviewed to identify cases of shoulder dystocia from January 1996 to January 2001 in a tertiary care center. For confirmation of the diagnosis and collection of data, both maternal and neonatal charts were then reviewed and neonatal injuries categorized as either neurological (brachial plexus injury) or skeletal (clavicular fracture, humeral fracture). Shoulder dystocia cases were divided into groups based on the presence of neonatal injury at delivery or at discharge (with or without Erb's palsy). The group with neonatal injury was compared for demographic and obstetrical factors to the group without injury (control). chi (2) test, Mann-Whitney test and logistic regression were used as appropriate.

RESULTS

During this 5-year period, there were 25,995 deliveries and 206 (0.8%) confirmed cases of shoulder dystocia. Of these cases, 36 (17.5%) had neonatal injury diagnosed at delivery and 25 (12%) remained with significant residual injury at discharge. Of these there were 19 cases of Erb's palsy and six cases of clavicular fracture. No association was found between neonatal injury and maternal age, ethnicity, diabetes, operative vaginal delivery or number of obstetrical maneuvers. However, maternal body mass index >30 kg/m2, a second stage of labor >20 min and a birth weight >4500 g were all associated with an increased risk of neonatal injury at delivery and at discharge, including Erb's palsy. After logistic regression analysis, only a second stage of delivery >20 min remained significantly associated with neonatal injury at discharge.

CONCLUSION

In our population, maternal obesity was associated with an increased risk of neonatal injury after shoulder dystocia. In addition, a short second stage of labor (<20 min) was associated with a lower rate of neonatal injury.

Part 1. Injuries to the brachial plexus: mechanisms of injury and identification of risk factors

Upper-arm weakness (paresis) or paralysis indicates peripheral-nerve damage to the brachial plexus, a network of lower cervical and upper thoracic spinal nerves supplying the arm, forearm, and hand. Physical findings reflect muscle paralysis from spinal nerve roots. The mechanism of injury includes maternal, obstetric, and infant factors that apply traction on or compression to the anatomically vulnerable brachial plexus. Nerve regeneration can occur if nerve tissue components are preserved. Recovery is affected by multiple factors, including the type and site of injury, intervention timing, and developmental factors. The majority of injuries recover in days or months; however, residual deficits can persist. Part 1 of 2 of this article provides an overview of the neurophysiology of peripheral-nerve damage and nerve regeneration. The multifactorial etiology of brachial plexus injuries will be reviewed. Photographs and on-line video clips will enhance the description of the brachial plexus injury classifications and illustrate mechanisms of shoulder dystocia and obstetric relief maneuvers. A systematic approach to the physical examination will be explored in Part 2. Serial evaluation of motor function recovery is essential and is accomplished by appropriate referrals and follow-up. Part 2 will also describe treatment options and discuss anticipatory parent guidance.

Prediction of brachial plexus stretching during shoulder dystocia using a computer simulation model

OBJECTIVE

The purpose was to study the impact of maternal endogenous and clinician-applied exogenous delivery forces on brachial plexus stretching during a shoulder dystocia event.

STUDY DESIGN

A computer software crash dummy model (MADYMO, version 5.4, TNO Automotive, Delft, The Netherlands) was modified on the basis of established maternal pelvis and fetal anatomic specifications. The brachial plexus was modeled as a spring, with mechanical properties that were based on previously reported experimental data. Increasing amounts of endogenous or exogenous loading forces were applied until delivery of the anterior fetal shoulder occurred. Brachial plexus deformation was assessed as percent stretch in the nerve (Change in length/Original length x 100).

RESULTS

With lithotomy positioning, both maternal endogenous and clinician-applied exogenous delivery forces were associated with brachial plexus stretching (15.7% vs 14.0%, respectively). McRoberts positioning reduced needed loading forces for delivery and resulted in 53% less brachial plexus stretch (6.6%). Downward lateral displacement of the fetal head was associated with a 30% increase in brachial plexus stretch (18.2%) compared with axial positioning of the head (14.0%).

CONCLUSION

Brachial plexus stretch varied as a result of the load required for delivery, the source of the applied force, pelvic orientation, and fetal head positioning. Maternally derived and clinician-applied delivery forces can both lead to brachial plexus deformation when shoulder dystocia is encountered. The McRoberts maneuver can reduce brachial plexus stretching. Management of fetal head position may also be important in reducing unnecessary brachial plexus stretch.

Defining forces that are associated with shoulder dystocia: the use of a mathematic dynamic computer model

OBJECTIVE

A computer model was modified to study the impact of maternal endogenous and clinician-applied exogenous delivery loads on the contact force between the anterior fetal shoulder and the maternal symphysis pubis.

STUDY DESIGN

Varying endogenous and exogenous loads were applied, and the contact force was determined. Experiments also examined the effect of pelvic orientation and the direction of load application on contact force behind the symphysis pubis.

RESULTS

Exogenous loading forces (50-100 N) resulted in anterior shoulder contact forces of 107 to 127 N, with delivery accomplished at 100 N of applied load. Higher contact forces (147-272 N) were noted for endogenously applied loads (100-400 N), with delivery occurring at 400 N of maternal force. Pelvic rotation from lithotomy to McRoberts' positioning resulted in reduced contact forces. Downward lateral flexion of the fetal head led to little difference in contact force but required 30% more exogenous load to achieve delivery.

CONCLUSION

Compared with clinician-applied exogenous force, larger maternally derived endogenous forces are needed to clear the impacted anterior fetal shoulder. This is associated with >2 times more contact force by the obstructing symphysis pubis. McRoberts' positioning reduces shoulder-symphysis pubis contact force. Lateral flexion of the fetal head results in the larger forces that are needed for delivery but has little effect on contact force. Model refinements are needed to examine delivery forces and brachial plexus stretching more specifically.

Management of obstetrical brachial plexus palsy evaluation, prognosis, and primary surgical treatment

Primary surgery for obstetrical brachial plexus lesions is a young field of surgical expertise that offers the possibility of improved functional ability in carefully selected patients who would otherwise be faced with lifelong impairment and secondary skeletal deformities. One major challenge in this area of peripheral nerve surgery is the selection of patients most likely to derive benefit from surgical intervention. The key to the development of selection criteria and to the resolution of other considerations (such as the determination of root avulsion) is consistency, accuracy, and careful reporting of natural history and outcome data. In particular, we strongly feel that a statistically sound technique of assessment must be consistently applied from the time of presentation through long-term follow-up. Advancement to date has resulted from the application of evidence-based recommendations from large, well-designed, meticulous studies. As the field of obstetrical brachial plexopathy management continues to evolve, we can expect that questions will continue to be answered using such scientific methodology.

Shoulder dystocia and brachial plexus injury: a case-control study

OBJECTIVE AND BACKGROUND

To evaluate risk factors for shoulder dystocia and brachial plexus injury using a case-control study at the departments of obstetrics and gynecology at the four largest hospitals in southern Sweden. All cases of shoulder dystocia between 1987 and 1993 inclusive were identified. For each case, two control infants with similar birthweight (+/- 100 g) and identical year of birth were randomly selected.

METHODS

Original maternal records were reviewed and information regarding 10 potential risk factors was extracted. Odds ratios (ORs) were calculated using the Mantel-Haenszel method. Stratification was made for year of delivery, parity (0, I, II, III+), and maternal age (5-year class).

RESULTS

In all, 107 infants with shoulder dystocia and 198 controls were included. The OR was greater than unity for all risk factors except gestational age. Three of the risk factors, induction of labor, epidural analgesia, and instrumental delivery, reached statistical significance. Thirty-four infants also suffered brachial plexus injury, giving a brachial plexus injury rate of 32% among the shoulder dystocia cases. We also made a separate analysis of the nine risk factors for brachial plexus injury following a shoulder dystocia, however none reached statistical significance.

CONCLUSION

In this case-control study based on more than 100,000 deliveries at four large hospitals during a 7-year period, induction of labor, epidural analgesia, and instrumental delivery turned out to be significant risk factors for shoulder dystocia. For brachial plexus injury following shoulder dystocia, no significant risk factor was identified.

Erb's palsy causation: a historical perspective

A better understanding of the forces involved when brachial plexus injury occurs has evolved over the past 10 to 15 years. A particular challenge was that all of the useful information had to be derived indirectly by identifying associations-a challenge that was met by individual researchers who made significant observations that, in turn, stimulated others to search for additional findings. Gradually the pieces of the puzzle began to form the picture. The significant steps in this journey were first, the recognition of the substantial number of injuries occurring without concurrent shoulder dystocia; second, the finding that a much greater frequency of injury is associated with an ultrashort second stage of labor; third, the observations that the injury rate is independent of the experience of the birth attendant; fourth, the recognition of the substantial numbers of injuries occurring in the posterior arm; and fifth, the anecdotal experience of countless delivery attendants, who relate that the forces applied in the injured cases were perceived to be no stronger than those applied when no injury occurred. We present a historical review for each step in this journey. We reviewed all articles published on this subject in Obstetrics and Gynecology and the American Journal of Obstetrics and Gynecology and some European journals. The period for review primarily covered articles published since 1980. Several textbooks on obstetrics and child neurology were also reviewed.

Shoulder dystocia

Shoulder dystocia is an uncommon but not rare obstetric emergency. Death of the infant is unusual but perinatal morbidity is frequent and can result in permanent injury. These cases carry significant medico-legal implications. This chapter covers the mechanisms, predisposing factors and management of shoulder dystocia. A well-rehearsed sequence of manoeuvres to manage shoulder dystocia will minimize fetal trauma.

Obstetric lesions of the brachial plexus

The few studies on prognosis of obstetric lesions of the brachial plexus that are not hampered by selection bias or a short follow-up suggest that functional impairment persists in 20-25% of cases, more than commonly thought. Electromyography (EMG), potentially useful for prognosis, is often considered of little value. Denervation in the first week of life has been interpreted as evidence of an antenatal lesion, but is the logical result of the short axonal length affected. EMG performed at close to the time of possible intervention (3 months) usually shows a discrepancy: motor unit potentials are seen in clinically paralyzed muscles. This can be explained in five ways: an overly pessimistic clinical examination; overestimation of EMG recruitment due to small muscle fibers; persistent fetal innervation; developmental apraxia; or misdirection, in which axons reach inappropriate muscles. Further research into the pathophysiology of obstetric lesions of the brachial plexus is needed to improve prognostication.