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.