A guest editorial: new insights to shoulder dystocia and brachial plexus palsy.

Shoulder dystocia is a relatively uncommon event that the general obstetrician may encounter just a few times, during an entire career that spans several decades. Only 0.2% to 3% of all vaginal deliveries are complicated by a failure of the fetal shoulder(s) to spontaneously deliver (1). Fetal morbidity associated with shoulder dystocia, mainly consisting of transient brachial plexus palsy, is even more unusual. Among 1,094,298 women who delivered over 2 years in 300 civilian acute care hospitals in California, Gilbert et al. (2) found 1611 (0.15%) cases of brachial plexus palsy. Transient brachial plexus palsy has been reported to complicate only 15% of all shoulder dystocia cases (3). Permanent brachial plexus palsy after a shoulder dystocia episode, however, is exceedingly rare (0.54–1.4%) (1). A commonly held misconception is that these brachial plexus palsies result from excessive lateral traction applied by the accoucheur. Res ipsa loquiteur (“the thing speaks for itself”) has implied that there is simply a single mechanism for this injury. The casecontrol study by McFarland et al. (4) provided an unreferenced statement that “injuries to the brachial plexus occur when there is a strong lateral traction on the head and neck or a downward traction on the shoulders. ” The textbook by O’Leary (5) likewise provided an unsupported claim that “. the vast majority of Erb palsy in patients with shoulder dystocia are caused by the care provider to a statistical probability of 95% to 98%. ” In a study that described two shoulder dystocia cases (one of which was associated with clavicular fracture and transient brachial plexus injury), Allen et al. (6) mysteriously concluded that there was a “possible threshold for the likelihood of birth injury. ” However, note that there were no statistically significant differences between the uninjured and injured neonates concerning the peak and average clinician-applied forces. The same author also studied 39 physicians and found that “injury-inducing” force levels are reached in 82% of shoulder dystocia cases but also in 31% of routine deliveries (7). Simply put, the findings from this nonclinical laboratory model are inconsistent with the fact that brachial plexus palsy has been found in only 0.5 to 3 cases per 1000 births (8). Over the last several years, multiple lines of evidence have emerged that have supported the concept that not all brachial plexus injuries are traction-mediated events. A recent review article (9), which extracted data from 14 published reports of neonatal brachial plexus palsy, found that slightly more than half of all brachial plexus injuries are associated with uncomplicated vaginal deliveries. Brachial plexus palsy has also been found to occur in the posterior arm of infants whose anterior shoulder was impacted behind the symphysis pubis (10, 11) and in vertexpresenting fetuses delivered by atraumatic cesarean delivery (2, 12, 13). If brachial plexus palsy resulted from excessive traction by the clinician, then the overwhelming majority of injuries should affect the anterior fetal shoulder (8). Walle and HartikainenSorri (14), however, found that one third of all injuries were located in the posterior shoulder. Rapid second stage and disproportionate descent of the Address correspondence to: Robert Gherman, MD, Dept. of Ob/Gyn, Division of Maternal/Fetal Medicine, Bethesda Naval Hospital, National Naval Medical Center, 8901 Jones Bridge Rd, Bethesda, MD 20889. Email: ghermtoo@aol.com The views expressed in this article are those of the authors and do not reflect the official position of the Department of Defense, Department of the Navy, or the United States Government. Volume 58, Number 1 OBSTETRICAL AND GYNECOLOGICAL SURVEY Copyright © 2002 by Lippincott Williams & Wilkins, Inc.