Spontaneous vaginal delivery. A risk factor for Erb's palsy?

OBJECTIVE: Our purpose was to determine whether Erb's palsies occurring in the absence of shoulder dystocia differ from those occurring after shoulder dystocia. STUDY DESIGN: We compared the time course of resolution and incidence of persistent injury at 1 year of age in 17 cases of Erb's palsy without shoulder dystocia and 23 cases associated with shoulder dystocia. RESULTS: The rate of persistence at 1 year was significantly higher in those Erb's cases without identified shoulder dystocia, 7 of 17 (41.2%) versus 2 of 23 (8.7%), p = 0.04. These cases of Erb's palsies also took longer to resolve (6.4 +/- 0.9 vs 2.6 +/- 0.7 months, p = 0.002), had a higher rate of associated clavicular fracture (12 of 17 vs 5 of 23, p = 0.006), and were more likely to occur in the posterior arm (10 of 15 vs 4 of 21, p = 0.009). CONCLUSIONS: Erb's palsy occurring without shoulder dystocia may be a qualitatively different injury than that occurring with shoulder dystocia.