Gherman et al (1998) examined cases of Erb's palsy, defined as brachial plexus injury involving C5-C6 nerve roots, and sought to determine whether there were differences in cases occurring in the absence of shoulder dystocia versus those occurring with shoulder dystocia. While Erb's palsy is in most cases associated with shoulder dystocia, a literature review in this study supports that some cases may have intrauterine origins, being noted in the posterior arm of infants whose anterior shoulder was impacted behind the symphysis and in fetuses delivered by atraumatic cesarean.