Aetiology

The incidence of obstetric brachial plexus birth injury (OBPI) is around 1 per 1000 live births. Around 25% of patients are left with permanent disability without intervention. The shoulder is the most commonly affected joint and, owing to the subsequent imbalance of musculature, the abnormal deforming forces cause dysplasia of the glenohumeral joint. In the growing child, this presents with a changing pattern of pathology, which requires a multidisciplinary approach and a broad range of treatment modalities to optimize function.

A common cause is a traction injury to the brachial plexus during the later stages of vaginal delivery when the head is pulled away from the shoulder. The mechanism of injury is a forced lateral flexion of the cervical spine, resulting in injury initially to the upper cervical roots (C5–C7), causing an Erb’s palsy, and, in more severe cases, the entire brachial plexus (C5–T1). With this mechanism, isolated lower root injuries (C8–T1, Klumpke’s palsy) do not tend to occur in OBPI. Other rare causes are abnormal forces on the shoulder over the sacral promontory or abnormal forces in an abnormal uterus, such as a bicornuate or fibroid uterus.