C: Posterior dislocation of the shoulder associated with obstetric brachial plexus palsy

Four cases of posterior dislocation of the shoulder at birth in association with obstetric brachial plexus palsy are presented. Review of the literature suggests that this association is not generally recognised. All cases were diagnosed late; two were treated by open reduction, one by humeral osteotomy and one managed 764 THE JOURNAL OF BONE AND JOINT SURGERY conservatively. Posterior dislocation of the shoulder is not generally recognised as a birth injury associated with obstetric brachial plexus palsy. Wickstrom, Haslam and Hutchin-son (1955) described five cases of posterior dislocation occurring late as a result of muscle imbalance. More recent reports describe anterior dislocation during birth (Angeletti 1970; Chari, Rao and Rao 1979). With improved obstetric care, this type ofinjury has become less frequent but the diagnosis of posterior dislocation may be missed unless considered. Four such cases are presented with the common feature of obstetric difficulty involving the shoulder. Two of the babies were overweight. A confirmed diagnosis of obstetric brachial plexus palsy was made in three cases; in the fourth there was evidence ofa resolving Erb’s palsy. CASE REPORTS Case 1. A nine-month-old infant was referred with a resolving Erb’s palsy. He had been born at full term weighing 10 lb 10 oz and delivered with extreme diffi-culty. The plexus lesion was initially complete, but the hand recovered by seven months. Radiographs taken at six months showed posterior dislocation of the shoulder. Open reduction was performed by a posterior approach and at the same time, exploration of the plexus by a supraclavicular incision confirmed a lesion in continuity. A year after exploration, the child had good recovery of biceps and deltoid, but the lateral rotators of the shoulder remained paralysed. There was good passive forward flexion of the shoulder, but abduction was restricted to 85#{176},and 20#{176}offixed medial rotation persisted