Posterior shoulder dislocation in infants with neonatal brachial plexus palsy

Glenoid dysplasia and posterior shoulder subluxation with resultant shoulder stiffness is a well-recognized complication in infants with neonatal brachial plexus palsy. It is generally considered to be the result of a slowly progressive glenohumeral deformation secondary to muscle imbalance, physeal trauma, or both. Recent publications about infantile posterior shoulder dislocation have suggested that the onset of dysplasia occurs at an earlier age than has been previously recognized. The prevalence of early dislocation in infants with this disorder has not been previously reported, to our knowledge.

We studied 134 consecutive infants with neonatal brachial plexus palsy who were seen at our institution over a period of two years. All infants were examined at monthly intervals to assess neurological recovery and the status of the upper extremity until recovery occurred or a treatment plan was established. The type of brachial plexus involvement was classified. Specific clinical signs associated with subluxation and dislocation were recorded. These included asymmetry of skin folds of the axilla or the proximal aspect of the arm, apparent shortening of the humeral segment, a palpable asymmetric fullness in the posterior region of the shoulder, or a palpable click during shoulder manipulation. The infants who were identified as having these clinical signs were evaluated with ultrasonographic imaging studies.

Eleven (8%) of the 134 infants had a posterior shoulder dislocation. The mean age at the time of diagnosis was six months (range, three to ten months). There was no correlation between the occurrence of dislocation and the type of initial neurological deficit. A rapid loss of passive external rotation between monthly examinations indicated a posterior shoulder dislocation.

Posterior shoulder dislocation can occur earlier (before the age of one year) and more rapidly in infants with neonatal brachial plexus palsy than has been appreciated previously. As with developmental dysplasia of the hip, a high index of suspicion, recognition of clinical signs, and the use of ultrasonography will allow the diagnosis to be established. Following early diagnosis, attention should be focused on improving the stability and congruency of the shoulder joint.