The ultrasound diagnosis of posterior shoulder dislocation associated with Erb's palsy.

A case is presented of an infant with Erb's palsy whose posterior dislocation of the humeral head was identified using high-resolution ultrasound following non-diagnostic plain radiographs. Posterior dislocation is associated with Erb's palsy but the diagnosis can be delayed. We suggest the early use of ultrasound in patients with Erb's palsy, as this technique is a safe, quick and reliable method of excluding posterior dislocation.