The sternoclavicular joint dislocates posteriorly if the costoclavicular ligaments, posterior capsule, and anterior capsule have all been disrupted. Diagnosis of a posteriorly dislocated sternoclavicular joint is difficult on clinical examination and with plain X-rays. The treatment objective is to obtain a closed reduction, and failing this an open reduction is indicated. In the intra-operative setting the evaluation of the reduction when performed through closed means can be somewhat difficult, and intra-operative plain films do not give clear answers. Ultrasound as an imaging modality for these injuries was shown to demonstrate the state of the joint in terms of reduction, more clearly than X-rays ( P<0.001). It was accurately interpreted by the vast majority of orthopaedic surgeons in an investigation, and is of great value in the intra-operative setting to confirm whether a closed reduction has been successful or not. A case is reported illustrating its use.