ASPECTS OF CURRENT MANAGEMENT Posterior dislocation of the shoulder

©2004 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.86B3. 14985 $2.00 J Bone Joint Surg [Br] 2004;86-B:324-32. Posterior dislocation of the shoulder is a rare but clinically and radiologically well-defined entity. It accounts for less than 2% of all dislocations of the shoulder,1,2 but is of diagnostic and therapeutic interest because most are missed on the initial examination.3-6 In a series of 24 patients with posterior dislocation, 21 had not been recognised initially.7 There is confusion between posterior subluxation and dislocation. Posterior dislocation is an acute entity associated with trauma and with an impression defect of the humeral head. Its treatment is determined by the size of the defect and the duration of the dislocation. The term dislocation has been applied, but in fact this represents subluxation because some of the articular surface of the humeral head is in contact with the glenoid and some behind it. Recurrent posterior subluxation is a distinct and separate entity which is often not associated with trauma and requires completely different management such as non-operative treatment or posterior reconstruction of the shoulder.8 The patient complains of pain and instability with his arm in a provocative position usually including forward flexion, adduction and internal rotation.9 There is also confusion between posterior dislocation and fracture-dislocation. Posterior dislocation may be associated with fractures of the surgical neck of the humerus or fractures of the tuberosities. Fracture-dislocations have been classified by Neer10 as two-, threeor four-part posterior fracture-dislocations. They require a different approach and treatment such as osteosynthesis or shoulder arthroplasty. This report describes the diagnosis and treatment of posterior dislocation of the shoulder with an associated impression fracture of the articular surface of the humeral head. Chronic posterior dislocation of the shoulder has often been referred to as being either ‘old’, ‘missed’, ‘locked’ or ‘fixed’. The terms ‘locked’ or ‘fixed’ have also been used to describe irreducible acute dislocations associated with an impression defect of the humeral head.11 Chronic posterior dislocation of the shoulder is a missed acute posterior dislocation which has been unrecognised for more than three weeks and characteristically there is an impression fracture of the articular surface of the humeral head.