Closed reduction for traumatic posterior dislocation of the shoulder using the 'lever principle': two case reports and a review of the literature

Journal of Orthopaedic Surgery, Dec 2006 by Mimura, T, Mori, K, Matsusue, Y, Tanaka, N, Et al

ABSTRACT

Traumatic posterior dislocation of the shoulder is frequently missed because of its rarity and the absence of characteristic symptoms. Several signs should be emphasised: an overlap of the humeral head and glenoid rim in a true anteroposterior view and the light-bulb sign in the anteroposterior view. To make an accurate and early diagnosis, use of multidirectional radiographs combined with computed tomography is recommended. Closed reduction was successfully performed under general anaesthesia using the DePalma method with slight modification-the lever principle-by pushing the medial side of the upper arm laterally to adduct the shoulder as far as possible. The dynamics of the lever principle make it a safer and more effective method of achieving a closed reduction of a posterior dislocation of the shoulder than the conventional method of solely pushing the humeral head anteriorly, especially in patients with locking of the glenohumeral joint and impression fractures.

Key words: shoulder dislocation; wounds and injuries

INTRODUCTION

Posterior dislocation of the shoulder is an uncommon injury, comprising 1 to 4% of all shoulder dislocations. McLaughlin1 reported 22 (3.8%) of 581 dislocations of the shoulder being posterior. Bilateral posterior dislocation is even rarer and accounts for less than 5% of all posterior dislocations of the shoulder.2 The main causes of posterior dislocation are trauma and seizure and indirect force is implicated.3 Its diagnosis is often missed and it becomes chronic and difficult to treat.4 To make an accurate and early diagnosis, multidirectional radiographs combined with effective diagnostic tools such as computed tomography (CT) are recommended.5,6 Closed reduction should be performed using the conventional DePalma methods7 if the defect in the humeral head caused by impression fracture (reverse Hill-sacks lesion) is less than 25% of the articular surface. Pressure is applied posteriorly on the humeral head and it is pushed anteriorly. Both original and modified closed reduction techniques have been reported.8,9

CASE REPORTS

Case 1

In September 2002, a 74-year-old woman presented to Soseikai General Hospital with shoulder pain following a fall from stairs. The patient recalled that her elbow, not shoulder, sustained the direct blow. Physical examination revealed that the upper limb was internally rotated and slightly adducted; the posterior area of the shoulder was swollen and tender and the shoulder could not be moved in any direction. No neurovascular deficit was seen. Radiography revealed a positive rim sign,10 absence of half-moon overlap,10 and the light-bulb sign on the anteroposterior (AP) view (Fig. 1a). An overlap of the glenoid rim and the humeral head were also demonstrated on a true AP view (Fig. 1b). CT clearly revealed the posterior dislocation.

Under general anaesthesia, closed reduction was successfully achieved using the DePalma method with slight modification: the patient was in a supine position and the uninjured shoulder was elevated to provide a true AP view. The injured arm was then placed in traction, with the elbow pointing caudally. Then, maintaining traction and internal rotation, the medial side of the upper arm was pushed laterally using the lever principle, making the humeral head detach from the glenoid rim (Fig. 2). The shoulder was then rotated externally and reduction achieved. As there was no indication of redislocation, the arm was immobilised using a sling and a bust band for 3 weeks. Range of motion (ROM) exercises were started afterwards. Six months later, the patient had no weakness or instability of her shoulder, and the shoulder had recovered a full ROM.

Case 2

In October 2002, a 55-year-old man was transferred to Soseikai General Hospital with shoulder pain following a traffic accident. The initial diagnosis made by another physician was contusion. The patient had sustained a direct blow to the elbow, not the shoulder, as in case 1. Clinical examination revealed swelling and tenderness in the posterior area of the shoulder. The shoulder was locked, adducted, and internally rotated.

An AP radiograph showed a slightly positive rim sign and absence of half-moon overlap; the trough line and light-bulb sign were clearly revealed, nonetheless (Fig. 3a). A true AP radiograph confirmed an overlap of the glenoid rim and the humeral head (Fig. 3b). CT and a 3-dimensional reconstructed CT revealed posterior dislocation with an impression fracture (Fig. 4).

Despite the presence of an impression fracture, good and safe reduction was successfully achieved using the technique described in case 1. The lever principle was very effective for releasing the impression fracture. As there was no indication of redislocation, the same immobilisation period and ROM exercises were prescribed. At 8-month followup, the patient had a slightly contracted shoulder (160� abduction, 160� flexion, and 40� external rotation), but no instability was noted.

DISCUSSION

Posterior dislocation of the shoulder was first described by Cooper in 1839 in an epileptic patient. Posterior dislocation of the shoulder associated with fractures is less common: being seen in 0.9% of 1500 cases reported by Neer.11 An impression fracture of the humeral head, known as a "locked posterior dislocation of the shoulder"1 is a common condition associated with this injury and a major factor in unsuccessful closed reduction.5,12 Its diagnosis is often missed as in our second patient, because of its rarity and the non-specific pain it causes. Approximately 60% of diagnoses are missed and a mean delay of one year between injury and diagnosis has been reported in a series of 40 patients12; only 30% of diagnoses are made within 6 weeks.7 The treatment selected for most delayed cases has been open reduction with percutaneous pinning or lesser tuberosity transfer.5,13 Indirect force is often implicated in this injury, as seen in our 2 patients.1,9,14 It is therefore important to carefully question the patient about how the injury occurred.