Clinical History
A patient with shoulder pain after a fall on her right outstretched and externally rotated arm.
Imaging Findings
The patient presented to the emergency department after a fall on her right outstretched and externally rotated arm. She supported her right arm at a slight abduction with the opposite hand. Physical examination revealed a flattened deltoid and a decreased range of motion. A clinical diagnosis of anterior dislocation of the glenohumeral joint was suggested.
A standard anteroposterior radiograph of the right shoulder showed the characteristic appearance of an anterior dislocation of the glenohumeral joint and a bony Bankart lesion (Fig. 1). Lateral scapular projection (not shown) confirmed the humeral head in the typical subcoracoid position and a Hill-Sachs lesion. All these findings were better demonstrated by helical computed tomography (CT) (Fig. 2).
Discussion
The glenohumeral joint is the most common site of subluxation or dislocation in the human body (1). This is a highly mobile joint, in which stability is provided in large part by a strong capsule, three glenohumeral ligaments, and the muscules around the shoulder, particularly the rotator cuff (2). Dislocations of the shoulder occur most commonly in the anterior direction (97%) (3). The usual mechanism is a combination of abduction, extension, and external rotation. These are also classified as subcoracoid, the most common subtype; subglenoid, the second in frequency; subclavicular and intrathoracic subtypes (rare). Approximately 40% of anterior dislocations are recurrent, and are more likely in subcoracoid and subglenoid subtypes (2). Anterior dislocation is readily diagnosed on the anteroposterior view of the shoulder, althought the Y view or the axillary projection are effective as well.
Hill-Sachs and bony Bankart lesions are fractures associated with anterior dislocations. Other associated injuries are avulsion fracture of the greater tuberosity of the humerus (10%-15%), disruption of the rotator cuff and injury of the brachial plexus (7%-45%) (2). The Hill-Sachs defect is a compression fracture on the posterolateral aspect of the humeral head at the junction with the neck, seen in 25% and 75% of acute and recurrent dislocations respectively (2). This is produced at the time of dislocation when the humeral head strikes the anteroinferior margin of the glenoid, and is frequently larger in shoulders dislocated for a long period of time and in recurrent dislocations. The Hill-Sachs lesion is best demonstrated on the anteroposterior projection of the shoulder with the arm internally rotated (3). Posterolateral bone contusions without humeral head indentation may also be identified on MR images (4). The bony Bankart lesion is a fracture of the anterior aspect of the inferior rim of the glenoid, and is less commonly seen (1). This is readily demonstrated on the anteroposterior view with the arm in the neutral position. Additional imaging techniques such as CT arthrography, MR and MR arthrography may be required in order to demonstrate labral and capsular abnormalities (2,4).
Differential Diagnosis List
Anterior dislocation of the glenohumeral joint: Bankart and Hill-Sachs fractures
Final Diagnosis
Anterior dislocation of the glenohumeral joint: Bankart and Hill-Sachs fractures
