Shoulder:Glenohumeral Instability/Posterior Instability
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Posterior shoulder instability is not as rare as previously though.
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Diagnosing posterior instability may be difficult because patients often report vague symptoms not linked to a clear history of traumatic shoulder dislocation.
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This condition is consequently often misdiagnosed or patients experience a delay in diagnosis.
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It that encompasses different acute and chronic pathologies involving the labrum, the cartilage, the capsule, bony lesions.
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A tear between the posterior labrum and the glenoid cartilage without complete detachment of the labrum is described as a Kim lesion. It is postulated that this lesion is due to posterior force acting on the posterior-inferior glenohumeral ligament as it attaches to the posterior labrum.
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Numerous classifications exit, none having done unanimity.
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Risk factors for recurrent instability are: (1) age below 40 at time of first instability; (2) dislocation during a seizure; (3) a large reverse Malgaigne (Hill-Sachs) lesion; (4) glenoid retroversion, and (5) a high and horizontally oriented acromion in the sagittal plan.
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Hyperlaxity is multidirectional but instability is almost exclusively unidirectional.
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Physical examination comprises the articular range of motion, the rotator cuff, and jerk, Kim and O’Brien tests.
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Three views plain radiographs, including true anteroposterior of the glenohumeral joint, scapular Y (scapular lateral), and Bernageau views are the mainstay of imaging in the setting of shoulder instability.
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An internally rotated humeral head gives a rounded appearance on anteroposterior view, which is called the lightbulb sign.
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In case of a suspicion about posterior dislocation of the shoulder, additional imaging including, depending of the type of instability, magnetic resonance arthrography (MRA) or computed tomography (CT) is required.
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Acute or recurrent posterior dislocations can be treated conservatively, by soft tissue or bony procedures.
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Surgical options include anatomic reconstruction as well as non-anatomic procedures such as subscapularis tendon transfer, allo-/autograft reconstruction, derotation osteotomy or shoulder arthroplasty.
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Treatment of locked dislocation depends on the extent of the articular defect size of the humeral head, duration of the dislocation and patient-specific conditions such as age and activity levels.
