Shoulder:Glenohumeral Instability/Posterior Instability
Bullet Points
Posterior shoulder instability is not as rare as previously though.
Diagnosing posterior instability may be difficult because patients often report vague symptoms not linked to a clear history of traumatic shoulder dislocation.
This condition is consequently often misdiagnosed or patients experience a delay in diagnosis.
It that encompasses different acute and chronic pathologies involving the labrum, the cartilage, the capsule, bony lesions.
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.
Numerous classifications exit, none having done unanimity.
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.
Hyperlaxity is multidirectional but instability is almost exclusively unidirectional. Physical examination comprises the articular range of motion, the rotator cuff, and jerk, Kim and O’Brien tests.
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.
An internally rotated humeral head gives a rounded appearance on anteroposterior view, which is called the lightbulb sign.
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.
Acute or recurrent posterior dislocations can be treated conservatively, by soft tissue or bony procedures.
Surgical options include anatomic reconstruction as well as non-anatomic procedures such as subscapularis tendon transfer, allo-/autograft reconstruction, derotation osteotomy or shoulder arthroplasty.
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.
