Review Question - QID 219766

This patient has a posterior labral tear and reverse Hill-Sachs lesion, findings consistent with a recent posterior glenohumeral dislocation. The most common mechanism for this injury is when an axial load is applied to a flexed and internally rotated shoulder (Answer 4).

Posterior glenohumeral dislocations, occurring less frequently than anterior dislocations, are more commonly missed and associated with numerous pathologic lesions. Up to 50% of patients evaluated for posterior glenohumeral instability report a prior posterior dislocation. Posterior instability, without frank dislocation, can also cause repetitive microtrauma to the posterior labrum and lead to labral tears and posterior glenoid bone loss. In the traumatic setting, these injuries occur when an axial load is passed through a flexed and internally rotated shoulder. In addition to trauma, both seizures and electric shock are well-known mechanisms through which a posterior glenohumeral dislocation can occur.

The primary restraints to posterior glenohumeral dislocation include the posterior band of the IGHL, the subscapularis, and the SGHL and CHL. Patients with an acute posterior dislocation often present with limited external rotation, and those with a chronic, undiagnosed/missed posterior dislocation may present with a shoulder locked in internal rotation. In the acute setting, radiographs must be carefully evaluated, and axial imaging is critically important.

Frank et al. review the management of posterior glenohumeral instability. They note that this pathology is becoming much more commonly encountered, especially among athletic patients. The authors highlight that sports where an axial load is frequently placed through a forward-flexed and internally rotated arm (e.g., football linemen, wrestlers) are at a heightened risk of experiencing this injury.

Sheean et al. review the diagnosis and management of posterior glenohumeral instability. Like Frank et al., the authors note this pathology is common in athletic populations. Athletes who frequently experience axial loads through flexed and internally rotated arms (e.g., football linemen and rugby players) often sustain microtrauma, which can lead to posterior labral tears. The authors also highlight that this pathology often coexists with SLAP tears, as injury to the superior labrum can propagate posteriorly, as is seen in Type VIII SLAP tears.

Scanaliato et al. report on the outcomes of posterior labral repair in active-duty military patients. Their study included 73 patients who underwent posterior labral repair. The authors highlighted that patients who underwent repair with all-suture anchors were more likely to meet the acceptable symptom state (PASS) for the ASES and SANE outcome instruments. Overall, the authors conclude that posterior labral repair is a reliable intervention for symptomatic posterior labral tears, with a return to active duty rate of 95.89%.

Figure A is a T2-weighted axial MRI of a left shoulder. The subscapularis is visible at the top of the image (anterior to the glenohumeral joint line). There is T2-fluid hyperintensity about the anterior humeral head, consistent with a reverse Hill-Sachs lesion and posterior labral tearing.

Incorrect Answers:
Answer 1: This mechanism is classically associated with anterior instability.
Answer 2-3: These mechanisms are not classically associated with a well-described pattern of glenohumeral instability.
Answer 5: This mechanism is classically associated with an inferior glenohumeral dislocation (luxatio erecta).