Posterior shoulder instability secondary to reverse humeral avulsion of the glenohumeral ligament

Background: Posterior shoulder instability resulting from a disruption of the posterior capsular structures has been reported. We present the largest series of these injuries in the published literature, propose a definition and highlight the clinical presentation, radiological findings, and associated injuries. Materials and methods: A retrospective review of a single shoulder surgeons database was performed identifying posterior instability cases associated with disruption of the posterior capsule. Chart, radiological imaging, and intra-operative findings were reviewed. Results: Nineteen patients were identified with an average age lower than the overall posterior instability group. All occurred via a traumatic mechanism, the most common being a forced cross-body adduction. The only consistent symptom was posterior joint line pain. MRI reporting was found to be only 50% sensitive, increased to 78.6% when reviewed by the treating surgeon. Associated injuries are common with 58% having a labral tear, 32% a SLAP lesion, 26% a reverse Bankart lesion, 21% a chondral injury, 21% rotator cuff injury, and 11% extension of the tear into the posterior band of the inferior glenohumeral ligament. Discussion: Disruption of the posterior capsule is a rare cause of recurrent posterior instability. There are no specific symptoms that identify the injury, though a mechanism of forced cross-body adduction should raise suspicion. Identification of the injury requires specific attention to the posterior capsule on MRI, preferably performed with the arm in slight external rotation and routine visualization of the posterior capsule via viewing from the anterior portal.