Summary Posterior shoulder instability and dislocations are less common than anterior shoulder instability and dislocations, but are much more commonly missed. Diagnosis is made radiographically in the setting of acute dislocations. Chronic instability can be diagnosed with presence of positive posterior instability provocative tests and confirmed with MRI studies showing posterior labral pathology. Treatment may be nonoperative or operative depending on chronicity of symptoms, recurrence of instability, and the severity of labrum and/or glenoid defects. Epidemiology Incidence 2% to 5% of all unstable shoulders 50% of traumatic posterior dislocations seen in the emergency department are undiagnosed Risk factors bony abnormality login to view 1 more bullet ligamentous laxity Etiology Pathophysiology mechanism login to view 12 more bullets biomechanical forces login to view 1 more bullet Associated conditions see table below Lesions Associated with Posterior Instability Avulsion of posterior band of IGHL Associated with acute subluxations Posterior Bankart lesions Characterized by detachment of posterior inferior capsulolabral complex Reverse Hill-Sachs lesions Associated with locked and difficult to reduce dislocations Posterior labral cyst Associated with chronic reverse Bankart lesion Posterior glenoid rim fracture Associated with chronic reverse Bankart lesion Lesser tuberosity fracture Associated with acute posterior dislocation Large capsular pouch Can see with MRI with contrast, often with chronic posterior instabiltiy Anatomy Glenohumeral anatomy Primary stabilizers of the posterior shoulder posterior band of IGHL login to view 1 more bullet subscapularis login to view 2 more bullets superior glenohumeral ligament and coracohumeral ligament login to view 2 more bullets Static restraint labrum deepens the glenoid by 50% Classification Acute versus chronic Acute = trauma, seizure, electric shock with dramatic presentation Chronic = microtrauma from repetition such as offense football lineman with insidious onset and presentation Voluntary versus involuntary Presentation History trauma or microtrauma with the arm in a flexed, adducted, and internally rotated position chronic instability often presents with insidious onset, and vague symptoms (usually pain and not instability as opposed to anterior instability) login to view 1 more bullet Symptoms pain with flexion, adduction, and internal rotation of the arm Physical exam inspection login to view 2 more bullets motion login to view 3 more bullets provocative tests - performed in the setting of chronic posterior instability login to view 14 more bullets Imaging Radiographs recommended views login to view 5 more bullets optional login to view 1 more bullet CT indications login to view 1 more bullet MRI indications login to view 3 more bullets Treatment Nonoperative acute reduction and immobilization in external rotation for 4 to 6 weeks login to view 6 more bullets physical therapy login to view 1 more bullet Operative open or arthroscopic posterior labral repair (Bankart) login to view 8 more bullets open or arthroscopic posterior capsular shift and rotator interval closure login to view 2 more bullets posterior glenoid opening wedge osteotomy login to view 3 more bullets open reduction with subscapularis transfer (McLaughlin) or lesser tuberosity transfer to the defect (Modified McLaughlin) login to view 3 more bullets hemiarthroplasty login to view 5 more bullets total shoulder arthroplasty login to view 2 more bullets Techniques Open or arthroscopic posterior labral repair and capsular shift goal is to repair any labral detachment or capsular tears, and/or reduce the posterior capsule volume approach login to view 3 more bullets posterior capsular shift login to view 1 more bullet closure of rotator interval login to view 2 more bullets thermal shrinkage of capsule (historical) login to view 4 more bullets complications login to view 3 more bullets postoperative care login to view 3 more bullets Open reduction with subscapularis with or without tuberosity transfer to defect approach login to view 1 more bullet technique to repair defect login to view 9 more bullets complications login to view 3 more bullets Complications Stiffness most common complication after labral repair Recurrence 2nd most common (7% to 50%) posterior glenoid bone loss as little as 11% of glenoid diameter is a risk factor for recurrence after isolated labral repair without bony augmentation login to view 1 more bullet Degenerative joint disease 3rd most common Adhesive capsulitis Overtightening of posterior capsule may lead to anterior subluxation or coracoid impingement Nerve injury axillary or suprascapular