Posterior shoulder instability is the loss of stability at the glenohumeral joint following a dislocation or repeated subluxation in which the humeral head displaces backward out of the glenoid socket. Posterior dislocations are much less common than anterior dislocations, accounting for less than 5 percent of all shoulder dislocations, and they are frequently missed on initial presentation. The injury patterns and treatment approach differ from anterior instability, and the clinical recognition is the first challenge.
What Is Posterior Shoulder Instability?
The posterior capsule and labrum are thinner and weaker than their anterior counterparts, which is part of why isolated posterior dislocations are rare. When they do occur, the humeral head drives backward, tearing the posterior labrum off the glenoid (a reverse Bankart lesion) and stretching or tearing the posterior capsule. Some dislocations also produce an impression defect on the anterior humeral head where it contacts the posterior glenoid rim on exit, called a reverse Hill-Sachs lesion.
Posterior instability takes two clinical forms. Traumatic dislocation produces an acute posterior displacement requiring reduction. Recurrent posterior subluxation produces repetitive partial dislocations without full displacement, often in athletes with repetitive posterior loading such as football offensive linemen, weightlifters performing bench press, and swimmers in specific stroke positions.
The chronic form is common in athletes and often under-recognized. Patients describe a clunk or shift rather than a dislocation.
Causes and Risk Factors
- Seizures, which produce forceful internal rotation and posterior dislocation
- Electrical shock injuries, which produce similar muscle contractions
- High-energy trauma with the arm in a forward flexed, adducted, internally rotated position
- Repetitive posterior loading in athletes (football blocking, bench press, swimming)
- Generalized ligamentous laxity, which predisposes to multidirectional instability including a posterior component
Symptoms
Acute posterior dislocation:
- Arm held in fixed internal rotation across the body
- Inability to externally rotate the arm (the hallmark finding that is often missed)
- Shoulder pain and visible prominence of the coracoid anteriorly
Chronic posterior instability:
- Pain and a sense of shifting in specific positions, particularly the arm flexed forward and across the body
- Pain and loss of power with bench press, push-ups, or blocking
- Clicking, catching, or a sensation the shoulder is coming out of the back of the joint
Diagnosis
Dr. Chudik’s evaluation includes the mechanism and the specific activities that provoke symptoms, followed by a physical examination with provocative maneuvers (jerk test, Kim test, posterior load-and-shift) that reproduce the posterior instability. X-rays in multiple views are essential because standard AP views can miss posterior dislocation; the axillary view is critical. MRI arthrogram characterizes the posterior labrum and capsule. The Westmont office has on-site high-field MRI and X-ray.
Treatment
Non-surgical treatment is the first line for recurrent subluxation without significant labral damage or bone loss. It includes activity modification, a targeted physical therapy program for the posterior rotator cuff and scapular stabilizers, and technique modification for overhead and posterior-loading athletes.
Surgery is indicated for recurrent instability that fails non-surgical treatment, for acute traumatic posterior dislocations in active patients with significant labral disruption, and for cases with bone loss on the posterior glenoid or anterior humeral head. Dr. Chudik performs arthroscopic posterior Bankart repair, reattaching the torn posterior labrum and capsule to the glenoid with suture anchors, with capsular plication to tighten the redundant posterior capsule. When significant bone loss is present, glenoid bone grafting or humeral head treatment may be added.
Recovery and Outcomes
Recovery after arthroscopic posterior stabilization typically includes six weeks of sling protection in a position of slight external rotation, progressive range of motion over two to three months, and strengthening over three to four months. Return to contact sport is typically five to six months. Return-to-sport outcomes are best when the injury is recognized and treated before multiple episodes.
When to See Dr. Chudik
Schedule an evaluation after any shoulder dislocation, if the shoulder feels unstable with specific loaded positions, or if pain and shifting interfere with activities such as bench press or blocking. Call 630-324-0402 or request an appointment online.