Posterior Shoulder Instability: Kim Test, Reverse Bankart Lesion, and Post-Op Rehab
In short
Posterior shoulder instability represents 2 to 5 percent of dislocations. Learn about reverse Bankart lesions, the Kim test, and specialized post-op rehab.
In this guide (4 sections)
Posterior glenohumeral instability is an uncommon and frequently missed clinical entity, accounting for approximately 2 to 5 percent of all documented shoulder dislocations. While anterior instability captures prominent clinical attention, posterior subluxation presents with subtle, insidious symptoms, often manifesting as deep posterior joint aching, loss of pushing strength, and vague instability rather than dramatic dislocations. Posterior instability can arise from high-energy traumatic axial loading (such as high-speed motor vehicle impacts or epileptic seizures), but it is equally prevalent as a chronic overuse micro-instability in gym athletes performing repetitive heavy bench presses and cricket batsmen absorbing high-impact ball defense through the leading shoulder.
Gym Bench Pressing, Commuter Scooter Impacts, and Seizure Emergencies
In Indian fitness and emergency settings, posterior instability stems from distinct mechanical scenarios. Young gym enthusiasts frequently overload the horizontal bench press with improper technique, flaring their elbows and dropping the barbell hard against the chest. This position transmits massive posterior axial loads that stretch the posterior-inferior capsule. On the roadways, a two-wheeler rider who braces both hands firmly against the handlebars during an impending head-on collision sustains high-energy axial compression down the humeral shafts, driving both humeral heads backward. Additionally, post-ictal patients following unmanaged epileptic seizures frequently sustain missed bilateral posterior dislocations requiring rapid diagnostic vigilance.
Reverse Bankart Avulsion, McLaughlin Defects, and Biomechanical Breakdown
The pathoanatomy of posterior instability centers on damage to the posterior-inferior labrum and posterior band of the inferior glenohumeral ligament (PIGHL). A traumatic posterior dislocation shears the posterior labrum off the glenoid rim between the 6 o clock and 9 o clock positions, an injury termed a Reverse Bankart lesion. In severe cases, an anterior-medial humeral head impaction fracture occurs as the humerus impacts the posterior glenoid rim, creating a McLaughlin lesion (Reverse Hill-Sachs). Provocative physical examination relies on the Kim Test and Jerk Test. The Kim test applies axial compression through the humerus at 90 degrees abduction while elevating the arm diagonally upward; sudden deep posterior shoulder pain confirms posterior-inferior labral avulsion.
Post-Operative Reverse Bankart Protection and Phased Physiotherapy
Following arthroscopic reverse Bankart repair and posterior capsular plication, rehabilitation must strictly respect posterior biological tissue healing. The limb is immobilized in a specialized gunslinger or neutral-rotation sling for 4 to 6 weeks, holding the arm in 10 to 15 degrees of external rotation to relax tension on the posterior capsule. Internal rotation beyond neutral, horizontal adduction, and cross-body reaching are strictly forbidden during the initial 6 weeks. Early rehabilitation focuses on submaximal isometric external rotation, scapular retraction, and gentle passive forward elevation in the scapular plane, gradually advancing to posterior rotator cuff strengthening (infraspinatus and teres minor) and serratus dynamic stability.
Prone Scapular Retraction with External Rotation in Scapular Plane
Objective: Strengthen the infraspinatus, teres minor, and rhomboids while preventing posterior humeral head translation
- 1Lie prone on a firm examination plinth with your forehead resting on a comfortable towel roll.
- 2Abduct your affected arm to 60 degrees in the scapular plane with your elbow bent to 90 degrees.
- 3Gently draw your shoulder blade toward your spine, engaging your mid-trapezius and rhomboids.
- 4Without elevating your elbow higher than your shoulder, rotate your wrist and forearm upward toward the ceiling.
- 5Hold this posterior-centering contraction steadily for 5 seconds, breathing calmly, then slowly lower.
| Diagnostic Domain | Anterior Glenohumeral Instability | Posterior Glenohumeral Instability |
|---|---|---|
| Incidence and Mechanism | Accounts for 95 percent of dislocations; mechanism involves abduction, external rotation, and extension | Accounts for 2-5 percent; mechanism involves axial load through flexed, adducted, and internally rotated humerus |
| Primary Labral Pathology | Classic Bankart lesion (anterior-inferior labral tear between 3 o clock and 6 o clock glenoid rim) | Reverse Bankart lesion (posterior-inferior labral avulsion between 6 o clock and 9 o clock glenoid rim) |
| Key Provocative Tests | Anterior Apprehension Test, Jobe Relocation Test, and Surprise / Release Test | Kim Test, Jerk Test, and Posterior Drawer Test with axial humeral compression |
| Early Post-Op Motion Restrictions | Restrict external rotation beyond neutral and avoid combined 90 abduction with external rotation | Restrict internal rotation, horizontal adduction (cross-body reaching), and weight-bearing push-ups for 8-12 weeks |
Up to 50 percent of posterior shoulder dislocations are initially missed on standard anteroposterior (AP) shoulder radiographs because the humeral head overlaps the glenoid fossa without obvious displacement. Clinicians must always obtain an axillary lateral or Velpeau view to confirm true concentric joint reduction.
Frequently Asked Questions
Why does pushing a door open or doing a push-up hurt my posterior shoulder?
Pushing activities transmit an axial compressive force down the humerus that drives the humeral head backward against the posterior-inferior capsule. When a reverse Bankart tear is present, the damaged posterior labral bumper cannot resist this backward translation, generating localized pain and joint instability.
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