REVERSE HILL-SACHS LESIONS

Mechanism of Injury

• Axial loading of the adducted and internally rotated arm.
• Violent muscle contraction: The internal rotators (Latissimus Dorsi, Pectoralis Major, Subscapularis) are stronger than external rotators.
• During a seizure, these muscles overpower the external rotators, forcing the humeral head posteriorly.

The Defect

• Location: Anteromedial humeral head.
• Comparison: A reflected image of a standard Hill-Sachs (which is posterolateral).
• Engagement: As the arm internally rotates, the defect engages the posterior glenoid.

Associated Pathology

• Reverse Bankart: Posterior labral tear.
• Posterior Glenoid Rim Fracture: "Reverse Bony Bankart".
• Lesser Tuberosity Fracture: Can be avulsed by subscapularis.
• Posterior Capsular Stretch: Typically present in chronic cases.

Classification by Articular Surface Involvement

Most clinically useful for decision making.

Gamma Angle Classification

Used to predict instability.

• Angle between the axis of the defect and the anatomical neck.
• Greater than 90 degrees: Suggests higher risk of engaging.

Specific Tests for Posterior Instability

1. Posterior Drawer Test: Supine. Axial load + posterior force.
2. Jerk Test: Seated. Flexion to 90 + Adduction + Axial Load. "Clunk" as head subluxes posteriorly.
3. Kim Test: Variation of Jerk test for inferior-posterior, labral pathology.
4. Load and Shift: Assess translation grading (Grade I-III).

ALWAYS compare to the contralateral side.

Neurovascular Exam

• Axillary Nerve: Sensation over regimental badge area. Deltoid function.
• Less commonly injured in posterior vs anterior dislocation, but verify.

Acute Management

Goal: Reduce and maintain stability.

1. Closed Reduction: Under conscious sedation/GA.
   • Traction + gentle anterior pressure. Avoid force (fracture risk).
2. Assess Stability:
   • Stable: Immobilize in External Rotation (gunslinger brace) for 4-6 weeks.
   • Unstable: If redislocates or engages in functional ROM to Surgery.

Early reduction minimizes cartilage damage.

Surgical Decision Making (Based on Size)

The Concept

Transferring the Subscapularis tendon (original McLaughlin) or Lesser Tuberosity (modified) into the defect.

• Effect: Fills the defects and acts as a check-rein preventing internal rotation.

Steps

1. Approach: Deltopectoral approach.
2. Identify Defect: Locate the anteromedial impression fracture.
3. Osteotomy: Lesser tuberosity osteotomy (with subscapularis attached).
4. Reduction: Reduce the humeral head into the glenoid.
5. Preparation: Prepare the defect bed (curette/burr) to encourage healing.
6. Fixation: Secure the lesser tuberosity bone block into the defect using screws or suture anchors.
7. Result: The bony plug fills the hole and the subscapularis tightens, preventing internal rotation.

Careful protection of the axillary nerve is required.

Segmental Allograft

Used when the defect is large but the joint is salvageable (young patient).

1. Approach: Deltopectoral.
2. Graft: Fresh femoral head or humeral head allograft.
3. Shaping: Graft shaped to match the defect ("snowman" or wedge shape).
4. Fixation: Countersunk headless compression screws.
5. Advantage: Restores spherical head shape effectively.

Allograft availability can be a limiting factor.

Hemi/Total Arthroplasty

Reserved for defects over 45-50% or older low-demand patients.

• Hemiarthroplasty: If glenoid is intact.
• Total Shoulder (Anatomic): If glenoid is arthritic but cuff intact.
• Reverse Total Shoulder: If cuff is deficient or in very elderly.

Hemiarthroplasty is less commonly used now due to glenoid erosion risk.