Glenohumeral instability

1. What is the difference between shoulder instability, subluxation, and dislocation?
2. What is the most common direction of instability? What is the mechanism and complications?
3. What is the presentation and mechanism of posterior GH instability?
4. What is a Bankart lesion? What sort of instability results from this?
5. What is a Hill-Sachs lesion? What sort of instability is associated with this lesion?

Answers:
1. Instability is translation of humeral head on glenoid fossa without separation. Subluxation is separation of humeral head from glenoid fossa with immediate reduction. Dislocation is separation of humeral head from glenoid fossa without immediate reduction.
2. Most common direction is anterior inferior, via arm abduction and external rotation. Complications include axillary nerve injury.
3. Mechanism is landing on a forward flexed adducted arm or as a result of seizure. The patient presents with an adducted, internally rotated arm.
4. Bankart lesion is a tear of the glenoid labrum off the front of the glenoid, allowing the humeral head to slip anteriorly --> anterior instability.
5. A Hill-Sachs lesion is a compression fracture of the posterolateral aspect of the humeral head caused by abutment against the anterior rim of the glenoid fossa due to recurring anterior shoulder dislocation.