**Question:** Mechanism of anterior dislocation of shoulder:

A. Direct blow to posterior aspect of shoulder disrupting the subscapularis muscle
B. Direct blow to anterior aspect of shoulder disrupting the coracoid process
C. Falling onto an outstretched hand with the elbow flexed
D. Falling onto an outstretched hand with the elbow extended

**Correct Answer:** D. Falling onto an outstretched hand with the elbow extended

**Core Concept:**
Anterior dislocation of the shoulder is a common type of shoulder injury caused by a traumatic event leading to the glenoid labrum and humeral head being displaced out of their normal anatomic position. The shoulder joint is a ball-and-socket joint, with the humeral head fitting snugly into the glenoid cavity of the scapula. Four primary stabilizers of the shoulder joint are:

1. Supraspinatus, infraspinatus, teres minor, and subscapularis muscles, collectively forming the rotator cuff.
2. Coracoclavicular ligament, which connects the coracoid process of the scapula to the clavicle.
3. Deltoid muscle, which is a powerful rotator and abductor of the shoulder.
4. Scapulothoracic joint, a synovial joint between the glenoid cavity and the scapula, providing additional stability to the joint.

**Why the Correct Answer is Right:**
The correct answer is D, falling onto an outstretched hand with the elbow extended. This mechanism puts the greatest strain on the subscapularis muscle, which is the most anterior stabilizer of the shoulder joint. When this muscle is overstretched, it tears, allowing the humeral head to dislocate anteriorly.

**Why Other Options are Incorrect:**
A) Option A involves a blow to the posterior aspect of the shoulder, which does not directly affect the stabilizers of the anterior shoulder joint, making it unlikely to cause an anterior dislocation.
B) Option B involves a blow to the anterior aspect of the shoulder, which would primarily affect the subscapularis muscle and the rotator cuff, making it less likely to result in anterior dislocation compared to option D.
C) Option C involves a mechanism involving the elbow flexed, which reduces the stability of the scapulothoracic joint, making it more prone to anterior dislocation. However, the subscapularis muscle is still the primary stabilizer, making option D the most likely cause of anterior dislocation.

**Clinical Pearl:**
Understanding the key stabilizers of the shoulder joint and the specific mechanism of injury is crucial in diagnosing and treating shoulder dislocations effectively. In clinical practice, the subscapularis muscle tear can be confirmed by a positive "hanging man test" or "splitting the subscapularis test." This test involves passive external rotation of the arm while applying pressure to the anterior aspect of the shoulder joint. In a subscapularis tear, the arm will drop posteriorly due to the loss of anterior glenohumeral stability.