**Question:** Posterior glenohumeral instability can be tested by:

A. Applying a posterior force to the arm while the patient internally rotates their shoulder.
B. Applying an anterior force to the arm while the patient externally rotates their shoulder.
C. Applying a posterior force to the arm while the patient externally rotates their shoulder.
D. Applying a posterior force to the arm while the patient internally rotates their shoulder and adducts the arm.

**Correct Answer:** .

**Core Concept:**
Glenohumeral instability refers to the dislocation or subluxation of the humeral head from its normal position in the glenoid fossa of the scapula. Posterior instability refers to the dislocation or subluxation of the humeral head posteriorly.

**Why the Correct Answer is Right:**
The correct answer, D, describes a test (McConnell's test) specifically designed to provoke posterior instability. In this test, a posterior force is applied to the arm while the patient internally rotates their shoulder and adducts the arm. This combination of maneuvers challenges the posterior joint stability, as it places the humeral head in a position of vulnerability due to the loss of the anterior glenohumeral joint stability.

**Why Each Wrong Option is Incorrect:**
A, B, and C address anterior instability, not posterior instability. Applying an anterior force and having the patient internally rotate or externally rotate the shoulder does not challenge the posterior stability effectively.

**Clinical Pearl:**
McConnell's test is a reliable clinical test for posterior instability. It helps in diagnosing patients with posterior labral tear or Bankart lesion, which are common causes of recurrent posterior shoulder instability. The test should be performed by a trained examiner and positive results should be confirmed by imaging studies like MRI or arthroscopy.