**Core Concept**
The question requires the identification of a specific abnormality in a shoulder radiograph. This involves analyzing the anatomical structures and relationships visible in the radiograph to determine the correct diagnosis. Posterior dislocation of the shoulder is a condition where the humeral head is displaced posteriorly relative to the glenoid cavity.

**Why the Correct Answer is Right**
Posterior dislocation of the shoulder typically occurs when there is a fall on an outstretched hand with the arm in external rotation. This mechanism of injury causes the humeral head to be pushed posteriorly out of the glenoid cavity. The radiographic findings of posterior dislocation include the "light bulb" sign, where the humeral head appears as a rounded, light bulb-shaped structure, and the "empty socket" sign, where the glenoid cavity appears empty due to the displaced humeral head. The presence of these signs in the radiograph suggests posterior dislocation of the shoulder.

**Why Each Wrong Option is Incorrect**
**Option A:** Anterior dislocation of the shoulder is a more common injury that occurs when the humeral head is displaced anteriorly out of the glenoid cavity. This typically occurs when there is a fall on an outstretched hand with the arm in internal rotation.

**Option C:** Chondrosarcoma is a type of malignant bone tumor that can occur in the shoulder region. However, it would not typically be visible on a plain radiograph and would not be characterized by the specific signs of posterior dislocation.

**Option D:** Simple bone cyst is a benign bone lesion that can occur in the humerus or other long bones. It would not be associated with the specific radiographic signs of posterior dislocation of the shoulder.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the "light bulb" sign and "empty socket" sign are characteristic radiographic findings of posterior dislocation of the shoulder. These signs can help differentiate posterior dislocation from other shoulder injuries and conditions.

**Correct Answer:**
✓ Correct Answer: B. Posterior Dislocation Of Shoulder