**Core Concept**
Posterior elbow dislocation involves the displacement of the ulna and radius bones in relation to the humerus, resulting in a characteristic radiographic appearance. This type of dislocation is due to the posterior capsule and medial collateral ligament being disrupted.

**Why the Correct Answer is Right**
In a posterior elbow dislocation, the radial head is displaced posteriorly, resulting in a characteristic "sail sign" or "sail-like" appearance on the anteroposterior (AP) x-ray. This occurs due to the radial head being displaced behind the capitellum of the humerus. Additionally, the ulna is often also displaced, resulting in a "cubitus varus" deformity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not accurately describe the radiographic appearance of a posterior elbow dislocation.
* **Option B:** This option is incorrect as it describes a different type of injury, such as a fracture or a different type of dislocation.

**Clinical Pearl / High-Yield Fact**
A posterior elbow dislocation is often associated with a "sail sign" or "sail-like" appearance on AP x-ray, which is a key radiographic feature to look for in suspected cases.

**Correct Answer: C. Sail sign.**