**Core Concept**
The elbow joint is a complex hinge joint that can be prone to dislocations due to its unique anatomy. The most common type of dislocation occurs when the ulna bone moves out of its normal position in relation to the humerus, resulting in a specific type of injury.

**Why the Correct Answer is Right**
The most common type of dislocation of the elbow joint is a posterior dislocation, also known as a posterior elbow dislocation. This type of injury occurs when the ulna bone is displaced posteriorly (towards the back) relative to the humerus. This can happen due to a fall onto an outstretched hand, a direct blow to the elbow, or a sudden contraction of the triceps muscle. The posterior capsule and medial collateral ligament are often torn in this type of injury.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lateral dislocation is less common and typically occurs due to a severe injury that causes the ulna to move laterally (towards the side) relative to the humerus.
* **Option B:** Medial dislocation is even less common and usually results from a severe injury that causes the ulna to move medially (towards the midline) relative to the humerus.
* **Option D:** Anterior dislocation is the least common type of elbow dislocation and typically occurs due to a severe injury that causes the ulna to move anteriorly (towards the front) relative to the humerus.

**Clinical Pearl / High-Yield Fact**
The McMurtry classification is a useful system for grading the severity of elbow dislocations, with type I being a simple posterior dislocation and type III being a complex dislocation with associated fractures.

**Correct Answer: C. Posterior elbow dislocation.**