**Core Concept**
Posterior elbow dislocation is a type of injury where the ulna and radius bones in the forearm are displaced out of place in relation to the humerus bone in the upper arm. This type of dislocation can lead to various deformities and complications.

**Why the Correct Answer is Right**
The deformity seen in posterior elbow dislocation is typically known as a "cubitus valgus" or "gunstock deformity". This occurs due to the displacement of the ulna and radius bones out of place, resulting in a valgus (or "knock-knee") deformity of the elbow joint. The mechanism of injury often involves a fall onto an outstretched hand, which can cause the elbow joint to hyperextend and dislocate posteriorly. The cubitus valgus deformity is characterized by a carrying angle of the elbow that is greater than normal, giving the appearance of a "gunstock" or "cubitus valgus" deformity.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the deformity seen in posterior elbow dislocation. A "cubitus varus" deformity, on the other hand, is a different type of deformity that can occur after a supracondylar fracture of the humerus.
* **Option B:** This option is not a recognized deformity associated with posterior elbow dislocation. A "cubitus valgus" deformity is the characteristic deformity seen in this type of injury.
* **Option D:** This option is not a specific deformity, but rather a general description of a possible complication of posterior elbow dislocation. The deformity seen in posterior elbow dislocation is a specific type of deformity known as "cubitus valgus".

**Clinical Pearl / High-Yield Fact**
The cubitus valgus deformity is a common complication of posterior elbow dislocation and can be challenging to treat. Early recognition and treatment of posterior elbow dislocation are essential to prevent this deformity from occurring.

**Correct Answer: C. Cubitus valgus (gunstock deformity)**