**Core Concept**
Osteochondritis dissecans is a joint condition characterized by the separation of cartilage and underlying bone, resulting from inadequate blood supply and subsequent necrosis. This condition is often seen in weight-bearing joints, particularly those subjected to repetitive stress and trauma.

**Why the Correct Answer is Right**
The knee joint is the most common site for osteochondritis dissecans, accounting for approximately 60% of all cases. This is due to the high degree of stress and load transmitted through the knee joint, particularly during activities such as running, jumping, and pivoting. The femoral condyles and tibial plateaus are the most frequently affected areas, as they bear the brunt of weight-bearing forces. The lack of a direct blood supply to the articular cartilage in these areas makes them more susceptible to ischemic damage.

**Why Each Wrong Option is Incorrect**
**Option A:** The ankle joint is less commonly affected by osteochondritis dissecans, as it is a lower-weight-bearing joint compared to the knee. While it can still occur, it is relatively rare.
**Option C:** The wrist joint is not typically associated with osteochondritis dissecans, as it is a non-weight-bearing joint and the condition is more commonly seen in joints subjected to repetitive stress and trauma.
**Option D:** The elbow joint can be affected by osteochondritis dissecans, particularly in the capitellum, but it is less common than the knee joint.

**Clinical Pearl / High-Yield Fact**
Osteochondritis dissecans is often seen in young, active individuals, particularly those involved in sports that involve repetitive jumping and landing, such as basketball and soccer. A thorough history and physical examination are essential in diagnosing this condition, and imaging studies such as X-rays and MRI may be necessary to confirm the diagnosis.

**✓ Correct Answer: B. Knee joint**