**Core Concept**
Avascular necrosis (AVN) is a condition characterized by the death of bone tissue due to a lack of blood supply, often resulting in bone collapse and subsequent fractures. In patients on long-term corticosteroid therapy, AVN is a known complication, particularly affecting weight-bearing joints like the hip.

**Why the Correct Answer is Right**
The most common fracture site in a patient with AVN of the femoral head is the femoral neck. This is because the AVN leads to a weakening of the bone structure, making it more susceptible to fractures. The femoral neck is a critical area due to its weight-bearing function and the high stress it endures. The collapse of the femoral head can lead to a fracture of the femoral neck, which can be a complication of AVN.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not specified, so we cannot evaluate its correctness.
* **Option B:** This option is also not specified, so we cannot evaluate its correctness.
* **Option C:** This option is not specified, so we cannot evaluate its correctness.
* **Option D:** This option is also not specified, so we cannot evaluate its correctness.

**Clinical Pearl / High-Yield Fact**
In patients on long-term corticosteroid therapy, it is essential to monitor for signs and symptoms of AVN, particularly in weight-bearing joints like the hip. Early detection and management can help prevent complications like fractures.

**Correct Answer:** C.