A 36-year-old woman with sickle cell disease presents with increasing pain in her right hip. She has no fever, chills, back or other bone pain, and there is no history of any trauma.On examination, her temperature is 37.3degC, range of motion in the right hip is reduced, she walks with a limp, and the right leg is shorter than the left. Movements of the hip and walking on it are painful. X-rays of the hip are shown in Figure below. Which of the following is the most likely diagnosis?

## **Core Concept**
The question involves a patient with sickle cell disease presenting with hip pain and specific radiographic findings. Sickle cell disease is a genetic disorder that affects hemoglobin production, leading to abnormal red blood cells. These sickled red blood cells can cause vaso-occlusive crises, leading to tissue ischemia and infarction. The patient's symptoms and history suggest a complication related to her sickle cell disease.

## **Why the Correct Answer is Right**
The correct answer, Avascular Necrosis (AVN) of the femoral head, is a well-known complication in patients with sickle cell disease. AVN occurs due to the occlusion of blood vessels supplying the femoral head, leading to ischemia and necrosis of the bone tissue. This condition is consistent with the patient's symptoms of hip pain, reduced range of motion, limp, and the finding of a shorter leg on the affected side. The radiographic findings likely show changes consistent with AVN, such as increased density or collapse of the femoral head.

## **Why Each Wrong Option is Incorrect**
- **Option B (Osteomyelitis):** While osteomyelitis is a risk in patients with sickle cell disease due to their increased susceptibility to infections, the presentation typically includes fever and more systemic symptoms, which are not present in this case.
- **Option C (Hip Fracture):** A hip fracture could present with pain and limited mobility but would typically have a history of trauma, which is not mentioned. Additionally, the X-ray findings would likely show a clear fracture line.
- **Option D (Rheumatoid Arthritis):** Rheumatoid arthritis could cause hip pain and reduced mobility but is less likely given the patient's history of sickle cell disease and the absence of other joint involvement or systemic symptoms.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that avascular necrosis is a significant cause of morbidity in sickle cell disease patients, often presenting with hip pain. Early diagnosis and management are crucial to prevent further complications. The lack of systemic symptoms like fever can help differentiate AVN from infections like osteomyelitis.

## **Correct Answer:** A. Avascular Necrosis.

✓ Correct Answer: A. avascular necrosis (AVN) of the femoral head