## **Core Concept**
The question revolves around a patient who had a renal transplant and was given steroids, presenting later with difficulty in walking and hip pain. This scenario suggests a complication related to long-term steroid use. Steroids, especially glucocorticoids, are known to have various side effects, including effects on bone health.

## **Why the Correct Answer is Right**
The correct answer, **. Avascular Necrosis (AVN)**, is a well-known complication of long-term steroid use. Steroids can lead to fat emboli that occlude the small blood vessels of the bone, leading to avascular necrosis. The femoral head is a common site for AVN due to its blood supply. AVN causes pain and can lead to difficulty in walking due to bone collapse. The patient's symptoms of difficulty in walking and pain in both hips after being on steroids for 2 years post-renal transplant align with AVN.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While osteoporosis is a side effect of long-term steroid use, leading to bone pain and increased risk of fractures, it doesn't specifically explain the localized pain and difficulty walking as seen in AVN.
- **Option B:** Septic arthritis could cause hip pain but typically presents acutely with signs of infection like redness, swelling, and fever, not mentioned here.
- **Option C:** Gout can cause joint pain but is less likely to cause bilateral hip pain and difficulty walking without other symptoms like acute onset of pain, redness, and swelling.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that avascular necrosis is a significant risk in patients on long-term steroids, and hip pain in such patients should prompt an investigation for AVN. MRI is the diagnostic modality of choice for AVN.

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