## **Core Concept**
Trendelenburg's sign is a test used to assess the integrity of the hip abductor mechanism, primarily the **gluteus medius** and **gluteus minimus** muscles, which are innervated by the **superior gluteal nerve**. A positive Trendelenburg's sign indicates weakness or paralysis of these muscles, leading to a compensatory gait pattern.

## **Why the Correct Answer is Right**
The correct answer, , involves injury to the **superior gluteal nerve**. This nerve innervates the gluteus medius and gluteus minimus muscles, which are crucial for hip abduction. When these muscles are weakened due to nerve injury, the pelvis will drop on the contralateral side during a single-leg stance, resulting in a positive Trendelenburg's sign.

## **Why Each Wrong Option is Incorrect**
* **Option A:** The **inferior gluteal nerve** primarily innervates the gluteus maximus muscle, which is involved in hip extension rather than abduction. Injury to this nerve would not directly cause a positive Trendelenburg's sign.
* **Option B:** The **obturator nerve** innervates the adductor muscles of the thigh, which are involved in hip adduction. Weakness of these muscles would not lead to a positive Trendelenburg's sign.
* **Option D:** The **femoral nerve** primarily innervates the quadriceps femoris muscle, which is involved in knee extension, and the iliopsoas muscle, involved in hip flexion. Its injury would not directly affect hip abduction.

## **Clinical Pearl / High-Yield Fact**
A positive Trendelenburg's sign is often seen in patients with **gluteus medius tendinopathy** or **superior gluteal nerve palsy**. Clinicians should consider Trendelenburg's gait (a compensatory mechanism where the trunk shifts towards the affected side) in patients with a positive sign, indicating weakness of the hip abductors.

## **Correct Answer:** . **Superior gluteal nerve**