“Trendelenburg sign” is positive in damage of the following nerve :
**Core Concept**
The Trendelenburg sign is a clinical indicator of hip abductor weakness, particularly involving the gluteus medius muscle. It is a key assessment tool in orthopedic and neurological examinations.
**Why the Correct Answer is Right**
The Trendelenburg sign is positive when the patient exhibits a drooping pelvis on the opposite side of the stance leg, indicating weakness of the hip abductors on the stance side. The primary muscle responsible for hip abduction is the gluteus medius, which is innervated by the superior gluteal nerve. Damage to this nerve can lead to weakness or paralysis of the gluteus medius, resulting in a positive Trendelenburg sign.
**Why Each Wrong Option is Incorrect**
**Option A:** The superior gluteal nerve is responsible for innervating the gluteus medius and minimus, making it the correct answer. The inferior gluteal nerve, however, innervates the gluteus maximus, which is not primarily responsible for hip abduction.
**Option B:** The femoral nerve innervates the iliopsoas muscle, which is responsible for hip flexion, not abduction.
**Option C:** The sciatic nerve is a mixed nerve that divides into the tibial and common peroneal nerves, but it does not innervate the gluteus medius.
**Clinical Pearl / High-Yield Fact**
Remember that the Trendelenburg sign is a sensitive indicator of hip abductor weakness, which can be caused by a variety of factors, including nerve damage, muscle weakness, or joint pathology.
**Correct Answer:** A. Superior gluteal nerve.