**Core Concept**
The Trendelenburg sign is a clinical test used to assess the integrity of the hip abductor muscles, specifically the gluteus medius and minimus. A positive Trendelenburg sign indicates weakness or paralysis of the hip abductor muscles, leading to a lateral shift of the pelvis on the unaffected side.

**Why the Correct Answer is Right**
The Trendelenburg sign is positive due to the imbalance between the gluteus medius and minimus muscles on the affected and unaffected sides. The gluteus medius and minimus muscles stabilize the pelvis during weight-bearing activities, and damage to the nerve supply of these muscles results in weakness or paralysis. The obturator nerve innervates the adductor muscles, but not the gluteus medius and minimus muscles. The femoral nerve innervates the iliopsoas muscle, but not the gluteus medius and minimus muscles. The superior gluteal nerve, which arises from the L4-S1 nerve roots, is the primary nerve supply of the gluteus medius and minimus muscles.

**Why Each Wrong Option is Incorrect**
**Option A:** The obturator nerve is primarily responsible for innervating the adductor muscles, not the gluteus medius and minimus muscles.
**Option B:** The femoral nerve is responsible for innervating the iliopsoas muscle, not the gluteus medius and minimus muscles.
**Option C:** The inferior gluteal nerve primarily innervates the gluteus maximus muscle, not the gluteus medius and minimus muscles.

**Clinical Pearl / High-Yield Fact**
The Trendelenburg sign is a sensitive indicator of hip abductor weakness, which can be a sign of superior gluteal nerve palsy, a common complication of surgeries such as hip arthroplasty.

**Correct Answer: D. The superior gluteal nerve.