The Trendelenburg sign is used to assess weakness of which muscle and nerve?

• A. Gluteus medius weakness due to superior gluteal nerve injury
• B. Tensor fasciae latae weakness due to femoral nerve injury
• C. Quadriceps weakness due to femoral nerve injury
• D. Hamstring weakness due to sciatic nerve injury

Answer: (A)

The Trendelenburg sign tests the hip abductors, mainly the gluteus medius and gluteus minimus, and their nerve supply from the superior gluteal nerve. When you stand on one leg, these muscles on that leg contract to keep the pelvis level. If they’re weak, the pelvis drops on the opposite side because the stance leg can’t hold it up. Patients may also lean their trunk toward the stance leg to compensate.

This is why the best answer is weakness of the gluteus medius due to superior gluteal nerve injury. The other options don’t fit because they involve muscles or nerves not primarily responsible for stabilizing the pelvis in single-leg stance: quadriceps weakness affects knee extension; hamstrings affect hip extension/knee flexion; and the tensor fasciae latae is also an abductor but is innervated differently and does not explain the classic pelvic drop pattern seen with gluteus medius/minimus weakness.