A positive Trendelenburg sign suggests weakness in which muscle?

A positive Trendelenburg sign indicates weakness in the gluteus medius muscle. This muscle plays a critical role in stabilizing the pelvis during walking or standing on one leg. When the gluteus medius is weak or not functioning properly, the pelvis cannot maintain a level position; it will drop on the side opposite to the weak muscle. This drop is observable during the single-leg stance or while walking, leading to the characteristic Trendelenburg gait.

Understanding the function of the gluteus medius is essential in assessing hip mechanics and overall lower extremity stability. The other muscles listed do not directly contribute to pelvic stabilization in the same manner, making them less relevant to the Trendelenburg sign. The gluteus maximus primarily extends the hip, the quadriceps are key in knee extension, and the hamstrings assist in knee flexion and hip extension, all of which are critical functions but do not specifically cause the pelvic drop associated with a positive Trendelenburg sign.