Trendelenburg gait is primarily caused by weakness in which muscle?

Trendelenburg gait is primarily associated with weakness in the gluteus medius muscle. This muscle plays a crucial role in stabilizing the pelvis during ambulation, particularly when weight is transferred from one leg to the other. When the gluteus medius is weak, the pelvis tends to drop on the side opposite to the affected muscle as the individual stands or walks on the affected leg. This deviation results in a characteristic gait pattern where the person leans toward the side of weakness during the stance phase of walking, making it visibly apparent.

In contrast, weaknesses in the gluteus maximus, quadriceps, or hip flexors would not specifically result in a Trendelenburg gait. For example, weakness in the gluteus maximus might affect hip extension and potentially lead to more posterior pelvic tilting or difficulty in pushing off during walking, which presents differently. Similarly, quadriceps weakness may lead to difficulty in controlling knee extension, and hip flexor weakness may affect lifting the leg forward, but neither directly contributes to the specific pelvic instability seen in Trendelenburg gait. Hence, the correct identification of gluteus medius weakness is key to understanding this specific gait abnormality.