Dynamic genu valgum during the stance phase is most associated with weakness of which muscle?

• A. Gluteus medius
• B. Gluteus maximus
• C. Quadriceps
• D. Hamstrings

Answer: (A)

Dynamic genu valgum during the stance phase points to poor control of the hip in the frontal plane. The gluteus medius is the main hip abductor that keeps the pelvis level and the femur aligned over the knee when you’re weight-bearing. If this muscle is weak, the stance-leg femur tends to adduct and internally rotate more, allowing the knee to drift inward (valgus). This medial collapse during stance is the classic pattern seen with gluteus medius weakness and helps explain the dynamic valgus. The other muscles listed don’t stabilize the knee in that frontal-plane manner during stance: gluteus maximus mainly controls hip extension and external rotation, the quadriceps primary function is knee extension and patellar tracking, and the hamstrings stabilize the knee but don’t specifically prevent valgus.