Which muscle crosses both the hip and knee and assists in hip flexion and knee extension?

• A. Rectus femoris
• B. Sartorius
• C. Iliopsoas
• D. Tensor fasciae latae

Answer: (A)

Biarticular muscles that span both the hip and knee can influence movements at both joints. Rectus femoris is one of the quadriceps that crosses both the hip and knee. It originates on the hip and inserts across the knee, allowing it to flex the hip and extend the knee. The other options either don’t cross both joints or don’t produce knee extension: sartorius does cross both joints but mainly supports hip flexion and knee flexion rather than knee extension; iliopsoas crosses only the hip and flexes the hip; tensor fasciae latae acts on the hip to flex and abduct but doesn’t extend the knee. So rectus femoris best fits the description.