What is the primary action of the iliopsoas muscle at the hip joint?

• A. Extension of the thigh at the hip
• B. Flexion of the thigh at the hip
• C. Abduction of the thigh at the hip
• D. Plantarflexion of the foot at the ankle

Answer: (B)

Verified step by step guidance

1. Identify the anatomical location and components of the iliopsoas muscle, which is formed by the iliacus and psoas major muscles, both attaching to the femur near the hip joint.
2. Understand the general function of the iliopsoas muscle by considering its origin (lumbar vertebrae and iliac fossa) and insertion (lesser trochanter of the femur), which positions it to influence movement at the hip joint.
3. Recall that muscles crossing the anterior side of a joint typically produce flexion, so since the iliopsoas crosses the front of the hip joint, its primary action is to flex the thigh at the hip.
4. Eliminate other options by recognizing that extension of the thigh is generally performed by muscles like the gluteus maximus, abduction by muscles such as the gluteus medius, and plantarflexion is an ankle movement, not related to the iliopsoas.
5. Conclude that the primary action of the iliopsoas muscle at the hip joint is flexion of the thigh.