Which action is primarily performed by the iliopsoas muscle at the hip joint?

• A. Hip extension
• B. Hip flexion (and assisting with external rotation of the femur)
• C. Hip abduction
• D. Knee extension

Answer: (B)

Verified step by step guidance

1. Identify the anatomical location and attachments of the iliopsoas muscle. It is composed of the psoas major and iliacus muscles, which originate from the lumbar vertebrae and iliac fossa, respectively, and insert on the lesser trochanter of the femur.
2. Understand the primary function of the iliopsoas muscle by considering its line of pull relative to the hip joint. Since it crosses the anterior aspect of the hip joint, it acts to pull the femur upward and forward.
3. Recall that hip flexion involves decreasing the angle between the thigh and the pelvis, which is consistent with the action of the iliopsoas muscle pulling the femur anteriorly.
4. Note that while the iliopsoas also assists with external rotation of the femur due to its insertion point and muscle fiber orientation, its main action is hip flexion.
5. Eliminate other options by understanding their primary movers: hip extension is mainly performed by the gluteus maximus and hamstrings, hip abduction by the gluteus medius and minimus, and knee extension by the quadriceps femoris.