Which muscle is the primary flexor of the thigh at the hip joint?

• A. Biceps femoris
• B. Gluteus medius
• C. Gluteus maximus
• D. Iliopsoas

Answer: (D)

Verified step by step guidance

1. Understand the action described: 'flexion of the thigh at the hip joint' means decreasing the angle between the thigh and the pelvis, essentially lifting the thigh forward.
2. Recall the main muscles involved in hip joint movements: flexors bring the thigh forward, extensors move it backward, abductors move it away from the midline, and so on.
3. Identify the function of each muscle listed: Biceps femoris is primarily a knee flexor and hip extensor; Gluteus medius mainly abducts the thigh; Gluteus maximus is the primary hip extensor.
4. Recognize that the Iliopsoas muscle group (consisting of the psoas major and iliacus) is the strongest and primary flexor of the thigh at the hip joint.
5. Conclude that since the Iliopsoas is responsible for hip flexion, it is the correct answer to the question.