Which muscle is the primary hip flexor and forms part of the iliopsoas group?

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

Answer: (D)

The main concept here is that the primary hip flexor is the iliopsoas, a composite muscle formed by the psoas major and the iliacus. This duo is the strongest muscle for lifting the thigh at the hip and also helps stabilize the pelvis and lumbar spine during movement. The psoas major originates from the lumbar vertebrae and travels with the iliacus, which arises from the iliac fossa; they join to insert on the lesser trochanter of the femur. Because they attach to the pelvis and lumbar spine and insert on the femur, they’re ideally placed to generate powerful hip flexion.

Other muscles listed can contribute to hip flexion, but they’re not the primary flexor. Sartorius crosses the hip and knee and can assist in hip flexion along with other actions. Rectus femoris, part of the quadriceps, also crosses the hip and can aid hip flexion but its main role is knee extension. Tensor fasciae latae assists with hip flexion as well, but its primary actions are abduction and medial rotation with a stabilizing role. The iliopsoas stands out as the main driver of hip flexion and is the muscle that forms the iliopsoas group.