Overview
This lecture explains the four main muscles responsible for hip flexion, their origins, insertions, and additional functions at both the hip and knee joints.
Primary Hip Flexors: Iliacus and Psoas Major
- Iliacus and psoas major are the main muscles responsible for flexion at the hip joint.
- Iliacus originates from most of the inner surface of the ilium's wing and the iliac crest.
- Psoas major originates from the transverse processes, intervertebral discs, and bodies of all five lumbar vertebrae.
- Both muscles pass downward, over the superior pubic ramus, and under the inguinal ligament.
- Iliacus and psoas major insert together on the lesser trochanter of the femur.
- Contracting these muscles flexes the hip, moving the thigh forward or bringing the body upright if legs are fixed.
Additional Hip Flexors: Rectus Femoris and Sartorius
- Rectus femoris and sartorius also assist in hip flexion but are more involved with knee movement.
- Rectus femoris is one of four heads of the quadriceps, the main knee extensor.
- Only rectus femoris of the quadriceps group acts as a hip flexor, because it originates above the hip joint.
- Rectus femoris arises from two heads just above the acetabulum and inserts on the tibia; it is a weak hip flexor.
- Sartorius is a long, narrow muscle starting at the anterior superior iliac spine and spiraling down to the tibia.
- Sartorius assists in hip flexion and can also cause lateral rotation at the hip.
Key Terms & Definitions
- Hip Flexion — movement that decreases the angle between the thigh and the torso.
- Iliacus — muscle originating from the ilium, a main hip flexor.
- Psoas Major — muscle originating from lumbar vertebrae, a main hip flexor.
- Rectus Femoris — part of quadriceps, weak hip flexor, more important in knee extension.
- Sartorius — long muscle from the pelvis to tibia, assists in hip flexion and lateral rotation.
- Inguinal Ligament — ligament under which the iliacus and psoas major pass.
- Lesser Trochanter — bony prominence on femur where iliacus and psoas major insert.
Action Items / Next Steps
- Review the anatomy and functions of quadriceps and sartorius in the next lecture section.
- Practice identifying origins and insertions of major hip flexors on anatomical diagrams.