Iliopsoas
The iliopsoas is a combination of two muscles (psoas major and iliacus) that work together as the most powerful hip flexor. It is crucial for walking, running, and maintaining upright posture.
Origin, Insertion, Action, Innervation
OOrigin
Psoas major: Transverse processes and bodies of T12-L5 vertebrae. Iliacus: Iliac fossa.
IInsertion
Lesser trochanter of femur (combined tendon)
AAction
- • Flexion of the hip (strongest hip flexor)
- • Lateral rotation of the hip (weak)
- • Flexion of the trunk on the lower limb (when limb is fixed)
NInnervation
Psoas major: Lumbar plexus (L1, L2, L3). Iliacus: Femoral nerve (L2, L3, L4).
Blood Supply
Iliolumbar artery and medial femoral circumflex artery
Clinical Relevance
Psoas abscess can occur with tuberculosis or other infections. Tight iliopsoas can cause anterior pelvic tilt and lower back pain. The psoas sign (pain with hip extension) may indicate appendicitis or psoas abscess. Hip flexor weakness affects gait and stair climbing.
Palpation
Deep muscle, difficult to palpate. Iliacus can sometimes be felt in the iliac fossa with deep palpation. Function tested by having patient flex hip against resistance.
Study Tips
- ✓Two muscles (psoas + iliacus) = one function (hip flexion)
- ✓Different innervation: psoas (L1-L3 direct), iliacus (femoral nerve)
- ✓Tight iliopsoas = anterior pelvic tilt = lower back pain
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Common questions about the iliopsoas
The iliopsoas consists of the psoas major and iliacus muscles. They have different origins but join to insert on the lesser trochanter of the femur. They function together as the most powerful hip flexor.
The iliopsoas connects the spine to the lower limb and plays a crucial role in maintaining upright posture. Tight iliopsoas can cause anterior pelvic tilt, increased lumbar lordosis, and lower back pain.
The psoas sign is pain elicited by extending the hip (stretching the psoas). It is positive in conditions that irritate the psoas muscle, such as appendicitis (right side) or psoas abscess.
The psoas major is innervated directly by branches from the lumbar plexus (L1, L2, L3). The iliacus is innervated by the femoral nerve (L2, L3, L4). Despite different innervation, they work together functionally.