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Iliopsoas muscle

The iliopsoas muscle is the most powerful flexor of the hip joint, formed by the union of the psoas major and the iliacus muscle. Together, they descend from the lumbar spine and iliac fossa to insert on the femur, bridging the abdomen and thigh. The iliopsoas plays a key role in walking, running, posture, and stabilizing the lumbar spine and pelvis. It is also clinically significant in psoas abscess, tendon injuries, and bursitis.

Synonyms

  • Psoas-iliacus muscle

  • Hip flexor muscle complex

  • Psoas major + iliacus

Origin and Insertion

  • Psoas major:

    • Originates from the transverse processes, bodies, and intervertebral discs of T12–L5 vertebrae

  • Iliacus:

    • Originates from the iliac fossa, iliac crest, sacrum, and sacroiliac ligaments

  • Course:

    • Fibers of both muscles converge, passing beneath the inguinal ligament, anterior to the hip joint capsule

  • Insertion:

    • Into the lesser trochanter of the femur via a common tendon

Nerve Supply

  • Psoas major: Ventral rami of L1–L3

  • Iliacus: Femoral nerve (L2–L4)

Arterial Supply

  • Lumbar arteries (from abdominal aorta)

  • Iliolumbar artery

  • Femoral artery branches (muscular branches)

Venous Drainage

  • Lumbar veins → IVC

  • Iliolumbar vein → common iliac vein

  • Femoral vein branches

Function

  • Hip joint: Strong flexion of the thigh

  • Lumbar spine: Flexion and stabilization of vertebral column

  • Assists in external rotation of the thigh

  • Key muscle in maintaining erect posture and gait

MRI Appearance

T1-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Fatty septa and surrounding retroperitoneal/iliac fat appear bright

  • Fatty infiltration or chronic atrophy may increase signal intensity

T2-weighted images:

  • Normal muscle shows low-to-intermediate signal intensity

  • Acute injury, edema, or abscess appears as bright hyperintense regions

STIR (Short Tau Inversion Recovery):

  • Normal iliopsoas muscle shows low-to-intermediate signal

  • Inflammation, abscess, hematoma, or strain shows bright hyperintensity

Proton Density Fat-Saturated (PD FS):

  • Normal muscle shows Intermediate signal

  • Pathology (strain, tear, bursitis, abscess) appears bright after fat suppression

T1 Fat-Sat Post-Contrast:

  • Normal muscle enhances mildly and uniformly

  • Abscess: peripheral rim enhancement with non-enhancing center

  • Tumors or inflammatory lesions: heterogeneous or nodular enhancement

CT Appearance

Non-Contrast CT:

  • Normal muscle appears as homogeneous soft tissue density

  • Fat planes surrounding iliopsoas enhance muscle definition

  • Abscess appears as a low-attenuation collection, sometimes with gas

  • Acute hematoma may appear as hyperdense areas

Post-Contrast CT:

  • Normal muscle enhances mildly and uniformly

  • Abscess shows rim enhancement with central hypodensity

  • Tumor infiltration or inflammatory changes show heterogeneous enhancement

  • Fat stranding in adjacent tissue may indicate infection or trauma

MRI image

Iliopsoas muscle MRI axial anatomy image-img-00000-00000

MRI image

Iliopsoas muscle MRI sagittal anatomy image-img-00000-00000

Iliopsoas muscle ct axial anatomy image-img-00000-00000

Iliopsoas muscle ct sagittal anatomy image-img-00000-00000