Iliacus fills the iliac fossa and is the broader, fan-shaped component of the iliopsoas. Unlike psoas (which also flexes the lumbar spine), iliacus acts only at the hip.
| Origin | Iliac fossa — inner surface, upper two-thirds; Iliac crest inner lip, anterior sacroiliac ligament |
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| Insertion | Lesser trochanter — combined with psoas as the iliopsoas tendon |
| Nerve Supply | Femoral nerve (L2, L3, L4) |
| Blood Supply | Iliolumbar and medial circumflex femoral arteries |
| Actions | Flexes the hip — primary contributor from the iliac fossa; Stabilises the hip joint by compressing the femoral head into the acetabulum |
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Iliacus haematoma from femoral nerve block complications or pelvic trauma presents as iliac fossa pain and femoral neuropathy. In direct anterior hip arthroplasty, the iliacus is elevated from the iliac fossa to access the hip joint. Iliopsoas tendinopathy affecting iliacus produces snapping in the iliac fossa during hip flexion.
Palpated deep in the iliac fossa during resisted hip flexion — the broad component alongside the ASIS.
Iliacus haematoma complicating femoral nerve block producing iliac fossa pain and femoral neuropathy, managed by haematoma monitoring and evacuation if expanding.
