The iliacus originates from the entire iliac fossa and joins the psoas major to form the iliopsoas, the primary hip flexor. It is innervated within the pelvis by the femoral nerve before it passes under the inguinal ligament. Iliacus haematoma from trauma or anticoagulation compresses the femoral nerve in the iliac fossa, producing femoral neuropathy — quadriceps weakness and anterior thigh numbness without leaving the pelvis.
| Origin | Iliac fossa (entire inner surface of the iliac blade); Anterior sacroiliac ligament and sacral ala |
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| Insertion | Lesser trochanter (with the psoas major tendon — the combined iliopsoas) |
| Nerve Supply | Femoral nerve (L2, L3, L4) — the iliacus is innervated from within the pelvis before the femoral nerve passes under the inguinal ligament |
| Blood Supply | Iliolumbar and medial circumflex femoral arteries |
| Actions | Hip flexion (combined with psoas major as iliopsoas — the most powerful hip flexor); Stabilises the hip joint in the flexed position |
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Iliacus haematoma (spontaneous in anticoagulated patients or post-traumatic) compresses the femoral nerve against the iliac fascia in the iliac fossa, producing quadriceps weakness and absent knee jerk. CT confirms haematoma. Most cases recover spontaneously as the haematoma resolves — surgical decompression for expanding haematomas or progressive neurological deficit.
The iliacus is not palpable from the surface but its lateral tendon is palpable deep to the inguinal ligament medial to the femoral nerve during hip flexion.
Spontaneous iliacus haematoma in anticoagulated patients compressing the femoral nerve producing quadriceps weakness managed with anticoagulation reversal and monitoring.
