The obturator internus originates inside the pelvis on the inner surface of the obturator membrane, makes a near right-angle turn around the lesser sciatic notch, and inserts on the greater trochanter. This unique U-shaped course around the ischium means it functions as an external rotator when the hip is extended but converts to an abductor when the hip is flexed. Together with the gemelli it forms the combined obturator-gemellus complex.
| Origin | Inner surface of the obturator membrane and surrounding pelvic bone; Greater sciatic notch above the lesser sciatic notch |
|---|---|
| Insertion | Medial surface of the greater trochanter of the femur after making a right-angle turn around the lesser sciatic notch |
| Nerve Supply | Nerve to obturator internus (L5, S1) |
| Blood Supply | Internal pudendal artery |
| Actions | External rotation of the hip when extended; Abduction of the hip when the hip is flexed beyond 90 degrees; Stabilisation of the femoral head in the acetabulum |
|---|
The right-angle tendon path around the lesser sciatic notch creates a pulley system that significantly alters its line of pull depending on hip position, a biomechanical feature unique among the deep external rotators and important for controlling hip rotation throughout the full range of flexion.
Deep gluteal syndrome often involves the obturator internus alongside the piriformis, and the sciatic nerve can be compressed by the obturator internus in the same region. Obturator internus tendinopathy is a recognised cause of deep groin and buttock pain in distance runners and military personnel. Pelvic floor physiotherapy often targets the obturator internus because it also forms part of the lateral pelvic floor.
The obturator internus can be assessed internally through pelvic floor physiotherapy techniques, or externally with deep pressure applied into the lesser sciatic notch region between the ischial tuberosity and the posterior greater trochanter.
Overuse degeneration producing deep groin and buttock pain in runners and military personnel, reproduced by resisted hip external rotation and passive internal rotation stretching, confirmed by MRI.
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