The obturator internus makes a 90-degree turn around the lesser sciatic notch (ischium), using it as a pulley. It then blends with the gemelli before inserting on the greater trochanter. This unique anatomy makes it the strongest external rotator when combined with the gemelli.
| Origin | Inner surface of the obturator membrane and the adjacent bone of the lesser pelvis; Passes through the lesser sciatic foramen making a 90-degree turn |
|---|---|
| Insertion | Medial surface of the greater trochanter |
| Nerve Supply | Nerve to obturator internus (L5, S1, S2) |
| Blood Supply | Internal pudendal artery |
| Actions | Externally rotates the hip — powerful lateral rotator; Abducts the hip when the hip is flexed |
|---|
The obturator internus is the lateral wall of the ischiorectal fossa (Alcock's canal — containing the pudendal nerve — runs in the obturator internus fascia). In pelvic floor surgery, the obturator internus fascia is the reference for sacral neuromodulation electrode placement and pelvic organ prolapse repairs. Internal snapping hip (rarely) involves the obturator internus.
Tested by resisted external rotation with the hip and knee flexed to 90 degrees (figure-four position).
The obturator internus fascia forming the lateral wall of Alcock's canal containing the pudendal nerve, relevant in perineal surgery and pudendal nerve blocks.
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