Anatomy Guide › Pelvis & perineum
Obturator Internus
The obturator internus is one of the body's best hidden muscles and one of its most geometrically surprising. It arises on the inner surface of the pelvis, fanning across the membrane that covers the obturator foramen — the large oval window in the hip bone. From there its fibers funnel backward, exit the pelvis through the lesser sciatic notch, and make a near-90-degree turn around the bone — using the notch as a pulley — to reach the inner surface of the femur's greater trochanter.
That right-angle turn is rare in muscular architecture; where the tendon bends over the bone, a lubricating bursa cushions it, and the notch's surface is even faced with cartilage. Functionally, the obturator internus is a lateral rotator of the hip — one of the 'deep six' that turn the thigh outward — and with the thigh flexed it helps pull the leg sideways. Like the rotator cuff at the shoulder, the deep six also steady the femoral head in its socket, a stabilizing role that outlasts their visible motion.
The muscle has a second identity inside the pelvis: its fascia-covered surface forms part of the pelvic sidewall, and the levator ani — the main muscle of the pelvic floor — actually takes part of its origin from a thickened band of the obturator internus fascia. A canal in the same fascia carries the pudendal nerve, which is why pelvic-floor pain syndromes and obturator internus tightness are discussed in the same breath by physiotherapists.
In Anamo, the obturator internus is an expert-level pelvic answer. It neighbors the obturator externus (its outside-the-pelvis twin), the coccygeus, and the pelvic bones; hot readings deep in the pelvis with muscle-category hints often point to this quiet rotator.
- Exits the pelvis and turns ~90° around the lesser sciatic notch
- One of the 'deep six' external rotators of the hip
- Its fascia anchors part of the pelvic floor's levator ani
- Steadies the femoral head like a rotator cuff for the hip
Think you could find the obturator internus on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.