Obturator internus

At a glance

English

Obturator internus

Latin (TA2)

Obturator internus

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the obturator internus

Obturator internus lies partly inside the pelvis and partly behind the hip. Its broad, fan-like belly lines the side wall of the lesser pelvis, and its tendon bends sharply around the ischium to reach the femur. In the buttock it belongs to the small group of short lateral rotators of the hip, sandwiched between the two gemelli.

The muscle arises from the inner face of the obturator membrane and from the bone around the obturator foramen: the pubic and ischial rami and the pelvic face of the hip bone beneath and behind the brim, reaching back almost to the greater sciatic notch. Only the area of the obturator canal is left free, bridged by a tendinous arch. The obturator fascia covering its pelvic surface gives origin to part of levator ani, which is why it forms part of the side wall of the pelvic floor.

The fibres converge on four or five tendinous bands lying on the muscle's deep aspect, and these bend sharply, at about ninety degrees, around the grooved bone between the ischial spine and tuberosity, the lesser sciatic notch, which is lined by cartilage, with a bursa between bone and tendon. Outside the pelvis the bands fuse into one flat tendon. It crosses the back of the hip capsule, receives the superior and inferior gemelli from above and below, and attaches to the inner face of the greater trochanter in front of and above the trochanteric fossa.

The muscle rotates the extended thigh laterally, abducts the thigh when the hip is flexed and steadies the femoral head in its socket. It has its own nerve to obturator internus from the sacral plexus, which also serves the superior gemellus, and its blood comes from the internal pudendal and obturator arteries. The sciatic nerve crosses the back of the muscle in the buttock, and the pudendal nerve runs on its inner side within the pelvis, so it is a key landmark in that region.

Attachments, action and supply

Origin

Inner surface of the obturator membrane and the surrounding pubis, ischium and ilium, beneath and behind the brim of the pelvis.

Insertion

Inner face of the greater trochanter, just above the trochanteric fossa, in common with the gemelli.

Action

Laterally rotates the extended thigh, abducts the flexed thigh and holds the femoral head steady in its socket.

Nerve supply

Nerve to obturator internus (L5, S1, S2).

Blood supply

Internal pudendal and obturator arteries, with branches of the inferior gluteal artery outside the pelvis.