Corpus: Internal obturator muscle

The internal obturator muscle is a skeletal muscle that belongs to the deep hip muscles and is part of the triceps coxae muscle.

The internal obturator muscle originates from the obturator membrane and its bony boundaries. The muscle initially extends towards the lesser sciatic notch of the ischium in a slightly oblique fashion laterally, cranially and dorsally. Here, it changes direction almost at a right angle over the cartilage-covered surface of the notch, functioning as a hypomochlion. Between the cartilage surface and the tendon is the ischiatic bursa of obturator internus.

The muscle tendon exits the pelvis through the lesser sciatic foramen, running obliquely laterally and ventrally. It finally inserts at the greater trochanter or the trochanteric fossa of the femur.

The internal obturator muscle is innervated by the nerve to the obturator internus from the lumbosacral plexus (segments L5-S2).

Contraction of the internal obturator muscle causes external rotation of the thigh. In the neutral position, it supports the extension and adduction of the thigh. During hip flexion, it assists in abduction.

The obturator internus muscle forms a functional unit with the neighbouring inferior and superior gemellus muscles.