Obturator internus

Origin

The obturator internus is a thick, fan-shaped muscle which originates from the From the inner surface of the obturator membrane and the surrounding bony margins of the obturator foramen, including the ischiopubic ramus and the inner surface of the ischium and pubis. It also arises from the tendinous arch that completes the obturator canal and partly from the obturator fascia covering the muscle.

Insertion

The muscle fibres converge toward the lesser sciatic foramen, forming several tendinous bands on its deep surface. These bands make a right-angled turn (reflection) over the grooved surface of the ischium between the ischial spine and tuberosity. The reflected tendon passes horizontally across the posterior hip joint capsule, joins the tendons of the superior and inferior gemelli, and inserts into the medial surface of the greater trochanter, just above the trochanteric fossa.

Relations

• Superiorly: Superior gemellus.

• Inferiorly: Inferior gemellus.

• Medially (within pelvis): Obturator vessels and nerve (on the obturator membrane).

• Fascia: The obturator fascia covering the pelvic surface contributes to the lateral wall of the ischioanal fossa and provides attachment to levator ani fibres.

Bursae

• Subtendinous bursa of obturator internus – lies between the tendon and the hip capsule (may communicate with the ischial bursa).

• Ischial bursa – separates the tendon from the ischium at the pulley-like reflection.