Obturator externus

The obturator externus is a short external rotators of the hip that originates from the external surface of the obturator membrane and the surrounding bone of the obturator foramen. The muscle fibers converge to form a tendon that passes posterior to the neck of the femur and inserts into the trochanteric fossa of the femur. The obturator externus acts primarily as an external rotator of the hip joint.

Origin: Obturator foramen and obturator membrane

Insertion: trochanteric fossa and medial aspect of greater trochanter of femur

Artery: Obturator artery

Nerve: Posterior branch of obturator nerve (L3, L4)

Action: Adduct thigh, rotate laterally thigh, assists in stabilizing the head of the femur within the acetabulum

Description: The Obturator externus is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis. It arises from the margin of bone immediately around the medial side of the obturator foramen, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves.

The fibers springing from the pubic arch extend on to the inner surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane. The fibers converge and pass backward, lateralward, and upward, and end in a tendon (Tendon of obturator externus) which runs across the back of the neck of the femur and lower part of the capsule of the hipjoint and is inserted into the trochanteric fossa of the femur.

The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the obturator nerve reaches the thigh by passing in front of the muscle, and the posterior branch by piercing it.