Obturator externus

At a glance

English

Obturator externus

Latin (TA2)

Obturator externus

System

Muscle

Region

Lower limb

Side

Paired, left and right

About the obturator externus

Obturator externus is a flat, roughly triangular muscle on the outer face of the front wall of the pelvis. It lies deep in the upper medial thigh, under pectineus and the adductors, and its tendon winds round to the back of the hip. Because of this course it is placed by some authors with the medial thigh muscles and by others with the short rotators of the gluteal region.

Its broad origin is the bony margin around the front and inner side of the obturator foramen, on the lower pubic ramus and the ischial ramus, together with most of the membrane's outer face. The fibres converge as they pass backwards, outwards and up beneath the hip joint. The tendon crosses behind the femoral neck and the lower part of the joint capsule and ends in the trochanteric fossa, the pit on the inner side of the greater trochanter.

Between the muscle and the membrane run the obturator vessels as they leave the obturator canal. The obturator nerve, which supplies the muscle, divides close by: its anterior branch runs across the muscle's front surface while its posterior branch pierces it to reach the adductors. This makes obturator externus a guide to the nerve in regional blocks. Blood reaches it from the obturator and medial circumflex femoral arteries.

The muscle is mainly a lateral rotator of the thigh. Like the other short muscles packed around the hip, it also holds the femoral head into the socket, acting as a stabiliser in posture and movement, and it can help adduct the hip when the joint is flexed. Its shape varies a good deal; extra bundles split from it may reach the pectineal line or the lesser trochanter, and the textbook form without them is in fact the less common.

Attachments, action and supply

Origin

Outer margin of the obturator foramen on the pubic and ischial rami, and the outer face of the obturator membrane.

Insertion

Trochanteric fossa of the femur.

Action

Laterally rotates the thigh, stabilises the femoral head in the acetabulum and assists adduction of the flexed hip.

Nerve supply

Posterior branch of the obturator nerve (L3, L4).

Blood supply

Obturator artery and medial circumflex femoral artery.