Obturator Externus - Muscle | Origin | Insertion | Nerve supply | Actions

Obturator externus muscle is a flat, triangular, paired muscle of the gluteal region. It is found on the anterior aspect of the obturator foramen, attached to the obturator membrane and the adjacent margin of the obturator foramen.

The obturator externus performs a few different actions. It externally rotates the femur when the hip is extended, but when the hip is flexed it actually abducts the thigh. Together with other short muscles around the hip joint, it contributes to the joint stability.

Origin Anterior surface of obturator membrane, bony boundaries of obturator foramen
Insertion Trochanteric fossa of femur
Action Hip joint: Thigh external rotation, thigh abduction (from flexed hip); Stabilizes head of femur in acetabulum
Innervation Obturator nerve (L3, L4)
Blood supply Obturator and medial circumflex femoral arteries.

Functions
External rotation of thigh (Rotatio externa femoris); Image: Paul Kim
External rotation of thigh (Rotatio externa femoris)
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Obturator externus has a dual primary function, which depends on the position of the thigh. When the hip is extended (body is in the anatomical position), the contraction of the obturator externus causes lateral, or external rotation of the thigh. This action is especially useful in climbing. It is also believed to play a role in walking, counteracting the medial rotation caused by the anterior adductors of the thigh.

When the hip joint is flexed, i.e. the thigh is closer to the body, obturator externus muscle abducts the thigh. It does this by pulling the superior part of the femur medially, which causes the inferior part to move away from the body.

It also contributes to the stability of the hip joint with other short muscles surrounding it (pectineus, piriformis, obturator internus, quadratus femoris and the gemelli superior and inferior). Although supporting the hip joint is generally described as a secondary function, it has been suggested that it may be more important than what’s considered to be the primary functions.