The obturator externus is a flat, fan-shaped muscle on the outer surface of the pelvis that fans from the obturator foramen to the trochanteric fossa of the femur. It is one of the six deep external rotators of the hip, acting alongside the piriformis, obturator internus, gemelli, and quadratus femoris to rotate the femur laterally and stabilise the femoral head. Its deep location makes it difficult to assess clinically and it is frequently overlooked as a pain source.
| Origin | Outer surface of the obturator membrane and surrounding bone of the pubis and ischium |
|---|---|
| Insertion | Trochanteric fossa of the femur |
| Nerve Supply | Obturator nerve (L3, L4) |
| Blood Supply | Obturator artery |
| Actions | External rotation of the hip; Stabilisation of the femoral head in the acetabulum |
|---|
It provides external rotation torque and acts as a passive stabiliser of the hip joint by compressing the femoral head into the acetabulum during weight-bearing, functions that are shared across the deep external rotator group.
Obturator externus strain or tendinopathy is an underrecognised cause of deep groin pain in athletes, producing discomfort that worsens with passive internal rotation stretching of the hip and resisted external rotation. MRI is required to visualise the muscle because it is not accessible to physical examination. Obturator externus bursitis can occur adjacent to the tendon insertion.
The obturator externus cannot be palpated directly due to its deep location beneath the adductor muscles. Assessment is functional, through resisted external rotation and passive internal rotation stretching of the hip.
Muscle or tendon injury producing deep groin pain reproduced by resisted external hip rotation, diagnosed by MRI because the muscle is not accessible to direct palpation.
