Obturator externus is the deepest of the short external hip rotators, passing posterior to the femoral neck to insert on the medial greater trochanter. Its tendon crosses posterior to the femoral neck where it is vulnerable in femoral neck fractures and during hip arthroplasty approaches. It is consistently below the obturator nerve and provides the deepest layer of posterior hip rotator coverage.
| Origin | External surface of the obturator membrane and surrounding bone (pubis and ischium); anterior and inferior to the obturator foramen |
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| Insertion | Trochanteric fossa of the femur (medial greater trochanter region, posteromedially) |
| Nerve Supply | Obturator nerve (L3-L4), posterior division |
| Blood Supply | Obturator artery; medial circumflex femoral artery |
| Actions | External rotation of the hip; assists in adduction; important stabilizer of the femoral head in the acetabulum from an inferior-anterior direction, counteracting the tendency for the femoral head to migrate anteriorly in hip flexion |
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In hip arthroscopy and the posterior approach to the hip, obturator externus must be identified and protected or released as part of capsulotomy. It is divided in the posterior approach to the hip (Kocher-Langenbeck) as part of the deep external rotator release. In medial circumflex femoral artery anatomy for femoral head blood supply, the artery passes between obturator externus and quadratus femoris to reach the posterior femoral neck and head, making obturator externus a key landmark in femoral head vascularity studies.
Posterior hip dislocation tears the posterior hip capsule and may avulse the obturator externus from its insertion at the trochanteric fossa; MRI demonstrates the torn tendon and associated posterior capsular injury, with the medial circumflex femoral artery at risk of injury producing femoral head ischaemia.
