The anatomy and function of the obturator externus.

There is limited knowledge regarding the anatomic relationships and functional anatomy of the Obturator Externus muscle (OE). It is described as a muscle which originates from the external bony margin of the obturator foramen with a cylindrical tendon which passes like a sling under the femoral neck and inserts in the trochanteric fossa. The primary aim of this study is to describe the OE morphology and its anatomic relationship to the acetabulum. A secondary aim is to postulate its action. Eighteen fresh human cadaveric hips were dissected to investigate the anatomy of the OE. A plastic model of the pelvis and femur was used to create a string model based on a technique previously described by Beck et al. The plastic model was used to determine the function of the OE.We conclude that the Obturator externus muscle helps to stabilise the head of the femur in the socket. The mechanical model demonstrated that the primary action of the obturator externus muscle was to externally rotate the femur when the hip was in neutral position and flexed at 90°. Its secondary function was as an adductor when the hip was in flexion.