Muscle · Lower limb
Obturator externus: origin, insertion, action and innervation
The obturator externus runs from the obturator membrane to the trochanteric fossa of the femur. It laterally rotates the hip; obturator nerve, posterior branch.
Quick answer
- Latin name
- Musculus obturatorius externus
- Origin
- Outer surface of the obturator membrane and the bony margin of the obturator foramen, on the pubis and ischium of the hip bone
- Insertion
- Trochanteric fossa of the femur
- Action
- Laterally rotates the hip; steadies the head of the femur in the acetabulum
- Innervation
- Obturator nerve, posterior branch (L3-L4)
- Blood supply
- Obturator artery and medial circumflex femoral artery
See it on the 3D body
The obturator externus lit on the 3D hip and thigh, as in the hip and thigh quiz. Turn the body, peel the layers, tap any structure for its name.
The obturator externus is a flat, fan-shaped muscle that covers the outer surface of the obturator foramen and sends a tendon under the neck of the femur to the trochanteric fossa. It laterally rotates the thigh and is supplied by the posterior branch of the obturator nerve (L3-L4).
Where it is
The obturator externus lies very deep at the top of the inner thigh. It covers the outside of the obturator foramen, the large hole in the hip bone between the pubis and the ischium. A sheet of tissue, the obturator membrane, closes most of that hole, and the muscle arises from its outer face. A muscle with a matching name, the obturator internus, covers the inner face of the same membrane, inside the pelvis.
In front, it is covered by the pectineus, the adductor longus and the adductor brevis. Its tendon then turns backward and runs below the neck of the femur, behind the hip joint, to reach the back of the femur. There it lies just under the quadratus femoris and next to the inferior gemellus.
Anatomists group it in two ways. By position and nerve it belongs to the medial compartment of the thigh, with the adductors. By action it belongs with the short lateral rotators of the hip. Both views are correct. See it with the adductors on muscles of the thigh.
Origin and insertion
- Origin: the outer surface of the obturator membrane and the bony rim of the obturator foramen, on the pubis and ischium.
- Insertion: the trochanteric fossa of the femur, the deep pit on the inner side of the greater trochanter.
Picture a strap passing under a door handle: the belly is in front, on the pelvis, and the tendon slings under the neck of the femur to pull from behind.
What it does
- Lateral rotation of the hip: it turns the thigh outward, so the toes point to the side. It works with the gemelli, the obturator internus, the quadratus femoris and the piriformis.
- Steadying the hip joint: its tendon wraps below the femoral neck and holds the head of the femur snug in the acetabulum, especially during walking.
- Possible weak adduction: some textbooks also credit it with a small adducting pull.
To see it, imagine removing the pectineus and the adductors one by one until the floor of the obturator foramen appears.
Innervation and blood supply
The obturator externus is supplied by the posterior branch of the obturator nerve (L3-L4). The obturator nerve leaves the pelvis through the obturator canal, a small tunnel at the top of the obturator foramen, and splits as it comes out. The posterior branch actually pierces the obturator externus on its way down, then runs behind the adductor brevis.
Its blood comes from the obturator artery, which travels with the nerve, and from the medial circumflex femoral artery, which passes near its tendon.
How to remember it
- External covers the outside: the obturator externus is on the outer face of the obturator membrane, the internus on the inner face.
- The posterior branch goes through it: say "the posterior branch pierces the externus", and you remember both its nerve and its relation to the nerve.
- Same nerve family, different job: it gets the obturator nerve like an adductor but rotates like a gluteal deep rotator.
- Fossa, not trochanter face: the obturator externus ends in the trochanteric fossa itself, lower and deeper than the obturator internus.
Test yourself in the hip and thigh quiz.
Frequently asked questions
What is the action of the obturator externus?
It laterally rotates the thigh at the hip and helps hold the head of the femur in the acetabulum.
What nerve supplies the obturator externus?
The posterior branch of the obturator nerve, from roots L3 and L4.
Where does the obturator externus insert?
In the trochanteric fossa of the femur, after its tendon passes below the neck of the femur.
What is the difference between the obturator externus and internus?
The externus covers the outside of the obturator membrane and gets the obturator nerve. The internus lines the inner face, inside the pelvis, and gets the nerve to obturator internus. Both laterally rotate the hip.
