Obturator Externus
Gluteal & Hip · Lower Limb
The obturator externus is a flat, triangular muscle of the deep gluteal and hip region lying on the external surface of the anterior pelvic wall. It arises from the external surface of the obturator membrane and the surrounding margins of the pubis and ischium, and its tendon passes below and behind the neck of the femur to insert into the trochanteric fossa. From this course wrapping around the back of the femoral neck, it laterally rotates the thigh and helps stabilise the head of the femur within the acetabulum. It is supplied by the obturator nerve (L3, L4). Unlike the other short lateral rotators, it is not innervated by branches of the sacral plexus, reflecting its position in the medial (adductor) group of the thigh.
Origin, Insertion, Action & Nerve
Origin
External surface of the obturator membrane and surrounding margins of the pubis and ischium
Insertion
Trochanteric fossa of the femur
Action
Laterally rotates the thigh and stabilizes the head of the femur in the acetabulum
Nerve
Obturator nerve (L3–L4)
Attachments explained
The Obturator Externus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
External surface of the obturator membrane and surrounding margins of the pubis and ischium
Insertion
Trochanteric fossa of the femur
Action & function
When the Obturator Externus contracts, it produces the following movement: Laterally rotates the thigh and stabilizes the head of the femur in the acetabulum.
As part of the Gluteal & Hip group of the Lower Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Obturator Externus receives its nerve supply from the Obturator nerve (L3–L4). This nerve carries fibres from spinal segment(s) L3, L4.
Because a muscle can only contract when its nerve is intact, injury to the Obturator nerve or to its spinal roots (L3, L4) can weaken or paralyse the Obturator Externus, impairing the movements it normally produces (laterally rotates the thigh and stabilizes the head of the femur in the acetabulum). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Obturator Externus (the OIANS method)
Fix the obturator externus by its unusual path: it sweeps across the external surface of the obturator membrane, then curls under and behind the femoral neck to reach the trochanteric fossa. That wrapping course explains why it laterally rotates the thigh and presses the femoral head into the socket, and it is the reason the muscle is grouped with the short lateral rotators despite lying more anteriorly.
Use its nerve to set it apart. Whereas the other short rotators are supplied by sacral plexus branches, the obturator externus is supplied by the obturator nerve (L3, L4), marking its kinship with the adductor group. Pairing the internal and external obturators in memory, one arising inside the pelvis and one outside, keeps their origins and different nerves clearly separated.
Frequently asked questions
Where is the Obturator Externus located?
The Obturator Externus is a muscle of the Gluteal & Hip group, located in the Lower Limb.
What is the origin of the Obturator Externus?
External surface of the obturator membrane and surrounding margins of the pubis and ischium
What is the insertion of the Obturator Externus?
Trochanteric fossa of the femur
What movements does the Obturator Externus produce?
Laterally rotates the thigh and stabilizes the head of the femur in the acetabulum
What nerve supplies the Obturator Externus?
Obturator nerve (L3–L4)
Is the Obturator Externus free to study in OIANS?
The Obturator Externus is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Lower Limb is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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