Obturator Internus
Gluteal & Hip · Lower Limb
The obturator internus is a fan-shaped muscle of the deep gluteal region that arises within the pelvis. It takes origin from the internal (pelvic) surface of the obturator membrane and the surrounding bony margins, and its tendon makes a sharp turn around the lesser sciatic notch, which acts as a pulley, before crossing the back of the hip to insert on the medial surface of the greater trochanter at the trochanteric fossa. Flanked by the two gemelli, it laterally rotates the extended thigh, abducts the flexed thigh, and steadies the femoral head in the acetabulum. It is supplied by the nerve to obturator internus (L5, S1, S2).
Origin, Insertion, Action & Nerve
Origin
Internal (pelvic) surface of the obturator membrane and surrounding bony margins
Insertion
Medial surface of the greater trochanter (trochanteric fossa) of the femur
Action
Laterally rotates the extended thigh; abducts the flexed thigh; stabilizes the hip
Nerve
Nerve to obturator internus (L5–S2)
Attachments explained
The Obturator Internus 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
Internal (pelvic) surface of the obturator membrane and surrounding bony margins
Insertion
Medial surface of the greater trochanter (trochanteric fossa) of the femur
Action & function
When the Obturator Internus contracts, it produces the following movements: Laterally rotates the extended thigh; abducts the flexed thigh; stabilizes the hip.
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 Internus receives its nerve supply from the Nerve to obturator internus (L5–S2). This nerve carries fibres from spinal segment(s) L5, S2.
Because a muscle can only contract when its nerve is intact, injury to the Nerve to obturator internus or to its spinal roots (L5, S2) can weaken or paralyse the Obturator Internus, impairing the movements it normally produces (laterally rotates the extended thigh). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Obturator Internus (the OIANS method)
Learn the obturator internus by its characteristic right-angled turn: it arises inside the pelvis, then bends around the lesser sciatic notch like a rope over a pulley to reach the greater trochanter. This change of direction is the detail that distinguishes it from the externally arising obturator externus and explains how a muscle that starts inside the pelvis ends up rotating the hip laterally on the outside.
Group it with the superior and inferior gemelli, which join its tendon so the three act together, and remember it carries the nerve to obturator internus (L5, S1, S2). Anchoring its actions to the general rule for short rotators, lateral rotation of the extended hip and abduction of the flexed hip, lets you deduce its function and keep it distinct from the obturator externus supplied by the obturator nerve.
Frequently asked questions
Where is the Obturator Internus located?
The Obturator Internus is a muscle of the Gluteal & Hip group, located in the Lower Limb.
What is the origin of the Obturator Internus?
Internal (pelvic) surface of the obturator membrane and surrounding bony margins
What is the insertion of the Obturator Internus?
Medial surface of the greater trochanter (trochanteric fossa) of the femur
What movements does the Obturator Internus produce?
Laterally rotates the extended thigh; abducts the flexed thigh; stabilizes the hip
What nerve supplies the Obturator Internus?
Nerve to obturator internus (L5–S2)
Is the Obturator Internus free to study in OIANS?
The Obturator Internus 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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