Obturator Internus

Gluteal & Hip · Lower Limb

The Obturator Internus is a Lower Limb muscle within the Gluteal & Hip group. Its origin is Internal (pelvic) surface of the obturator membrane and surrounding bony margins, and it inserts onto Medial surface of the greater trochanter (trochanteric fossa) of the femur. It is responsible for several movements: Laterally rotates the extended thigh; abducts the flexed thigh; stabilizes the hip. Its nerve supply is the Nerve to obturator internus (L5–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)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Obturator Internus, work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the Obturator Internus fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.