Muscle · Lower limb
Inferior gemellus: origin, insertion, action and innervation
The inferior gemellus runs from the ischial tuberosity to the greater trochanter. It laterally rotates the hip and has the nerve to quadratus femoris.
Quick answer
- Latin name
- Musculus gemellus inferior
- Origin
- Upper part of the ischial tuberosity of the hip bone
- Insertion
- Medial surface of the greater trochanter of the femur, through the tendon of the obturator internus
- Action
- Laterally rotates the extended hip; helps abduct the flexed hip; holds the head of the femur in the acetabulum
- Innervation
- Nerve to quadratus femoris (L4-S1)
- Blood supply
- Medial circumflex femoral artery
See it on the 3D body
The inferior gemellus 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 inferior gemellus is a small strip of muscle deep in the buttock that runs from the ischial tuberosity to the greater trochanter of the femur, along the lower edge of the obturator internus tendon. It turns the extended thigh outward and is supplied by the nerve to quadratus femoris (L4-S1).
Where it is
Under the gluteus maximus, a row of short muscles crosses the back of the hip joint almost horizontally. From top to bottom they are the piriformis, the superior gemellus, the obturator internus, the inferior gemellus and the quadratus femoris.
The inferior gemellus is the fourth in that row. It lies just below the tendon of the obturator internus and just above the quadratus femoris. Gemellus is Latin for "little twin": the superior and inferior gemelli are a matched pair that hug the obturator internus tendon from above and below, like two thin cushions on either side of a rope.
The sciatic nerve runs down over the back of these short rotators on its way to the thigh, so the inferior gemellus lies in front of (deep to) the nerve. See the full row on muscles of the hip.
Origin and insertion
- Origin: the upper part of the ischial tuberosity, the sitting bone of the hip bone, along the lower edge of the lesser sciatic notch.
- Insertion: it blends with the lower border of the obturator internus tendon, which inserts on the medial surface of the greater trochanter of the femur, above the trochanteric fossa.
So the inferior gemellus has no separate insertion of its own in most bodies. It hitches a ride on the obturator internus tendon and pulls through it.
What it does
- Lateral rotation of the extended hip: with the hip straight, it turns the thigh so the toes point outward. It works with the piriformis, the obturator internus, the superior gemellus and the quadratus femoris.
- Abduction of the flexed hip: when the hip is bent to about a right angle, the line of pull changes and the same muscle helps move the thigh outward.
- Holding the joint together: it presses the head of the femur into the acetabulum from behind.
On its own it is too small to produce much force. Its pull adds to that of the obturator internus, since both act through the same tendon.
Innervation and blood supply
The inferior gemellus is supplied by the nerve to quadratus femoris (L4-S1), a small branch of the sacral plexus. This nerve runs down in front of the short rotators, gives a twig to the inferior gemellus, then ends in the quadratus femoris below it. This is the classic exam trap: the superior gemellus gets a different nerve, the nerve to obturator internus.
Its blood comes from the medial circumflex femoral artery, which also feeds the quadratus femoris next to it.
How to remember it
- Shares a nerve with the muscle below: the inferior gemellus rests on the quadratus femoris and takes the nerve to quadratus femoris, which reaches it on the way down.
- "Inferior sits on the sitting bone": its origin is the ischial tuberosity, while the superior twin starts higher, on the ischial spine.
- The twins and the rope: obturator internus is the rope, the two gemelli are the cushions above and below it, and all three share one tendon.
- P-G-O-G-Q: Piriformis, Gemellus superior, Obturator internus, Gemellus inferior, Quadratus femoris, top to bottom.
Test yourself in the hip and thigh quiz.
Frequently asked questions
What does the inferior gemellus do?
It laterally rotates the thigh when the hip is extended, helps abduct it when the hip is flexed, and holds the head of the femur in its socket.
What nerve supplies the inferior gemellus?
The nerve to quadratus femoris, from roots L4 to S1.
Where does the inferior gemellus attach?
It arises from the upper ischial tuberosity and joins the obturator internus tendon, which inserts on the medial surface of the greater trochanter.
Is the inferior gemellus a deep gluteal muscle?
Yes. It is one of the short lateral rotators that lie deep to the gluteus maximus.
