Inferior Gemellus Muscle Anatomy

Location & Overview

The inferior gemellus is one of the two gemellus muscles. The inferior gemellus is located inferior to (below) the superior gemellus and is also superior to (above) the quadratus femoris muscle. Both of these gemellus muscles are collectively known as the gemelli muscles, and they are two of the six external rotator muscles of the gluteal region. The other four muscles are: the obturator externus, obturator internus, quadratus femoris, and piriformis. Both gemelli muscles connect to the obturator internus muscle via a conjoined tendon. The combination of these three muscles is sometimes referred to as the ‘triceps coxae’ ^{[1] [2]}.

Here we can see the inferior gemellus muscle from a posterior view.

Pictured here are the deep six hip external rotator muscles: the piriformis, gemellus superior, gemellus inferior, obturator internus, obturator externus, and quadratus femoris. These muscles play an important role in stabilising the hip joint and facilitating hip lateral rotation.

Origin & Insertion

The inferior gemellus originates on the ischial tuberosity. The ischial tuberosity is a prominent bony protrusion on the ischium, one of the three bones that make up the pelvis. The insertion for the inferior gemellus is located on the trochanteric fossa of the femur. The trochanteric fossa is a deep depression located on the medial side of the greater trochanter of the femur ^{[3] [4]}.

Here we can see the origin of the inferior gemellus muscle marked in red on the ischial tuberosity.

Here we can see the insertion of the inferior gemellus muscle marked in blue on the trochanteric fossa of the femur.

Actions

The primary action of the inferior gemellus is lateral (external) rotation of the hip joint. Additionally, when the hip is flexed, the muscle can also aid in abduction of the hip. However, it’s worth noting that the force the gemelli muscles provide for abduction is significantly weaker than that of larger muscles, such as the gluteal muscles ^{[5] [6]}.

This image shows an example of hip external rotation, which involves rotating the leg from the hip joint outwards (laterally). External rotation is also referred to as lateral rotation. The opposite of external rotation (lateral rotation) is internal rotation (medial rotation). External (lateral) rotation of the hip joint is the primary action of the inferior gemellus.

This image shows an example of hip abduction, which involves moving the leg out to the side (laterally). The opposite of hip abduction is hip adduction. The inferior gemellus can assist with hip abduction, but only when the hip is flexed.

Innervation

The inferior gemellus is innervated by the ‘nerve to quadratus femoris’, which originates from the spinal roots of L5 and S1. This nerve also innervates the quadratus femoris muscle. This nerve passes through the greater sciatic foramen as it leaves the pelvic cavity. It also passes underneath the piriformis muscle as it enters the gluteal region ^{[7] [8]}.

This image shows the nerve to quadratus femoris which innervates the inferior gemellus muscle.

Blood Supply

Blood is supplied to the inferior gemellus muscle via the inferior gluteal artery. This artery arises from the anterior trunk of the internal iliac artery ^[9]