Superior gemellus muscle

Origin and insertion

The superior gemellus muscle originates from the posterior (gluteal) surface of ischial spine of bony pelvis. It courses laterally towards the femur, passing through the lesser sciatic foramen. The tendons of both gemelli muscles and obturator internus fuse anterosuperiorly to the trochanteric fossa of femur, finally inserting to the medial surface of greater trochanter as a unique triceps coxae muscle.

Relations

Triceps coxae muscle, or the three-headed muscle of the pelvis, is located deep to gluteus maximus, filling the space bounded by piriformis muscle superiorly and quadratus femoris inferiorly. From superior to inferior, the triceps coxae is composed of the superior gemellus, obturator internus and inferior gemellus. These three muscles have their own origins, yet share a common insertion. In some instances, the three muscles insert to the femur independently in the same superoinferior order they extend through the gluteal region of the pelvis.

Superior gemellus is the smaller of the two gemelli. Its proximal and distal parts sit inferiorly and deep to the piriformis, respectively. In some cases, the fibers of the piriformis muscle can partially blend with the superior gemellus and thus insert to the femur with triceps coxae common tendon.

The neurovascular bundle of the hip and thigh, containing the sciatic nerve, pudendal nerve, inferior gluteal artery, posterior femoral cutaneous and inferior gluteal nerves, passes through a slit between the piriformis and superior gemellus on its way from pelvis to the lower limb.

Innervation

Superior gemellus is supplied by the sacral plexus, via the nerve to obturator internus (L5-S1/2).

Blood supply

The muscle is supplied by branches of the internal iliac artery; internal pudendal, inferior gluteal and occasionally by the superior gluteal artery as well.

Function

Superior gemellus acts as a part of the triceps coxae muscle group to produce external (lateral) rotation and abduction of the thigh. The movement produced by contraction of this muscle group is dependant upon the position of the leg.

• External (lateral) rotation - when the lower limb is in an anatomical position, the triceps coxae acts to rotate the proximal femur externally. This function is important as along with gluteus maximus, part of gluteus medius, piriformis, obturator externus and quadratus femoris, the triceps coxae muscles externally rotate the lower extremity in the carry-through phase of the gait cycle. 
• Abduction - when the hip is flexed at 90 degrees, triceps coxae action pulls the proximal femur medially. The distal femur moves correspondingly laterally, and the end result is abduction of the thigh. This abduction from a seated position is the movement you perform when positioning your lower limb out of the car, for example.

In addition, attaching between the proximal end of femur and the hip bone, the superior gemellus plays a role in stabilizing the head of femur in the acetabulum of pelvis.

Learn more about the types of body movements with our learning materials about the topic.