Inferior Gemellus Muscle – Origin, Nerve Supply, Function

Inferior gemellus muscle and the superior gemellus muscle, two small accessory fasciculi to the tendon of the internal obturator muscle. The Gemelli’s muscles belong to the lateral rotator group of six muscles of the hip that rotate the femur in the hip joint.

Superior gemellus muscle is a small triangular muscle in the gluteal region that together with the inferior gemellus and obturator internus muscles form the tricipital (three-headed) triceps coxae which occupy the space between the piriformis muscle (superiorly) and quadratus femoris muscle (inferiorly). Together these muscles act primarily to laterally rotate the extended thigh and are also hip stabilizers steadying the femoral head in the acetabulum.

The superior and inferior gemellus muscles are a pair of small triangle-shaped muscles found among the posterior hip and gluteal musculature in the posterior proximal lower extremity commonly referred to together as the Gemelli’s muscles. The Gemelli’s muscles are two of six short external rotator muscles in the gluteal region of the proximal thigh. The remaining external rotators include the piriformis, obturator internus, quadratus femoris, and obturator externus muscles. The superior and inferior Gemelli join the obturator internus is a conjoint tendon, sometimes referred to as the triceps coxae.[rx]

Origin

• The superior gemellus muscle originates at the ischial spine, while the inferior gemellus muscle originates from the ischial tuberosity. Together with the obturator internus, the two gemelli muscles insert on the posteromedial surface of the greater trochanter of the femur.[rx]
• Inserts into the medial surface of the greater trochanter of femur via this tendon.

Nerve Supply

• Inferior gemellus receives innervation from the nerve to quadratus femoris which is a branch of the sacral plexus. It arises from L4/5 and S1 spinal nerves.
• The nerve innervates the superior gemellus muscle to the obturator internus (L4-S2), and the nerve innervates the inferior gemellus to the quadratus femoris (L4-S1). Each of these nerves is a branch of the sacral plexus, which is formed by the fourth and fifth lumbar ventral rami and the first four sacral ventral rami (L4-S4).
• The nerve to the obturator internus passes through the greater sciatic foramen as it exits the pelvis inferior to the piriformis muscle. The nerve provides innervation to the superior gemellus as it passes and then returns into the pelvis through the lesser sciatic foramen and provides innervation to the obturator internus.
• Superior gemellus is supplied by the sacral plexus, via the nerve to obturator internus (L5-S1/2).

Blood Supply

• The inferior gluteal artery supplies the superior and inferior Gemelli muscles.
• The inferior gluteal artery arises from the anterior trunk of the internal iliac artery before passing between the second and third sacral segments of the sacral plexus and exiting the greater sciatic foramen under the piriformis to supply the Gemelli’s muscles.
• The lower limb lymphatic vessels can divide into two major groups—superficial and deep vessels. The superficial lymph vessels of the lower limb can further divide into two groups: a medial group, which follows the greater saphenous vein, and a lateral group, which follows the small saphenous vein.[rx]
• There are also deep lymph vessels, including the anterior tibial, posterior tibial, and peroneal vessels that follow the course of the corresponding blood vessels.[rx] The lymph vessels of the lower limb drain into the popliteal, superficial inguinal, deep inguinal, external iliac and lumbar or aortic lymph nodes.[rx]
• The muscle is supplied by branches of the internal iliac artery; internal pudendal, inferior gluteal, and occasionally by the superior gluteal artery as well.
• The inferior gemellus muscle receives arterial blood from the medial circumflex femoral artery, which arises from the deep femoral artery. After vascularizing the muscle, the medial circumflex femoral artery continues further to supply the neck of the femur.

Function

• The primary function of the Gemelli’s muscles is to externally (laterally) rotate the thigh and extend the hip. They also contribute to the abduction of the hip while in a flexed position. The two Gemelli muscles work synergistically with the obturator internus and the remaining short external rotator to produce movement.[rx]
• Inferior gemellus muscle acts on the hip joint, causing two major movements. When the thigh is in an anatomical position, it pulls the greater trochanter of femur posteriorly, around the bone’s longitudinal axis, causing external (lateral) rotation of the thigh. When the hip, and hence the thigh, are flexed, inferior gemellus pulls the upper femur medially. This action is compensated by the lower femur moving laterally, resulting in thigh abduction. Inferior gemellus also reinforces the integrity of the hip joint, stabilizing the head of femur inside the acetabulum.

References

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