The gracilis muscle is one of the most superficial and easily identifiable muscles located in the medial compartment of the thigh. Its name, derived from the Latin word for “slender,” accurately describes its long, thin, strap-like appearance. This muscle acts across both the hip and knee joints, playing a considerable role in lower limb movement and stability.
Anatomical Placement of the Gracilis
The gracilis muscle originates high on the pelvis, taking its origin from the inferior ramus of the pubic bone and the adjacent ischiopubic ramus near the pubic symphysis. From this origin, the muscle fibers run vertically downward along the inner thigh, making it the most superficial of the entire adductor muscle group.
The muscle extends the full length of the thigh before its tendon crosses the knee joint on the medial side. It inserts onto the upper part of the medial surface of the tibia. This final attachment point is part of a combined tendon structure known as the pes anserinus, or “goose’s foot,” which it shares with the tendons of the sartorius and semitendinosus muscles. Because it crosses both the hip and the knee joints, the gracilis is classified as a bi-articular muscle.
The Specific Actions of the Gracilis Muscle
The primary function of the gracilis muscle is to adduct the thigh, pulling the leg toward the midline of the body. This movement is essential for keeping the legs together, such as when riding a horse or stabilizing posture during standing. It works synergistically with the other adductor muscles in the medial compartment to achieve inward motion at the hip joint.
Because its tendon crosses the knee joint, the gracilis also contributes to two distinct movements of the lower leg. When the knee is extended, the muscle helps to flex, or bend, the knee. This action is most effective when the muscle is slightly lengthened, such as during the swing phase of walking.
A third action is the internal rotation of the lower leg, specifically when the knee is already bent. As the muscle contracts, its insertion point on the tibia pulls the shin bone inward, contributing to the medial rotation of the leg. This rotational force is an important component for changing direction and maintaining balance.
Clinical and Functional Relevance
The gracilis receives its functional commands from the Obturator nerve, which branches from the lumbar plexus and supplies most of the medial thigh muscles. This control allows the gracilis to function in coordination with other muscles during complex activities. Functionally, the muscle is important for maintaining pelvic stability, particularly during activities that involve a single-leg stance, such as walking or running. It provides dynamic support to the inner thigh, preventing excessive outward motion of the leg.
Despite its multiple actions, the gracilis is not a dominant muscle for any single movement. Its removal causes minimal functional deficit in the leg, making it a common choice for reconstructive surgeons as a muscle flap or tendon transfer. The muscle is frequently harvested for procedures like facial reanimation, breast reconstruction, or to repair the anal sphincter in a procedure known as graciloplasty.
Like other muscles in the medial thigh compartment, the gracilis is susceptible to strain, often referred to as a groin strain, especially in athletes requiring sudden acceleration or forceful leg movements. However, a direct tear of the gracilis muscle belly is less common than injuries to the nearby adductor longus muscle. Its reliable blood and nerve supply contribute to its utility in medical procedures, where its consistent anatomy is valued.