Gracilis Muscle Anatomy

Location & Overview

The gracilis muscle is named for its long and slender shape, from the Latin ‘gracilis’, which means thin or slender. The gracilis is located in the medial compartment of the thigh. As a superficial muscle, it is located close to the skin’s surface, which makes it easy to palpate.^[1,2]

The gracilis is one of the adductor muscles of the hip (its other actions are covered in the actions section below). It is situated immediately adjacent to the adductor longus muscle and beneath the adductor magnus muscle. Its position in the medial compartment of the thigh places it closer to the body’s midline. This gives it a strategic role in the movements of the lower limb, such as adduction.^[3,2]

The gracilis is part of the pes anserinus, which is formed by a collection of tendons. The term is derived from Latin and translates to ‘goose foot’, due to its three-pronged structure of tendons, similar to the foot of a goose. The tendons involved in the pes anserinus consist of three muscles: the gracilis, the semitendinosus, and the sartorius. These tendons converge at their insertion point on the proximal tibia, forming a robust structure that plays a significant role in stabilizing the medial side of the knee joint.^[4,5]

Origin & Insertion

The gracilis muscle originates on the lower half of the hip, more specifically on a structure called the ischiopubic ramus.^[2,1] The ischiopubic ramus is a bony structure formed by the fusion of the ischium and the pubis, two of the three bones that compose the hip. This structure creates a kind of bridge at the lower anterior part of the hip, contributing to the formation of the obturator foramen, which is a large opening in the hip bone. The gracilis muscle originates from the anterior aspect of this bridge-like structure. Its origin is on the anterior aspect of the ischiopubic ramus.^[4,1]

The gracilis then extends down the inner part of the thigh in a relatively straight path, due to being the most medial of the thigh muscles. It runs almost parallel to the femur, providing a clear path that indicates the muscle’s direction.^[1]

The muscle terminates at its insertion point located on the medial surface of the proximal tibia. To be more precise, the gracilis inserts just below the knee, attaching to an area on the tibia known as the pes anserinus.^[2] This insertion is just medial to the tibial tuberosity, where the quadriceps insert via the patellar tendon. The common tendinous insertion of the gracilis is shared with two other muscles, the sartorius and semitendinosus. The insertion of these tendons forms a ‘goose foot’ pattern known as the pes anserinus, on the inner side of the upper tibia.^[4,1]

This anatomical path, from the hip bone to the tibia, allows the gracilis muscle to span two joints: the hip and the knee. Thus, it is capable of influencing the movements of both of these joints.^[4,1] This is discussed in more detail in the actions section next.

Action & Function

The gracilis muscle performs several important actions in the lower body. Its positioning, origin, and insertion enable it to influence movements at both the hip and the knee joints.^[4,1] These actions, with accompanying illustrations, are outlined below.

Hip adduction: This is the primary action of the gracilis muscle. Adduction of the hip joint refers to the movement that brings the leg toward the midline of the body. For example, if you were standing with your legs apart, the act of bringing your feet together would be accomplished through hip adduction. The gracilis muscle works together with the other adductor muscles to accomplish this (such as the adductor longus, adductor brevis, adductor magnus, and pectineus).^[3,2]

Knee flexion: The gracilis muscle also contributes to flexion of the knee joint, an action that involves bending the knee to decrease the angle between the thigh and the lower leg.^[2]

Tibia medial rotation (i.e knee internal rotation): When the knee is flexed, the gracilis can contribute to internal rotation of the tibia (also known as medial rotation of the tibia). This action involves turning the tibia inward, toward the midline of the body, which would result in the foot also turning inward if the foot was off the ground.^[2]

Hip flexion: The gracilis muscle assists in flexion of the hip joint. This action involves lifting the thigh or moving it in the direction of the abdomen.^[3,2]

Hip internal rotation: When the hip is flexed, the gracilis can contribute to the internal rotation of the hip. This is a movement that turns the femur and thereby the leg and foot inward, toward the midline of the body.^[2]

Innervation

The gracilis muscle, located in the medial compartment of the thigh, is innervated by the anterior branch of the obturator nerve. The obturator nerve arises from the anterior divisions of the L2, L3, and L4 nerve roots within the lumbar plexus.^[6,7]

After forming within the lumbar plexus, the obturator nerve descends through the fibers of psoas major and emerges from its medial border near the pelvic brim. It then passes posterior to the common iliac vessels, continues along the lateral pelvic wall on the lateral side of the internal iliac vessels, and travels toward the obturator canal. The nerve exits the pelvis through the obturator canal to reach the medial compartment of the thigh, where its anterior and posterior divisions supply the medial thigh musculature.^[6]

The point at which the obturator nerve divides into anterior and posterior branches is variable and may be intrapelvic, within the obturator canal, or in the thigh. The anterior branch typically descends between the adductor longus and adductor brevis, commonly giving muscular branches to the adductor longus, adductor brevis, and gracilis, and it may also give a variable cutaneous branch to the skin of the medial thigh. The posterior branch more commonly supplies the obturator externus and the adductor part of adductor magnus, with variable contribution to adductor brevis.^[6,7]

Blood Supply

The gracilis muscle receives its blood supply from the medial circumflex femoral artery, superficial femoral artery, deep femoral artery, descending genicular artery, and the anterior branch of the obturator artery.^[2]

The gracilis muscle’s primary blood supply is the medial circumflex femoral artery. This artery originates from the deep femoral artery, which is a major branch of the femoral artery, which is responsible for supplying most of the thigh muscles. The medial circumflex femoral artery, after its origin, courses around the posterior aspect of the femur.^[2]

In addition to the medial circumflex femoral artery, the superficial femoral artery also plays a significant role in providing blood to the gracilis muscle. This artery is a continuation of the common femoral artery, which gives off the deep femoral artery. The superficial femoral artery travels down the thigh’s anterior compartment, providing blood supply to the various muscles it encounters, including the gracilis.^[2]

The deep femoral artery, also known as the profunda femoris artery, also contributes to the blood supply of the gracilis muscle. After its emergence from the common femoral artery, it dives deep into the posterior compartment of the thigh, sending numerous branches to the muscles, including the gracilis.^[2]

The descending genicular artery, a branch of the femoral artery, is another artery that provides blood to the gracilis muscle. After its origin, it travels toward the knee, giving off articular and muscular branches that supply the knee joint and adjacent muscles, including the gracilis.^[2]

The last artery supplying blood to the gracilis is the anterior branch of the obturator artery. The obturator artery originates from the internal iliac artery, where it then travels through the obturator canal to reach the medial compartment of the thigh. Its anterior branch follows the obturator nerve, supplying blood to the adductor muscles, including the gracilis.^[2]