The sartorius muscle is a long, narrow, ribbon-like structure located superficially along the front of the thigh. It is the longest muscle in the human body, spanning both the hip and knee joints. It is nicknamed the “tailor’s muscle” because of the unique cross-legged sitting position historically adopted by tailors while working.
Defining the Muscle’s Pathway
The course of the sartorius muscle follows a diagonal trajectory across the thigh, running from the outside of the hip down toward the inner side of the knee. This strap-like muscle runs obliquely, or inferomedially, across the quadriceps muscles. Its exceptional length allows the sartorius to influence movement at two separate joints.
Origin and the Starting Point
The sartorius muscle begins its attachment proximally at the pelvic girdle, specifically originating from the Anterior Superior Iliac Spine (ASIS). The ASIS is a prominent, easily felt bony projection located at the front and side of the hip bone. This starting point dictates the muscle’s long, oblique path across the thigh.
The Insertion Point
The sartorius muscle inserts on the medial side of the lower leg, just below the knee joint. The muscle’s tendon attaches to the anteromedial surface of the proximal part of the tibia, the larger of the two lower leg bones. This specific insertion point is part of a broader, shared tendinous structure known as the Pes Anserinus, Latin for “goose’s foot.”
The Pes Anserinus is formed by the conjoined tendons of three different muscles from separate compartments of the thigh, all meeting at this common point. The sartorius tendon is the most anterior of the three contributing tendons, joining with the tendons of the gracilis and the semitendinosus muscles. This collective insertion occurs approximately five centimeters below the joint line on the inside of the knee.
This shared insertion site stabilizes the knee against rotational forces and houses a small, fluid-filled sac called the anserine bursa. The proximity of the tendon insertion and the bursa to the bone can make the area susceptible to inflammation, a condition known as pes anserinus bursitis or tendinitis. The location is often tender and painful, especially in individuals who participate in sports requiring repetitive knee movement.
Primary Actions and Movement
Because the sartorius crosses both the hip and the knee joints diagonally, its contraction results in a combination of movements. At the hip, it is a weak flexor, helping to lift the leg forward, and it also contributes to the abduction, or moving the leg outward away from the body’s midline, and lateral rotation of the thigh. At the knee, the sartorius is a flexor, bending the knee joint. When the knee is bent, the muscle can also act as an internal rotator of the lower leg, twisting the tibia inward. The combined effect of these four separate actions—hip flexion, abduction, lateral rotation, and knee flexion—allows a person to bring their ankle up to rest on the opposite knee, a position known as the “figure-four” or tailor sitting stance.