The sartorius muscle is a long, narrow muscle running obliquely across the front of the thigh. It is often called the “tailor’s muscle” because its action allows the cross-legged sitting position historically used by tailors. This superficial muscle plays a role in moving both the hip and knee joints. Understanding its specific nerve supply is important for diagnosing and treating injuries that affect leg movement and stability.
The Innervating Nerve
The nerve responsible for the motor control of the sartorius muscle is the Femoral Nerve. This large nerve originates from the lumbar plexus, a network of nerves formed by the anterior rami of the L2, L3, and L4 spinal nerve segments. The Femoral Nerve enters the thigh by passing beneath the inguinal ligament, lying lateral to the femoral artery and vein within the femoral triangle. A specific branch of the Femoral Nerve directly innervates the sartorius muscle, relaying signals to initiate movement.
Location and Movement
The sartorius is recognized as the longest muscle in the human body, stretching from the pelvis down to the lower leg. Its origin is the anterior superior iliac spine (ASIS), a prominent bony projection on the front of the pelvis. The muscle fibers run diagonally across the thigh toward the knee, inserting on the superior medial surface of the tibia. Here, it joins the tendons of the gracilis and semitendinosus muscles to form the pes anserinus.
This long path allows the sartorius to act on both the hip and the knee joints simultaneously. The muscle is a weak synergist, assisting other, stronger muscles in their movements. The actions facilitated by the sartorius include flexion, abduction, and lateral rotation of the hip. At the knee, the sartorius aids in flexion. These compound movements work together to achieve the classic “tailor sitting” position.
Clinical Relevance of Nerve Damage
Damage to the Femoral Nerve, often resulting from trauma, surgical procedures, or compression, has direct consequences for the function of the sartorius. Injury to this nerve leads to weakness or complete paralysis of the muscles it innervates. Since the sartorius is a hip flexor and lateral rotator, its loss significantly impairs movement. Patients may experience difficulty performing complex actions necessary to lift and rotate the leg, such as bringing the heel up toward the opposite knee. The resulting weakness in hip flexion makes simple tasks like climbing stairs or rising from a seated position challenging.