Sartorius Muscle Anatomy

Location & Overview

The sartorius muscle is recognized as the longest muscle in the human body, positioned anterolaterally in the thigh, with its path crossing both the hip and knee joints. It resides in the anterior compartment of the thigh. It assumes a unique diagonal orientation, stretching from the lateral aspect of the hip, crossing over the thigh’s superoanterior portion, and then descending down toward the medial side of the knee. Its unique location enables it to play a role in the movements of both the hip and knee joints. This muscle is a superficial muscle, located close to the skin’s surface, which makes it easily palpable and visible in lean individuals.^[1,2,3,4]

In terms of its location compared with other muscles, it is situated anterior to the quadriceps femoris muscle and posterior to the fascia lata, a deep fascia of the thigh. Medially, the sartorius muscle neighbors the adductor longus, and laterally, it borders the tensor fasciae latae muscle. The muscle’s unique diagonal orientation distinguishes it from other muscles of the thigh region, which predominantly run vertically.^[4,2,3]

The term “sartorius” is derived from the Latin word ‘sartor’, which means tailor. This name is believed to originate from the cross-legged position that tailors historically adopted while working. The sartorius muscle, when contracted, enables such a position by flexing both the hip and knee joints and externally rotating and abducting the hip.^[1,2]

Origin & Insertion

The sartorius muscle originates from a bony prominence of the pelvis known as the anterior superior iliac spine (ASIS). The ASIS is a palpable and prominent bony point located at the front and upper part of the ilium. The ilium is the largest of the three bones that make up the hip bone.^[4,2]

From its origin, the sartorius extends inferiorly, crossing the front of the thigh diagonally to insert medially at the knee. Its insertion point is the medial surface of the proximal part of the tibia, as part of the pes anserinus. The tibial tuberosity is a palpable bony prominence found just below the kneecap, where the patellar ligament attaches. It can be used as a landmark: from the tibial tuberosity, the sartorius insertion is located medially on the proximal tibia.^[3,2] This region of the sartorius’ insertion is often referred to as the ‘pes anserinus’, or ‘goose’s foot’, due to the combined insertion of the sartorius, gracilis, and semitendinosus tendons, which bear a resemblance to a goose’s foot.^[5,2]

Action & Function

The sartorius muscle is versatile and capable of acting on both the hip and knee joints due to the unique way it crosses over the thigh. At the hip joint, the sartorius functions in flexion, abduction, and lateral rotation. Flexion of the hip, facilitated by the sartorius, involves reducing the angle between the thigh and the torso, akin to lifting the knee toward the chest.^[6,1] Abduction, another action at the hip, involves moving the leg laterally, away from the midline of the body, like when spreading the legs apart while standing.^[1,6] Finally, the sartorius also contributes to lateral rotation (external rotation) of the hip. This movement involves turning the thigh outward.^[1,6]

At the knee joint, the sartorius assists in flexion and medial rotation. Flexion of the knee is the action of reducing the angle between the lower leg and the thigh, similar to bending the knee as you swing it back to kick a football.^[1] Medial rotation (internal rotation), on the other hand, involves turning the tibia (shinbone) inward while the knee is flexed. An example of this would be turning the foot inward while keeping the thigh still. You will notice that the shin also rotates slightly inward, which would be medial rotation of the tibia.^[1]

Innervation

The sartorius muscle is innervated by the anterior division of the femoral nerve, which arises from the second, third, and fourth lumbar spinal nerves (L2, L3, L4). These nerves emerge from the lumbar section of the spinal cord, which is located in the lower back. These nerves are part of the larger lumbosacral plexus, a network of intersecting nerves that provide motor and sensory function to the lower body.^[1,2]

The femoral nerve, the largest branch of the lumbar plexus, originates from the dorsal divisions of the second, third, and fourth lumbar nerves (L2, L3, L4). The nerve descends posteriorly to the psoas major, running between this muscle and the iliacus. It then passes beneath the inguinal ligament, a band of connective tissue that runs from the hip to the pubic bone, and enters the femoral triangle, an area in the upper thigh.^[1,2]

Within the femoral triangle, the femoral nerve splits into two main divisions: anterior and posterior. The anterior division, from which the sartorius muscle receives its innervation, also provides nerve supply to the pectineus and iliacus muscles. The posterior division primarily innervates the quadriceps muscle group, which includes the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius.^[1,2]

Blood Supply

The primary blood supply to the sartorius muscle originates from the muscular branches of the femoral artery, which is a direct continuation of the external iliac artery after it crosses the inguinal ligament.^[7,3] The femoral artery provides more than half of the blood supply to the sartorius muscle.^[1]

In addition to the femoral artery, the sartorius receives collateral blood flow from several other arteries. The proximal part of the sartorius muscle receives some of its supply from the superficial circumflex iliac artery, a branch of the femoral artery that primarily supplies the skin over the inguinal ligament and the upper part of the thigh. Another source of collateral blood supply, particularly to the middle part of the sartorius, is the descending branch of the lateral circumflex femoral artery. This artery mainly supplies the vastus lateralis and rectus femoris muscles.^[1]

The distal portion of the sartorius muscle receives collateral blood supply from the descending genicular artery and the superior medial genicular artery, both of which predominantly supply the knee joint and muscles in its vicinity.^[1]