The sartorius muscle is the longest muscle in the human body, running from the hip to the knee. The technical origin is the anterior superior iliac spine (the top and front of the hip bone) and the insertion is the medial aspect of the proximal end of the tibia (the bottom of the knee on the inside). The sartorius muscle flexes the hip and knee, rotates the hip externally and abducts the hip.
Flexion of the Hip
Hip flexion occurs when the upper body is lowered or when the leg is raised, which can happen with the knee flexed or extended. In addition to the sartorius, other muscles that work to flex the hip are iliacus, psoas, rectus femoris and pectineus.
Flexion of the Knee
Knee flexion is when the lower leg is moved toward the thigh and the angle is decreased. Flexion of the knee happens with the sartorius and six other muscles: semitendinosus, semimembranosus, biceps femoris, gracilis, popliteus and gastrocnemius.
External Rotation of the Hip
External or lateral rotation of the hip is when the thigh and/or pelvis are rotated outward, away from the body. Gluteus maximus, gluteus medius, piriformis, quadratus femoris, obturator internal and external, and gemellus superior and inferior all work with sartorius to externally rotate the hip.
Abduction of the Hip
Hip abduction is when the leg is kept straight and moved away from the body. Gluteus maximus, gluteus medius, and tensor fasciae latae perform this motion with sartorius.
Sartorius in Action
The sartorius muscle is biarticulate in that it crosses two joints, in this case the hip and knee joints. The motion of crossing the legs takes the sartorius through all of its actions, and it remains active and engaged in that position. The sartorius muscle got its name from the Latin word for tailor, which is sartor, because tailors used to sit cross-legged on the floor while they worked.
