Sartorius
| |
| Sartorius | |
|---|---|
| Muscle Type | |
| Origin | Anterior superior iliac spine |
| Insertion | Medial condyle of the tibia - superficial Pes Anserinus |
| Action | Flexion, abduction, and lateral rotation of the hip, flexion of the knee |
| Synergists | |
| Antagonists | |
| Spinal innervation | |
| Peripheral Innervation | |
| Vasculature | |
The muscle crosses the thigh obliquely from proximal and lateral to distal and medial.
The sartorius is the longest muscle in the human body, running obliquely across the front of the thigh to flex the hip and knee joints, in rotating the thigh.
Muscle Type
The sartorius is a long, strap-like skeletal muscle in the anterior compartment of the thigh. It is a biarticular muscle (crossing both the hip and knee) and lies superficially, forming the lateral border of the femoral triangle in the upper thigh. Its name, Latin for “tailor,” arises from the cross-legged posture tailors once used, which the sartorius helps produce (the “figure-4” position).
Origin
The sartorius originates from the anterior superior iliac spine (ASIS) of the pelvic bone. A portion of the origin is shared with the nearby tensor fasciae latae muscle on the ASIS.
Insertion
It inserts on the proximal medial surface of the tibia, specifically at the superior part of the medial tibial shaft, via the pes anserinus tendon. At the insertion, the sartorius joins with the tendons of gracilis and semitendinosus to form the pes anserinus (“goose’s foot”), a conjoined tendon on the medial knee.
Action
The sartorius flexes, abducts, and laterally (externally) rotates the thigh at the hip, and it also flexes the leg at the knee. Because of its course across the knee, it assists in medial (internal) rotation of the flexed leg at the knee joint. These combined actions contribute to the cross-legged sitting position. Notably, sartorius is a weak muscle in these movements, typically acting synergistically with stronger muscles rather than as a prime mover.
Synergists
At the hip, sartorius works with the iliopsoas (primary hip flexor) and other flexors such as rectus femoris and pectineus to flex the thigh. It also assists the lateral rotators of the hip (e.g. gluteus maximus, piriformis, obturator internus/externus) in thigh external rotation. For knee flexion, sartorius contracts alongside the hamstrings (biceps femoris, semitendinosus, semimembranosus) and gracilis. It works with semitendinosus and gracilis to internally rotate the tibia when the knee is flexed.
Antagonists
The sartorius’ hip flexion is opposed by the hip extensors, primarily the gluteus maximus and hamstring muscles (especially the long head of biceps femoris, semitendinosus, semimembranosus) which extend the hip. Its lateral rotation at the hip is antagonized by the medial rotators (tensor fasciae latae and anterior fibers of gluteus medius/minimus). At the knee, sartorius (a flexor) is antagonized by the quadriceps femoris group, which extend the knee.
Spinal Innervation
The sartorius is predominantly innervated by fibers from the L2 and L3 spinal nerve roots (lumbar plexus). (Occasionally contributions from L4 may be present as well, reflecting the femoral nerve root origin.)
Peripheral Innervation
Femoral nerve (anterior division) is the nerve that innervates the sartorius. In rare cases, the obturator nerve may provide a minor accessory innervation to the sartorius, but typically femoral nerve is solely responsible.
Vasculature
The muscle is supplied chiefly by the muscular branches of the femoral artery. Collateral blood supply comes from branches such as the superficial circumflex iliac artery and lateral circumflex femoral artery. Venous drainage accompanies the arterial supply, emptying into the femoral vein.
Clinical Application
Weakness or injury of the sartorius itself is uncommon and often overshadowed by stronger muscles. However, tenderness at its origin or insertion can occur with strain. The pes anserinus insertion is a site of bursitis (pes anserine bursitis) causing medial knee pain. During a physical exam, asking a re-4 position (hip flexion, abduction, external rotation) tests sartorius function, as this movement will be painful or weak if the muscle or its nerve supply is compromised. The sartorius may be utilised as a flap in reconstructive surgery because of and reliable blood supply.
