Monday, February 8, 2021

Anatomy of the Sartorius Muscle

 


The sartorius muscle arises from the anterior superior iliac spine (ASIS) of the pelvic bone. The sartorius muscle crosses the upper third of the thigh obliquely, downwards medially and then descends vertically towards its insertion. It is a superficial muscle, the longest muscle, and its fibers are parallel. The sartorius muscle is inserted into the anteromedial surface of the upper tibia. Other tendons are inserted into the same location. These tendons are called the Pes Anserine tendons. Surgical approach to the Pes Anserine insertion for harvesting of the semitendinosus and gracilis tendons puts the terminal branch of the saphenous nerve at risk as it emerges between the sartorius and the gracilis tendons. The sartorius muscle is innervated by the femoral nerve. The sartorius muscle flexes, abducts, and rotates the hip laterally as well as flexes the knee. It is sometimes referred to as the “tailor’s muscle” in reference to the cross-legged position in which tailors once sat. the “tailor” position helps to understand the function of the sartorius muscle. The upper third of the sartorius muscle forms the lateral border of the femoral triangle, and its middle third forms the roof of the adductor (subsartorial) canal which contains the femoral vessels and the saphenous nerve. The femoral triangle is a superficial triangular space located on the anterior aspect of the thigh just inferior to the inguinal ligament. The boundaries of the femoral triangle include the lateral border (formed by the medial border of the sartorius muscle), the medial border (formed by the medial border of the adductor longus muscle), and the base (formed by the inguinal ligament). The femoral triangle contains three important structures: femoral nerve, femoral artery, and femoral vein (from lateral to medial), and it also contains the deep inguinal lymph nodes. The lateral cutaneous nerve of the thigh crosses the lateral corner of the triangle and supplies the skin on the lateral part of the thigh. It appears that the neurovascular bundle is medial to the sartorius muscle. Therefore, in the anterior approach to the hip, it is always safe to go lateral to the sartorius muscle in order to avoid the important structures within the femoral triangle. It is important to remember when performing this approach to avoid injury to the lateral cutaneous nerve of the thigh. For the Hip Anterior Approach (Smith-Petersen) the internervous plane superficially between the sartorius (supplied by the femoral nerve) and the tensor fascia lata (supplied by the superior gluteal nerve). Bony avulsion of the sartorius tendon occurs from a strong sudden pull of the sartorius with the hip in extension and the knee in flexion. Avulsion of the sartorius from its attachment site most commonly occurs in sprinters and other running athletes. The avulsion can also occur after anterior iliac crest bone graft. It is advisable to start harvesting the bone graft approximately 3 cm from the anterior superior iliac spine to avoid weakening of the bone and avulsion fracture. harvesting bone less than 3 cm of the ASIS may cause an avulsion fracture of the sartorius muscle. If there is a persistent hip pain after anterior iliac crest bone graft, get an x-ray of the pelvis to check for an avulsion fracture. The adductor canal (subsartorial canal) is an aponeurotic tunnel in the middle third of the thigh, extending from the apex of the femoral triangle to the opening in the adductor magnus, which is called the adductor hiatus. The canal contains the femoral artery, femoral vein, and the saphenous nerve, which is a branch of the femoral nerve. It is important to recognize the relationship of the saphenous nerve to the sartorius muscle and tendon. The saphenous nerve is posterior to the sartorius tendon. The pes anserine bursa is a small fluid filled sac located between the tibia and three tendons of the sartorius, gracilis, and the semitendinosus. The pes anserine is the common area of insertion for the three tendons along the proximal medial aspect of the tibia. The sartorius is innervated by the femoral nerve. The gracilis is innervated by the obturator nerve. The semitendinosus is innervated by the tibial branch of the sciatic nerve. Pes anserine bursitis, or “breaststroke knee”, is an inflammatory condition of the medial knee at the pes anserine bursa that is common in swimmers. Pes anserine bursitis is usually seen as causing pain, tenderness, and localized swelling after trauma or total knee replacement. The pain is seen below the joint line on the medial part of the proximal tibia with the bursa deep to the tendons. Pain at the joint line is probably a meniscal tear. Pain below the joint line is probably bursitis.