Anatomy of the Subscapularis Muscle

The subscapularis muscle is a large muscle that originates on the anterior surface of the scapula and lies in front of the shoulder. The muscle passes to its insertion into the humeral head underneath the arch formed by the coracoid process and the combined origins of the coracobrachialis muscle and short head of the biceps. The subscapularis muscle is the largest of the four rotator cuff muscles, and it provides about 50% of the total cuff strength. The subscapularis muscle inserts into the lesser tuberosity of the humerus, while the other rotator cuff muscles have an insertion into the greater tuberosity. The subscapularis muscle acts as a dynamic stabilizer of the humeral head and aids in lifting across the chest. The function of the subscapularis muscle is to adduct and rotate the arm medially. At the insertion of the subscapularis tendon into the humerus lies the transverse humeral ligament. The long head of the biceps tendon lies within the bicipital groove and is held in place by the transverse humeral ligament. When a complete rupture of the subscapularis tendon occurs, the transverse humeral ligament may also become torn causing medial dislocation of the biceps tendon from the bicipital groove. Tears of the subscapularis tendon may be diagnosed by using MRI or ultrasound. With ultrasound imaging, the probe is placed transversely over the bicipital groove to identify the groove and biceps tendon while the arm is in a neutral position. The arm is then externally rotated to view the subscapularis tendon. Tears are not uncommon and can be missed. Subscapularis rupture can be either acute or chronic and can also be partial or complete. The patient will have pain, anterior shoulder swelling, decreased range of motion, weakness of internal rotation, increased external rotation of the shoulder compared to the other side. For the lift off test, the patient places the hand behind their back at the lumbar level and lifts the hand away from the back when the patient has an intact subscapularis tendon. If the patient is unable to lift the hand off of the lower back, then a tear of the subscapularis tendon is suspected. For the lift off lag test, the examiner will hold the patient’s hand away from the back at the lumbar region and let go. Patient will be unable to keep the hand away from the back if the tendon is torn. For the belly-press test, the patient presses the palm of the hand against the abdomen with the wrist in a neutral position. This is an example of an intact subscapularis tendon. A positive sign for the belly-press test occurs if the patient is unable to press his belly without wrist volar flexion or the elbow falling posteriorly. Treatment for a complete tear of the subscapularis tendon is surgical repair; repair may be either open or arthroscopic. Biceps tenodesis during repair is associated with improved outcomes. Biceps tenodesis is usually done if the biceps is involved in the process, otherwise subluxation of the biceps will stress and fail the repair. Pectoral major muscle transfer is the procedure of choice for chronic muscle tear. Posterior dislocation of the humeral head with a “reverse Hill-Sachs lesion” is a rare condition. The condition can be repaired after reduction of the dislocation with the Mclaughlin procedure utilizing the subscapularis tendon if the lesion is between 20-40% of the humeral head. The subscapularis tendon is used to fill the reverse Hill-Sachs lesion using suture anchors or screws inserted in the humeral head defect. The screws are inserted into a portion of the lesser tuberosity that is attached to the subscapularis. The subscapularis muscle is supplied by the upper and lower subscapular nerves. The upper and lower subscapular nerves originate from the posterior cord of the brachial plexus. The subscapular artery, which is the largest branch of the axillary artery, supplies the subscapularis muscle.

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.

Claw Toe and More

Claw toes have PIP flexion and MTP hyperextension (irreducible). You may also find DIP flexion. The claw toe deformity is usually associated with an underlying neurologic condition such as diabetic peripheral neuropathy and Charcot-Marie-tooth disease. Claw toes deformity of the lesser toes can follow severe closed calcaneal fracture as a result of contracture of the intrinsic flexor muscles of the foot. Excision of the lateral and medial sesamoids may lead to claw toes. In claw toes, there is a muscle imbalance where the extrinsic muscle overpowers the weaker intrinsic muscle and can cause claw toes. The claw toe and hammer toe deformities are associated with dorsal subluxation of the interossei, which can no longer serve to flex the metatarsophalangeal joint. Once the MTP joint extends, the tendon imbalance becomes a vicious cycle. It is important to recognize if these deformities are rigid (fixed) or flexible. Claw toes is different from mallet toe, hammer toe, curly toe, and crossover second toe. The isolated hammer toe and the mallet toe usually result from an acute injury or from chronic pressure from shoes. Hammer toe rarely occurs by itself, and you may have a disorder of the plantar plate. The hammer toe and the claw toe differ by the position of the DIP joint. In the hammer toes, you will find flexion of the PIP and extension of the MTP joint, but it is reducible. Hammer toe can occur by itself, and there might be an associated dorsal PIP callus. You may also find second toe metatarsalgia. The condition of hammer toe can be flexible or rigid. In mallet toe, there is a DIP flexion deformity. You can find nail pain and end bearing callus. In mallet toe, the extensor digitorum longus will lose its tenodesis effect on the proximal interphalangeal and distal interphalangeal joints. Curly toe is associated with contracture of the flexor tendons and usually occurs in children. Curly toe is usually bilateral and usually affects the third or the fourth toe. The affected toe is usually flexed and curved medially, so that toe lies underneath the neighboring medial toe. The curly toe is usually asymptomatic, and it may improve by itself. The nail of the curly toe may cut the plantar surface of the overlying toe. The condition of curly toes is usually caused by tight flexors of the toe. The condition usually does not need treatment, and you may need to stretch the toe. If stretching of the toe fails, then you may need to do release of the flexor tendon (flexor tenotomy). Crossover second toe usually occurs due to attenuation or rupture of the plantar plate and the lateral collateral ligament. They are associated with a varying degree of instability. With crossover second toe, there will be progressive migration of the digit towards the big toe (usually the second one) with dislocation or subluxation of the MTP joint.