The musculotendinous unit of the rotator cuff is subjected to an amazing variation of stresses as it performs its function to allow range of motion of the shoulder while at the same time providing shoulder stability. The relatively poor blood supply limits the ability of these muscles and tendons to heal when traumatized. Over time, muscle tears and tendinopathy develop, further weakening the musculotendinous units and making them susceptible to additional damage.

The subscapularis tendon of the rotator cuff may develop tendonitis after overuse or misuse, especially when performing activities that require repeated upper extremity adduction and medial rotation of the humerus. The pain of subscapularis tendonitis is constant and severe and is localized to the deltoid region. The patient suffering from subscapularis tendonitis often complains of sleep disturbance and is unable to sleep on the affected shoulder. Patients with subscapularis tendonitis exhibit pain with active resisted medial rotation and on active adduction of the humerus. In an effort to decrease pain, patients suffering from subscapularis tendonitis often splint the inflamed tendon by limiting medial rotation of the humerus to remove tension from the inflamed tendon. The patient with subscapularis tendonitis will exhibit pain on the Gerber lift-off test, whereas the patient with complete rupture of the subscapularis tendon or muscle will exhibit weakness (Fig. 40.1). If untreated, patients suffering from subscapularis tendonitis may experience difficulty in performing any task that requires adduction medial rotation of the upper extremity, making simple everyday tasks such as turning off a faucet difficult. Over time, muscle atrophy and calcific tendonitis may result.

Plain radiographs are indicated in all patients who present with shoulder pain. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or ultrasound imaging of the shoulder is indicated if a rotator cuff tear is suspected (Fig. 40.2). Magnetic resonance imaging or ultrasound evaluation of the affected area may also help delineate the presence of calcific tendonitis or other shoulder pathology.

The subscapularis muscle, as part of the rotator cuff, provides shoulder stability in combination with the supraspinatus, infraspinatus, and teres minor muscle (Fig. 40.3). The subscapularis muscle adducts the upper extremity and medially rotates the arm at the shoulder. The subscapularis muscle is innervated by branches of the posterior cord of the brachial plexus and the upper and lower subscapular nerves. The subscapularis muscle finds its origin in the subscapular fossa of the anterior scapula and inserts into the lesser tuberosity of the humerus (Fig. 40.4). It is at this insertion that subscapularis tendonitis and rupture most commonly occurs (Fig. 40.5).

The benefits, risks, and alternative treatments are explained to the patient and informed consent is obtained. The patient is then placed in the sitting position with the shoulder externally rotated (Fig. 40.6). The physician stands behind or at the side of the patient.