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 potential for impingement as the supraspinatus musculotendinous unit passes beneath the coracoacromial arch can further exacerbate the problem and further inflame and damage the structures (Fig. 38.1). Contributing to the susceptibility of the musculotendinous unit of the supraspinatus muscle to microtrauma is the fact that the supraspinatus tendon fibers interpolate themselves in the substance of the supraspinatus muscle in an oblique fashion meaning that eccentric force is applied to the musculotendinous unit when the muscle contracts (Fig. 38.2). Over time, if the inflammation continues, calcium deposition around the tendon with resultant calcific tendonitis may occur, making subsequent treatment more difficult (Fig. 38.3). Tendonitis of the musculotendinous units of the shoulder frequently coexists with bursitis of the associated bursae of the shoulder joint, creating additional pain and functional disability (Fig. 38.4).

The supraspinatus tendon of the rotator cuff is susceptible to the development of tendonitis following even seemingly minor trauma. The onset of supraspinatus tendonitis is usually acute, occurring after overuse or misuse of the shoulder joint. Inciting factors may include carrying heavy loads in front and away from the body or the vigorous use of exercise equipment. The pain of supraspinatus tendonitis is constant and severe. The patient often complains of sleep disturbance and is unable to sleep on the affected shoulder. In an effort to decrease pain, patients suffering from supraspinatus tendonitis often splint the inflamed tendon by elevating the scapula to remove tension from the ligament, giving the patient a “shrugging” appearance. Patients with supraspinatus tendonitis exhibit a positive Dawbarn sign, which is pain to palpation over the greater tuberosity of the humerus when the arm is hanging down and which disappears when the arm is fully abducted. If untreated, patients suffering from supraspinatus tendonitis may experience difficulty in performing any task that requires initial abduction of the upper extremity, making simple everyday tasks such as brushing one’s teeth or eating difficult. Over time, muscle atrophy, calcific tendonitis, and ultimately adhesive capsulitis may result (see Fig. 38.3).

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. 38.5). Magnetic resonance imaging or ultrasound imaging of the affected area may also help delineate the presence of calcific tendonitis or other shoulder pathology (Fig. 38.6).