Pathophysiology:

The subscapularis is a humeral head depressor and, in certain positions, an internal rotator. The infraspinatus and teres minor are external rotators. These muscles work as a unit, rather than individually, to maintain the dynamic glenohumeral stability of the shoulder. All are innervated by subscapular and axillary nerves. Microscopically, all of the tendons of the rotator cuff fuse to form one continuous band, which is composed of a 5-layer structure. Because of this structure, none of the individual muscles have a higher incidence of tear, per se.

Most of the tears of the cuff are the end result of chronic degeneration, which makes them susceptible to rupture. The chronic deterioration of the cuff results from the coracoacromial arch, which is composed of the bony acromion, the coracoacromial ligament, and coracoid process. Because of its position above the rotator cuff, the coracoacromial arch forms the roof through which the supraspinatus tendon must pass (ie, supraspinatus outlet). Repetitive microtrauma and anatomical variations lead to most of the rotator cuff injuries.

Tendon degeneration is classified in 3 stages (classification of the impingement syndrome) based on the supraspinatus outlet. Stage I - Edema and hemorrhage, affecting persons younger than 25 years; Stage II - Fibrosis and tendinitis, affecting persons aged 25-40 years; Stage III - Tears of cuff, affecting persons older than 50 years.

Frequency/Mortality/Morbidity:

An estimated 4% of cuff ruptures develop a cuff arthropathy. Various authors report a rate of success with conservative treatment ranging from 33-90%, with longer recovery time in older patients. Surgery results in improved function regardless of the patient's age.

History/Physical:

Physical exam involves assessing active and passive range of motion. Pain, loss of muscle strength, and loss of motion should be noted. The supraspinatus is isolated with the arm forward 90 degrees in the scapular plane and the forearm rotated into pronation (ie, thumbs down). If drooping of this position occurs, full thickness rotator cuff tears are suggested. The subscapularis may be tested with the arm at the side with internal rotation resistance. However, this can produce false-negative test results; instead, the arm should be internally rotated with the dorsum on the buttock surface and actively lift hand from the buttocks against resistance. The external rotators, teres minor, and infraspinatus can be tested with the arm on the side and in 90 degrees of abduction.

Causes:

Imaging Studies:

Arthrography of glenohumeral joint has been used to diagnose rotator cuff disease. A complete tear is diagnosed when communication between the glenohumeral joint cavity and the bursae, either subacromial or subdeltoid, is evident. Partial tears are better evaluated with ultrasound or MRI.

Ultrasonography also is used to evaluate rotator cuff disease. The 4 criteria for rotator cuff pathology are nonvisualization of the cuff, localized absence or focal nonvisualization, discontinuity, and focal abnormal echogenicity. Sensitivity and specificity are operator dependent and have been reported to be greater than 90%.

A magnetic resonance imaging (MRI) can reveal a great spectrum of rotator cuff disease from degeneration to partial or complete tears. MRI also can reveal soft tissue injuries. As a postoperative imaging modality, it has proven to be invaluable.

Treatment:

Follow-up should be scheduled regularly to assess the healing process. If the patient has not improved by a 6-week assessment, surgical therapy should be considered. In general, surgical therapy is indicated in patients younger than 60 years with a full-thickness tear demonstrated clinically or arthrographically, in patients who fail to improve after 6 weeks of rehabilitation, or in patients performing activity that requires shoulder use. One important caveat is that emergent orthopedic evaluation is warranted in acute injuries or even severe extension of chronic rotator cuff injuries because they have poor prognosis if conservative modalities are used.

The success rate of surgical therapy is reported to be 77-86%. Findings generally suggest that early treatment precipitates a better outcome than late treatment. Many studies have concluded that the need for surgery should consider not only age but also type of tear, duration of symptoms, and the patient's ability to comply with the rehabilitation regimen.

Medical/Legal Concerns:

Despite the fact that the prevalence of rotator cuff tendinitis has been found to be as high as 18% among certain heavy manual laborers, and, the fact that there is evidence for a positive association between highly repetitive activities and shoulder musculoskeletal disorders, establishing the relation between a degenerative rotator cuff disease and a work- related injury may be a challenge for the physician who is called as an expert witness. Because the injury occurs over a long period of repetitive movements and because there is often no initial traumatic event, the correlation may be difficult to establish.

Since there is evidence for a relationship between sustained shoulder postures with greater than 60° of flexion or abduction and shoulder musculoskeletal disorders in persons with highly repetitive work, those ergonomic factors must be systematically assessed and emphasized, if possible by an occupational or physical therapist or by video. On that basis, it is possible to demonstrate that a degenerative rotator cuff disease may be a work-related disorder associated with repeated trauma.