The shoulder is a complex structure that affords great mobility at the expense of stability. What stability is present has both static and dynamic components. Statically, the bony glenoid, cartilaginous labrum, glenohumeral ligaments, and joint capsule provide moderate stability. The rotator cuff (supraspinatus, infraspinatus, teres minor, and subscapularis) and the biceps tendon function dynamically to assist with stability. The rotator cuff plays a key role, especially with the arm in overhead elevation, where it must tonically contract to keep the humeral head anchored in the shallow glenoid fossa . The rotator cuff rests in the subacromial space, defined by the acromion, subacromial bursa, and coracoacromial ligament above; the coracoid process at the medial border; and the humeral head below. Numerous anatomic and pathophysiologic factors may lead to a narrowing of the space and predisposition to rotator cuff impingement. Bicipital tendonitis may occur in concert with rotator cuff tendonitis as the biceps passes underneath the subscapularis and supraspinatus tendons.
The impingement syndrome has been well described as a progression of changes to the rotator cuff eventually leading to a tearing of the tendons. The causes of rotator cuff impingement can be classified as intrinsic or extrinsic . Intrinsic causes include trauma or degeneration of the rotator cuff with instability or laxity of the shoulder complex. Extrinsic causes include bony changes to the acromion, coracoid, acromioclavicular joint or greater tuberosity, cervical nerve root compression, and other systemic conditions, including rheumatic disorders . Morrison and Bigliani reported the relationship between acromial morphology (type I flat, type II curved, type III hooked) and rotator cuff impingement. Individuals with a hooked acromion were most likely to develop rotator cuff abnormalities . The positioning of the rotator cuff has also been reported as having a relationship to rotator cuff pathology. Rathbun and MacNab reported the “wringing out” phenomenon, whereby a hypovascular region in the supraspinatus tendon was created with the arm held in adduction . Glenohumeral instability has been described as an inciting cause, with rotator cuff impingement occurring secondary to increased humeral motion . The torque placed on the rotator cuff is greatest at arm elevation of 90 degrees, which may predispose to overuse injury in the overhead position . Loss of scapular motion, or asynchrony between the scapulothoracic and glenohumeral musculature, may also predispose to impingement.
Rotator cuff injury was the third most common diagnosis encountered in workers, accounting for 8.3% of cases . In a fish-processing plant, shoulder girdle pain was encountered in 30.9% of workers and was more prevalent in workers who performed both repetitive and forceful movements of their upper limbs during work . Among electricians, 29% reported shoulder symptoms that occurred at least three times or lasted greater than 1 week . Shoulder pain was also reported in 37% of construction workers, 19.6% of garment workers, and 8.8% of hospital workers . Herberts et al. reported 18% of shipyard welders, and 16% of steel plate workers had shoulder pain . Welch noted a prevalence of 32% for rotator cuff injury in sheet metal workers, with most occurring from overhead duct work . Rotator cuff injury is more common overall in individuals who perform overhead activities or who require internal rotation of the shoulder, awkward or static postures; lack of rest, and vibration .
The individual with rotator cuff tendonitis or the impingement syndrome will report pain deep within the shoulder or posteriorly, with referral to the deltoid muscle insertion region. There may also be loss of strength and motion secondary to the pain. The discomfort is worsened by activities at shoulder level or above. Pain will occasionally occur at night while resting on the involved shoulder, perhaps from a concomitant subacromial bursitis. On physical examination, pain may be reproduced with palpation within the subacromial space or over the biceps tendon. Several methods are used to reproduce impingement of the rotator cuff (impingement signs). Hawkins described a method in which the arm is forward-flexed 90 degrees, and with the elbow flexed 90 degrees the arm is forcibly internally rotated . Neer described forced forward flexion of the arm, maintaining pressure on the acromion, so as to impinge the humeral head under the acromion . The impingement test was described as a method of obtaining pain relief from rotator cuff impingement . It is performed by the injection of lidocaine into the subacromial space and is interpreted as positive if there is a return of strength and an improved range after infiltration of the space. Strength testing of the rotator cuff should be performed in all involved subjects, with weakness and pain of the supraspinatus with or without external shoulder rotators usually most apparent. A complete neurologic examination should also be performed to rule out the presence of an underlying cervical radiculopathy. Further evaluation can occur with the use of x-rays, magnetic resonance imaging (MRI), and electrodiagnosis.
In the industrial setting, rehabilitation of shoulder impingement emphasizes decreasing overhead work, particularly for activities that also promote internal rotation of the shoulder. Acute intervention emphasizes pain reduction, including NSAIDs, ice, and occasionally, corticosteroid injection into the subacromial space. Range of motion of both the glenohumeral and scapulothoracic articulations will decrease the likelihood of asynchronous motion leading to impingement. Finally, strengthening of the glenohumeral and scapulothoracic musculature concentrically and eccentrically will help to prevent future injury. Strengthening of the scapular stabilizers should be started immediately; the remainder of the strengthening program (i.e., of the cuff itself) is prescribed when such activity no longer reproduces much pain. Copyright: Copyright©2005 Lippincott Williams & Wilkins – Physical Medicine & Rehabilitation: Principles and Practice – Joel A. Delisa
