Shoulder Anterior Impingement
Shoulder Anterior Impingement Syndrome, first described by Neer in 1972, is caused when the supraspinatus tendon becomes painfully entrapped between the acromion and the greater tuberosity of the humerus during elevation and internal rotation of the arm. Repetitive impingement is thought to precipitate a cascade of shoulder dysfunction including supraspinatus tendon disruption, subacromial bursitis, biceps tendonitis, degeneration of associated joints and eventually, rotator cuff rupture. Neer suggested that 95% of chronic rotator cuff tears are due to impingement. (1)
Rotator cuff lesion progress is a self-perpetuating cycle of dysfunction. Repetitive insults damage the tendon, leading to tendon degeneration and weakening which diminishes the tendon's ability to oppose superior shearing force produced by the large movers during arm raising. Through this process the tendon becomes impinged, leading to further insult. As tendon fibers fail, the enduring fibers remain under tension and take up the slack of the failed fibers, leading to ultimate rotator cuff failure.
Shoulder impingement is the most common disorder of the shoulder and accounts for 44-65% of all shoulder complaints seen by physicians. (2) Rotator cuff problems are common in younger and middle-aged populations. Those who perform repetitive overhead activity are at greatest risk for SAIS. This group includes athletes who participate in: swimming, baseball, volleyball, weightlifting, and tennis as well as professions like carpenters, electricians, painters and wallpaper hangers.
Neer CE III. Impingement lesions. Clin Orthop. 1983;173:70–77.
Van der Windt DA, Koes BW, de Jong BA, Bouter LM. Shoulder disorders in general practice: incidence, patient characteristics, and management. Annals of the rheumatic diseases. 1995 Dec 1;54(12):959-64.
