The shoulder is the most complex joint in the body. It is capable of moving in more than 16,000 positions. Many of its ailments, including the most common ones, involve biomechanical mechanisms that are unique to the shoulder. The most common shoulder problem for which professional help is sought out for is shoulder impingement (Haig 1996). Shoulder impingement is primarily an overuse injury that involves a mechanical compression of the supraspinatus tendon, subacromial bursa, and the long head of the biceps tendon, all of which are located under the coracoacromial arch (Prentice 2001). Impingement has been described as a continuum during which repetitive compression eventually leads to irritation and inflammation that progresses to fibrosis and eventually to rupture of the rotator cuff. Because impingement involves a spectrum of lesions of tissue in the shoulder, a working knowledge of its structural relationships will facilitate an understanding of the factors that result in abnormalities. This paper will provide knowledge of the anatomy, biomechanics, and correct rehabilitation involved with shoulder impingement.
Impingement syndrome was originally described by Dr. Charles Neer as mechanical impingement of the supraspinatus muscle and the long head of the biceps tendon underneath the acromial arch. Neer classified three stages of impingement. Stage I is characterized by edema and hemorrhage of the rotator cuff and suprahumeral tissue. Stage II is characterized by fibrosis of the glenohumeral capsule and subacromial bursa and tendonitis of the involved tendons. Patients usually demonstrate a loss of active and passive range of motion because of capsular fibrosis. Stage III is the most difficult to treat and is characterized by disruption of the rotator cuff tendons. This includes rotator cuff tears, biceps rupture, and bone changes. Since this is a continuous disease process, there is often overlap of signs and symptoms (Hawkins and Abrams 1987).
For descriptive purposes, factors related to shoulder impingement can be divided into intrinsic and extrinsic categories. Intrinsic factors directly involve the subacromial space and include changes in vascularity of the rotator cuff, degeneration, and anatomy or bony anomalies. Extrinsic factors include muscle imbalances and motor control problems of the rotator cuff and parascapular muscles, functional arc of movement, postural changes, training errors, and occupational or environmental hazards. More likely, the cause of impingement has multiple factors. However, all factors may be important and the key factor in any case depends on individual circumstances.
According to Neer, the anterioinferior one third of the acromion is thought to be the causative factor in mechanical wear of the rotator cuff through a process called impingement (Donatelli 2004). Neer believes that the supraspinatus and long head of the...