Does your shoulder ache after overhead activity? Is it getting worse and now restricting that activity? Has a period of rest apparently resolved the problem only for the pain to recur when you returned to sport? Chronic shoulder pain is unfortunately an all-too-common consequence of repetitive 'overhead activity', such as serving and smashing in tennis, freestyle or butterfly swimming, bowling in cricket, javelin or baseball throwing and above-shoulder weight-training exercises. Chronic pain in the 'overhead athlete' is usually the result of damage to the rotator-cuff muscles of the shoulder (a group of four, small, deeply situated, strap-like muscles). This article will look at how such repetitive damage is caused and how the athlete may be able to prevent it occurring in the first place.
Structure of the shoulder
The shoulder joint complex is in fact made up by four joints: the glenohumeral joint (the 'ball-and-socket' joint between the upper arm or humerus and the shoulder blade or scapula, that most non-experts consider to be the shoulder joint), the acromio-clavicular joint (the joint between the lateral end of the collar bone or clavicle and the scapula), the sternoclavicular joint (the joint between the medial end of the clavicle and the breast bone or sternum) and the scapulo-thoracic joint (the 'virtual' joint between the undersurface of the scapula and the chest wall). Problems at any of these four joints may result in ineffective function of the shoulder joint complex and consequently pain.
There is more movement possible at the shoulder joint than at any other joint in the body. Over 1600 positions in three-dimensional space can be assumed by the shoulder. The price to be paid for such an extreme range of movement is an inherent lack of stability. To achieve peak performance during overhead activity, there must be optimal balance between mobility and stability. It is well known that swimmers who over-stretch their shoulders in an attempt to increase the range of their stroke, without improving their functional stability, are at increased risk of injury to the rotator cuff. Tennis players and throwing athletes, activities that are essentially asymmetrical, tend to develop greater shoulder external rotation in their dominant shoulder and this is commonly associated with functional instability. Shoulder-injury prevention strategies need to focus on improving shoulder stability.
Impingement and the rotator cuff
The bony anatomy of the glenohumeral joint comprises a large ball (the head of the humerus) and small socket (the glenoid of the scapula) with the muscles of the rotator cuff and scapular rotating (stabilising) muscles acting as the most important dynamic stabilisers of the joint. The muscles of the rotator cuff envelop the glenohumeral joint itself, and comprise the supraspinatus, infraspinatus, teres minor and subscapularis muscles. Supraspinatus abducts the arm (moves it laterally away from the side of the body), infraspinatus and teres minor externally rotate the shoulder, and subscapularis is prin-cipally an internal rotator of the shoulder. Sitting above the cuff is the coracoacromial arch, made up of the coracoid and acromion bony processes of the scapula and a ligament connecting the two processes. As the arm is abducted away from the body or flexed (brought forward), 'impingement' or squeezing of the rotator cuff between the head of the humerus below and the coracoacromial arch above can occur. The healthy, conditioned rotator cuff functions effectively as an integrated unit to stabilise and depress the head of the humerus, opposing the action of the large deltoid muscle and thereby preventing impingement. Any overhead activity that involves the arm being taken often enough from below shoulder level to above shoulder level has the capacity to damage the rotator cuff. With repeated impingement, a poorly conditioned cuff can become damaged, and a cycle of cuff damage, impaired function, further impingement and worsening cuff damage is initiated.
This form of primary impingement is most commonly seen