 in weight trainers who over-emphasise the development of their 'prime moving muscles' (pectoralis major, latissimus dorsi and deltoid) at the expense of their rotator cuff. It seems to be increasingly common in athletes as they reach their thirties. Primary impingement is preventable and, if the cuff is appropriately conditioned, exercises such as behind-the-neck press, incline bench press and extended front laterals, will not lead to pain. Differences in the shape and bony configuration of the undersurface of the acromion may dispose an athlete to this particular injury. A Type II (curved) or Type III (hooked) acromion will reduce the effective space through which the supraspinatus tendon slides during abduction. Plain X-rays should enable these two variations to be identified.
Secondary impingement refers to impingement secondary to underlying glenohumeral instability, when the rotator cuff is fatigued by its efforts to keep the humerus centred on the glenoid and consequently allows the head of the humerus to ride up, reducing the subacromial space. This is probably the most common mechanism of cuff injury seen in younger athletes, particularly those with increased joint laxity, and is seen frequently in swimmers and throwers. The primary problem here is instability and, unless this is treated, pain will be ongoing and progressive.
A strong and healthy rotator cuff is essential to the overhead athlete. In recent years, the role of the scapula-stabilising muscles in positioning the glenohumeral joint for optimal rotator-cuff function has been increasingly emphasised. Co-ordinated action of this group of muscles is needed to provide a stable base for pain-free overhead activity. The overly simplistic 'ball and socket' model of the shoulder joint has been superceded by a model similar to the performing seal that can balance a ball on its nose. The seal equates to the scapula, and constant small adjustments by the seal (scapula) are needed to prevent the ball falling off its nose (glenoid). Overhead athletes must be able to effectively control the position of their scapula for optimal cuff function.
Injury prevention strategies
Most cuff injuries can be prevented relatively simply. The crucial point is not to overwork the rotator cuff by increasing shoulder work too rapidly. Keeping increases in workload to less than 10% per week will significantly reduce the risk of injury. The important balance between stability and range of shoulder movement has already been emphasised. Athletes with access to sports medicine support will benefit from a formal assessment of dynamic shoulder function.. This should encompass a comprehensive review of static and dynamic anatomy, range of motion at all four joints of the shoulder joint complex, muscle strength and balance (particularly of the rotator cuff and scapular stabilisers) and an assessment of inherent glenohumeral stability in all three planes. Significant abnormalities detected need to be address and corrected. Such screening is becoming increasingly routine for the more elite overhead athlete and validated assessment and treatment protocols have been defined. Technique should be evaluated by the coach and appropriate technical changes integrated into the rehabilitation programme.
The role of the kinetic chain
Increasingly, the role of force generation by other body components is being assessed. For instance, the power generated by the shoulder in the tennis serve has been preceded by power generated by the legs, trunk and back. The muscle mass of the shoulder is relatively small, and if inadequate power is generated by the preceding links in the kinetic chain the shoulder has to play 'catch-up' and generate power rather than acting as a force regulator. Improving the server's leg action, lumbar strength and trunk rotation during the serve will reduce the incidence of rotator-cuff injury. Such biomechanical analysis is difficult but, in skilled hands, is a crucial and effective element in injury prevention.
How can an athlete prevent injury?
Although shoulder rehabilitation proto