Shoulder Rotator Cuff Disease

The rotator cuff is a musculotendinous cuff which surrounds the humeral head and through which the shoulder stabilising and movement muscles exert their forces onto the shoulder. The cuff enables us to put our shoulder through a very large range of motion, the greatest range of any joint in the body, for the purpose of putting our hands in functional positions. The shoulder’s function is to allow our hands to be put in useful positions within our visual field so we can perform the intricate activities that define being human to a degree.

As the muscles approach their insertions on the humeral head they become more and more fibrous until they become wholly tendinous. Many bodily tendons are cylindrical and long but the shoulder tendons are flatter structures which coalesce over the top of the humeral head. The rotator cuff has a relatively poor blood supply and little or no ability to heal and with time and physical stresses tears appear which are often painful but not always so. Rotator cuff tears are a major part of a shoulder surgeon’s work and rotator cuff surgery is common, complex and demands detailed physiotherapy follow up for successful outcomes.

Many causes of rotator cuff tears have been postulated by there is no agreed single cause, with competing ideas which favour external factors to the tendon and its rival which favours internal degeneration of the tendon itself. The leading shoulder surgeon Neer named impingement syndrome as a condition where the shoulder tendons are repeatedly stressed against the anatomical structures which overlie them. These structures include the acromio-clavicular joint and the front of the acromion, the outside end of the shoulder blade. The supraspinatus tendon can be compressed regularly as the shoulder goes into repetitive flexion and medial rotation,

The natural anatomical shape of our acromion plays a role in the likelihood of us having impingement type problems and therefore the tendency to get cuff tears. X-ray studies have shown that a hooked acromion is strongly related to the development of cuff tears although a proven causal link is not yet clear. The acromioclavicular joint develops degenerative outgrowths on its underside and the underlying cuff tendons are pressed against this area on repetitive movement. Repeated overhead work in younger people can cause bleeding and oedema in the tendon, with inflammation and scarring of the tendon after many such small injuries. With time in patients older than forty years complete or partial tears and bony spurs can develop.

A third impingement type can occur in throwing as the arm is cocked back for the throw and the edge of the glenoid socket can be forced repeatedly against the lower surface of the supraspinatus tendon. Minor trauma is produced each time this occurs, gradually developing into small tears particularly in athletes who throw a lot. The biceps and supraspinatus tendons and the lesser tuberosity impinge against the coracoid process. Most rotator cuff tears are probably contributed to by these three impingement process.

The intrinsic view holds that the external factors may be contributory but that the fundamental underlying process is age-related degeneration inside the tendons themselves. This helps explain why young people rarely suffer cuff tears and that tears increase strongly with age, for example after fifty years old. Under the supraspinatus tendon near to its insertion onto the greater tuberosity is an area which has been called the critical zone and postulated to have a poor vascular supply. This could increase the risk of injury and poor healing in this area but further studies have not confirmed this idea so degenerative changes in the tendons may still be important.

It is likely that the cause of rotator cuff degeneration is a combination of both extrinsic and intrinsic causes, with the tendon tending to fail first in the areas of greatest load, leading to rupture of small tendon fibres. This causes increased forces being loaded onto close fibres, detachment of some fibres from bone, reduction in cuff power and compromised blood supply due to kinked fibres. Wound healing could be reduced and this would impair the possibility of repair.

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