TACF Articles

The shoulder is a highly mobile and relatively unstable joint with the largest range of motion of all the body’s joints. The shoulder is designed to allow us to put our hands in front of our vision so we can watch as we perform complex manual manoeuvres, a defining feature of primates and humans. The shoulder has a group of muscles which stabilise and move the joint, a group known as the rotator cuff, which forms a tendinous cuff around the head of the humerus so that it can exert the necessary forces.

Tendons in the human body take a number of forms and we are most familiar with the slim round ones such as near the wrist, but the rotator cuff tendons are a connective tissue sheet, flat and covering the head of the humerus. The blood supply and healing ability of the rotator cuff may be limited for several reasons and with time tears in the cuff tendons appear, which are not always painful. Shoulder surgeons spend a lot of time diagnosing rotator cuff disease and operating on cuff tears. Physiotherapists follow detailed protocols post-operatively in the rehabilitation of rotator cuff repairs.

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,

Impingement may be the largest cause of cuff tears and it appears that the shape of the acromion is related to the likelihood of the development of tears. A hooked shape is connected with cuff tears but may not be a simple causal link. A degenerative process occurs with age which forms bony outgrowths under the acromioclavicular joint and this impinges on the underlying tendons. In younger people who perform a lot of overhead work there can be swelling and bleeding in the tendon, progressing to tendon inflammation and fibrosis after repeated episodes of inflammation from physical stresses. Finally bone spurs develop and partial or complete tears of the rotator cuff but these patients are always over 40.

Another type of impingement occurs when the arm is taken back into the cocking part of the throwing action where the under surface of the supraspinatus contacts the edge of the glenoid repeatedly, producing minor trauma each time. This leads to small tears and explains this process in athletes, especially those involved in throwing. Impingement can also occur between the lesser tuberosity, the biceps and supraspinatus tendons and the coracoid process. These three mechanisms of impingement may be at least partly responsible for some rotator cuff tears.

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.