The rotator cuff is a sheet of tough fibrous tendon tissue connecting muscles from the shoulder blade (scapula) to the arm bone (humerus). It is formed by the tendons of four muscles: an elevator (supraspinatus), an internal rotator (subscapularis) and two external rotators (infraspinatus and teres minor). The main task of the rotator cuff is to keep the ball (humeral head) of the shoulder joint firmly in the socket (glenoid) so that powerful muscles around the shoulder can rotate and position the arm for functional movements. The rotator cuff lies deep underneath the deltoid, pectoralis major and trapezius muscles.

Although problems can arise in any of the tendons of the rotator cuff, the supraspinatus is the most commonly affected. The tendon has a relatively poor blood supply and passes through a narrow arch under the tip of the shoulder blade (acromion). Normally there is a lubricating membrane called the subacromial bursa which allows the tendon to glide smoothly under the acromion as the arm moves.

The rotator cuff can be damaged by traumatic injuries or repetitive overuse during work or sport activities. It may also be affected by degenerative processes due to aging, calcification or spur formation in the overlying acromion.

The supraspinatus tendon may become swollen and inflamed (tendonitis), it may rub against the overlying acromion (impingement). This may cause the bursa to also become inflamed (bursitis) and eventually the tendon may tear. Tears of the rotator cuff may be either partial-thickness or full-thickness, and may involve one, two or all the tendons. In the late stage of the disease, a special type of arthritis may develop, called cuff tear arthropathy. Not all patients with rotator cuff disease will progress through all these stages.

Pain from rotator cuff disease is usually felt around the shoulder, with radiation of pain down to the arm, often as far as the elbow. The pain is typically associated with particular actions such as lifting, reaching, throwing but may also be triggered by lying or sleeping on the affected shoulder. As the disease progresses, the arm may become weaker and may grind or catch. In severe cases it may not be possible to elevate the arm.

The diagnosis is usually made by a consultation and physical examination with your surgeon. Often imaging tests are used to determine the location, extent and nature of any bone spur or tendon tear. Diagnostics may include x-rays, ultrasound scans or magnetic resonance (MRI) scans.

Treatment depends on the stage of the disease. In the early stage of tendonitis, anti-inflammatory medication and simple painkillers may help, in addition to modifying daily activities to avoid excessive or repetitive lifting of the arm, where possible. 

If these measures do not help, injections of cortisone (an anti-inflammatory drug and one of the body's natural hormones) into the bursa may help relieve inflammation more directly. However, if there is a more mechanical element to the pain, then physiotherapy to rebalance the muscle strength around the shoulder and open up the space for the tendon, may also prove effective.

In some cases where there has been no response to these treatments, surgery may be indicated. The most common surgical procedure for impingement syndrome is arthroscopic acrominioplasty (also called subacromial decompression). In this ‘keyhole’ operation a small amount of bone is shaved from the underside of the acromion to make more room for the tendon to slide underneath. If a tear is present, it may be combined with trimming of the tendon (debridement) or repair of the tendon. In more complex cases repair may not be possible through a keyhole approach and an open incision may be required. If the tendons are not repairable, then sometimes a debridement procedure can provide good pain relief, although other options include using other tendons to replace the torn tendon, or a special type of joint replacement.