When the rotator cuff impinges (gets pinched between the shoulder blade and the ball part of the shoulder joint) it causes pain. This is caused by the rotator cuff not functioning properly.
The rotator cuff is a group of muscles around the shoulder joint which keeps the ball in the centre of the socket and rotates the shoulder joint.
There are four muscles forming the rotator cuff: the supraspinatus, infraspinatus, subscapualris and teres minor.
Each of these muscles have a different function in the shoulder joint. The act like the strings of a marionette to keep the ball in the socket and to turn it. If one of these strings snap, the marionette will lose its balance.
The same happens with the rotator cuff. If one of the tendons tears, the balance of the shoulder joint is lost and the ball is no longer held in the centre of the socket.
The specific tendon which got torn can not rotate the shoulder anymore and a certain movement is weaker or completely impossible and painful.
Apart from tears, rotator cuff function can also be affected by calcific tendonitis, rotator cuff strain and rotator cuff tendonopathy.
Conditions which can indirectly affect the rotator cuff include SLAP tears and glenohumeral instability.
The acromion, the bony part of the shoulder blade which forms the roof of the shoulder joint, can have an abnormal shape. This can also be a cause of impingement.
Dr. Louis Bigliani, an internationally renowned expert in the treament of shoulder disorders, described three types of curves which are also believed to cause impingement.
In older patients a bony spur can develop at the edge of the acromion. When the arm is raised, this spur then press on the rotator cuff muscles and may cause a tear.
The treatment of this impingement involves anti inflammatory medication, physiotherapy and injections with cortisone.
When all of the above have failed, or if a rotator cuff tear has developed, surgery will probably be required.
An arthroscopic (keyhole surgery) subacromial decompression will be done and the bursa or gel pad underneath the acromion will be removed, the tendons will be repaired or cleaned up and the bony spur will be removed.