The Rotator Cuff is the name given to the four muscles that surround the shoulder joint. Each is a large muscle that arises from the Scapula (shoulder blade) and forms a broad flat tendon that runs across the shoulder joint to attach to the top of the Humerus (arm bone).
The most important tendons of the rotator cuff are the subscapularis tendon, which runs across the front of the shoulder joint, the supraspinatus tendon, which runs across the top of the shoulder joint, and the infraspinatus tendon, which runs across the back of the shoulder joint. Of these three tendons, the supraspinatus tendon is the one that is commonly problematic.
This arrangement of tendons is unique to the shoulder joint and provides the shoulder with unparalleled range of motion. The rotator cuff is unique to humans and, as with other unique structures in the body, it has specific problems related to it. The other structure that is specific to the shoulder joint is the acromion. The acromion is a projection of bone that extends out from the shoulder blade and expands across the top of the shoulder. The acromion forms the hard point to the shoulder. At the front of the shoulder it forms a joint with the clavicle called the acromioclavicular (or AC) joint.
As you raise your shoulder up, the supraspinatus tendon has to pass under the acromion. There is not a large amount of room for this to occur and when injuries affect the supraspinatus tendon it can swell and have trouble fitting underneath the acromion. When this occurs pain is experienced in the shoulder, this is due to the rotator cuff being pinched on the under surface of the acromion. This pain is termed impingement pain. Impingement is a common presenting symptom in patients with shoulder conditions.
There are several common problems that affect the rotator cuff. The rotator cuff can be torn. These rotator cuff tears can be due to acute trauma or they can form as a degenerative phenomenon associated with the normal ageing process. The tears may be either partial or full thickness. The rotator cuff tendons can become inflammed and this is called tendonitis. The tendonitis may be associated with calcium in the rotator cuff tendons, in which case the condition is then called calcific tendonitis. Long standing massive tears of the rotator cuff can lead to the development of arthritic change within the shoulder joint. This arthritic change to the shoulder joint has a characteristic pattern and appearance and is called Cuff Tear Arthropathy.