The supraspinatus is one of the muscles that control movement of the shoulder and upper arm. It runs along the upper groove of the shoulder blade. The supraspinatus is one of the four muscles comprising the rotator cuff of the shoulder. Rotator cuff inflammation and injury are common causes of shoulder complaints. Testing the functions of the supraspinatus and the other muscles of the rotator cuff helps determine the source of the injury or malfunction. Many shoulder injuries and other problems involve the supraspinatus muscle and tendon.
Arm Abduction
The supraspinatus muscle works with the deltoid muscle to raise the arm outward from the side of the body. Your doctor can test this function of the supraspinatus muscles by having you raise your arms up to a 90-degree angle from your sides. She may push down against your upper arms while they are raised to test your supraspinatus strength. Pain or weakness with this test indicates a problem with the supraspinatus muscle or tendon.
External Rotation of the Arm
The supraspinatus muscle helps externally rotate the upper arm. External rotation is twisting the arm away from the body. If you put your arm in front of you with your elbow bent then move your hand (elbow still bent) out to the side, you have externally rotated your arm--with the help of your supraspinatus muscle. If pain occurs during this maneuver, there may be a problem with the supraspinatus muscle, such as a tear or tendinitis.
Stabilization of the Shoulder Joint
The shoulder is a ball and socket joint. The inner head of the upper arm bone (the humerus) has a smooth ball-like shape. It fits into a shallow cup-like socket (the glenoid fossa) at the outer edge of the shoulder blade. The supraspinatus stretches from the inner part of the shoulder blade (the side near the spine) to the head of the humerus, thereby holding the humerus in place within the glenoid fossa. A tear in the supraspinatus or the supraspinatus tendon typically causes shoulder pain and loosening of the shoulder joint. Most rotator cuff tears involve the supraspinatus. Although a rotator cuff tear may occur with a traumatic injury, most are caused by repetitive overuse that takes place over a period of years. Tennis, pitching, volleyball and rowing are some activities that may cause rotator cuff injuries over a prolonged period. People whose work requires them to use their arms above their heads are also prone to rotator cuff inflammation or injury.
