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A supraspinatus injury describes any damage to the supraspinatus muscle, the most frequently injured of the four muscles of the rotator cuff. The supraspinatus is the most superior of these muscles, supporting the joint from its position on top of the shoulder. All four muscles are responsible for stabilizing the glenohumeral or shoulder joint, supporting it through 360 degrees of movement, and maintaining the position of the head of the humerus bone in the glenoid fossa of the scapula. In addition, the supraspinatus initiates abduction of the arm, or lifting it away from the body out to one side. Common types of supraspinatus injury include tendonitis of its attaching tendon in the shoulder, muscle tears, and impingement of the tendon against the acromion process of the shoulder blade.
This muscle originates on the supraspinatus fossa, a cavity on the top of the posterior surface of the scapula on the side nearest the spine. Running almost horizontally out of the fossa, the supraspinatus converges to form a tendon that passes just anteriorly and slightly superiorly to the acromion of the scapula. A club-shaped bony prominence that arises from the scapular ridge on the shoulder blade’s posterior surface, the acromion can be felt at the peak of the shoulder where the collar bone meets the scapula. The tendon of the supraspinatus, after passing just in front of the acromion, inserts on the top of the humerus bone just anterior to the glenohumeral joint on the greater tubercle.
This tendon’s location adjacent to the acromion leaves it susceptible to a condition known as impingement syndome. Impingement occurs when the space through which the tendon passes narrows, putting pressure and friction on the tissue. Supraspinatus impingement is a common type of supraspinatus injury, as muscle imbalances in many individuals, particularly weight-lifters and athletes, cause the shoulders to roll forward and internally rotate. This postural imbalance narrows the space between the acromion and the humerus and pinches the supraspinatus tendon, an imbalance that can be treated with corrective exercise. Similarly, growths on the acromion like bone spurs can result in supraspinatus impingement, which presents with pain, shoulder weakness, and a restricted range of motion at the shoulder joint.
Supraspinatus impingement is often accompanied by tendonitis, a type of supraspinatus injury in which the tendon becomes inflamed and irritated from rubbing against the adjacent bone. Tendonitis is typically brought on by frequent, repetitive movements, and supraspinatus tendonitis is often seen in athletes whose sports require an overhead throwing motion, as in baseball pitchers. This injury is accompanied by pain, stiffness, tenderness, and limited range of motion at the afflicted joint, and it is usually treated with ice, anti-inflammatory pain medicine, and avoidance of the movement patterns that brought it on.
A third category of supraspinatus injury is a muscle tear. Though an abrupt trauma can cause this injury, it is more likely to be caused by the same repetitive movements that weakened the tendon and brought on tendonitis. In other words, an untreated case of supraspinatus tendonitis can result in further breakdown of the tendon that results in a tear.
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