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Supraspinatus impingement is a condition that occurs when the supraspinatus, one of four muscles of the rotator cuff, becomes pinched against the acromion process, a projection of the scapula bone, or shoulder blade. Situated on top of the shoulder, the supraspinatus muscle runs laterally across the shoulder, ending in a tendon that crosses beneath the acromion before extending over the top of the shoulder joint. As this muscle is an abductor of the arm, meaning that it helps to raise the arm laterally, its tendon can become inflamed as a consequence of repetitive abduction of the shoulder joint as the tendon rubs against the acromion process. The resulting supraspinatus impingement can worsen if not treated, as the inflamed tendon often increases in size, creating more and more friction against the bone.
Originating on a facet of the upper posterior scapula known as the supraspinatus fossa, this rotator cuff muscle crosses slightly behind the top of the shoulder. It can be felt just behind the shoulder between the acromion, which forms a ridge running nearly horizontally across the top of the shoulder blade, and the coracoid process, another projection of the scapula felt on the top of and slightly anterior to the shoulder joint. Ending in a tendon that runs under the outermost aspect of the acromion, a lateral projection of bone shaped like a club, it crosses the head of the humerus bone at the ball-and-socket joint of the shoulder. It inserts shortly thereafter on the greater tubercle of the humerus, the outermost surface of the head of the humerus.
During motions requiring repeated abduction of the shoulder joint, such as performing the butterfly stroke while swimming or raising the arm sideways to swing a tennis racket, the supraspinatus muscle encounters friction where its upper surface meets the underside of the acromion. This is especially true when, as it’s abducting, the arm is held slightly forward and the shoulder internally rotated. If this motion is performed frequently and repetitively, supraspinatus impingement can develop.
Supraspinatus impingement is characterized by acute pain and inflammation felt at the top of the shoulder, particularly on performing the movements described. It may occasionally be accompanied by swelling and bruising at the injury site. When in its early stages, typically as seen in individuals under 25, it may be treated with rest and anti-inflammatory treatments like ice and NSAID pain relievers. More advanced supraspinatus impingement as seen in older patients may require surgery to correct.