In most of the body, bone is surrounded by muscle. The shoulder is unique because several muscles and tendons of the shoulder are surrounded by the upper arm bone and shoulder blade. When the muscles and tendons of the rotator cuff and the bursa (an overlaying sac that lubricates the joint) are injured or aggravated, they can swell and lead to discomfort caused by the pressure exerted by the surrounding bone on the tissue. The compressive forces of the bone on the inflamed muscles and tendons can decrease the blood flow and cause the tissue to breakdown and result in weakness in the shoulder.
Other symptoms of shoulder impingement include anterolateral pain (on the front and to the side) of the shoulder and upper arm that is dull and becomes intensified when laying on the affected shoulder at night. The symptoms are very similar to those of a rotator cuff tear and should be closely monitored as shoulder impingement can lead to a partial or full rotator cuff tear as well as a labrum tear. Three of the most common types of impingement are subacromial, internal, and subcoracoid impingement. Subacromial impingement occurs when the rotator cuff impinges on the undersurface of the acromion (extended process of the shoulder blade at the top of the shoulder) and the coracoclavicular ligament that connects the acromion to the rest of the shoulder. Internal impingement occurs when the rotator cuff comes into contact with the labrum and causes instability and a decrease in range of internal rotation. Subcoracoid impingement occurs when the rotator cuff impinges on the coracoid (small, bony extension of the shoulder blade) and causes pain while reaching forward and inside.
Anti-inflammatory drugs (like ibuprofen) and therapy are used to strengthen, stabilize, and reduce inflammation of the muscles in the shoulder. Corticosteroid injections can also be used to treat patients with severe pain. Once the pain has resolved and full strength and motion is recovered, athletes can return back to full activity.