Shoulder impingement is a common cause of shoulder pain. Usually, a bone spur on the undersurface of the acromion (a portion of the shoulder blade) develops slowly over time for unknown reasons in some individuals. If big enough, this spur can pinch or "impinge" on the underlying soft tissues, especially the subacromial bursa and the rotator cuff tendons. Raising the arm above shoulder level can bring these structures against the undersurface of the acromion to where a bone spur can rub on them ("impinge") and cause inflammation such as bursitis and tendinitis. Eventually, this repetitive impingement can lead to a rotator cuff tear (see section on rotator cuff tears).
If no rotator cuff tear exists, the symptoms of impingement syndrome can usually be controlled without surgical intervention. Exercises, activity modification, and time can often lead to resolution of the impingement syndrome. Sometimes, an injection of cortisone-type medication may be required for resolution.
If the spur is very large, or if conservative treatment does not work, surgical excision of the bone spur may be required. This can be done arthroscopically on an outpatient basis.