The most common manifestation of periarthritis of the shoulder is the chronic impingement syndrome, which represents an "entrapment situation". When the arm is raised, the supraspinatus tendon that forms part of the rotator cuff, comes into contact with the coracoacromial arch. The complains can often be improved by conservative treatment. If, however, the problem persists--in about 10 to 20% of the cases--surgical decompression of the coracoacromial arch by resecting the coracoacromial ligament and the subacromial bursa is indicated. This limited intervention carries only a low risk and, as studies have shown, has such a high rate of success that, in the individual case, the indication for surgery can be established earlier than has so far been assumed.