The role of the coracoacromial ligament in the impingement syndrome. A clinical, radiological and histological study.

Seventeen patients with a painful arc syndrome and tenderness over the coracoacromial ligament were selected to demonstrate the changes in the coracoacromial ligament in the impingement syndrome. Plain X-ray examination was normal and a preoperative subacromial bursogram demonstrated impingement in only three out of 17 patients. However, at operation the subacromial space under the coracoacromial ligament, which normally admits the tip of the little finger, appeared unusually tight and barely accessible in 15 out of 17 patients. Histological examination of the biopsied ligament showed degenerative changes but no increase in fibrous tissue. We conclude that in the absence of bony overgrowth the initial change is an increased volume of the soft tissues in the subacromial space. Consequently, the space is compromised by the swelling of its contents, which exert abnormal pressure on the overlying coracoacromial ligament and cause degenerative changes in the ligament. The symptoms of impingement appear because of the unyielding nature of the coracoacromial ligament. Subacromial bursography may not be a reliable test when the coracoacromial ligament is the site of impingement.