The os acromiale: another cause of impingement.

Impingement of the shoulder is a relatively common clinical entity. The os acromiale anomaly is an uncommon one (1-8%) but can be an important cause of the impingement syndrome. The most common place of nonfusion is between the meso- and meta-acromion. The key to diagnosis is a history and physical examination compatible with the impingement syndrome and appropriate radiologic studies (i.e., an axillary view or profile view or computed tomographic scan if necessary). After diagnosis, the initial treatment is conservative with rest, ice, nonsteroidal anti-inflammatory drugs (NSAIDs), injections of corticosteroids in the subacromial space, and most importantly, an appropriate rehabilitation program. If unsuccessful, treatment should be planned based on the size of the unfused fragments. Small fragments (< 4 cm) may be removed by either arthroscopic or open means. Larger fragments may require an attempt at bone grafting and fixation since their removal may result in loss of strength of the deltoid.