OS ACROMIALE IN A BASEBALL CATCHER

Throwing injuries of the shoulder can result from an acute traumatic e vent or chronic overuse. Shoulder impingement has multiple etiologies; the most common being rotator cuff weakness/overuse and resultant gle nohumeral instability. However, an uncommon cause of shoulder impingem ent syndrome is that of a nonfused os acromiale. There are three cente rs of ossification in the acromion which are usually completely fused by 18 yr of age. The most common site of nonunion is between the meso- acromion and meta-acromion. Os acromiale is reported at a rate of 14/1 000 (1.4%) and is bilateral in approximately 62% of cases. The classic diagnosis is radiographically defined with both AP and axillary later al views, and a contralateral comparison view may be helpful. Computer ized axial tomography also aids in the diagnosis. Most os acromiale ar e asymptomatic. However, if recalcitrant impingement syndrome and/or r otator cuff tears are found in association with os acromiale, then sur gical fusion or resection of the ossicle is recommended.