Characterization of acromial concavity. An in vitro computer analysis.

Variations in the shape and orientation of the anterior acromion have been implicated as predisposing factors for the development of rotator cuff problems. We determined and analyzed by computer digitization the anterior and posterior acromial slopes for 141 cadaver shoulders (whose rotator cuff status had been previously assessed). No significant differences in either the anterior or posterior angle were found between the intact and rotator cuff tear groups. Frequency histograms of both angles demonstrated continuous, normal distributions. The individual acromions were consistently asymmetric in that the anterior slope was larger than the posterior slope. However, the anterior slope distribution did not reveal groupings indicative of the specific acromial types previously reported. These results suggest that acromial classification into flat, curved, and hooked types does not accurately describe the actual anatomical findings.