Three-Dimensional Topography of the Acromion: A Quantitative Study and Simulation of Surgical Alterations

The morphology of the inferior surface of the acromion has been implicated as an etiologic factor in rotator cuff disease. Bigliani et al [2] correlated different acromial shapes with the incidence of cuff tears, while Zuckerman et al [6] reported that acromions with decreased supraspinatus outlet areas are associated with full thickness cuff tears. Most surgical procedures have been designed to decompress subacromial arch pathology and reduce wear on the rotator cuff and bursa. To adequately decompress the subacromial space from impingement, Neer described the technique of anterior acromioplasty [4]. However, failures from this procedure have been reported and hence controversy exists regarding the amount and location of acromial bone that should be removed. Insufficient bone removal will result in residual impingement and a persistence of symptoms. On the other hand, too much bone may be removed, and this can damage the deltoid origin. Despite these clinical suggestions, little quantitative information exists on the curvature of the inferior acromion, and the precise amount of bone removal required to achieve a successful decompression. In this study, we report on the precise three-dimensional geometry of the inferior surface of the acromion based on optical stereophotogrammetry (SPG) data and differential geometry. We then utilize a computer based technique which simulates different acromioplasties, using experimentally determined glenohumeral kinematics as well as acromial and supraspinatus tendon surface geometry, to determine an optimal location and amount of bone removal.