The acromion: morphologic condition and age-related changes. A study of 420 scapulas.

Two hundred ten specimens (420 scapulas) from the Hamann-Todd Osteological Collection at the Cleveland Museum of Natural History were evaluated to determine the influence of age on acromial morphologic condition. Equal numbers of specimens from female and male and black and white subjects were evaluated. The length, width, and anterior thickness of the acromion and the acromial facet of the acromioclavicular joint were measured with digital calipers, examined visually, and evaluated radiographically. Distribution of acromial morphologic types was type I, (flat) 32%, type II (curved), 42%, and type III (hooked), 26%. Analysis of the data revealed no consistent, statistically significant impact of age on morphologic condition. The incidence of os acromiale was 8% (17 of 210), with 7 (41%) of 17 specimens having bilateral involvement. Mean acromial dimensions in men were length = 48.5 mm, width = 19.5 mm, and anterior thickness = 7.7 mm. Mean dimensions in women were length = 40.6 mm, width = 18.4 mm, and thickness = 6.7 mm. Multiple regression analysis revealed no significant changes in any dimension with increasing age. Observation of the acromial facet of the acromioclavicular joint revealed 49% were medially inclined, 48% were vertically inclined, and only 3% were laterally inclined in relationship to the sagittal plane. A statistically significant age-related increase in degenerative changes was noted. Anterior acromial spur formation as determined by visual inspection of the acromion was observed in 7% of specimens from patients younger than 50 years compared with 30% of specimens from patients older than 50 years (p < 0.05). Spur formation on the anterior acromion is an age-dependent process. Acromial morphologic condition as evaluated by outlet radiographs is independent of age and appears to be a primary anatomic characteristic. The variations seen in acromial morphologic condition are not acquired from age-related changes and spur formation and thus contribute to impingement disease independent of and in addition to age-related processes.