Changes in acromial morphology with age.

It has not been determined whether acromial morphology is an innate anatomic characteristic or whether it represents a degenerative process with type I acromions changing to type III acromions over time. The purpose of this study was to determine the incidence of the three types of acromial morphology with respect to age. The acromial morphology of 272 patients (176 patients with no signs of mechanical impingement or rotator cuff disease and 96 patients with mechanical impingement) was determined by supraspinatus outlet radiographs. In the entire group of 272 patients there was a significant increase in the incidence of type III acromions and a decrease in the incidence of type I acromions in patients older than 50 years of age (p = 0.046). In 176 patients with no symptoms there was a very significant increase in the number of type III acromions in those patients older than 50 years of age (p = 0.004) with a corresponding decrease in the incidence of type I acromions. The incidence of the three acromial types also varied between patients with and without symptoms of mechanical impingement. The incidence of the three acromial types varies with respect to the age of the patient and whether he or she has symptoms of mechanical impingement. This raises the possibility that type I acromions may progress to type II acromions and then further change into type III acromions over time.