Comparison of MRI and radiographs in the evaluation of acromial morphology.

This study compared the accuracy of magnetic resonance imaging (MRI) grading of acromions using supraspinatus outlet view radiographs. Thirty-two consecutive patients (17 men and 15 women) treated for shoulder disorders were included in the study. Average patient age was 58.5 years. All patients had both a supraspinatus outlet radiograph and an MRI of the shoulder. Each acromion was graded by three independent observers at separate intervals by radiographs and MRI and the results were compared. The incidence of the three acromial types determined by radiographs was: type I=6%, type II=66%, and type III=28%. The incidence of the three acromial types determined by MRI was: type 1=6%, type II=69%, and type III=25%. There was essentially no difference in the incidence of acromial morphology between the two groups. Magnetic resonance imaging demonstrated the same shape as shown on the plain radiographs in 97% of the patients (95% confidence interval, 0.84-0.99). Magnetic resonance imaging is similar to supraspinatus outlet radiographs in determining acromial type. Acromial grading by MRI is a valid method of determining acromial morphology.