Purpose: The purpose of this study was to offer objective and standardized criteria for classifying acromial morphology.
Type of study: Blinded study.
Methods: Two of the authors independently classified 106 supraspinatus outlet radiographs (SOR), obtained from 100 skeletally mature patients with impingement syndrome of the shoulder, using both Bigliani's and Park's standardized criteria. The same authors classified the 106 SOR again using the same criteria 2 weeks later. In addition, 2 orthopaedic residents independently classified the same SOR on the basis of the Bigliani and Park criteria in the same manner.
Results: The rate of agreement was 66.0% (70 of 106) on the basis of Bigliani's criteria and 95.3% (101 of 106) on the basis of Park's criteria. The interobserver reliability coefficient of the 2 authors the first time was 0.448 (poor) and 0.914 (good to excellent). Their mean intraobserver reliability coefficient was 0.834 (good to excellent) and 0.87 (good to excellent) each. For the 2 orthopaedic residents, the rate of agreement was 58.5% (62 of 106) on the basis of Bigliani's criteria and 86.8% (92 of 106) on the basis of Park's criteria, and the interobserver reliability coefficient the first time was 0.28 (poor) and 0.77 (good to excellent) each. The mean intraobserver reliability coefficient was 0.738 (fair) and 0.844 (good to excellent) each.
Conclusions: In conclusion, regarding the classification for acromial morphology, Park's standardized criteria were far more objective, reliable, and reproducible rather than Bigliani's criteria through naked eye observations, especially for distinguishing the type II and type III acromion.