Categorization of acromial shape: Interobserver variability with MR imaging and conventional radiography

OBJECTIVE. Our purpose was to determine interobserver variability in the interpretation of the shape of the acromion on sagittal oblique MR images and conventional radiographs. The shape of the acromion was defined according to a previously described classification scheme. MATERIALS AND METHODS. We reviewed 26 sets of sagittal oblique MR images and corresponding conventional Y- or outlet-view radiographs of the shoulder. The shape of the acromion was graded for each study independently by four reviewers. Interobserver agreement was measured by using the kappa statistic. Analysis of variance and the χ²-test were used for univariate analysis. RESULTS. The acromion was interpreted most often as being curved. The observers scored 9% of MR images and 28% of conventional radiographs as nondiagnostic (p < .001) (41% of transscapular Y views and 3% of supraspinatus outlet views were also considered nondiagnostic [p < .0001]). Kappa values were .23 for MR images and .43 for conventional radiographs. Variability in interpretation between techniques when controlled for observer was not statistically significant. CONCLUSION. Although sagittal oblique MR images were significantly more likely than conventional radiographs to be considered diagnostic by observers, interobserver agreement for MR examinations was poor. There was moderate agreement with conventional radiographs. This calls into question the usefulness of the previous system of interpretation and suggests that it might be more applicable with conventional radiographs than with MR images.