Reliability of radiographic evaluation for acromial morphology

Abstract

Objective: Bigliani's classification system of acromial morphology utilizing the standard outlet radiograph has become in accepted method for evaluating patients with rotator cuff disease. This study evaluates the interobserver and intraobserver reliability of Bigliani's classification system using observers at various levels of training.

Patients and design: Supraspinatus outlet view radiographs of 40 patients (aged 18-78 years) with shoulder pain were reviewed twice, 4 months apart, in a masked protocol by six reviewers, including two attending (fellowship-trained) shoulder surgeons, an attending musculoskeletal radiologist, an orthopedic surgery sports fellow, and two orthopedic residents (PGY-2 and PGY-5). The reviewers were given standard diagrams of the Bigliani classification system and were asked to classify each film as a type I, II, or III acromion. Interobserver reliability and intraobserver repeatability values were calculated using kappa statistic analysis (0-0.2 slight, 0.21-0.4 fair, 0.41-0.6 moderate, 0.61-0.8 substantial, and 0.8-1.0 excellent).

Results and conclusion: For each of the two readings, all six observers agreed only 18% of the time. Kappa values for pairwise comparison of interobserver reliability among the six observers ranged from 0.01 to 0.75 (mean 0.35), and intraobserver repeatability ranged from 0.26 (PGY-5 resident) to 0.80 (fellowship-trained surgeon), with a mean of 0.55. Intraobserver repeatability was not significantly different for the different levels of expertise. More definitive criteria are needed to distinguish and classify the acromion.