An independent inter- and intra-observer agreement assessment of the Eno classification of sacroiliac joint degeneration

Background Recently, a scoring system to grade sacroiliac joint (SIJ) degeneration using computed tomography (CT) scans was described. No independent evaluation has determined the inter- and intra-observer agreement using this scheme. Purpose To perform an independent inter- and intra-observer agreement assessment using the Eno classification and determining gas in the SIJ. Material and Methods We studied 64 patients aged >= 60 years who were evaluated with abdominal and pelvic computed tomography scans. Six physicians (three orthopaedic spine surgeons and three musculoskeletal radiologists) assessed axial images to grade SIJ degeneration into grade 0 (normal), grade 1 (mild degeneration), grade 2 (significant degeneration), and grade 3 (ankylosis). We also evaluated the agreement assessing the presence of gas in the SIJ. After a four-week interval, all cases were presented in a random sequence for repeat assessment. We determined the agreement using the kappa (kappa) or weighted kappa coefficient (w kappa). Results The inter-observer agreement was moderate (w kappa = 0.50 [0.44-0.56]), without differences among surgeons (w kappa = 0.53 [0.45-0.61]) and radiologists (w kappa = 0.49 [0.42-0.57]). The agreement evaluating the presence of gas was also moderate (kappa = 0.45 [0.35-0.54]), but radiologists obtained better agreement (kappa = 0.61 [0.48-0.72]) than surgeons (kappa = 0.29 [0.18-0.39]). The intra-observer agreement using the classification was substantial (w kappa = 0.79 [0.76-0.82]), without differences comparing surgeons (w kappa = 0.75 [0.70-0.80]) and radiologists (w kappa = 0.83 [0.79-0.87]). The intra-rater agreement evaluating gas was substantial (kappa = 0.77 [0.72-0.82]), without differences between surgeons (kappa = 0.71 [0.63-0.78]) and radiologists (kappa = 0.84 [0.78-0.90]). Conclusion Given the only moderate agreement obtained using the Eno classification, it does not seem adequate to be used in clinical practice or in research.