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 (κ) or weighted kappa coefficient (wκ). Results The inter-observer agreement was moderate (wκ = 0.50 [0.44–0.56]), without differences among surgeons (wκ = 0.53 [0.45–0.61]) and radiologists (wκ = 0.49 [0.42–0.57]). The agreement evaluating the presence of gas was also moderate (κ = 0.45 [0.35–0.54]), but radiologists obtained better agreement (κ = 0.61 [0.48–0.72]) than surgeons (κ = 0.29 [0.18–0.39]). The intra-observer agreement using the classification was substantial (wκ = 0.79 [0.76–0.82]), without differences comparing surgeons (wκ = 0.75 [0.70–0.80]) and radiologists (wκ = 0.83 [0.79–0.87]). The intra-rater agreement evaluating gas was substantial (κ = 0.77 [0.72–0.82]), without differences between surgeons (κ = 0.71 [0.63–0.78]) and radiologists (κ = 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.