The Knee Osteoarthritis Grading System (KOGS) for arthroplasty

Background The aim of this study is to validate the Knee Osteoarthritis Grading system (KOGS) of progressive osteoarthritic (OA) degeneration for the Tri-compartmental knee. This system defines the site and severity of OA to determine a specific knee replacement. Methods The radiographic sequence for KOGS includes standing coronal (antero-posterior), lateral, 30° skyline patella, 15° and 45° Rosenberg and stress views in 20° of flexion. Cohen’s Kappa and related agreement statistical methods were used to assess the level of concordance of the seven evaluators between A and B cohorts for each evaluator and also against the actual arthroplasty used. Sensitivity and specificity was also assessed for the KOGS in identifying true partial knee replacements (PKR) and total knee replacements (TKR) as decided from the cohort A evaluations. Results From a cohort of 330 patients who were included in the study, 71 (22.5%) underwent a TKR procedure, 258 (78.2%) a PKR and 1 (0.3%) was neither a TKR nor PKR. KOGS was able to identify true PKRs (sensitivity) in the range of 92.2% to 98.5% across all the different evaluators. The KOGS method was able to identify a PKR or a TKR with an accuracy ranging from 92% to 98.8% across all different evaluators. The surgical results after 20 months are at least comparable with the expected average in the academic literature. Conclusion The KOGS classification provides a reliable and accurate tool to assess suitability of an individual patient for undergoing partial or total knee replacement