A practical MRI grading system for osteoarthritis of the knee: association with Kellgren-Lawrence radiographic scores.

PURPOSE To propose a reproducible and constant MR grading system for osteoarthritis of the knee joint that provides high interobserver and intraoberver agreement and that does not require complicated calculation procedures. MATERIALS AND METHODS This retrospective study sample included 44 men and 65 women who underwent both MRI and plain radiography of the knee at our institution. All patients were older than 50 years of age (mean 57.7) and had clinically suspected osteoarthritis of the knee. The standard of 4 grades on the MR grade scale was based mainly on cartilage injury and additional findings. Kellgren-Lawrence grades were assessed for the same patient group. The relationship between the results was determined. Statistical analyses were performed including kappa statistics, categorical regression analysis and nonparametric correlation analysis. RESULTS The interobserver and intraoberver agreements between the two readers in the grading of osteoarthritis were found to be almost perfect. Interobserver and intraobserver agreements were slightly lower for the MR grading system than for the Kellgren-Lawrence grading scale. The correlation between the MR grade and Kellgren-Lawrence grade was very high and did not differ with patient age. The MR grades were highly correlated with the Kellgren-Lawrence grades and showed excellent interobserver and intraobserver agreements. CONCLUSION This new MR grading system for osteoarthritis of the knee joint is reproducible and may be helpful for the grading of osteoarthritis of the knee without requiring reference to plain radiography.