Validity and responsiveness of a new measure of knee osteophytes for osteoarthritis studies: data from the osteoarthritis initiative

Purpose: To validate a novel quantitative MRI method to measure osteophyte volume. Methods: 90 subjects were selected from the Progression Cohort of the Osteoarthritis Initiative (OAI) at baseline and 48 months, and analyzed using a semi-automated software tool. Marginal osteophyte volume was calculated for four compartments of the central weight-bearing region of the tibiofemoral joint. Standardized response mean (SRM) for change in volume was used to quantify responsiveness. Concurrent validity was assessed via a comparison with MRI Osteoarthritis Knee Score (MOAKS) using Kruskal-Wallis analysis and Spearman's correlation coefficient. Intra-and inter-reader reliability was assessed on a subset of 20 knees using intra-class correlation coefficients (ICCs) and the root mean square standard deviation (RMSSD). Results: The average change in osteophyte volume (DV) was 196 mm(3) (SD = 272 mm(3)), and the baseline to 48-month SRM was 0.72. An increase in osteophyte volume was observed for 84% (76/90) of the subjects. Kruskal-Wallis analysis across the four MOAKS osteophyte categories was significant for medial and lateral compartments of both the tibia and femur (P < 0.001 for all). The intra-reader ICC was 0.98, and RMSSD was 82 mm(3), while inter-reader ICC was 0.97 and RMSSD was 91 mm(3). A statistically significant positive correlation was observed between osteophyte volume and several MOAKS cartilage and BML scores. The reader time was approximately 10 min per knee. Conclusions: The method is responsive, efficient, and precise, making it practical for use in large cohort studies and observational research. (C) 2015 Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International.