Using ordered values of subregional cartilage thickness change increases sensitivity in detecting risk factors for osteoarthritis progression

Objective: To examine whether ordered values of (sub)regional femorotibial cartilage thickness change are superior to region-based approaches in detecting risk factors for cartilage loss in osteoarthritis (OA). Methods: 58 women with knee OA had 3 Tesla MR images acquired at baseline and 24 months. Changes in cartilage thickness (Delta ThCtAB) were determined in eight medial femorotibial subregions. An ascending sort of individual Delta ThCtAB measurements was done to create "ordered values". Risk factors for cartilage loss considered were: age, BMI, anatomical knee axis (AAA), minimal (medial) joint space width (mJSW), and percent of medial tibial plateau covered by the meniscus (percent cover). All change metrics were tested for association with the risk factors using Kendall's tau and relative sensitivity of multiple tests of subregions and ordered values were compared with single metrics of change from plate and compartment summaries and the first ordered value. Results: The associations between subregion Delta ThCtAB and AAA (P = 0.0002), mJSW (P = 0.016), and age (P = 0.011) were significant, but only AAA (at alpha = 0.05) and age (at alpha = 0.1) remained significant after adjusting for multiple subregions. In contrast, cMFTC had P-values < 0.05 for AAA (P = 0.0001), mJSW (P = 0.016), and meniscus subluxation (0.04). The first ordered value had significant associations with AAA (P = 0.0004), mJSW (P = 0.003), meniscus subluxation (P = 0.02) and percent cover (P = 0.031) all of which were significant at alpha = 0.05 after adjusting for tests on multiple risk factors. Conclusion: Ordered values of Delta ThCtAB were more sensitive in detecting risk factors of cartilage loss than subregional Delta ThCtAB. Sensitivity was further enhanced by considering the minimum ordered value as a single test, thus not requiring adjustment for multiple tests. Using ordered values there was a significant association between Delta ThCtAB and baseline AAA, mJSW, meniscus subluxation and meniscus percent cover. This study provides an important step in validating ordered values of cartilage change. (C) 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.