Does the use of ordered values of subregional change in cartilage thickness improve the detection of disease progression in longitudinal studies of osteoarthritis?

OBJECTIVE: To propose a novel strategy for more efficiently measuring changes in cartilage thickness in osteoarthritis (OA) using magnetic resonance imaging, and to hypothesize that determining the magnitude of thickness change independent of the anatomic location provides improved discrimination between healthy subjects and OA participants longitudinally.
METHODS: A total of 148 women were imaged; 90 were Kellgren/Lawrence (K/L) grade 0, 30 were K/L grade 2, and 28 were K/L grade 3. Magnetic resonance images (3T) were acquired at baseline and at 24 months. Changes in femorotibial cartilage thickness were determined in 5 tibial and 3 femoral medial and lateral subregions, respectively (conventional approach). The new strategy provided ordered values of subregional change in each compartment, ranked according to the direction and magnitude of change.
RESULTS: Using the new ordered values approach, the minimal P value for the differences in 2-year change in medial cartilage thickness of K/L grade 3 and K/L grade 0 participants was 0.001 (Wilcoxon test), with 4 ordered medial subregions differing significantly between both groups. With the conventional approach, only 1 medial subregion differed significantly between K/L grade 3 and K/L grade 0 (P = 0.037). Cartilage thickening was significantly greater in K/L grade 2 versus K/L grade 0 participants in 1 medial subregion using the conventional approach (P = 0.016), and in 2 medial subregions (minimal P = 0.007) using the ordered values approach.
CONCLUSION: The novel ordered values approach is more sensitive in detecting cartilage thinning in K/L grade 3 and cartilage thickening in K/L grade 2 versus K/L grade 0 participants. The new method may be particularly useful in the context of other comparisons, e.g., a group treated with a disease-modifying OA drug versus one treated with a placebo.