Osteoarthritis may not be a one-way-road of cartilage loss--comparison of spatial patterns of cartilage change between osteoarthritic and healthy knees.

Objective: To explore whether longitudinal change in cartilage thickness in femorotibial subregions of knees with radiographic osteoarthritis (ROA) differs from that in healthy knees.

Methods: 3T coronal magnetic resonance (MR) images were acquired in 152 women at seven clinical centers at baseline (BL) and 24 months. Knees from 75 women with signs of ROA in either anterior-posterior or Lyon schuss radiographs were compared with those from 77 asymptomatic healthy controls without ROA to identify knees showing greater change in cartilage thickness than expected based on observations in healthy knees. The femorotibial cartilage thickness was determined in BL and follow-up MR images across five tibial and three femoral subregions in the medial/lateral compartment, respectively.

Results: A substantial portion of knees with ROA were classified as having longitudinal cartilage thinning (28%) or thickening (20%) in at least one medial femorotibial subregion based on comparisons to longitudinal changes observed in healthy knees; only 5% showed both subregional thinning and thickening across (different) medial subregions at the same time. Whereas the estimated proportion of Kellgren Lawrence grade (KLG) 3 knees (n=28) with significant medial cartilage thinning (46%) was substantially greater than that with cartilage thickening (18%), the estimated percentages of KLG2 knees (n=30) with significant medial thinning (20%) and thickening (23%) were similar.

Conclusion: This exploratory study indicates that OA may not be a one-way-road of cartilage loss. Subregional analysis suggests that, compared with healthy knees, cartilage changes in ROA may occur in both directions. Medial femorotibial cartilage thickening was observed as frequently as cartilage thinning in KLG2 knees.