Radiographic‐based measurement of tibiofemoral joint space width and magnetic resonance imaging derived articular cartilage thickness are not related in subjects at risk for post traumatic arthritis of the knee

Joint space width (JSW), measured as the distance between the femoral and tibial subchondral bone margins on two‐dimensional weight‐bearing radiographs, is the initial imaging modality used in clinical settings to diagnose and evaluate the progression of osteoarthritis (OA). While, JSW is the only structural outcome approved by the FDA for studying the treatment of this disease in phase III clinical trials, recent reports suggest that magnetic resonance imaging (MRI)‐based measurements of OA changes are superior due to increased sensitivity and specificity to the structural changes associated with progression of this disease. In the current study, we examined the relationship between radiographic JSW and MRI‐derived articular cartilage thickness in subjects 4 years post anterior cruciate ligament reconstruction (ACLR) who were at increased risk for the onset and early progression of post‐traumatic OA, and in uninjured subjects with normal knees (Control). In both ACLR and Control groups, there were large measurement biases, wide limits of agreement, and poor correlation between the two measurement techniques. Clinical significance: The finding from this study suggest that the two methods of examining changes associated with the onset and early progression of PTOA either characterize different structures about the knee and should not be used interchangeably, or two‐dimensional JSW measurements are not sensitive to small changes in articular cartilage thickness.