LIÈGE, Belgium—Measurement of joint space width (JSW) on standard x-rays is still the regulatory gold standard for assessing potential disease-modifying drugs in osteoarthritis (OA), but new research suggests that magnetic resonance imaging (MRI) might be a reasonable alternative. Olivier Bruyere, PhD, with the department of public health, epidemiology, and health economics at the University of Liège, in Belgium, reports similar results from both MRI and standard x-rays in monitoring progression of knee OA over time. He also points out that MRI might be particularly useful for monitoring early changes because it provides a more precise image of the three-dimensional structure of the knee joint.

"Our study is the first one to show a significant association between MRI and x-ray in the assessment of knee OA progression." —Olivier Bruyere, PhD.
"[O]ur results reemphasize the fact that JSW assessed on standard x-ray is only an indirect assessment of cartilage loss and that more data on MRI should be provided before accepting it as primary endpoint in clinical phase III trials of disease-modifying OA drugs," Dr. Bruyere writes in OsteoArthritis and Cartilage.1 His longitudinal comparison of MRI and standard x-rays showed a significant association between the two modalities in the assessment of knee OA progression.

X-rays assess JSW but cannot detect early structural damage or monitor OA progression in daily practice, the researchers point out. MRI can assess normal articular cartilage and lesions. It can also capture other important morphologic information and is a valuable tool for whole-organ imaging.

"Our study is the first one to show a significant association between MRI and x-ray in the assessment of knee OA progression," Dr. Bruyere told CIAOMed. The results "are very important for the research [including] the design of the randomized controlled trials and [the use of] MRI as endpoint in trials."

Researchers followed OA patients for 1 year

In the new study, researchers examined the relationship between x-ray and MRI findings in 62 patients with knee OA. They assessed volume and thickness of cartilage of the medial tibia, the lateral tibia, and the femur by MRI at baseline and after 1 year. Patients received a global score from the multifeature whole-organ MRI scoring system (WORMS) at baseline and after 1 year. This score combined individual scores for articular cartilage, osteophytes, bone marrow abnormality, subchondral cysts, and bone attrition in 14 locations. It also incorporated scores for the medial and lateral menisci, anterior and posterior cruciate ligaments, medial and lateral collateral ligaments, and synovial distension. The researchers assessed lateral and medial femorotibial joint space width measurements, performed by digital image analysis, from fixed-flexion, posteroanterior knee x-rays.

At 1 year, MRI showed changes of 6.7% in medial femorotibial joint space width, .4% in medial cartilage volume, and 11.3% in medial cartilage thickness. Medial femorotibial joint space narrowing after 1 year as assessed by x-ray was significantly correlated with the loss of medial tibial cartilage volume (P = .046) and medial tibial cartilage thickness (P = .025). There was also significant correlation between the progression of the WORMS score and radiographic medial joint space narrowing over 1 year (P = .006).

Cartilage volume and thickness changes over 1 year did not reach statistical significance in this study, which the investigators attribute in part to the small (256 x 92) matrix size, chosen in an effort to save time (they average about 60 minutes) and prevent patient discomfort. "To increase matrix size...would provide a more accurate measurement of cartilage loss and could then modify our results," the authors suggest.

"We have also shown an absence of association between WORMS changes and lateral JSW changes. This reemphasizes the importance of medial, not lateral, JSW in the progression of knee OA," Dr. Bruyere adds.

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Reference

1. Bruyere O, Genant H, Kothari M, et al. Longitudinal study of magnetic resonance imaging and standard x-rays to assess disease progression in osteoarthritis. OsteoArthritis Cartilage. 2007;15:98-103.