Are Knee OA Stats Reliable? Maybe Not

When you read about the prevalence of knee osteoarthritis (OA) in the literature, can you trust it?

Researchers from Australia and Norway set out to dig into that question. Their work, “A quantitative metric for knee osteoarthritis: reference values of joint space loss,” appears in the May 26, 2018 edition of Osteoarthritis and Cartilage.

Chuck Ratzlaff, Ph.D., P.T., research assistant professor in the Department of Medicine at the University of Arizona College of Medicine and Arthritis Center and study co-author told OTW, “In osteoarthritis research, entry into trials and cohort studies is usually made on the base of 1 of 2 ordinal scales (Kellgren-Lawrence or Osteoarthritis Research Society International Joint Space Narrowing [OARSI JSN]) where readers look at X-rays and give grades 0-4 or 0-3, respectively.”

“None of these is tied to the actual joint space width quantitatively…there are gray areas between grades, and a knee can progress quite significantly in some cases without changing grade.”

“Since joint space width on X-ray is the only imaging biomarker currently recommended by the FDA as a structural endpoint in clinical trials of knee OA, it makes it difficult in trials at times to see if an intervention has actually made a difference.”

“For researchers, it is also difficult to know what a given grade actually represents—the two classification scales are considered to be similar in how they classify cases (or non-cases) of OA, yet as we show here, they are not.”

“Our aim was to provide a reference ‘measuring stick’ to quantify annual change in joint space width, anchored to transitions in the conventionally reported KL and OARSI JSN grades. A secondary aim was to lay the groundwork for investigating the merits of a transition to a more reliable, accurate quantitative method of measuring OA on X-ray—the fixed joint space width method.”

“The most important result was that there is variation and discrepancy as to how OA radiographic definition and progression are being used in OA research.

“A quantitative, reliable inexpensive software-assisted method of measuring joint space width is available and could improve definitions and is more sensitive to measuring change (progression of disease). The choice of radiographic scale to define OA and outcome in research (especially trials), should be made thoughtfully, considering the population and phenotypes of OA and intervention under investigation.”

“The problems with ordinal qualitative scales like Kellgren-Lawrence and OARSI could make it difficult to demonstrate change in trials and cohort studies, that they do not quantitatively measure joint space width, and that there is there is considerable discrepancy between, and even within, these classification systems for the definition and progression of knee OA.”

“Using a direct responsive quantitative measure of joint space width, it is possible to more fully characterize the natural history of joint space loss and better evaluate preventive and/or therapeutic interventions in randomized controlled trials and observational studies of exposures with pathological processes that produce distinct phenotypes of knee OA.”