Predictors of pain in osteoarthritis ‘vary with disease severity’
medwireNews: An evaluation of inflammation and lower-limb alignment in patients with knee osteoarthritis has found that the factors that predict pain vary according to the severity of disease.
The researchers found that higher serum levels of interleukin (IL)-6 was associated with pain in early-stage disease while varus alignment of the joint was associated with pain in advanced-stage disease.
Muneaki Ishijima (Juntendo University Graduate School of Medicine, Tokyo, Japan) and team recruited 160 women (mean age 70.5 years) with knee osteoarthritis. Using Kellgren-Lawrence grading of radiographs, 67 were classified as having early-stage disease (grade 2), while 93 had advanced disease (grade 3/4).
Pain was evaluated using a visual analog scale (0-100) and with the Japanese Knee Osteoarthritis Measure (JKOM; 0-32). Mean scores were 52.9 with the former and 14.8 with the latter.
A comparison of patients with early versus advanced disease revealed no differences in pain scores or in serum levels of IL-6 or high sensitivity C-reactive protein (CRP). However, the internal angle between the femoral and tibial axes, designated the anatomic alignment angle (AAA), was significantly less in those with advanced versus early disease (178.8° vs 182.9°).
In multiple linear regression analysis, serum IL-6 levels and AAA were both significantly associated with pain severity as assessed on the visual analog scale.
Further analyses according to disease severity found that serum IL-6 predicted pain severity only in patients with early-stage osteoarthritis, while the AAA was associated with pain scores only in those with advanced-stage osteoarthritis.
The same pattern emerged whether pain severity was indicated by the visual analog scale or with the JKOM.
Writing in Osteoarthritis and Cartilage, Ishijima et al say that their study reveals “for the first time” that the factors associated with pain severity in patients with knee osteoarthritis vary with the radiographic disease severity.
IL-6 levels are mainly indicative of synovitis, they note, which is seen from the earliest stages of osteoarthritis. Meanwhile, mechanical loading across the knee joint, as estimated by AAA, declines as the disease progresses.
“[T]he results of the present study suggest that the pain in the advanced-stage of knee osteoarthritis is associated with the mechanical loading across the knee joint, which is associated with a deterioration of the lower limb alignment,” the researchers speculate.
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By Joanna Lyford, Senior medwireNews Reporter