To investigate whether serum concentrations of various inflammatory markers are associated with physical function and disease severity among older obese adults with knee osteoarthritis (OA).
Data are from baseline assessments in 274 patients with knee OA participating in an exercise and nutrition intervention study. The Western Ontario and McMaster University Osteoarthritis Index (WOMAC) was used to assess self-reported physical function, pain, and stiffness. The presence of disability was assessed, walking speed was calculated on the basis of the 6-minute walk test, and knee radiographs determined the radiographic severity of OA. Serum concentration of interleukin 6 (IL-6), C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-alpha), and the soluble receptors IL-6sR, IL-2sR, TNF-sR1 and TNF-sR2 were measured by ELISA.
In multivariate regression analyses adjusted for age, sex, race, body mass index, comorbid conditions, and use of nonsteroid antiinflammatory drugs, higher serum levels of TNF-sR1 and TNF-sR2 were significantly associated with lower scores on the WOMAC physical function, with more symptoms of pain and stiffness, and with more reported physical disability. In addition, higher serum levels of TNF-sR1 and TNF-sR2 were significantly associated with slower walking speed, and tended to be associated with worse radiographic scores. Higher serum levels of IL-6 tended to be associated with slower walking speed, but no significant associations were observed for CRP, IL-6sR, or IL-2sR.
Especially high levels of the soluble receptors of TNF-alpha were found to be associated with lower physical function, increased OA symptoms, and worse knee radiographic scores in older obese adults with knee OA.