Background/Purpose: Guidelines recommend 150 minutes a week in moderate-intensity physical activity (PA) to improve health in knee osteoarthritis (KOA). Despite that, individuals with KOA do not engage in the recommended amount of PA and physicians refrain from prescribing the PA recommendations due to concerns that large amounts of PA may worsen KOA. Only few studies have investigated the effects of PA on cartilage health and this issue needs further clarification. Serum biomarkers have been validated to identify cartilage degradation. The aim of this study was to determine the associations between changes in PA and changes in concentration of a biomarker of cartilage degradation.

Methods: This is a secondary analysis from a randomized trial that compared the effects of an intensive exercise program (comprehensive behavioral intervention [CBI]) to a less intensive program (standard of care exercise [SCE]) on physical function and PA after total knee replacement. Subjects with available serum and PA measured at baseline and 3-month follow-up were included. Blood samples were collected in the morning after a 12-hour fasting. Samples were frozen for future analysis. Cartilage degradation was assessed by analyzing the concentration of cartilage oligomeric matrix protein (COMP) using standardized enzyme-linked immunosorbent assay (ELISA). Daily time in moderate PA was assessed using the Sensewear Armband activity monitor worn for 7 days. Pearson correlation coefficients were used to determine associations between changes in PA and changes in COMP.

Results: Data on 33 subjects were available and analyzed. Subjects were 67±6 years old, 67% female and 92% white, with BMI of 30±4 kg/m². They had mild pain on surgical (2±2) and non-surgical (3±3) knees, and moderate functional limitations (17.9±9.5) measured by the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) physical function subscale. Demographics between CBI (n=14) and SCE (n=19) were similar at baseline. Forty three percent of the subjects in the CBI arm improved PA above the standard error of measurement (11 minutes of moderate PA per day) and experienced an increase in COMP (145±418 ng/ml), while only 26% of the subjects in the SCE improved PA and showed a slight decrease in COMP (-49±725 ng/ml), suggesting that perhaps more PA may increase cartilage degradation. However, upon further assessment of the direct associations between changes in PA and COMP, we observed negative associations between changes in PA and changes in COMP in the CBI (r=-.65; p=.012) and in the SCE (r=-.45; p=.056), indicating that individuals who increased PA actually had a decrease in COMP concentration.

Conclusion: These preliminary results indicate that moderate PA does not seem to contribute to cartilage degradation in individuals with KOA and strengthen to body of evidence in this area. In this study, individuals with KOA appear to engage in activities of low impact such as brisk walk, which may not be detrimental to the knee joint. A larger study is warranted to validate our findings. Participation in moderate PA could be encouraged by physicians since its benefits outweigh the harms.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effect-of-changes-in-physical-activity-on-cartilage-degradation-in-knee-osteoarthritis/