Background/Purpose: Knee pain is the presenting symptom in knee osteoarthritis (OA), but the impact of knee pain burden in OA has been understudied. We examined the effect of knee pain on objectively measured moderate/vigorous physical activity among community-dwelling adults with or at high risk for knee OA.

Methods: Physical activity was objectively measured by accelerometer on participants with or at risk for radiographic knee OA in the Osteoarthritis Initiative (OAI) at the 48-month clinic visit, using ActiGraph GT1M uniaxial accelerometers (ActiGraph; Pensacola, FL), and calibrated using activity definitions published by Trioano. Participants were instructed to wear the sensor for seven consecutive days for at least 10 hours per day. Analysis was restricted to those participants with four or more valid days of wear.  Knee pain burden was assessed using the Higher Western Ontario McMaster Osteoarthritis Index (WOMAC) knee pain score, and categorized as no pain, and approximate quartiles of the non-zero pain score distribution.  Analysis of covariance was used to estimate sex-specific means (± standard error) for time spent engaging in moderate/vigorous physical activity across the five categories of WOMAC pain, with adjustment for age, race, and body mass index (BMI).  We considered the effect of WOMAC pain categories on meeting the 2008 Physical Activity Guidelines for Americans, issued by the U.S. Department of Health and Human Services (DHHS) using logistic regression to estimate adjusted odds ratios (aOR) and 95% confidence intervals (95%CI), adjusted for age, sex, race, and BMI.

Results: We included 1,907 participants, 55% female, with a mean age of 65.1(±9.1) years.  As shown in Table 1, increasing knee pain burden was associated with decreasing mean average daily bout of moderate/vigorous activity among both men (p=0.0480) and women (p=<0.0001), and decreasing mean average daily minutes of moderate/vigorous activity among both men (p=0.0094) and women (p<0.0001), after adjustment for age, race, and BMI.

Participants with WOMAC pain scores of 2 to 3 had significantly lower odds of meeting the DHHS guidelines (aOR=0.63; 95%CI: 0.43, 0.93), as did participants with scores of 4 to 6 (aOR=0.61; 95%CI: 0.39, 0.96), and those with scores > 6 (aOR=0.32; 95%CI: 0.16, 0.63), as compared to participants reporting no pain. When considering the DHHS guidelines for people with arthritis, point estimates and confidence intervals were similar.

Conclusion: High knee pain burden is associated with less moderate/vigorous physical activity, and may be an impediment to meeting national physical activity guidelines. Targeted interventions to reduce knee pain among adults with or at risk of knee osteoarthritis may increase moderate/vigorous physical activity levels.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/knee-pain-burden-is-associated-with-decreased-motor-performance-data-from-the-osteoarthritis-initiative/