Purpose: Despite the benefits of physical activity (PA) for health and quality of life, persons with knee osteoarthritis (OA) engage in relatively little walking and PA. It is generally held that knee pain is an important barrier to physical activity in patients with OA and that total knee replacement (TKR) may increase patients' physical activity by reducing pain. However, the contention that pain limits physical activity has not been formally evaluated. We sought to determine the independent impact of pain, after accounting for age, obesity, and sex, on the amount of walking and PA among persons with advanced knee OA. Methods: Participants enrolled in the SPARKS (Study of Physical Activity Rewards after Knee Surgery) Trial wore Fitbit Zip accelerometers for one week and provided demographic and anthropometric data prior to undergoing TKR. Using the minute-by-minute Fitbit data, we calculated the average daily step count of each participant. Additionally, we calculated the number of minutes of moderate PA per week using a threshold pace of 100 steps per minute, requiring bouts of at least 10 minutes as specified by CDC criteria. Pain was assessed using inverted KOOS pain score (100 is worst) and was stratified in four quartiles: low (<25), low-medium (25-40), medium (40-55) and high (>55). We built regression models and used standardized coefficients to establish the relative importance of pain, age, sex, race and BMI) in relation to the number of steps and engagement in moderate PA. Results: The sample consisted of 103 persons , 60% female, average age 66 (SD 8) years. 14% were non-White, 29% had less than a college education and 20% screened positive for depressive symptoms. The average BMI was 30 (SD 7) kg/m2 and average KOOS pain score was 41 (SD 20). Study participants walked a mean of 5,000 (SD 3,038) steps per day and spent 16 (SD 43) minutes engaging in moderate PA per week. Only 27% of subjects engaged in any moderate PA. Adjusted analyses showed that, on average, women walked fewer steps than men (4,225 vs. 6,277, p= 0.0003) and non-White study participants walked fewer steps than Whites (3,899 vs. 5,209, p=0.0897). Adjusting for pain, study participants younger than 60 years of age walked, on average, 6,236 steps per day, compared to 5,300 steps per day in those aged between 60 and 70 years of age and 3,456 steps per day in those older than 70 years of age (Figure, p=0.0131). The impact of BMI on number of steps differed among men and women (Figure, p-value for interaction 0.0385): Higher BMI was associated with fewer steps in women but not in men. The intensity of pain had a smaller impact on the number of steps per day, ranging from 5,853 steps per day for those in KOOS<25, to 4,803, 5,182 and 4,510 steps per day on average among those with KOOS pain between 25-40, 40-55 and >55 respectively (Figure, p=0.2344). In addition, age (p=0.0352) and sex (p=0.0445), but not pain (p=0.6234) or BMI (p=0.8982), were associated with doing any moderate physical activity in this sample of persons with advanced knee OA requiring TKR. Conclusions: Among persons with advanced knee OA, the number of daily steps and engagement in moderate physical activity is driven primarily by age, sex and race, with no appreciable independent effect of knee pain. These findings have critical implications for outcomes of TKR: Relieving pain may not translate into greater physical activity and walking. Thus, interventions that effectively promote walking and moderate physical activity among persons with knee OA, including those undergoing TKR, are urgently needed. Older, obese and non- White women may stand most to gain from such interventions. (Figure Presented).
Losina, E., Collins, J. E., Michl, G., Smith, S., Deshpande, B. R., Usiskin, I., … Katz, J. N. (2015). Walking and physical activity in persons with advanced knee osteoarthritis: Role of pain, age, sex and BMI. Osteoarthritis and Cartilage, 23, A186. https://doi.org/10.1016/j.joca.2015.02.963