Background It is clear that exercise helps the symptoms of osteoarthritis. However, the relationship between physical activity (PA) and progression of knee osteoarthritis (OA) remains controversial. Moreover, no guideline on the amount of PA to prevent OA progression in general older population has been recommended, and it is still uncertain whether PA should be promoted among subgroups with knee OA such as female gender, obesity, radiographic osteoarthritis (ROA) and knee injury history. Osteophyte (OP) has long been viewed as a defining structural feature of knee OA. Recently, MRI-detected OPs have been shown to be more sensitive to change than radiographs.
Objectives The aims of this study were to describe the longitudinal association between objectively-measured PA and knee MRI-detected (OPs), and to test the interactions between PA and gender, obesity, ROA or knee injury history on the increases in MRI-detected OPs.
Methods 408 community-dwelling adults aged 51–81 were randomly selected from local community and measured at baseline and 2.6 years later. T1-weighted fat suppressed MRI was used to evaluate knee OPs at baseline and after 2.6 years. PA was assessed at baseline by pedometers (steps per day) and categorized as 3 groups: low PA (≤7499 steps per day), moderate PA (7500 to 9999 steps per day) and high PA (≥10000 steps per day). Radiographs were obtained and scored for individual features of radiographic osteoarthritis (ROA). Knee injury history was recorded by questionnaire and body mass index (BMI) was calculated. Logistic regression and log binomial regression were used in longitudinal analyses.
Results In total study sample, doing moderate PA was associated with reduced risk of an increase in MRI-detected OPs, comparing to low PA (RR=0.73, p=0.03). There were significant interactions between PA and gender, obesity, ROA or knee injury history (all p<0.05) for an increase in MRI-detected OPs. In stratified analyses, moderate PA was protective against an increase in MRI-detected OPs in females (OR=0.23, p<0.01), obese participants (OR=0.23, p<0.01), participants with ROA (OR=0.45, p=0.02) and participants with knee injury history (OR=0.05, p=0.02). These significant associations still existed after further adjustments for age, sex, BMI, ROA and/or knee injury history (where appropriate). High PA was not associated with an increase in MRI-detected OPs in total sample or the stratified analyses but there were relatively few in this category.
Conclusions Moderate PA is protective for change in MRI-detected OPs in older adults, especially in those with female gender, ROA, obesity and knee injury history. This implies older people with above risks of knee OA may need to aim for a range from 7500 to 9999 steps per day.
Dore DA, Winzenberg TM, Ding C, Otahal P, Pelletier JP, Martel-Pelletier J, et al. The association between objectively measured physical activity and knee structural change using MRI. Ann Rheum Dis 2013; 72: 1170–1175.
Acknowledgements The authors thank the participants who made this study possible, and acknowledge the role of the staff and volunteers in collecting the data, particularly research nurses Boon C and Boon P. Warren R assessed MRIs and Dr Srikanth V and Dr Cooley H assessed radiographs.
Disclosure of Interest None declared