Purpose: It is unclear whether habitual running is beneficial versus harmful to the knee. Chronic mechanical overloading could potentially damage structures within the knee. Alternatively, runners have a lower body mass index (BMI), protective of knee osteoarthritis (OA). We recently found that runners do not have a greater prevalence of symptomatic and radiographic knee OA compared to non-runners. However the question of whether running is harmful or beneficial in those with pre-existing knee OA has not been systematically addressed. Therefore, we aimed to evaluate the relationship of habitual running with symptomatic and structural progression in those with pre-existing radiographic knee OA in the Osteoarthritis Initiative (OAI), an observational study designed to evaluate potential and known biomarkers and risk factors of knee OA.
Methods: This is a nested cohort study within the OAI, which included participants over the age of 50 years at OAI baseline who had radiographic OA in at least one knee at the time of OAI enrollment. Those knees that had a replacement (TKR) at OAI baseline were excluded. Only knees that had radiographic OA (i.e. Kellgren-Lawrence (KL) grade > 2) at the time of enrollment were included in this study. All participants had to complete a modified version of the Lifetime Physical Activity Questionnaire (LPAQ) that asked participants to identify the top 3 most frequently performed physical activities (≥ 10 times in life) during ages >50 years at the OAI 96 month visit. Those indicating running as an activity were defined as a runner. The frequent knee pain question (i.e. pain on most days of the month for at least one month in the last year) for each knee was administered at the baseline and 48 month visits. Posterior-Anterior semi-flexed knee radiographs were obtained at baseline and 48 month visits, and were scored for KL grade (2-4). New knee pain was defined as a knee transitioning from not having frequent knee pain at baseline to having had frequent knee pain at the 48 month visit. KL worsening was defined as an increase in KL grade between baseline and the 48 month visit. Medial JSN worsening was defined as an increase medial JSN score, including within OARSI grade worsening between baseline and the 48 month. Anyone who had a TKR between enrollment and the 48 month visit was classified as having knee pain, KL worsening, and medial JSN worsening at the 48 month visit. Improving knee pain was defined as having frequent knee pain at baseline and not having frequent knee pain at the 48 month visit. If 48 month data was missing, data from the 36 month visit was carried forward.
We performed logistic regression analyses, using generalized estimating equations to account for correlation within knees, where the predictor was running over the age of 50. The outcomes were new knee pain, KL worsening, medial JSN worsening, and improving knee pain; adjusted analyses included covariates age, sex, BMI, and injury. Those who already had the extremes of the outcomes of interest were excluded from those respective analyses (e.g. those with KL = 4 were excluded from KL worsening analyses). Additionally, baseline KL score was added into the models as a covariate in all models.
1251 participants were included in this analysis, 11.0% were runners. From lowest to highest BMI tertile, 14.6%, 10.7%, and 7.8% were runners. Characteristics of runners compared to non-runners are shown in (Table 1).
Table 1Baseline and 48 month characteristics of non-runners, runners, and all participants.
Table 2Odds ratios of worsening or improving outcomes in non-runners v. runners; ∗adjusted for age, sex, BMI, and knee injury between OAI baseline and 48 month follow up visit.
When additionally adjusting for baseline KL grade, all results remain unchanged.
Conclusions: Our findings suggest that among individuals over 50 years of age with pre-existing knee OA an exposure to running is not associated with worsening knee pain or radiographically defined structural progression over a 4 year observation period. A limitation is that this is an observational study wherein the runners are self-selected. Running should not be discouraged in those with pre-existing knee OA.
© 2015 Published by Elsevier Inc.