Physical activity and associations with computed tomography–detected lumbar zygapophyseal joint osteoarthritis

Background contextThere are no previous epidemiologic studies examining associations between physical activity and imaging-detected lumbar zygapophyseal joint osteoarthritis (ZJO) in a community-based sample.PurposeTo determine whether physical activity is associated with prevalent lumbar ZJO on computed tomography (CT).Study design/settingA community-based cross-sectional study.Patient sampleFour hundred twenty-four older adults from the Framingham Heart Study.Outcome measuresParticipants received standardized CT assessments of lumbar ZJO at the L2–S1 levels. Severe lumbar ZJO was defined according to the presence and/or degree of joint space narrowing, osteophytosis, articular process hypertrophy, articular erosions, subchondral cysts, and intra-articular vacuum phenomenon. This definition of lumbar ZJO was based entirely on CT imaging findings and did not include any clinical criteria such as low back pain.MethodsPhysical activity was measured using the Physical Activity Index, which estimate hours per day typically spent in these activity categories: sleeping, sitting, slight activity, moderate activity, and heavy activity. Participants reported on usual frequency of walking, running, swimming, and weightlifting. We used multivariable logistic regression to examine associations between self-reported activity and severe lumbar ZJO, while adjusting for key covariates including age, sex, height, and weight.ResultsIn multivariable analyses, ordinal categories of heavy physical activity duration per day were significantly associated with severe lumbar ZJO (p for trend=.04), with the greatest risk observed for the category 3 or more hours per day, odds ratio 2.13 (95% confidence interval [CI] 0.97–4.67). When heavy activity was modeled as a continuous independent variable, each hour was independently associated with 1.19 times the odds of severe lumbar ZJO (95% CI 1.03–1.38, p=.02). Less vigorous types of physical activity and the type of exercise were not associated with severe lumbar ZJO. Older age, lesser height, and greater weight were independently and significantly associated with severe lumbar ZJO. In multivariable models predicting lumbar ZJO, neither model discrimination nor reclassification improved with the addition of physical activity variables, compared with a multivariable model including age, sex, height, and weight.ConclusionsOur findings demonstrate a statistically significant cross-sectional association between heavy physical activity and CT-detected severe lumbar ZJO. However, the additional discriminatory capability of heavy physical activity above and beyond that contributed by other factors was negligible.