Abstract
OBJECTIVE: Previous studies have demonstrated that low physical activity levels during youth are associated with the development of thin knee cartilage, which may increase susceptibility to osteoarthritis later in life. Here, we propose and test the hypothesis that reductions in physical activity impair knee cartilage growth among people in developing countries experiencing urbanization and increased market integration. METHODS: Ultrasonography was used to measure knee cartilage thickness in 168 children and adolescents (aged 8-17 years) from two groups in western Kenya: a rural, physically active group from a small-scale farming community and an urban, less physically active group from the nearby city of Eldoret. We used general linear models to assess the relative effects of age on cartilage thickness in these two groups, controlling for sex and leg length. RESULTS: Both groups exhibited significant reductions in knee cartilage thickness with increasing age (P < 0.0001; 95% confidence interval [CI] 0.15-0.06 mm), yet the rate of reduction was significantly less in the rural than in the urban group (P = 0.012; 95% CI 0.01-0.10 mm). CONCLUSION: The results support our hypothesis by showing that individuals from the more physically active rural group exhibited less knee cartilage loss during youth than the more sedentary urban group. Our findings suggest that reduced physical activity associated with urbanization in developing nations may affect adult knee cartilage thickness and thus could be a factor that increases susceptibility to osteoarthritis.