Psychosocial Factors and Knee Pain Among Older People in Japan The JAGES Cross-Sectional Study

Objectives: Psychosocial factors are known to affect knee pain. However, the magnitude of depression on the associations between socioeconomic status (SES) and knee pain in older individuals remains unknown. This study aimed to determine (1) the associations between SES and knee pain and (2) how depression mediates the associations between SES and knee pain. Materials and Methods: We conducted a survey across 30 Japanese municipalities to collect cross-sectional data. Functionally independent, community-dwelling adults aged 65 years or above (n=26,037) were eligible for the study. Self-reported knee pain in the past year was used as the dependent variable. Past occupation and equivalized household income were separately added to the models as independent variables. Poisson regression analysis was used to examine the associations between SES and knee pain, adjusting for covariates. Mediation analysis was applied to estimate how depression explains these associations. Results: The 1-year prevalence of knee pain was 56.0% in our study population. We found that income levels were significantly associated with knee pain: the lowest income level was more prone to experience knee pain compared with the highest income level at a prevalence ratio of 1.22 (95% confidence interval, 1.15-1.28). Depression explained 36.8% of the association of income with knee pain in females and 41.9% in males. Discussion: Significant socioeconomic inequalities were observed regarding knee pain among older individuals in Japan. Depression somewhat explained the association between SES and knee pain.