Abstract
BACKGROUND: Little is known about the temporal evolution of pain severity in persons with knee osteoarthritis (OA). We sought to describe the pain trajectory over 6 years in a cohort of subjects with radiographic, symptomatic knee OA. METHODS: We used data from the Osteoarthritis Initiative (OAI), a multi-center, longitudinal study of subjects with diagnosed radiographic evidence of knee OA. Pain was assessed at baseline and annually for 6 years. Our analysis cohort included subjects with symptomatic knee OA at baseline, defined as baseline Kellgren-Lawrence (KL) score ≥2 with Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score >0. We used group-based trajectory modeling to identify distinct patterns of pain progression over a 6-year follow-up. Factors examined included sex, race, education, comorbidities, age, body mass index (BMI), alignment, KL grade, and depression. RESULTS: We used data from 1753 OAI participants with symptomatic knee OA. Mean baseline WOMAC pain score was 26.5 (0-100, 100=worst) with standard deviation (SD) 19. Group-based trajectory modeling identified five distinct pain trajectories; baseline pain scores for each ranged from 15 to 62. None of the trajectories exhibited substantial worsening. One fifth of subjects in the two trajectories with the greatest pain underwent total knee replacement (TKR) over follow-up. Higher KL grade, obesity, depression, medical comorbidities, female sex, non-white race, lower education, and younger age were associated with trajectories characterized by greater pain. CONCLUSION: We found that knee pain changes little, on average, over 6 years in most subjects. These observations suggest knee OA is characterized by persistent rather than inexorably worsening symptoms.