Trajectories and risk profiles of pain in persons with radiographic, symptomatic knee osteoarthritis: data from the osteoarthritis initiative

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.

Keywords: Cohort study; Group-based trajectory modeling; Osteoarthritis; Pain; Trajectories.

Figure 1. Group-Based Trajectories

WOMAC pain is along the Y-axis and follow-up month is along the X-axis. Each line represents one distinct trajectory. The labels next to each trajectory indicate the percent of the population in that trajectory. The first trajectory contains 11% of the cohort, the second trajectory contains 34% of the cohort, the third trajectory contains 32% of the cohort, the fourth trajectory contains 17% of the cohort, and the fifth trajectory contains 6% of the cohort.

Figure 2. Mean WOMAC Pain by TKR Status and Visit

Mean WOMAC pain is along the Y-axis and follow-up month is along the X-axis. Subjects are split into 7 groups based on when TKR was reported and each line represents one of these groups. The lines show mean WOMAC pain over time. The black line with a circle symbol shows the group that did not have TKR. The green line with the square symbol shows the group that had TKR prior to month 72. The navy line with the diamond symbol shows the group that had TKR prior to month 60. The aqua line with the octagon symbol shows the group that had TKR prior to month 48. The maroon line with the triangle symbol shows the group that had TKR prior to month 36. The green line with the triangle symbol shows the group that had TKR prior to month 24. The pink square symbol shows the group that had TKR prior to month 12.

Figure 3. Group-Based Trajectories by Baseline KL Group

Each of the 3 plots displays a different Baseline KL group. For each graph, WOMAC pain is along the Y-axis and follow-up month is along the X-axis. Each line represents one distinct trajectory. The labels next to each trajectory indicate the percent of the population in that trajectory.