The relation between radiographic knee osteoarthritis severity and pain is stronger among more frail people.

Introduction/objectives: Knee osteoarthritis is a leading cause of disability in older adults; with treatment complicated by inconsistent associations between radiographic and symptomatic severity. Frailty describes the heterogeneity in aging and is quantified via the accumulation of health deficits. We test if frailty moderates the relation between radiographic and symptomatic knee osteoarthritis.

Method: This cohort study included participants (n = 3,271; 58% female, 45-79 years) from the Osteoarthritis Initiative were included. Radiographic severity was assessed using the Kellgren-Lawrence Grade (KLG). Frailty was quantified via a 31-item frailty index, categorizing participants as non-frail (≤ 0.10), very mild frailty (< 0.1-to- ≤ 0.2), mild frailty (< 0.2-to- ≤ 0.3), and moderate-to-severe frailty (> 0.3). Self-reported pain was assessed via the Knee Injury and Osteoarthritis Outcome Score (KOOS). Moderation models using generalized estimating equations adjusted for age, sex, and body mass index were performed to test the interaction between frailty and KLG on KOOS pain scores.

Results: Radiographic severity (β = -3.82, 95%CI: -4.16:-3.49; p < 0.001) and frailty (β = -4.76, 95%CI: -5.36:-4.17; p < 0.001) were negatively associated with KOOS pain scores. Frailty moderated this relation (interaction term: β = -1.18, 95%CI: -1.63:-0.73, p < 0.001), where higher frailty strengthened the association between radiographic severity and pain. Simple slopes analysis indicated stronger associations between KLG and KOOS pain scores in participants with mild to moderate-to-severe frailty compared to non-frail and very mild frailty (non-frail: β = -2.71, 95%CI: -3.41:-2.02, p < 0.001; moderate-to-severe frailty: β = -5.57, 95%CI: -7.23:-3.87, p < 0.001).

Conclusion: These findings underscore the importance of incorporating frailty assessments into knee osteoarthritis management, as individuals with similar radiographic severity may experience substantially worse pain if they have higher frailty levels.