Abstract
BACKGROUND: Pain and frailty are associated, but this relationship is insufficiently understood. We aimed to test whether there is a unidirectional or bidirectional relationship between joint pain and frailty. METHODS: Data were from Investigating Musculoskeletal Health and Wellbeing, a UK-based cohort. Average joint pain severity over the previous month was assessed using an 11-point numerical rating scale (NRS). Frailty was classified as present/absent using the FRAIL questionnaire. Multivariable regression assessed the association between joint pain and frailty, adjusted for age, sex, and BMI class. Two-wave cross-lagged path modelling permitted simultaneous exploration of plausible causal pathways between pain intensity and frailty at baseline and 1-year. Transitions were assessed using t-tests. RESULTS: One thousand one hundred seventy-nine participants were studied, 53% female, with a median age of 73 (range 60 to 95) years. FRAIL classified 176 (15%) participants as frail at baseline. Mean (SD) baseline pain score was 5.2 (2.5). Pain NRS ≥ 4 was observed in 172 (99%) of frail participants. Pain severity was associated with frailty at baseline (aOR 1.72 (95%CI 1.56 to 1.92)). In cross-lagged path analysis, higher baseline pain predicted 1-year frailty [β = 0.25, (95%CI 0.14 to 0.36), p < 0.001] and baseline frailty predicted higher 1-year pain [β = 0.06, (95%CI 0.003 to 0.11), p = 0.040]. Participants transitioning to frailty over one year had higher mean pain scores (6.4 (95%CI 5.8 to 7.1)) at baseline than those who remained non-frail (4.7 (95%CI 4.5 to 4.8)), p < 0.001. CONCLUSIONS: The bidirectional relationship between pain and frailty could lead to a vicious cycle in which each accelerates the other's progression. This justifies attempts to prevent frailty by addressing pain and to include pain measures as an outcome in frailty studies.