Characterising flare-ups of knee osteoarthritis in community-dwelling adults: who gets them and how long do they last?
Problem
Acute flare-ups are experienced by a substantial proportion of adults with osteoarthritis (OA), but these events remain poorly understood. As part of a wider programme of research, the current study aimed to (i) identify participant or knee symptom characteristics associated with higher risk of flare-ups, (ii) describe the time course and consequences of flare-ups of knee OA to provide better information for healthcare professionals and patients on the likely short-term prognosis.
Approach
The ACT-FLARE study (ACuTe FLAREs in knee OA) is a 13-week web-based case-crossover study of knee pain in people aged ≥40 years resident in England, with or without a recorded diagnosis of knee OA, and no inflammatory arthropathy. Participants were recruited from 15 general practice registers, and from the community via distributed flyers/posters and online social media advertisement. After completing a baseline questionnaire, participants were encouraged to self-report a flare-up at any time during the study period via the website. A flare-up was defined as the sudden onset of worsening signs and symptoms, sustained for ≥24 hours. After characterising their flare-up, from notification date through to flare-up resolution participants completed four daily questions about the last 24 hours: i) average pain (0-10 NRS), ii) level of bothersomeness, iii) pain medication use, and iv) whether the flare-up had resolved. Associations between selected participant and knee symptom characteristics at baseline and the occurrence of flare-ups were estimated using Poisson regression and expressed as unadjusted incidence rate ratios (IRR; 95%CI). Flare-up characteristics, course and consequences were analysed descriptively.
Findings
Of 744 participants recruited between July 2018 and February 2019 (mean age (SD) 62.1 (10.2) years; 60% female, body mass index 29.2 (5.7) kg/m2), 493 participants reported 714 flare-ups. Among participants who engaged throughout study follow-up, 242 (51%) reported ≥1 flare-up. Flare-ups were more common in younger ages (IRR 0.98: 95%CI 0.97, 0.99), females (1.85: 1.43, 2.39), and those with severe frequent knee pain at baseline (2.06: 1.17, 3.63). Associations with prior knee injury/surgery and socioeconomic status were weak or absent. Among those whose end dates were known, number of flare-ups per participant ranged between 1 and 6 (mean (SD) 1.32 (0.64)) and median (IQR) flare-up duration was 5 (3, 8) days. Knee changes noticed since flare-up onset included: stiffness (64%), limping (58%), increased difficulty with everyday activities (57%), sleep disturbance (48%) and swelling (33%). Levels of pain, bothersomeness and medication usage reduced over the period between flare-up onset and resolution.
Consequences
Knee OA flare-ups are most commonly reported by working age adults, females and those with more persistent pain patterns. Most flare-ups appear to last between 3 and 8 days.