Short‐term recovery trajectories of acute flares in knee pain: a UK‐Netherlands multi‐centre prospective cohort analysis

OBJECTIVE: To identify distinct recovery trajectories of acute flares of knee pain and associated participant characteristics. METHODS: Data were from FLARE RCT, a multicentre trial in 27 primary care centres in UK and Netherlands of three regimes of oral nonsteroidal anti-inflammatory therapy for acute flares of knee pain. Individuals with a history of inflammatory/crystal arthritis, fibromyalgia, and chronic pain syndrome were excluded. Latent class growth analysis was applied to measures of pain intensity repeated over five days to identify distinct recovery trajectories. The concurrent courses of interference with activity, stiffness, and swelling for each trajectory group were modelled using generalised estimating equations. Participant age, sex, obesity, and osteoarthritis diagnosis were described for each trajectory group. RESULTS: 449 participants were included (median age 55 years, 41% female, 35% obese, 42% diagnosed osteoarthritis). A six-group cubic model was deemed optimal, with trajectories distinguished by rate of pain reduction and absolute level at final measurement. At the extremes, were rapid and near-complete resolution (n=41, 9%) and persistent, high pain (n=25, 6%), but most showed a reduction and plateau in pain severity within 3-5 days. Within each pain trajectory group, interference with activity, stiffness, and swelling followed the same course as pain. Baseline characteristics did not differ substantially between trajectory groups. CONCLUSION: Even under a well-adhered to regime of oral nonsteroidal anti-inflammatory medication, recovery following acute flares of knee pain is heterogeneous. Our observations that favourable trajectories are apparent within 3-5 days can help to inform treatment decision-making in the patient-healthcare professional consultation.