Developing a Preliminary Definition and Domains of Flare in Knee and Hip Osteoarthritis (OA): Consensus Building of the Flare-in-OA OMERACT Group.

Flare in knee and hip osteoarthritis (OA) is more than just an exacerbation of pain. Unstructured, semistructured, and focus group interviews followed by Delphi surveys with patients and health professionals (HP) generated candidate domains of an OA flare. Content analysis of interviews with 29 patients and 16 HP extracted 180 statements, which were grouped into 9 clusters. Delphi consensus with 50 patients (Australia, Canada, and France) and 116 HP (17 countries on 4 continents) identified 5 flare domains: pain, swelling, stiffness, psychological aspects, and effect of symptoms. Elements for a preliminary definition of an OA flare are proposed. Registered at clinicaltrials.gov NCT02892058.