Developing an Outcome Measures in Rheumatology (OMERACT) Core set of Outcome Measures for FOot and ankle disorders in RheumaTic and musculoskeletal diseases (COMFORT): core domain set study protocol.

Background: Foot and ankle involvement is common in rheumatic and musculoskeletal diseases (RMDs). High-quality evidence is lacking to determine the effectiveness of treatments for these disorders. Heterogeneity in the outcomes used across clinical trials and observational studies hinders the ability to compare findings, and some outcomes are not always meaningful to patients and end-users. The Core set of Outcome Measures for FOot and ankle disorders in RheumaTic and musculoskeletal diseases (COMFORT) study aims to develop a core outcome set (COS) for use in all trials of interventions for foot and ankle disorders in RMDs. This protocol addresses core outcome domains (what to measure) only. Future work will focus on core outcome measurement instruments (how to measure).

Methods: COMFORT: Core Domain Set is a mixed-methods study involving the following: (i) identification of important outcome domains through literature reviews, qualitative interviews and focus groups with patients and (ii) prioritisation of domains through an online, modified Delphi consensus study and subsequent consensus meeting with representation from all stakeholder groups. Findings will be disseminated widely to enhance uptake.

Conclusions: This protocol details the development process and methodology to identify and prioritise domains for a COS in the novel area of foot and ankle disorders in RMDs. Future use of this standardised set of outcome domains, developed with all key stakeholders, will help address issues with outcome variability. This will facilitate comparing and combining study findings, thus improving the evidence base for treatments of these conditions. Future work will identify suitable outcome measurement instruments for each of the core domains.

Trial Registration: This study is registered with the Core Outcome Measures in Effectiveness Trials (COMET) database, as of June 2022: https://www.comet-initiative.org/Studies/Details/2081.