Development of a patient-reported outcome measure for the foot affected by rheumatoid arthritis.

Objective: To develop an idiographic and nomothetic patient-reported outcome measure (PROM) for the assessment and evaluation of patients with feet affected by rheumatoid arthritis (RA).

Study Design And Setting: The development of the Salford Rheumatoid Arthritis Foot Evaluation (SAFE) Instrument PROM was divided into four stages: establishment of the PROM's conceptual basis and content generation, following a descriptive phenomenological study; clinimetric instrument development; instrument pretesting, involving expert reviews and cognitive interviews; and demonstration of instrument measurement properties, including convergent validity and test-retest reliability of the nomothetic scale.

Results: A total of 123 items were initially generated for the SAFE, with 25 of them clinimetrically selected for nomothetic scale (SAFE-Part A) and 80 items initially included in the idiographic scale (SAFE-Part B). The pretesting strategy proved effective for improving and refining the SAFE, with the final draft consisting of 19 items in Part A and 42 items in Part B. The SAFE-Part A has strong evidence for convergent validity and test-retest reliability.

Conclusion: The SAFE features a nomothetic and idiographic assessment strategy that, with further development, will prove to be a valuable tool for clinicians involved in managing the foot health problems associated with RA.