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

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).

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.

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.

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.