Modified Scoring of the QuickDASH Can Achieve Previously-unattained Interval-level Measurement in Dupuytren Disease and Carpal Tunnel Syndrome.

BACKGROUND: Rasch measurement theory can be used to identify scales within questionnaires and to map responses to more precise continuous scales. The aim of this article was to use RMT to refine the scoring of the QuickDASH in patients with Dupuytren disease and carpal tunnel syndrome (CTS). METHODS: Data were collected between 2013 and 2019 from a single center in the UK. Preoperative QuickDASH responses from patients diagnosed with Dupuytren disease and CTS were used. RMT was used to reduce the number of items in the QuickDASH and examine the reliability and validity of each subscale. RESULTS: The preoperative QuickDASH responses of 750 patients with Dupuytren disease and 1916 patients with CTS were used. The median age of participants was 61 years, and 46% were men. Exploratory factor analysis suggested two distinct subscales within the QuickDASH: task items 1-6 and symptom items 9-11. These items were fitted to the Rasch model, and disordered response thresholds were collapsed. In Dupuytren disease, the two worst responses or each item were disordered. After collapsing these options, good Rasch model fit was demonstrated. CTS responses fitted without modification. Item targeting was more appropriate for CTS than Dupuytren disease. CONCLUSIONS: This study proposes a modification to the scoring system for the QuickDASH that provides high-quality, continuous, and condition-specific scales for the QuickDASH. The identification of distinct subscales within the QuickDASH can be used to identify distinct improvements in hand function and/or symptoms in previous, current, and future work.