Validity, reliability and responsiveness of a goniometer watch to measure pure forearm rotation

Introduction: Innovative instruments have been designed to assess forearm rotation, an anatomically challenging motion to measure. This study assessed the concurrent validity, interrater reliability and responsiveness of a novel goniometer watch (GoWatch) to measure pure forearm rotation. The modified finger goniometer (MFG) was the criterion reference. Methods: Forty participants with restricted forearm rotation were recruited. Two raters measured supination and pronation using the GoWatch and MFG before and after a hand therapy session. Repeated-measures ANOVA assessed for systematic bias with an apriori residual error of 5° deemed as acceptable. Secondary analysis used intraclass coefficients (ICCs) to categorise interrater reliability. Responsiveness of the GoWatch was calculated using Cohen’s d Results: The GoWatch demonstrated acceptable agreement with the MFG with a mean difference for supination 1.19° and pronation 0.20°. Interrater reliability was also within acceptable limits with a mean difference GoWatch supination 4.43° and pronation 2.23°. Interrater reliability for GoWatch supination and pronation were categorized as excellent (ICC = 0.94) and good (ICC = 0.85) respectively. Systematic bias was observed in the instrument by rater interaction with rater two consistently underestimating GoWatch measures (p<.05). GoWatch supination showed small to medium responsiveness (Rater 1: d = 0.14; Rater 2: d = 0.29) and pronation very small to medium responsiveness (Rater 1: d = 0.29; Rater 2: d = 0.05). Conclusion: The GoWatch is a viable and user-friendly alternative to measure forearm rotation with demonstrable validity, interrater reliability and responsiveness. Further research is required to ensure systematic bias is not endemic when used across multiple raters.