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

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.

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.

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).

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.