BackgroundThe ankle joint is a common site of musculoskeletal pathology. Measurement of its functional range of motion is a primary indicator for rehabilitation outcomes in therapy settings. The present study was designed to assess reliability and validity of a new standardised method using a D-Flex device to assess ankle range of motion.MethodsA cohort of 20 healthy volunteers were recruited to measure the weight-bearing ankle range of motion using three assessment tools, namely, a goniometer, inclinometer and the D-Flex measurement devices. Repeated measures were performed both between and within observers for each device over a 48 h period. Performance evaluation of each device and their reliability was assessed using intra-class correlation coefficients and Bland and Altman plots.ResultsAlthough significant correlations (p < 0.05) were observed between devices, there were large mean differences in ankle range of motion values ranging from 4.3°-15.7°. The D-flex produced the highest inter- and intra-rater reliability (ICCs 0.76–0.95), compared to values of 0.55–0.85 and 0.32–0.71 for the goniometer and inclinometer, respectively. The Bland and Altman plots revealed a low mean observer difference for the D-Flex (mean difference = 0.7°), with the vast majority of data coincident within the 95% confidence intervals. For both the goniometer and inclinometer mean differences were higher, with values of 3.1° and 5.7° respectively.ConclusionThe results of the present study provide evidence to support the use of the D-Flex system as a valid, portable, and easy to use alternative to the weight-bearing lunge test when assessing ankle dorsiflexion ROM in healthy participants.