# Reliability and validity of the fixed-frame portable dynamometer in assessing ankle force sense in individuals with and without chronic ankle instability

## TL;DR

A new portable device accurately measures ankle force sense and can help identify balance issues in people with chronic ankle instability.

## Contribution

The study introduces a cost-effective, portable dynamometer validated for assessing ankle force sense in clinical populations.

## Key findings

- The FF-PD showed moderate-to-strong correlations with the CON-TREX system for measuring ankle force sense.
- The FF-PD reliably distinguished individuals with chronic ankle instability from healthy controls.
- The device demonstrated good-to-excellent test–retest reliability with low measurement error.

## Abstract

Deficits in sagittal-plane ankle force sense impair the ankle strategy for counteracting perturbations and are associated with balance impairments in individuals with chronic ankle instability (CAI). However, standardized assessment devices, such as the CON-TREX dynamometry system, are expensive and impractical. In this study, a fixed-frame portable dynamometer (FF-PD) was developed, and its concurrent validity, discriminant validity, and test–retest inter-session reliability were evaluated in measuring ankle plantarflexion and dorsiflexion force sense in individuals with CAI, copers, and healthy controls.

A total of 72 participants (24 with CAI, 24 copers, and 24 healthy controls) performed force-matching tests utilizing the FF-PD and CON-TREX, and the FF-PD retested one week later. Concurrent validity was evaluated with Pearson correlations; discriminant validity, with one-way ANOVA and receiver operating characteristic (ROC) analyses; and reliability, with intraclass correlation coefficients (ICC), standard error of measurement (SEM), and minimal detectable change at the 95% confidence level (MDC95).

FF-PD exhibited moderate-to-strong correlations with CON-TREX (r = 0.597–0.770, p ≤ 0.002). For discriminant validity, the FF-PD effectively distinguished individuals with CAI from healthy controls in plantarflexion (p = 0.011) and dorsiflexion (p = 0.034). ROC-derived cutoffs were 12.06% for plantarflexion and 9.57% for dorsiflexion. Test–retest inter-session reliability was good-to-excellent (ICC = 0.794–0.960), with low SEM (0.9%–2.6%) and clinically meaningful MDC95 (2.5%–7.4%).

The FF-PD is a valid and reliable device for assessing ankle force sense in plantarflexion and dorsiflexion. It effectively differentiates individuals with CAI from healthy controls, and ROC-derived cutoff values provide clinically interpretable thresholds that may support clinical screening and decision-making, as well as the potential use in monitoring changes during clinical screening and rehabilitation.