Evaluation of 3D printed stabilizer for the Biodex: Effects on torque reliability and rate of force development

Sammanfattning

Reliable ankle torque measurements are important in rehabilitation, where strength assessments are used to evaluate recovery and guide treatment. Isokinetic dynamometers, such as the Biodex system, are commonly used to provide controlled measurements of joint torque. However, these measurements rely on the ankle being held in a stable and reproducible position. Mechanical play in the ankle-attachment plate may therefore cause the angle of the ankle joint to deviate during testing, potentially contributing to measurement variability. This project investigated whether a custom 3D printed stabilizer for the Biodex ankle-attachment plate could improve mechanical stability and measurement reliability during isometric tests of ankle plantarflexion and dorsiflexion. The project was performed at MoRe Lab, Biomedical Centre, Lund University. Five healthy participants completed test-retest measurements with and without the stabilizer. Peak torque and average peak torque were analyzed using intraclass correlation coefficients (ICC) and coefficient of variation of the typical error (CVTE). A separate dataset was also collected to compare the ankle angle recorded by the Biodex system with the actual ankle angle estimated from video analysis. The same dataset was used to analyze whether the stabilizer affected early and late rate of force development (RFD). The results showed that the stabilizer reduced the discrepancy between the Biodex angle output and the ankle angle estimated from video analysis, although the reduction was small, approximately half a degree for peak angular difference. Test-retest reliability for peak torque and average peak torque was good to excellent in all conditions, but the stabilizer did not consistently improve ICC or CVTE. In contrast, RFD was significantly higher with the stabilizer during plantarflexion, but not during dorsiflexion.