Improvement of hand motor function through a vibrotactile feedback system for hand prostheses

Abstract

Amputation severely impacts daily life, and despite advanced prosthetic technology, many users reject their prosthesis. This is primarily due to unnatural sensation, imprecise control and limb pain, making embodiment difficult. Current research investigated various sensory feedback methods, from invasive neural implants to non-invasive vibrotactile feedback, to address these issues but their everyday usability remains largely unexplored. To approach these problems, the primary objective of this diploma thesis was to assess the effectiveness of the vibrotactile feedback system Feelix, designed for hand prostheses by Saphenus Medical Technology GmbH, along with evaluating the procedure of a study conducted using this system. A pilot study was performed in real-world settings to determine whether the sensory feedback improves prosthetic control and hand motor function, reduces phantom pain, and therefore increases the user's sense of embodiment and acceptance. A detailed redesign of the Feelix glove focused on improving its usability and functionality in everyday life. This included enlarging the silicon glove and adjusting the pressure sensors and connection pad to improve the range of tactile feedback. The pilot study involved one participant and used both performance-based and patient-reported outcome measures, as well as newly developed questionnaires. Various validated outcome measures were chosen to quantify improvements in prosthetic control and user experience, including Box and Block Test (BBT), Southampton Hand Assessment Procedure (SHAP) and Assessment of Capacity for Myoelectric Control (ACMC) as well as Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) questionnaire, Patient-Specific Functional Scale (PSFS) and Short Form (36) Health Survey (SF-36). A pain diary, phantom sensation log, activity diary as well as a questionnaire about the Feelix system and study procedure were included to assess the feedback effect on the user’s daily life. The pilot study revealed significant improvements in the participant's ability to control the prosthesis, with notable enhancements in both gross and fine motor skills. After 30 days, the participant improved the average BBT score by 66.6% and the SHAP score by 41.88%. The final ACMC result improved by 15.53% and the QuickDASH score increased by 25%. The total PSFS score increased by 23.53% and the SF-36 result improved by 10.26%. The subject reported greater confidence in using the prosthesis and a stronger sense of embodiment as supported by an 81.82% improvement in the Prothesis Embodiment Scale for Upper Limb Amputees. Phantom pain could not be assessed as the participant did not experience it. Additionally, inconsistencies in the sensory feedback and design limitations of the glove were identified, highlighting areas for further development. The results suggested that the Feelix feedback glove could significantly improve the functionality and acceptance of hand prostheses. Although the pilot study provided valuable insights, limitations such as the small sample size and short duration must be addressed in further studies. Future research should also focus on refining the glove and investigating its long-term effects with a broader target group.