Bimanual function after cervical spinal cord injury: Development of the Berlin Bimanual Test for Tetraplegia (BeBiTT) and brain/neural hand exoskeleton assessment

Abstract

Introduction: Individuals with cervical spinal cord injury (cSCI) face immense difficulties in daily life. Due to impaired hand function, the performance of activities of daily living are largely restricted. A promising approach in restoration of hand function following cSCI is represented by assistive devices (e.g., hand exoskeletons) controlled via brain-computer interfaces (BCIs). To date, BCI-based hand exoskeletons have only been assessed on their capability to improve unilateral hand function. However, as bimanual tasks are of high relevance in daily life, such devices have yet to demonstrate a positive impact on bimanual function in persons with tetraplegia. Since there are no measurement tools available for such purpose, the Berlin Bimanual Test for Tetraplegia (BeBiTT) was developed in the context of this work and used to assess functional change in bimanual function induced by brain/neural hand exoskeleton (B/NHE) application. Methods: Items of the BeBiTT were generated with help of patients and experts and selected according to a predefined theoretical framework. Content validity assessment of items was conducted by an expert panel consisting of nine subject matter field experts. In a feasibility study with five individuals with tetraplegia, items were assessed regarding practicability, comprehensibility, administration time, task difficulty and safety. A scoring system was developed that allows to systemically administer the BeBiTT. Psychometric evaluation of the BeBiTT was conducted based on interrater-reliability, internal consistency, and construct validity. An interventional study with 10 tetraplegic individuals was conducted to evaluate improvement on bimanual function induced by B/NHE application. Here, the BeBiTT was first performed before (baseline) and while wearing a B/NHE (intervention) by the participants. For online brain/neural control of the B/NHE, sensorimotor rhythm-based electroencephalography and electrooculography signals were used and translated in close/open commands of the hand exoskeleton. Results: The final version of the BeBiTT consists of 9 items representing bimanual tasks that are impaired following cSCI. Items were regarded as content valid by the expert panel. In the feasibility study, items showed to be practical and quick to assess, comprehensible, safe, and affordable. The BeBiTT showed to have excellent interrater reliability and internal consistency. Content and construct validity assessment proved substantial evidence for the BeBiTT’s overall validity. Application of the B/NHE showed to significantly increase BeBiTT scores among participants. On average, the performance of all items of the BeBiTT improved with support of the B/NHE. Conclusion: The BeBiTT represents a reliable and valid test that comprehensively assesses bimanual function in persons with tetraplegia and is suitable to evaluate state-of-the-art tools in neurotechnology. The application of a B/NHE system substantially improves bimanual function in persons with tetraplegia, demonstrated by increased scores in the BeBiTT. These findings highlight the role of modern neurotechnology in restoration of hand function following cSCI.