Tetragrip: a functional electrical stimulation (FES) device for enhancing upper limb function in people with tetraplegia – development, technical evaluation, and pilot clinical investigation

This paper describes the development and initial evaluation of Tetragrip, a five-channel functional electrical stimulation (FES) device designed to enhance upper limb function in people with C5-C7 spinal cord injury (SCI) resulting in tetraplegia. Tetragrip uses an inertial measurement unit (IMU) on the upper arm to control stimulation through opposite shoulder movements. A Finite State Machine enables users to start and stop stimulation, select grip patterns and adjust intensity. Reusable Etexsense fabric electrodes are embedded in custom Lycra sleeves and positioned over motor points to activate specific muscle groups. Clinicians preset stimulation levels, allowing users to perform "Key" and "Power" grips without complex adjustments. Initial testing with a healthy volunteer demonstrated reliable IMU control and highlighted the importance of accurate electrode placement. A pilot clinical investigation was subsequently conducted at the Duke of Cornwall Spinal Injuries Centre, Salisbury. Thirteen potential participants were identified and assessed; four met the inclusion criteria, but only two were able to meaningfully evaluate the system because of clinical factors. These participants provided positive feedback on its design and usability. The recruitment challenges encountered are discussed, while changes in SCI demographics are analysed in a companion paper.