Effect of Wrist Posture on the Intensity, Size, and Location of Hand Sensations Evoked by Transcutaneous Nerve Stimulation at the Wrist.

The long-term goal of this research is to restore sensorimotor function to individuals with upper-limb loss. Partial hand amputation accounts for 92% of all upper-limb amputations and results in up to a 90% loss of total upper extremity ability. Prostheses used by these individuals are often abandoned due to a lack of sensory feedback, which is key to dexterous hand movement while using a prosthesis. Transcutaneous electrical nerve stimulation (TENS) at the wrist is a promising modality of sensory feedback for individuals with partial hand amputations, as it can evoke sensations on the missing digits through a socially acceptable form factor like a watch or bracelet. However, the wrist may also present challenges for TENS because the underlying nerves change position relative to the electrodes on the surface of the skin during wrist motions. Here, we show that wrist posture significantly alters the percept intensity, size, and location. This was true for wrist flexion/extension, rotation and deviation, as well as for percepts on the thumb, middle, and pinky fingers. Future work should determine if the observed changes in percept intensity, size, and location have a clinically meaningful impact on sensory function. More complex stimulation parameters and/or real-time adjustments in response to wrist motion could enable more consistent haptic feedback if necessary. Ultimately, robust wrist-worn haptic feedback could have broad implications for prosthetics, orthotics, and virtual and augmented reality.Clinical Relevance- Artificial sensations evoked by transcutaneous nerve stimulation at the wrist change with wrist motion, which may necessitate more robust or adaptable stimulation parameters.