Our hands are the primary means by which we explore and manipulate our environment. They perform thousands of intricate movements without conscious thought or even visual attention. Sensory feedback is a critical element of these complex activities. Lack of sensory feedback in myoelectric upper limb prostheses makes fluid and complex motions difficult and requires the user to maintain visual attention on the prosthesis to perform even the simplest task. In this project, we will address the need for sensory feedback by implanting non-penetrating cuff electrodes on the residual upper limb nerves. Our central hypothesis is that direct nerve stimulation with selective, non-penetrating cuff electrodes on the residual upper limb nerves can elicit graded sensation and proprioception at multiple locations in the perceptual hand. Further, restoration of sensory feedback with cuff electrodes will reduce visual and cognitive load during prosthesis usage, improve functional performance, and result in embodiment of the prosthesis. In the first funded merit review, the electrode and stimulation technology was developed and fully prepared for clinical implementation. The FDA and local IRB approved investigation of the system in amputees under an investigational device exemption, IDE #G110043. The first subject was implanted in May of 2012. In the first subject, stimulation through 19 active contacts produced 19 unique locations of sensory perception on the subject's perceptual hand. The locations of the perception and the stimulation parameters continue to remain stable, which is more than six month at time of this proposal submission. Further, by modulating stimulation patterns, several perceptions can be produced at each location on the phantom, including pressure, slip, tingling, and pricking. We have, for the first time, shown peripheral nerve stimulation produces highly selective, stable, and normal sensory perception in many places on the phantom of the person with limb loss. The purpose of this project is to study these results in a full cohort of five subjects, demonstrate home use of sensory feedback, and demonstrate improved usage and sense of embodiment resulting from natural sensory feedback. We have a strong working relationship with Otto Bock and Hanger Clinic, providing a solid team poised to make a significant and real impact on veterans, wounded warriors, and the upper limb loss community, as a whole. Specifically, the aims for this project are:
Aim 1 : Characterize sensory perception. Upper extremity peripheral nerve stimulation elicits graded sensory perceptions in more than one location on the phantom limb and the perceptions are stable up to at least two years.
Aim 2 : Demonstrate functional improvement. Stable sensory perception elicited by cuff electrodes will reduce attention and visual load required for adequate prosthesis control and will improve functional performance.
Aim 3 : Demonstrate embodiment. Stable sensory perception elicited by cuff electrodes in synchrony with physical stimuli applied to the artificial limb will result in embodiment of the artificial limb.
Aim 4 : Design and verify an implantable stimulator for permanent sensory restoration. To reach a larger population, a fully implanted system will be required. While it is premature for investment in a fully implanted device, the stimulation circuity will be developed in a bench-top system to prepare for future implant development. In collaboration with Otto Bock, the Michelangelo AxonBus hand and wrist system will be our prosthesis development platform. Collaboration with Hanger Clinic will provide valuable patient-centric guidance and access to a substantial candidate pool. Following successful execution of the work proposed, we expect to show permanent improvement in upper limb prosthesis performance and user embodiment due to permanent, natural sensory feedback through peripheral nerves.
Upper limb amputation is a significant non-fatal co-morbidity of combat operations and one of the more prevalent disabilities among veterans. Unfortunately, available prosthetic options, especially for upper limb loss do not offer the veteran the quality of life they deserve after thei sacrifice in service for our country. Upper limb prostheses have undergone a significant revolution in their mechatronics over the past decade, but the inclusion of natural sensory feedback has lagged due to the limited availability of reliable neural interfaces. This project provides natural sensory feedback to veteran and general amputee limb loss patients and is highly relevant as it employs technologies that can be generally available within the next four to eight years.
