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American Association for Hand Surgery

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Wireless Implantable Multi-electrode System for High-bandwidth Prosthetic Interfacing
Clemens Gstoettner, MD1, Christopher Festin, MD2, Cosima Prahm, PhD1, Konstantin D Bergmeister, MD PhD1, Stefan Salminger, MD Ph.D.3, Agnes Sturma, Ph.D.4, Daniel McDonnall, Ph.D.5, Dario Farina, PhD6 and Oskar C. Aszmann, MD3, (1)Medical University of Vienna, Vienna, Austria, (2)Medical University Vienna, Vienna, Austria, (3)Department of Surgery/ CD Laboratory for Restoration of Extremity Function & Division of Plastic and Reconstructive Surgery, Medical University of Vienna, Vienna, Austria, (4)CD Laboratory for Restoration of Extremity Function, Medical University of Vienna, Vienna, Austria, (5)Ripple Neuro LLC, Salt Lake City, UT, (6)Imperial College London, London, United Kingdom

Background
Currently employed prosthetic solutions in upper extremity amputation largely fail to create a natural substitute for the lost limb. Limited functionality is a major concern of users, which is owed to low information transfer rates of neuromuscular interfacing. While surgical innovations have expanded the functional potential of the residual limb, current interfaces are inefficacious in translating this potential into improved prosthetic control. Implantable interfaces lack the necessary information transfer rates and their use is limited to particular levels of amputation.

Methods
In this study we present a novel neuromuscular implant, the Myoelectric Implantable Recording Array (MIRA). It is the first fully implantable system for prosthetic interfacing with large channel count, comprising 32 intramuscular electrodes. Biocompatibility of the novel intramuscular leads was evaluated in a small animal study. The full system was implanted in canines and sheep in order to assess long-term in vivo functionality and analyse intramuscular EMG recordings. Furthermore, surgical approach and placement of the implant were explored in a fresh human cadaver study.

Results
Evaluation of foreign body reaction revealed favorable biocompatibility and low-grade tissue response. Long-term implantation of the MIRA demonstrated low and stable impedances and continuous functionality over a period of six months. EMG recordings showed minimal crosstalk and a consistently high signal-to-noise ratio. Surgical approaches and appropriate device placement were developed and assessed for all levels of major upper limb amputation.

Conclusions
The MIRA is the first implant for high-bandwidth prosthetic interfacing which offers sufficient intramuscular electrode sites for accessing spinal motor neuron activity after targeted muscle reinnervation. Moreover, it is the only system that can be implanted at all levels of limb amputation. In combination with recent innovations in amputation surgery it will enable vastly improved control approaches for upper limb amputees.


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