American Society for Peripheral Nerve

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Osseointegrated Neural Interface (ONI): Evaluating the Capacity to Interface Peripheral Nerves Transposed to Bone Following Amputation for Advanced Prostheses
Aaron M. Dingle, PhD1; Joseph R. Novello, MS1; Jared P Ness, MS2; Jacqueline S. Israel, MD3; Lisa Krugner-Higby, DVM, Ph.D4; Brett Nemke, BS5; Yan Lu, MD5; Weifeng Zeng, MD2; Sarah K. Brodnick, BS6; Mark D Markel, DVM5; Justin C. Williams, PhD1; Samuel O. Poore, MD, PhD7; (1)University of Wisconsin - Madison, Madison, WI, (2)University of Wisconsin, Madison, WI, (3)Plastic and Reconstructive Surgery, University of Wisconsin - Madison, Madison, WI, (4)University of Wisconson, Madison, WI, (5)University Wisconsin, Madison, WI, (6)Department of Biomedical Engineering, University of Wisconsin, Madison, Madison, WI, (7)Plastic and Reconstructive Surgery, University of Wisconsin, Madison, WI

Introduction: Peripheral nerve interfaces represent a paradigm shift in the treatment and prevention of amputation neuromas. Rather than simply bury a transected nerve in muscle or bone in an effort to prevent/treat painful neuromas, attention has moved to exploiting the regenerative capacity of these nerves to power advanced robotic prostheses.

The Osseointegrated Neural Interface (ONI) represents a novel approach to peripheral nerve interfacing; utilizing the medullary cavity of the amputated long bone to house and protect the amputated nerve and the delicate electrode interface. The medullary cavity of long bones is known to be the bone marrow stem cell niche as well as being highly vascular; representing two key components of peripheral nerve tissue engineering and regeneration. This unique environment therefore acts as a native in vivo bioreactor for the interfacing severed nerves and electronic prosthetic devices. The purpose of this study was to further develop the ONI model and evaluate the nerve viability in bone at 12 weeks post implantation.

Materials and Methods: Transfemoral amputation was performed in New Zealand white rabbits. Briefly, a transfemoral amputation was performed, and the terminal end of the amputated sciatic was passed through a proximal corticotomy and threaded into the medullary cavity, secured in a PDMS cuff distally. Animals were explored at 5 and 12 weeks via morphological histology and electrophysiology. Electrophysiology was performed terminally, with a penetrating stimulation probe inserted into the distal end of the amputated femur and recording proximally using hook electrodes placed under the nerve external to bone. Monophasic and biphasic pulses of varying amplitudes for 40Ás duration were recorded at 20kHz with an AM Systems model 2100 stimulator box coupled with a TDT acquisition system.

Results and Discussion: Morphological examination of the amputated sciatic within the bone demonstrated neuroma formation. In animals that received a PDMS cuff, lateral nerve sprouting (S100+ Schwann cells) through the perforations of the PDMS cuff (representing potential electrodes) indicates that three-dimensional sprouting of nerves is possible (n=4). This sprouting was only evident by 12 weeks, and absent at 5 weeks. For animals that did not receive the PDMS cuff (n=4), S100+ Schwann cells take over an increasingly large proportion of the medullary cavity by 12 weeks. Endoneurial collagen deposition increases between 5 and 12 weeks, with small myelinated axons visible. Electrophysiological data at 5 weeks was indistinguishable from noise (n=4); however, action potentials from within the bone are obtainable by 12 weeks (n=4).

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