NEUROMUSCULAR REORGANIZATION FOR PROSTHESIS CONTROL

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DESCRIPTION (Adapted from Applicant's Abstract): The candidate is a board- certified physiatrist with clinical and research interests in the care of amputees and improvement of artificial limbs. Currently amputees can only control a single degree-of-freedom at a time with myoelectric prostheses, which is very insufficient. By grafting residual nerve endings to muscles in or near an amputated limb, it may be possible to produce additional surface EMG control signals for an externally powered prosthesis allowing multiple degrees-of-freedom to be controlled simultaneously. The technique has potential for improving the control of upper limb prostheses, especially with high level amputations where the need is greatest. For this technique to be successful, multiple nerves would have to reinnervate separate areas of a muscle and produce independent control signals for operation of the artificial limb. To develop this technique a two-phase education and research plan is proposed. In the first phase, the candidate will learn field theory and finite-element (FE) analysis techniques to become expert in FE modeling of electromagnetic systems. For the second phase, acute animal experimentation, mathematical modeling and chronic experimentation is proposed to study the factors affecting surface EMG signal independence. Acute cat experiments will be performed to map the surface EMG of various muscles in the cat hind limb. A finite-element (FE) model of the cat hind limb will be developed using published dielectric properties for muscle, fat, skin, bone and fibrous tissue, as well as cross sections of the hind limb. The model will be refined and validated with the measured surface EMG data. The FE model will then be used to study the factors affecting EMG field distribution including the size of muscles, the shape of the muscles, and the effect of overlap in reinnervation fields. The FE model will also be used to determine if surgical manipulation of soft tissues could be used to improve the independence of myoelectric signals from nerve-muscle grafts. For optimal signal independence it will be important for the grafted nerves to reinnervate separate regions of muscle. Therefore, the candidate proposes to study the competition between reinnervating nerves in chronic cat experiments. Multiple nerves will be grafted simultaneously onto cat hind limb muscles, and then the topography of reinnervation be characterized using physiological and glycogen depletion techniques. In a second set of experiments, the nerve- muscle grafts will be surgically separated to see if the scar that forms between the grafts will create a barrier to regenerating axons and thus guide the topography of the reinnervation fields.