Gait optimization with a real-time closed-loop artificial sensory feedback
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Individuals with unilateral lower limb musculoskeletal and neurological conditions, including prosthetic users, experience asymmetric walking. It may result in undesirable compensations by the body and secondary conditions (osteoarthritis, low back pain, etc.). My goal was to develop a real-time closed-loop control system for a sensing, bone-anchored transtibial prosthesis interfaced with residual peripheral nerves and muscles. The prosthesis and control system would allow users to sense ground contact during walking and control the prosthetic ankle using natural motor commands to automatically correct asymmetries and instability of walking. To inform the design of the prosthesis and control system, I investigated in walking cats the effects of manipulating tactile sensory feedback from paw pads and stretch-dependent feedback from thigh muscles on symmetry and stability of walking. I found that removal of tactile and muscle length-dependent feedback resulted in profound changes in symmetry and stability of walking. In addition, electrical stimulation of the distal tibial nerve, innervating paw pads, during the stance phase of walking substantially reduced and sometimes reversed effects of sensory feedback removal. I then demonstrated that a real-time closed-loop gait control system could control step length symmetry of walking cats by stimulation of the distal tibial nerve. This system could be used for correcting asymmetries during walking in people with sensorimotor deficits. I also developed a prototype of a sensing transtibial prosthesis with an ankle joint controlled by activity of residual muscles. The results of this study provide new insights into the role of sensory feedback in control of locomotion and offer new engineering solutions for bone-anchored, limb neuro-prostheses and for improving pathological gait.