Restoring Proprioception to Improve Balance and Gait in Lower-Limb Amputees

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Abstract Lower-limb amputees can suffer from a wide range of gait impairments, ranging from compensatory movements to a substantially higher fall risk than the average population. This increased fall risk can be partially attributed to reduced or complete lack of tactile and proprioceptive feedback from the prosthetic limb. There has been significant recent interest in providing sensory feedback via sensorized neuroprostheses. However, these studies have primarily focused on restoring tactile feedback in upper-limb amputees. The aim of this study is to provide natural proprioceptive feedback in lower-limb amputees through lumbosacral spinal cord stimulation (SCS). Experiments will be conducted as an addition to an ongoing NIH-funded project using FDA-cleared SCS leads implanted percutaneously into the lateral lumbar epidural space. To determine the parameters required to evoke naturalistic percepts of joint motion, we will first evaluate the effects of stimulus patterning on the naturalness of evoked proprioceptive sensations. Using an adapted cross-modal congruency effect (CCE) test as a proxy for naturalness, we will quantify which stimulation patterns (constant frequency or biomimetic) create a more natural percept, as indicated by a higher CCE score. To evaluate the effect of stimulation on the subject’s ability to incorporate these percepts as proprioception, we will use a variety of stimulation patterns with varying degrees of naturalness and evaluate the proprioceptive accuracy for either static or dynamic percepts. We will also study the effect of evoked proprioceptive sensations on improving gait and function using a sensorized prosthesis to provide real-time feedback about joint angles. We will use both clinical and scientific measures of proprioception and gait function to evaluate the efficacy of stimulation. We hypothesize that more natural sensations of proprioception will provide greater accuracy in clinical tests of proprioception and greater improvements in more complex motor control tasks, such as gait, thereby improving the mobility and safety of lower-limb amputees.