Researchers conducted a study demonstrating that spinal cord stimulation (SCS) can restore sensation in a missing lower limb without disrupting the existing motor activation of the residual limb muscles. The goal of the study was to characterize SCS-evoked spinal reflexes in people with lower-limb amputations and quantify the effects on gait parameters, including step-cycle duration and limb-alternation symmetry.
The research team implanted percutaneous SCS electrodes over the lumbosacral enlargement in three people with transtibial amputations (two with diabetic neuropathy and one with a traumatic cause) for 28 or 84 days. SCS was delivered to restore sensation in the missing limb during walking based on signals from a pressure-sensing insole in the shoe under the prosthesis.
The researchers used electromyography to record posterior root-muscle reflexes in the residual limb while participants were seated, standing, or walking, and characterized rate-dependent depression and recruitment properties of the posterior root-muscle reflexes. They used pressure data from instrumented insoles to measure the step-cycle duration and limb alternation symmetry with and without SCS.
SCS evoked posterior root-muscle reflexes in the residual limb muscles in all participants, according to the authors. Overall, they found that there was broad activation of residual limb muscles with SCS that varied with the position of the stimulating electrode relative to the lumbar spinal cord. Posterior root-muscle reflexes were also activated during walking, as confirmed by the presence of rate-dependent depression. However, SCS-evoked reflexes did not disrupt gait, with similar step-cycle duration or limb alternation symmetry with and without SCS, the study concluded.
The open-access study, “Characterizing spinal reflexes evoked by sensory spinal cord stimulation in people with lower-limb amputation” was published in the Journal of NeuroEngineering and Rehabilitation.
