Cutaneous whole nerve recordings used for correction of footdrop in hemiplegic man

Abstract

One hemiplegic patient with a dropfoot was chronically implanted with a cuff on the sural nerve, and recordings were made regularly during a period of two years. The results showed that the human sural nerve responded in a similar way to mechanical inputs applied on the skin, as the tibial nerve did in cats (M.K. Haugland, et al., ibid., vol. 2, p. 18-28, 1994), indicating that previous experimental systems using natural sensory feedback for closed-loop FNS are possible to adapt to humans. During walking, the recorded nerve signal modulated strongly and gave a clearly detectable response at foot contact and a silent period when the foot was in the air through the swing phase of the walking cycle. A portable system was built that used the recorded signal to control a peroneal stimulator to correct for footdrop. There were two reasons for this: first, to show in a relatively simple system the possibility of solving the practical problems involved in recording nerve activity during stimulation and second, to remove the external heel switch used in existing systems for footdrop correction, thereby making it possible to use such systems without footwear and preparing it to be a totally implantable system. The method for removing artifacts, as developed in animal experiments, was adapted to provide usable nerve signals while stimulating the ankle dorsiflexor muscles.