Initial results with fully implanted Neurostep TM FES system for foot drop

In a pilot feasibility study, a prototype closedloop FES walking assist system (Neurostep TM ) was fully implanted in the thigh of a 70 yr old male hemiplegic subject with hypotonia and foot drop who, 3 yr after the stroke, required ankle and knee braces and contact guard assistance and could only walk 5-10 m without fatiguing. Two multi-chambered Neurocuffs TM were implanted on the common peroneal (CP) and tibial (TIB) nerves and connected to a control unit that included custom low-power, low- noise ASIC amplifiers and a pacemaker battery. The Neurostep TM was programmed via telemetry to automatically turn On when the subject stood up, detect heel contact (HC) and toe lift (TL) events from the sensed nerve signals and stimulate selected nerve channels to control the foot trajectory during walking. An “Exercise Mode” provided trains of stimuli that strengthened the disused dorsiflexor muscles and supported walking. The subject was tested and trained with Neurostep TM in the laboratory and received gait re-education for 10 wk before he started to use the device at home. After 6 months, he was able to routinely walk 250 m without fatigue. Although the long-term benefit of using this prototype was limited by a connector malfunction, this pilot study shows the feasibility of treating foot drop with a totally implanted, neuroelectrically controlled FES system. The Neurostep TM technology is now being refined and expanded into an implantable assistive device platform for disabilities such as foot drop, incontinence, limb amputation, paraplegia and chronic pain.