Closed-loop control using a stretch sensor for restoration of standing with functional electrical stimulation in...

A closed-loop control system for standing with functional electrical stimulation (FES) using percutaneous intramuscular electrodes in complete paraplegia is described. The system consisted of ultrafine percutaneous intramuscular electrodes, a 32-channel stimulator and a stretch sensor with active current control to detect knee buckling. The closed-loop control system was applied in a T8 completely paraplegic patient. Compared to the stretch sensor with a wide use flexible goniometer for direct current control during standing, the stretch sensor was superior to the flexible goniometer in both ease of use and response. The average time delay from the start of knee buckling until the sensor turned on was 0.56+/-0.19 seconds (Mean+/-S.D.) in the goniometer and 0.21+/-0.06 seconds in the stretch sensor. The average time delay from the start of knee buckling until the recovery from knee buckling was 1.01+/-0.05 seconds in the goniometer and 0.78+/-0.06 seconds in the stretch sensor. The continuous standing ability of the patient increased from 12 minutes with open-loop stimulation to 30 minutes with the closed-loop control. No complications such as falling occurred during clinical use. This system prevented falling due to knee buckling during standing and prolonged upright activities in complete paraplegics.