Preliminary evaluation of a neural prosthesis for standing after spinal cord injury with four contact nerve-cuff electrodes for quadriceps stimulation.

This study describes the preliminary performance of an implanted neuroprosthesis for standing and transfers after spinal cord injury. The system is a 16-channel version of the 8-channel Case Western Reserve University/Veteran Affairs (CWRU/VA) standing/transfer neural prosthesis. It includes bilateral four channel femoral nerve cuff electrodes for stimulation of the vastii to provide knee extension. To date, the prosthesis has been implanted in one subject who was previously a user of the original 8-channel CWRU/VA system. In the first four months after implantation of the new neuroprosthesis, this subject has been able to stand for approximately 2.5 minutes with up to 86% of total body weight supported by the lower extremities. These values far exceed the stand time (approximately 1 minute) and body weight distributions (55% on the legs) for the same subject when using the 8-channel system four months after implantation. The nerve cuff electrodes have been stable over the four months since implantation, with little change in stimulation threshold and saturation values, which suggests that there have been no biological effects on the electrodes. These results suggest that the second generation 16-channel neuroprosthesis with nerve-cuff electrodes will provide stronger knee extension moments over a longer duration before fatigue during standing and transfers.