Abstract
We developed percutaneous intramuscular electrodes for controlling paralyzed extremities by FES and also applied them to TES. In this study, the mechanical and electrical properties of stainless steel SUS 316L, Co-Cr based alloy NAS 604 PH and newly developed high nitrogen high manganese stainless steel NAS 106N were investigated. Furthermore, we performed a clinical evaluation of the newly developed estimation method of the implanted electrodes using impedance characteristics which we proposed in previous papers. NAS 106N showed superior mechanical properties at rotating-bending fatigue test both in air and in 0.9% NaCl solution. Noise spectrum analysis proved that all three electrodes had low noise properties, i. e., no excessive noise. Therefore, those stainless steel electrodes are useful not only for stimulation but also for detection of small signals from the nerve-muscular system. In the clinical verification of the electrodes after implantation, the failure of terminals had occurred when the electrode impedance was inversely proportional to the measurement frequency. It was also confirmed with X-ray photographs that a complete breakage in the body corresponded to estimation by the impedance characteristic. Furthermore, we performed an cross-sectional investigation of 730 electrodes (SUS 316L) implanted for 0-to 72-month periods with the proposed method in 30 patients. 620 electrodes (85%) continued to produce stable muscle contractions. In the 110 electrodes that didn't work well, 96 (13.1%) and 14 (1.9%) electrodes were estimated to have suffered complete breakage, and failure of the terminal, respectively. From these results, it has been shown that the evaluation method proposed by the authors was available for clinical usage.
