Implanted neuroprosthetic systems have been successfully used to provide upper-limb function for over 16 years. A critical aspect of these implanted systems is the safety, stability, and reliability of the stimulating electrodes and leads. These components are (1) the stimulating electrode itself, (2) the electrode lead, and (3) the lead-to-device connector. A failure in any of these components causes the direct loss of the capability to activate a muscle consistently, usually resulting in a decrement in the function provided by the neuroprosthesis. Our results indicate that the electrode, lead, and connector system are extremely durable. We analyzed 238 electrodes that have been implanted as part of an upper-limb neuroprosthesis. Each electrode had been implanted at least 3 years, with a maximum implantation time of over 16 years. Only three electrode-lead failures and one electrode infection occurred, for a survival rate of almost 99 percent. Electrode threshold measurements indicate that the electrode response is stable over time, with no evidence of electrode migration or continual encapsulation in any of the electrodes studied. These results have an impact on the design of implantable neuroprosthetic systems. The electrode-lead component of these systems should no longer be considered a weak technological link.
The design, implementation, and preliminary testing of an implantable in-line connector for individual lead-wires is presented. The connector provides for replacement of implanted components without disturbing other elements of the implanted system. Its flexibility and size makes it suitable for implantation in neuromuscular applications.
An intramuscular electrode has been developed for functional neuromuscular stimulation applications, to be used in conjunction with a surgically implanted neuromuscular receiver-stimulator.In vitro experiments indicated that the electrode will maintain a stable position, but is capable of being removed intact, if removal is necessary. When tested in an unbuffered saline environment at the maximum stimulation parameters, the stimulating surface experienced minimal non-progressive corrosion. A preliminary animal evaluation was performed to compare four surgicallyimplanted intramuscular electrodes with four epimysial electrodes, connected to an implantable neuromuscular receiver-stimulator. The intramuscular electrodes all operated properly throughout the study, producing functional responses indistinguishable from epimysial electrodes. IN T R 0 DUCT IONAn eight-channel implantable stimulator has been developed for functional neuromuscular stimulation (FNS) of the upper or lower extremities of spinal cord injured individuals [I]. The stimulator is currently implemented in the upper extremity of a C5/C6 level quadriplegic, utilizing eight epimysial electrodes. Although the epimysial electrodes have functioned successfully, an intramuscular electrode could allow easier access to deeper muscles and could allow the implantation of several muscles from one incision site. Intramuscular electrodes currently in use with a percutaneous FNS system [2] do not have a longevity that is adequate for a permanently implanted system. A surgical implantation procedure allows the use of larger electrodes with mechanically-supportive components that should provide the necessary longevity for a permanently implanted electrode. ELECTRODE DESIGNThe surgically-implanted intramuscular electrode ( Fig. I ) is fabricated from two sections of Teflon-insulated type-3 16LVM stainless steel wire that are coiled into a tandem helical configuration and inserted into Silastic tubing. At the stimulating end of the electrode the coiled wire exits the tubing and a deinsulated section of the wire is wrapped around the outside of the tubing, forming the stimulating surface. The wire is secured by inserting it into a perforation in the tubing, which is subsequently sealed with silicon adhesive. The stimulating surface area is approximately 14.5 mm'. The electrode is held in place by a polypropylene anchor that is thermally-molded from size 3-0 polypropylene sutures. The anchor has five 2 mm long barbs and a 2 cm long core. The core is inserted down the center of the electrode lead and is thermally-molded to the shape of the coils, locking it in place. At the opposite end of the lead, the wire is welded to a section of 316 stainless steel tubing (protected by strain relief springs) to allow attachment to the in-line connector used with the CWRU-VA implantable stimulator [I].The electrode design should greatly increase the electrode longevity. The stimulating tip design minimizes the stress A SURGICULY-IMPUNTED INTRIMUSUJLAA ELECTRODE Figure 1. Schematic of...
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