Neural and connective tissue response to long-term implantation of multiple contact nerve cuff electrodes

The objective of this study was to characterize the tissue response to mult iple contact spiral nerve cuff electrodes implanted on the sciatic nerve of seven cats for 28-34 weeks. The cuffs were surrounded by fibrous tissue en capsulation consisting of foreign body cells, collagen, and fibroblasts. Fo cal areas of abnormal neural morphology including perineurial thickening, e ndoneurial fibrosis, thinly myelinated axons, and focal reduction in the de nsity of myelinated axons were noted in five of seven nerves, in three impl ants, the percutaneous lead cable was destroyed by the animal pulling on th e external leads. Morphological changes were observed in two of three nerve s from implants sustaining no known animal induced trauma (group A), and in three of four nerves from implants damaged by the animal pulling at the le ads (group B). All nerves appeared normal 2 cm proximal to the cuff. At the cuff level, small regions of one fascicle in each of two nerves (both grou p B) exhibited abnormalities, while the proximal and distal sections of bot h nerves were normal. Distal to the cuff, small regions of seven fascicles distributed among three nerves (two group A, one group B) exhibited abnorma lities. These nerves were normal at the cuff level but exhibited abnormalit ies in individual nerve branches distal to the cuff. The incidence and char acteristics of the morphological abnormalities at the cuff level are consis tent with those observed in previous studies of nerve cuff electrodes, and support the hypothesis that spiral cuff electrodes can be implanted with an internal diameter less than that of the nerve and expand to accommodate th e nerve without compression The pattern of morphological abnormalities indi cated that mechanical trauma had occurred at some time in the past, and the distribution suggested animal intervention and the lead cable as possible causes. (C) 2000 John Wiley & Sons, Inc.