Extraction force and tissue change during removal of a tined intramuscular electrode from rat gastrocnemius

Many electrical stimulation protocols employ intramuscular electrodes for the activation of targeted muscles. Electrode displacement from the initial implant site can result in degradation of optimal stimulus parameters. Electrodes with tined tips were developed to reduce electrode migration. In the study reported here, intramuscular electrodes with polypropylene tines at the tip were implanted aseptically in the gastrocnemii of adult rats. Test electrodes were explanted immediately following implant in one group and after periods of 1, 3, 7, 14 and 28 days in others. Force as a function of displacement was recorded during removal of the electrodes. Analysis of the results showed that the electrodes were most vulnerable to movement during the first five days. Between 5 and 7 days after implantation there was significant increase in the force required to dislodge the electrode tip. Histology of muscles from which electrodes had been explanted did not show any increase in the area showing tissue changes as compared to control muscles in which the electrode remained in situ. These results indicated that electrode removal caused disruption of encapsulation tissues, with the surrounding muscle mainly unaffected by the explant process.