Position information in whole nerve cuff recordings of muscle afferents in a rabbit model of normal and paraplegic standing

Information about ankle joint position in whole nerve cuff recordings of muscle spindle afferents was examined in a rabbit model of one normal and one paraplegic subject during standing. The ankle angle of the human subjects was recorded in three experiments, and then used to simulate standing in a rabbit model. The rabbit's ankle joint was moved passively by a servo controlled motor. The tibial and the common peroneal nerve activity were recorded at 3 different initial positions of the rabbit's ankle joint. The results showed a change in amplitude dependent on the initial position. The tibial nerve responded in all three experiments. The peroneal nerve responded in one experiment, where the ankle angle velocity was the highest. The correlation coefficient was calculated between the nerve signal and the ankle angle. The best correlation was found when the amplitude was high and the ankle angle velocity was low. The results indicate that cuff recordings of the tibial nerve provide some information about ankle angle position when the velocity is very low. It is suggested that whole nerve cuff recordings of muscle afferents may be used as position feedback in a closed loop FES system for stabilising the ankle joint of paraplegic subjects during standing.