LUMBAR ROOT STIMULATION FOR RESTORING LEG FUNCTION - RESULTS IN PARAPLEGIA

We have implanted an intradural array of 12 tripolar electrodes on the anterior roots L2-S2, left and right, at cauda equina level, in a 33- year-old woman with a complete T9 cord lesion of 3 years' duration. Th ey are driven by an implanted multiplexed stimulator system using radi o frequency (RF) power and control signals. All channels generate move ments, in patterns that might be predicted from the known anatomy of t he cauda equina. In particular, stimulation of L2 and L3 gives hip add uction; L3, L4, and L5 gives quadriceps femoris movements; L5, S1, and S2 gives hamstrings movement; and S1 and S2 give plantar flexion. Sti mulation of L5 gives mixed movements at the ankle. Surprisingly, stimu lation of the L2 roots has not given strong hip flexion. Responses hav e been stable. Some thresholds have varied, probably as a result of ti ssue encapsulation. The moment generated within each degree of freedom of the legs has been measured for each root, using a specially design ed multimoment measurement apparatus. For several roots, a movement of lower threshold may be accompanied by a second movement of higher ele ctrical threshold, suggesting that different muscles may have fiber po pulations that differ in their diameter or their location in the root. The use of stimulus forms that enable selective anodal block may, in the future, enable separation of two distinct movements from a single motor root.