The design of a steerable introduction shaft for electrode implantation on the dorsal root ganglion

Abstract

Sensory nerve roots (DRGs) that emerge from the spinal cord can be stimulated with electrodes to prevent neuropathic pain. Proper functionality of DRG stimulation strongly depends on electrode placement, and conventional pre-curved introduction shafts limit DRG coverage of the implanted electrode lead. The goal of this thesis is to design an introduction shaft with a steerable tip in one direction to decrease the minimum radius of curvature and increase the angle of curvature of the implanted electrode leads around DRGs. The steerable tip design consists of clamped stainless-steel rings on a nitinol rod and an internal braided stainless-steel pulling cable attached to the distal ring to bend the tip. A handle provides minimum radius of curvature adjustment for different DRG sizes, and combined shaft translation and tip bending for circular motion around the DRG. A scale-up prototype was manufactured, and the tip had an outer diameter of 2.40 mm and a length of 20.00 mm. A tip bending fatigue test was performed, during which the steerable tip showed no plastic deformation. The steerability of the tip was tested in gelatin and resulted in a DRG circumference coverage of 51.4% ± 1.1% compared to a 25% potential coverage of conventional introduction shafts. The minimum radius of curvature was adjustable between 42 ± 14 mm and 6 ± 1 mm. An electrode lead was successfully implanted in an artificial environment that mimicked a section of the spine. In the future, the outer diameter of the prototype tip should be decreased to reach the required size for the procedure (1.60 mm), and the handle should contain a mechanism to increase shaft translation relative to the tip bending in order to improve circular motion of the steerable tip.