Topography of the Human Ulnar Nerve for Mounting a Neuro-Prosthesis with Sensory Feedback

This article presents the performed experimental measurements for connecting a sensory feedback neuro-prosthesis to the peripheral nervous system of a patient with forearm amputation. The experiments focused on the ring finger motion s neuron control in the forearm prosthesis and on the neural path transmission of the tactile sensation coming from the pressure sensors fitted on the small finger phalanges (F5). For the ring finger, both motor control and sensory feedback are transmitted through the ulnar nerve s motor axons, respectively by the ulnar nerve s sensory axons. At the beginning of this study, the topography of the ulnar nerve has been performed, in order to identify the axons by which motor controls are transmitted for the small finger movement (F5) and the axons through which small finger (F5) tactile information is transmitted. A Carl Zeiss S8 electronic microscope was used to analyze the ulnar nerve s transverse sections for an anonymous patient. Cross sections in the ulnar nerve have been examined, from the tip of the small finger (F5) to the shoulder area. The separately mappings of motor and sensory axons from the ulnar nerve at the wrist s level and at the elbow s level were then performed. 3D modeling was performed using CATIA software solution for mapping the axon topography in the ulnar nerve. By means of the ulnar nerve s 3D topographic map, the optimal place for the implantation of both motor control electrodes and small finger (F5) sensory feedback electrodes were identified in the particular case of a patient with forearm amputation. Subsequently, by surgical procedures, experimental implantation of a motor control electrode for the small finger (F5) from a neuro-prosthesis was performed as well as a sensory feedback electrode for the same finger. For the next two weeks, measurements were made while the patient has been learning to move the small finger (F5) of the neuro-prosthesis and feel the tactile sensation from this finger. After these two weeks the electrodes were extracted from the patient s stump by surgery.