These findings present for the first time, the influence of spinal cord anatomy on the effects of epidural stimulation and the role of specific orientation of electrodes on the dorsal surface of the dura mater in relation to the dorsal roots. Linear regression analysis between intersegmental landmarks was performed and L2 intervertebral spinous process length was selected as the anatomical reference in order to correlate vertebral landmarks and the spinal cord structures. Based on anatomical measurements of the lumbar spine and spinal cord, significant differences were found between L1-L4 to L5-L6 segments in terms of spinal cord gross anatomy, dorsal roots and spine landmarks. Positioning the electrode close to the dorsal roots produced a significantly higher impact on motor evoked responses than rostro-caudal shift of electrode from segment to segment. We found that the proximity of the stimulating electrode to the dorsal roots entry zone across spinal segments was a critical factor to evoke higher peak-to-peak motor responses. In this study, the neuroanatomy of the swine lumbar spinal cord, particularly the spatial orientation of dorsal roots was correlated to the anatomical landmarks of the lumbar spine and to the magnitude of motor evoked potentials during epidural electrical stimulation (EES).

6Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russia.

5Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States.

4Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, MN, United States.3Department of Biological Sciences, Lehigh University, Bethlehem, PA, United States.2Mayo Clinic Graduate School of Biomedical Sciences, Mayo Clinic, Rochester, MN, United States.1Department of Neurologic Surgery, Mayo Clinic, Rochester, MN, United States.

Grahn 1 Bruce Knudsen 1 Tuan Pham 3 Kendall H.

Spinal cord dorsal column stimulator