MR-based measurement of spinal cord motion during flexion of the spine: implications for intradural spinal cord stimulator systems

This study develops a means of delivering electrical stimuli directly to the pial surface of the spinal cord for treatment of intractable pain. This intradural implant must remain in direct contact with the cord as it moves within the spinal canal. Therefore, magnetic resonance imaging was used to measure the movement of the spinal cord between neutral and flexed-back positions in a series of volunteers (n = 16). Following flexion of the back, the mean change in the pedicle-to-spinal cord dorsal root entry zone distance at the T10-11 level was (8.5 ± 6.0) mm, i.e. a 71% variation in the range of rostral-caudal movement of the spinal cord across all patients. There will be a large spectrum of spinal cord strains associated with this observed range of rostral-caudal motions, thus calling for suitable axial compliance within the electrode bearing portion of the intradural implant.