Modeling the impact of spinal cord stimulation paddle lead position on impedance, stimulation threshold, and activation region

The effectiveness of spinal cord stimulation (SCS) for chronic pain treatment depends on selection of appropriate stimulation settings, which can be especially challenging following posture change or SCS lead migration. The objective of this work was to investigate the feasibility of using SCS lead impedance for determining the location of a SCS lead and for detecting lead migration, as well as the impact of axial movement and rotation of the St. Jude Medical PENTA™ paddle in the dorsal-ventral or medial-lateral directions on dorsal column (DC) stimulation thresholds and neural activation regions. We used a two-stage computational model, including a finite element method model of field potentials in the spinal cord during stimulation, coupled to a biophysical cable model of mammalian, myelinated nerve fibers to calculate tissue impedance and nerve fiber activation within the DC. We found that SCS lead impedance was highly sensitive to the distance between the lead and cerebrospinal fluid (CSF) layer. In addition, among all the lead positions studied, medial-lateral movement resulted in the most substantial changes to SC activation regions. These results suggest that impedance can be used for detecting paddle position and lead migration, and therefore for guiding SCS programming.