The Importance of the Location of Dorsal Root Ganglion Stimulator Electrodes Within the Nerve Root Exit Foramen

Abstract

Objective To quantify the relationship between the electrical power requirement to achieve pain relief and the position of the active electrode of dorsal root ganglion stimulators within the spinal nerve root exit foramen. Materials and Methods Retrospective analysis of prospectively collected data of 92 consecutive patients undergoing dorsal root ganglion stimulation (DRGS) for chronic pain in a single center. Cervical and sacral cases, and failed trials/explanted DRGS were excluded, so we report on 57 patients with 78 implanted leads. Anteroposterior and lateral fluoroscopic images of the lead in the exit foramen were examined, and the active electrode positions were put into categories depending on their location relative to fixed anatomical landmarks. The clinical outcome and the power requirements for each of these groups of electrodes were then analyzed. Overall pain outcome was assessed by numeric pain rating scale score pre‐operatively and post‐operatively. Results There was no significant relationship between power requirements and mediolateral electrode position, although the lowest average was observed with electrode positions directly below the center of the pedicle. On lateral x‐ray, the lowest power requirements were observed in the electrodes positioned superodorsally or dorsally within the foramen. Importantly, power requirements in this location were consistently low, while the power requirements in other locations were not only higher but also much more variable. Electrodes in the superodorsal position required a median output power almost four times lower than electrodes in other positions (p = 0.002). Clinical outcome was not significantly related to power requirement or foraminal position. Conclusion Aiming for a superodorsal electrode position on lateral intraoperative fluoroscopy is desirable, since siting leads in this location reduces the required stimulator output power very substantially and thus will extend battery life. Position within the foramen does not determine clinical outcome, and so the implanter can safely aim for the low power site without detriment to the analgesic efficacy of the system.

The Effect of Clinically Controllable Factors on Neural Activation During Dorsal Root Ganglion Stimulation

“…Recent clinical studies have highlighted the importance of the electrode location relative to the ganglion to DRGS‐induced pain relief (65, 66). To examine the effect of electrode position on DRGS‐induced neural activation, we calculated activation thresholds for each cell type in response to DRGS applied with several electrode locations relative to the ganglion.…”

“…This positioning likely resembles our models where the second and third contacts are straddling the ganglion, as lumbar DRG are typically located in the “foraminal zone” (i.e., beneath the pedicle) (27). Martin and colleagues found that power consumption by the implanted pulse generator (IPG) was minimized by electrodes placed superodorsally in the foramen, a similar position to what the NACC suggests to be optimal (65). However, Martin and colleagues found that clinical outcomes were not dependent on the position of the electrode in the foramen.…”

A Literature Review of Dorsal Root Entry Zone Complex (DREZC) Lesions: Integration of Translational Data for an Evolution to More Accurate Nomenclature

“… 9 , 14 , 45–52 A similar process is utilized during surgical implantation of DRG stimulators. 53 Irrespective of the procedure being performed, this neurosensory stimulation is a process non-specific to any one component of the DREZC, as any component within this linear sensory pathway will transmit a similar positive sensory response as any adjacent segment of the DREZC. 11 This positive correlation between sensory capture and positive clinical outcomes is a direct reflection of sensory capture of the DREZC, rather than capture of any one component alone.…”

“…Intraoperatively, both surgical exposure with direct visualization and the use of fluoroscopy have their limitations with resultant failure rates ( Figures 5 and 6 , Table 3 ). When neurosensory mapping is used to supplement surgical exposure of fluoroscopic imaging to identify the dorsal segments correlating with the patient’s pain, the technology utilized for neurosensory mapping does not itself differentiate between the individual DREZC components, and yet efficacy is not compromised, 38 , 43 , 44 , 53 further supporting the assertion for the nomenclature to rightfully evolve to the more sensitive and inclusive terminology, “DREZC lesions.”…”

Invasive Electrical Neuromodulation for the Treatment of Painful Diabetic Neuropathy: Systematic Review and Meta-Analysis

“…Although more economical stimulation paradigms for SCS are being developed, DRGS benefits from markedly (~90%) lower energy consumption than typical SCS, largely due to the negligible layer of subdural cerebrospinal fluid at the DRG. This can be further optimized with prudent DRG electrode placement (64). This decreases the clinical and economic burden of IPG replacements: the most expensive hardware component.…”