Relationship between the Anatomic & Physiologic Midline in Spinal Cord Stimulation

1. Relationship between the Anatomic & Physiologic Midline in Spinal Cord Stimulation Nicholas Kormylo MD1, Tobias Moeller-Bertram MD1, Kerry Bradley MS2, Joanne Olecko MS2, Brad Hershey MS2, Michael Gallucci MS2, Nitzan Mekel-Bobrov PhD2, Lilly Chen MD2, Jay Schnitzer MD PhD2 1University of California, San Diego, San Diego, CA 2Boston Scientific Neuromodulation, Valencia, CA

2. Disclaimer • This study was supported by Boston Scientific Neuromodulation. No disclosures to report.

3. Lead placement at physiologic midline can maximize dorsal column (DC) stimulation Law 1987 Holsheimer et al 1993 Barolat et al 1993 North et al 2002 However, anatomic and physiologic midline may not be coincident Background: Anatomic vs Physiological Midline

4. Background: Anatomic vs Physiological Midline • Only 27% of combinations from leads on radiological midline result in symmetric paresthesia • Contacts may be as far as 3mm lateral to radiological midline and still generate bilateral paresthesia

5. Anatomic vs Physiologic Midline: Modern Technology Assessment • Objective: Investigate relationship between anatomic/radiologic midline and physiologic midline in modern SCS • Study Design: • Prospective, Single-center, Single-visit, Retrospective Analysis • Evaluated: • N = 10 (7M/3F; 13 ± 9 months post-IPG) • Chronic pain patients with low back/leg pain implanted for > 3 months with: • Precision Plus™ SCS IPG • 1 or 2 Linear™ octapolar percutaneous leads positioned between T8-10 (verified by fluoroscopy) • 500us, 50Hz

6. Anatomic vs Physiologic Midline : Performance • With patient in supine position, a variety of pre-randomized bipole combinations were programmed, on the most midline lead, determined by subject-reported paresthesia L-R balance. • For each combination, subjects drew location of paresthesia on electronic body figure at usage amplitude (80% of range between perception and max tolerable). Figure adapted from North et al 2002

7. Anatomic vs Physiologic Midline:Data Analysis Methods: Paresthesia Symmetry Total Left Pixels Total Right Pixels • Paresthesia Coverage: • Body figure segmented along lines defined by Barolat et al 1993 • Total pixels to left • and right side of body tallied • Paresthesia Symmetry = • Total Left Pixels/(Total Right Pixels + Total Left Pixels) • Average the symmetry scores for all bipoles using a given cathode • Regression of cathode position with respect to anatomic midline and symmetry of paresthesia.

8. Anatomic vs Physiologic Midline:Data Analysis Methods: Cathode Position • Cathode Position: • Only fluoro images deemed to be ‘pure AP’ • Definition:Anatomic Midline: • the piecewise continuous line joining the geometric midpoint between the pedicles • at multiple vertebral levels (T7 - T11) flanking the leads. • To determine contact offset from Anatomic Midline: • calculated the perpendicular distance of the center of each programmed cathode • from estimated anatomic midline

9. Anatomic vs Physiologic Midline:Correlation Analysis Anatomically Off-midline, but Symmetric Paresthesia Near Anatomic Midline, but highly Asymmetric Paresthesia Paresthesia 100% to Left Side of Body Paresthesia Balanced on Both Sides Paresthesia 100% to Right Side of Body

10. Anatomic vs Physiologic Midline:Conclusions • We observed high coincidence of perfectly symmetrical paresthesia and anatomic cathode ‘midlinity’ • Approximately 20% of subjects demonstrated clear deviations from anatomic-physiologic midline coincidence. • Contributed to significant variability in the data (SE = 0.05) • Our results suggest that percutaneous leads may be less sensitive to anatomic/physiologic midline discrepancy than leads with wide contacts