Anatomic Midline

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
of California, San Diego, San Diego, CA
2Boston Scientific Neuromodulation, Valencia, CA
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This study was supported by Boston Scientific Neuromodulation. No
disclosures to report.
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Background: Anatomic vs Physiological Midline
•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
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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
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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
• 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
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Anatomic vs Physiologic Midline :
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).
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Figure adapted from North et al 2002
Anatomic vs Physiologic Midline:
Data Analysis Methods: Paresthesia Symmetry
Paresthesia Coverage:
Body figure segmented along lines
defined by Barolat et al 1993
Total Left Pixels
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.
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Total Right Pixels
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
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Anatomic vs Physiologic Midline:
Correlation Analysis
Paresthesia Distribution vs Anatomic Midline
Paresthesia 100% to Left Side of Body
Anatomically Offmidline, but Symmetric
Paresthesia Balanced on Both Sides
Near Anatomic Midline,
but highly Asymmetric
R2 = 0.522
P < 0.001
Paresthesia 100% to Right Side of Body
Number of mm Left (-) or Right (+) of Anatomic Midline
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Anatomic vs Physiologic Midline:
• 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
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