Neuromodulation for Failed Back Surgery Syndrome Part I

Report
Neuromodulation for Failed
Back Surgery Syndrome
Part I
Richard K. Osenbach, M.D.
Director of Neuroscience and Neurosurgery
Cape Fear Valley Health System
Fayetteville, NC
Pain Treatment Continuum
8/3/2006
Why Neuromodulation?
Testable
Completely reversible
Non-destructive
No limitation to future therapy
8/3/2006
Patient Selection Criteria for
Implantable Pain Therapies
SCS and IT Drug Delivery
Failure of more conservative therapies
Further surgical intervention is not indicated
Absence of serious untreated drug habituation
Psychological evaluation and clearance for
implantation has been obtained
No contraindications to implantation exist.
sepsis, coagulopathy, etc.
Successful screening trial
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Indications for Psychological Consult
Outcome of diagnostic testing, suspected
pathology, signs & symptoms do not fit
Markedly unusual reaction either positive or
negative to medicine / treatments
Suspicion of emotional “instability”
“Personality” concerns
Suspicion of poor / inadequate / inappropriate
coping, fears, beliefs, distress, expectations, and /
or attributions
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Suggested Referral Questions for
Psychological/Behavioral Evaluation
Identify any untreated or under treated major affective disorder
Axis II (personality/character) disorder – Affects if such disorder
on the perception of pain, compliance, cooperation, etc.
Any untreated or under treated alcohol or drug problems; present
or past
Exceptions/attributions regarding pain and proposed therapy
Nonphysical factors – Their contribution to patient’s pain
perception and behavior
Type and degree of social support
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Psychological Report
Name:__________________
Date:___________________
Diagnosis:
Crazy:
Not Crazy:
_____
_____
Signed: U. R. Nuts, Psychologist
8/3/2006
Principles of Screening
Identify and accurately select patients who will achieve
long-term success following implantation of a SCS or
ITDD system
Goals should be discussed and defined by both the
physician and patient BEFORE the trial
Goals are not uniform across patients – they need to be
defined on a case-by-case basis
Trial should approximate as closely as possible the
conditions of long-term therapy
SCS represents a SINGLE element in overall long-term
pain management for a given patient
8/3/2006
Assessment of SCS Trial
What Constitutes Success?
Success of an SCS trial must be defined in the context of
the goals that are set prior to the trial
Functional improvement
Mood
Medication use
Analgesic response
What is significant?
“One man’s junk is
another man’s treasure”
8/3/2006
• A SUCCESSFUL TRIAL
DOES NOT GUARANTEE
LONG-TERM SUCCESS OF
A PAIN IMPLANT
• 50% OF PATIENTS WHO
HAVE IPG FAILURE OR
PUMP BATTERY FAILURE
NEVER HAVE THEIR
DEVICE REVISED
8/3/2006
Everything Isn’t A Nail
Treating chronic pain is like building a house…..you need
more than one tool to successfully build a house. Similarly,
chronic pain can not be successfully managed over the long
term with a single modality.
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History of Spinal Cord Stimulation
Gate Control Theory of Pain
Melzack and Wall
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History of Spinal Cord Stimulation
Shealy, 1969
1967 – Long and Wall, PNS
1969 – Shealy, SCS in humans
1975 – Dooley, perc. electrode
Mid 1970s – self-powered battery
1980s - programmable quad
electrode
1980s -1990s – Primary cell IPG
2004 – Rechargeable IPG
8/3/2006
Mechanisms of SCS
Gate control theory
Direct inhibition of spinothalamic neurons
Descending modulatory effects
Alteration of sympathetic activity
Neurochemical modulation
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Duration of Screening Trial
Standard of care - trial of at least a couple days duration
No clear data to suggest that trial duration has a
significant influence on outcome
Do longer trials confer any advantage?
Allows adjustment of stimulation parameters if needed
Is there a “placebo” effect?
Do positive effects of stimulation persist through the
entire duration of the trial?
Assessment of function
8/3/2006
Essential Information from Trial
Is there adequate paresthesia overlap of the pain?
Can coverage be obtained with multiple contacts?
Did coverage of different pain areas require different
electrode combinations?
Stimulation parameters to achieve the ideal results?
Were there any adverse effects of stimulation?
Painful stimulation, root/trunk stimulation
What degree of analgesia was achieved?
Were the goals of the trial as determined by the patient and
physician met?
8/3/2006
Screening Methods for SCS
Temporary percutaneous trial
Electrode removed at conclusion of trial
Ideal screening method
Lower expectation of success
Tunneled percutaneous trial
Electrode intended to be permanent
No considerations for surgical lead
High likelihood trial will be successful
2nd procedure always required
Higher risk of infection (?)
Ensures reproducible stimulation pattern
Surgical lead trial
Inability to place percutaneous leads
Prior spinal decompression
C1-2 electrodes
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8/3/2006
SCS – The Biggest Lies Ever Told
“This device is going to
relieve all of your pain”
“Don’t worry, the
permanent stimulator
will work better than
the trial”
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Permanent Implant Decision Making
Percutaneous or surgical lead
Complexity of pain pattern
Likelihood of lead migration
Prior spinal surgery
Single or multiple electrodes
Bilateral pain = multiple electrodes
Component of axial pain
Likelihood of pain to change over time
Primary cell vs. rechargeable IPG
Power requirements
Patient convenience and compliance
Cognitive capacity of patient
8/3/2006
Percutaneous (Wire) Electrodes
Easy to insert
Ability to “custom design” system
Ideal for screening trial
Avoids 2nd procedure
Subject to migration
Especially in cervical spine
Insertion difficult following
posterior decompression
Circumferential contacts
May have higher power
requirements
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Plate or Surgical Electrodes
Laminotomy required
Less migration and reduced
revision rates
Easier to place after
laminectomy
Insulated contacts may
reduce power requirements
Fixed arrays
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Spinal Cord Stimulation
8/3/2006
Power Sources
External RF system
More power and flexibility
Inconvenience for patient
Unable to use during certain activities
Difficulty in manipulating system
Coupling problem
Primary cell IPG system
More convenient
Finite battery life
Rechargeable IPG system
Extended battery life
16 contacts –
Increased programming flexibility
Requires recharging by patient
8/3/2006
Device Selection Matrix
Primary Cell IPG
Rechargeable IPG
RF System
Power Needs
Low to
moderate
Moderate to high
Very high
Frequency Needs
Low
Moderate to high
Very high
Pain Targets
Single
Multiple
Multiple
Disease State
Stable
Stable or likely to progress
Stable or likely to progress to
multiple extremeties
Coverage Needs
1 or 2 leads
1, 2, 3, or 4 leads
1, 2, 3, or 4 leads
Compliance Requirements
Easiest to use
Requires following specific battery
management procedures
Requires daily effort
Competence
(physical or mental limitations)
Appropriate for
all levels
Moderate level required
Moderate to high level required
Programming Needs (programs
running in parallel)
Simple, <2
Moderate, <3
Complex, >3
Skin Sensitivity
N/A
Moderate to low sensitivity
Low to no sensitivity
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Anesthesia for SCS Implant
Local anesthesia with IV sedation
Avoid benzodiazepines
Infiltration of periosteum
Injection of local anesthetic epidurally
General anesthesia
Radiological position
Evoked motor responses
• C1-2 paddles
• Lumbar nerve root
• Sacral paddles
Spinal anesthesia
Require less patient sedation
Does not usually influence ability to produce stimulation
Perception thresholds may be slightly higher
8/3/2006
Complications of SCS
Bleeding problems
Spinal epidural hematoma
Wound hematoma/seroma
Infection
Wound infection
Spinal epidural abscess
Neurological injury
Lumbar puncture headache
Electrode migration or
fracture
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Probability of Success
High
Moderate
Low
Reflex sympathetic dystrophy
Radicular pain
Brachial plexitis
Peripheral vascular disease
Angina
Low back pain
Perineal pain
Rectal pain
Zoster pain
Anesthesia dolorosa
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Persistent Pain in a
Radicular Distribution
That Does Not Respond
To Conventional Treatment
8/3/2006
T10-S1 Fusion for L3 Neuropathic Pain !!!!!
In a 70 Y/O Woman no less!!!
8/3/2006
The Low Back
So what about getting the
low back?
Several hypothetical
reasons for why it is a
challenging target
Sensory homunculus
Small body area relative to
legs
Probably evenly distributed
in DC
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L2-L5 Dermatomes
If the ‘receptive fields’ per nerve are equal, then there would be at
least 4 times fewer fibers for back coverage than leg coverage
80%
20%
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Fiber Distribution within Dorsal
Columns DC fibers of L2
Finally, within the
“slice” of DC that
our L2 dermatome
represents, it makes
sense to think that
leg fibers and back
fibers would be
evenly spread out
in the slice
In other words, a
low back fiber is
just as likely to be
on top of the DC’s
as at the bottom
Dermatome
Anterior leg fiber
Low Back Fiber
8/3/2006
What Does All of This Mean
DC fibers of L2
Dermatome
So, Low Back fibers aren’t
especially important from a
functional standpoint
Few…
And Low Back fibers don’t
cover much body surface
area (relative to legs, with
which they share
dermatomes)
Fewer…
And Low Back fibers aren’t
especially “available” for
stimulation in the DC’s
May be hard to reach
enough of them to get
good coverage
Sacral Fibers
Lumbar Fibers
Thoracic Fibers
Anterior leg fiber
Low Back Fiber
8/3/2006
What Do We Want to Stimulate and
Where Should We Place the Lead???
Target: Usually Dorsal Columns.
Why?
• Minimal Side-Effects:
– DC has primarily sensory
fibers – if you activate them,
the patient will pretty much
only get sensation, not motor
or autonomic effects
• Efficient:
– DC is very “rich” – all the
body parts/dermatomes below
the level of the lead may be
stimulated from that lead
position
– Example: sometimes if you
stimulate in the cervical
region, you can get whole
body paresthesia.
To avoid (generally): Dorsal Roots.
Why?
• Side-Effects:
– DR’s carry all sorts of sensory
fibers, not just touch and
vibration, but also pain and motor
reflex. If you maximize DR
stimulation, the patient might
start feeling sharp pain or actually
get muscle contractions
• Inefficient/Inadequate:
– DR’s will only generate
paresthesia in a few dermatomes,
those represented at that spinal
level
– Example: if the lead is at T9, and
you stimulate the DR fibers there,
the patient will report a “narrow
band” of paresthesia in the chest
wall.
8/3/2006
General Principles of Lead Postioning
Clinically, the most effective stimulation is
elicited from electrodes placed within 3mm
of midline
Axial structures best stimulated with
midline electrodes
Upper extremity stimulated relatively easily
with either midline or laterally-placed
electrodes
Chest/abdomen best stimulated with more
laterally-placed electrodes
Lower thoracic region – lateral electrodes
more common stimulate anterior part of leg;
posterior leg more easily stimulated from
midline
Avoid overdriving one area to achieve
stimulation in another
8/3/2006
Electrical Field Shaping
Single Lead Bipole
Single Lead Guarded Array
Dual Lead Bipole
Transverse Guarded Array
8/3/2006
Pitfalls of Spinal Cord Stimulation
Lack of patience (not patients) during
intraoperative screening
Trial too short in duration – placebo effect
“False negative” trial
Use of different electrode configurations
from screening to permanent implant
8/3/2006
Brachial Plexus Stretch Injury
C2-3
Pain in the jaw,
neck, upper
extremity
Electrode
Location
C7-T1
Pain in the axilla, upper
chest wall and C8-T1
distribution
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SCS for Axial Low Back Pain
North et. al., Spine, 2005
Stimulation Coverage of LBP
Relief of LBP
100
100
80
80
60
60
40
40
20
20
0
0
6 month
2 years
6 months
2 years
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SCS vs. Reoperation vs. DRG
100
Dorsal Root
Ganglionectomy
80
70
60
50
40
30
20
Reoperation
Spinal Cord Stimulation
Percent of Patients*
90
10
0
6 Wks
6 Mos
2 Yrs
* Patients reporting pain relief in excess of 50%
North et al., Neurosurgery, 1991
5 Yrs
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Reduction in Pain
50% - 60%
ofMean
patients will
# of
Reference
Patients
Follow-up Results
North
171
7 years
 52%
with > 50% relief
derive
at
least
50%
reduction
Pain, 1993
 60% would repeat
Turner in pain
39 study
meta 16spinal
months  59% with
>50% relief
with
cord
Neurosurgery, 1995
analysis
De La Porte
64
4 years
 55% good to excellent relief
stimulation
Pain, 1993
Kupers
Pain, 1994
Kumar
Neurosurgery, 1991
Burchiel
Spine, 1996
70
3.5 years
 52% good to very good effect
94
3+ years
 66% good to excellent results
70
Multi-center
1 year
 55% with >50% relief
8/3/2006
SCS - Analgesic Consumption
Reference
Ohnmeiss
Spine, 1996
North
Neurosurg, 1993
De La Porte
Pain, 1993
Kumar
Neurosurg, 1991
Racz
Spine, 1989
# of
Patients
Mean
Follow-up Results
40
2 years
171
7 years
64
4 years
94
3+ years
26
1.8 years
 84% decreased or eliminated
narcotics use
 58% reduced or eliminated
analgesics
 90% reduced medication
 40% no longer needed
analgesics
 81% reduced or eliminated
narcotics use
8/3/2006
SCS - Enhanced ADL
Reference
De La Porte
Pain, 1993
Racz
Spine, 1989
Ohnmeiss
Spine, 1996
# of
Patients
64
Mean
Follow-up Results
4 years  61% improved ADLs
26
1.8 years  66% improved ADLs
40
2 years
 Statistically significant
improvement in “pain’s
effect on lifestyle”
8/3/2006
Length of Time Off Work
Return to Work
>2 years
2%
19%
> 90 days
< 90 days
94%
0%
25%
50%
75%
100%
Percentage Who Return to Work
J. McGill, J Occupational Medicine, 1968
8/3/2006
Cost Benefit Analysis of Neurostimulation
Mekhail et. al., Clin J Pain, 2004:462-468
Assessment of healthcare utilization prior to SCS implantation
Net differences in events per year calculated and modeled to 2000
cost data from CMS Fee Schedule and Healthcare Financing
Administration
Net annual savings of $30,221; $93,685 over 3 year implant
duration
$17,903 net per patient per year cost savings
Reduction in physician office visits, ER visits,
imaging procedure, nerve blocks,
hospitalizations, and surgical procedures
8/3/2006
SCS Cost Benefit Analysis
CONCLUSION:
Despite the high cost of SCS, there may
be substantial long-term economic benefit
based on the fact the patient treated with
neurostimulaion is more likely to
consume healthcare resources at a
significantly reduced rate.
8/3/2006

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