Neuromodulation for Failed Back Surgery Syndrome Part I

Neuromodulation for Failed Back Surgery Syndrome

Part I

Richard K. Osenbach, M.D.Director of Neuroscience and Neurosurgery

Cape Fear Valley Health SystemFayetteville, NC

8/3/2006

Pain Treatment Continuum

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Why Neuromodulation?

Testable

Completely reversible

Non-destructive

No limitation to future therapy

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Patient Selection Criteria forImplantable Pain Therapies

SCS and IT Drug Delivery

Failure of more conservative therapiesFurther surgical intervention is not indicatedAbsence of serious untreated drug habituation Psychological evaluation and clearance for implantation has been obtainedNo contraindications to implantation exist.

sepsis, coagulopathy, etc.

Successful screening trial

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Indications for Psychological ConsultOutcome 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 forPsychological/Behavioral Evaluation

Identify any untreated or under treated major affective disorderAxis 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 pastExceptions/attributions regarding pain and proposed therapyNonphysical factors – Their contribution to patient’s pain perception and behaviorType and degree of social support

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Psychological Report

Name:__________________Date:___________________Diagnosis: Crazy: _____Not Crazy: _____

Signed: U. R. Nuts, Psychologist

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Principles of ScreeningIdentify and accurately select patients who will achieve long-term success following implantation of a SCS or ITDD systemGoals 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 basisTrial should approximate as closely as possible the conditions of long-term therapySCS represents a SINGLE element in overall long-term pain management for a given patient

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Assessment of SCS TrialWhat 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 responseWhat is significant?“One man’s junk is

another man’s treasure”

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• 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

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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 StimulationGate Control Theory of Pain

Melzack and Wall

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History of Spinal Cord StimulationShealy, 1969

1967 – Long and Wall, PNS1969 – Shealy, SCS in humans1975 – Dooley, perc. electrodeMid 1970s – self-powered battery1980s - programmable quad electrode1980s -1990s – Primary cell IPG2004 – Rechargeable IPG

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Mechanisms of SCSGate 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 durationNo clear data to suggest that trial duration has a significant influence on outcomeDo longer trials confer any advantage?

Allows adjustment of stimulation parameters if neededIs there a “placebo” effect?Do positive effects of stimulation persist through the entire duration of the trial?Assessment of function

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Essential Information from TrialIs 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 stimulationWhat degree of analgesia was achieved?Were the goals of the trial as determined by the patient and physician met?

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Screening Methods for SCSTemporary percutaneous trial

Electrode removed at conclusion of trialIdeal screening methodLower expectation of success

Tunneled percutaneous trialElectrode intended to be permanent No considerations for surgical leadHigh likelihood trial will be successful2nd procedure always required Higher risk of infection (?)Ensures reproducible stimulation pattern

Surgical lead trialInability to place percutaneous leadsPrior spinal decompressionC1-2 electrodes

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SCS – The Biggest Lies Ever Told“Don’t worry, the permanent stimulator will work better than the trial”

“This device is going to relieve all of your pain”

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Permanent Implant Decision MakingPercutaneous or surgical lead

Complexity of pain patternLikelihood of lead migrationPrior spinal surgery

Single or multiple electrodesBilateral pain = multiple electrodesComponent of axial painLikelihood of pain to change over time

Primary cell vs. rechargeable IPGPower requirementsPatient convenience and complianceCognitive capacity of patient

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Percutaneous (Wire) ElectrodesEasy to insertAbility to “custom design” systemIdeal for screening trial

Avoids 2nd procedure Subject to migration

Especially in cervical spineInsertion difficult following posterior decompressionCircumferential contacts

May have higher power requirements

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Plate or Surgical ElectrodesLaminotomy 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

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Power SourcesExternal RF system

More power and flexibilityInconvenience for patientUnable to use during certain activitiesDifficulty in manipulating systemCoupling problem

Primary cell IPG systemMore convenientFinite battery life

Rechargeable IPG systemExtended battery life16 contacts – Increased programming flexibilityRequires recharging by patient

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Device Selection Matrix

 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

Primary Cell IPG Rechargeable IPG RF System

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Anesthesia for SCS ImplantLocal 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

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Complications of SCSBleeding problems

Spinal epidural hematomaWound hematoma/seroma

InfectionWound infectionSpinal epidural abscess

Neurological injuryLumbar puncture headacheElectrode migration or fracture

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Reflex sympathetic dystrophy Radicular pain Brachial plexitis Peripheral vascular disease Angina

High

ModerateModerate

Low Perineal pain Rectal pain Zoster pain Anesthesia dolorosa

Low back pain

Probability of Success

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Persistent Pain in aPersistent Pain in a RadicularRadicular Distribution Distribution

That Does Not RespondThat Does Not Respond To Conventional TreatmentTo Conventional Treatment

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T10-S1 Fusion for L3 Neuropathic Pain !!!!!T10-S1 Fusion for L3 Neuropathic Pain !!!!!

In a 70 Y/O Woman no less!!!In a 70 Y/O Woman no less!!!

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The Low Back

So what about getting the low back?Several hypothetical reasons for why it is a challenging target

Sensory homunculusSmall body area relative to legsProbably 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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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

DC fibers of L2 Dermatome

Fiber Distribution within Dorsal Columns

Low Back Fiber

Anterior leg fiber

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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

DC fibers of L2 Dermatome

What Does All of This Mean

Sacral FibersLumbar FibersThoracic Fibers

Low Back Fiber

Anterior leg fiber

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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.

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General Principles of Lead PostioningClinically, the most effective stimulation is elicited from electrodes placed within 3mm of midlineAxial structures best stimulated with midline electrodesUpper extremity stimulated relatively easily with either midline or laterally-placed electrodesChest/abdomen best stimulated with more laterally-placed electrodesLower thoracic region – lateral electrodes more common stimulate anterior part of leg; posterior leg more easily stimulated from midlineAvoid overdriving one area to achieve stimulation in another

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Electrical Field ShapingSingle Lead Bipole Dual Lead Bipole

Transverse Guarded ArraySingle Lead Guarded Array

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Pitfalls of Spinal Cord StimulationLack 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

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C2-3C2-3 C7-T1C7-T1Electrode Electrode LocationLocationPain in the jaw, Pain in the jaw,

neck, upper neck, upper extremityextremity

Pain in the axilla, upper Pain in the axilla, upper chest wall and C8-T1 chest wall and C8-T1

distributiondistribution

Brachial Plexus Stretch Injury

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SCS for Axial Low Back PainNorth et. al., Spine, 2005

0

20

40

60

80

100

6 month 2 years

Stimulation Coverage of LBP

0

20

40

60

80

100

6 months 2 years

Relief of LBP

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SCS vs. Reoperation vs. DRG

** Patients reporting pain relief in excess of 50%Patients reporting pain relief in excess of 50%North et al., North et al., NeurosurgeryNeurosurgery, 1991, 1991

Per

cent

of P

atie

nts*

Dorsal RootGanglionectomy

Reoperation Spinal Cord Stimulation

0

1020

3040

50

6070

8090

100

6 Wks 6 Mos 2 Yrs 5 Yrs

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Reduction in Pain

50% - 60% of patients will derive at least 50% reduction

in pain with spinal cord stimulation

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SCS - Analgesic Consumption

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SCS - Enhanced ADL

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Return to Work

J. McGill, J Occupational Medicine, 1968

Percentage Who Return to Work

Leng

th o

f Tim

e O

ff W

ork

2%

19%

94%

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Cost Benefit Analysis of Neurostimulation Mekhail et. al., Clin J Pain, 2004:462-468

Assessment of healthcare utilization prior to SCS implantationNet differences in events per year calculated and modeled to 2000 cost data from CMS Fee Schedule and Healthcare Financing AdministrationNet 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

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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.