Spinal Cord Stimulation - Indications, Trial Period, and Complications

Quick Answer

What is spinal cord stimulation (SCS)?

Spinal cord stimulation is a neuromodulation therapy that delivers electrical impulses to the dorsal columns of the spinal cord via implanted electrodes, modulating pain signals before they reach the brain. It is indicated for chronic intractable neuropathic pain that has failed conservative management. [1,2]

Key indications:

• Failed back surgery syndrome (FBSS) - Most common indication (40-50% of implants)
• Complex regional pain syndrome (CRPS) types I and II
• Peripheral neuropathy (diabetic, chemotherapy-induced, idiopathic)
• Refractory angina pectoris (when revascularization not possible)
• Peripheral vascular disease (limb salvage)
• Phantom limb pain and post-amputation pain

Patient selection criteria:

1. Chronic pain >6 months duration
2. Failed conservative management (medications, physical therapy, injections)
3. No further surgical options or surgery unlikely to help
4. Neuropathic pain component (responds better than pure nociceptive pain)
5. Realistic expectations (pain reduction, not cure; improved function)
6. Psychological clearance (no untreated psychiatric comorbidity)
7. Ability to comply with therapy and follow-up
8. Trial stimulation successful (>50% pain reduction)

Trial-to-implant process:

Expected outcomes:

• 50-70% of patients achieve >50% pain reduction
• Reduced opioid consumption
• Improved function, sleep, and quality of life
• Cost-effective at 2-3 years

Complications:

• Lead migration (5-15% - most common technical issue)
• Infection (2-5%)
• Hardware failure/fracture
• Loss of efficacy over time (tolerance, electrode encapsulation)
• Dural puncture headache (rare)
• Epidural hematoma (rare)

Key principle: SCS is not a first-line therapy but an effective option for carefully selected patients with refractory neuropathic pain. Success requires comprehensive patient selection, successful trial, and ongoing multidisciplinary management.

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Clinical Overview

Mechanism of Action

Gate Control Theory (Melzack & Wall, 1965):

The fundamental mechanism of SCS is based on the gate control theory of pain:

1. Aβ fibers (large, myelinated) carrying non-nociceptive input from peripheral mechanoreceptors
2. Aδ and C fibers (small) carrying nociceptive input
3. First-order neuron in dorsal horn (transmission cell)
4. Inhibitory interneurons modulate transmission

Mechanism:

• Orthodromic stimulation of Aβ fibers (via SCS) activates inhibitory interneurons
• Inhibitory neurotransmitters (GABA, glycine) released
• Reduced excitability of transmission cells (second-order neurons)
• Nociceptive signals blocked from ascending to thalamus and cortex
• "Closes the gate" to pain transmission

Additional mechanisms identified:

Supraspinal mechanisms:

• Activation of descending inhibitory pathways (periaqueductal gray, rostral ventromedial medulla)
• Release of endogenous opioids, serotonin, norepinephrine
• Modulation of thalamic and cortical pain processing

Neurochemical effects:

• Increased GABA and glycine in dorsal horn (inhibitory)
• Decreased glutamate, aspartate (excitatory)
• Reduced substance P release from primary afferents
• Modulation of adenosine, nitric oxide

Cellular effects:

• Hyperpolarization of second-order neurons
• Reduced calcium influx in presynaptic terminals
• Long-term depression of synaptic transmission

10 kHz High-Frequency Stimulation (HF10):

• Newer paradigm using 10,000 Hz stimulation
• Mechanism different from traditional SCS (paresthesia-free)
• May work through inhibition of wide dynamic range neurons without orthodromic conduction
• Potential for better coverage, less tolerance

History and Evolution

Timeline of SCS development:

Technological advances:

• Rechargeable vs. non-rechargeable IPGs
• Multi-channel programming
• Anatomically targeted leads
• Wireless communication
• Patient programmer apps
• Burst stimulation patterns

Classification of SCS Systems

By electrode type:

By power source:

By stimulation paradigm:

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Indications and Patient Selection

FDA-Approved and Established Indications

Failed Back Surgery Syndrome (FBSS):

• Most common indication (40-50% of all implants)
• Persistent leg pain following lumbar surgery (decompression, fusion)
• No further surgical options identified
• Evidence: Level I RCTs show SCS superior to reoperation (North et al.) and conventional medical management (Kumar et al.)
• Success rate: 50-70% achieve >50% pain relief

Complex Regional Pain Syndrome (CRPS):

• CRPS Type I (reflex sympathetic dystrophy)
• CRPS Type II (causalgia)
• Especially effective for upper limb CRPS
• Early intervention more effective (<2 years duration)
• Evidence: Kemler et al. RCT showed significant benefit at 2 years
• Note: Physical therapy must continue alongside SCS

Peripheral Neuropathy:

• Diabetic peripheral neuropathy (refractory cases)
• Chemotherapy-induced peripheral neuropathy
• Idiopathic peripheral neuropathy
• Painful polyneuropathy
• Evidence growing; NNT ~3

Refractory Angina Pectoris:

• When revascularization not possible or incomplete
• Reduces angina frequency, improves exercise tolerance
• Does NOT mask acute MI symptoms (patients still feel ischemia differently)
• Mechanism: Improved myocardial perfusion (coronary blood flow redistribution)
• Cost-effective alternative to repeated revascularization

Peripheral Arterial Disease:

• Critical limb ischemia (limb salvage)
• Non-reconstructable PAD
• Improves microcirculatory blood flow
• Reduces amputation rates

Other Established Uses:

• Phantom limb pain
• Post-amputation pain
• Post-herpetic neuralgia
• Painful diabetic neuropathy
• Spinal cord injury pain (limited evidence)

Off-Label and Emerging Indications

• Chronic abdominal/pelvic pain
• Chronic migraine/cluster headache (occipital nerve stimulation)
• Visceral pain
• Fibromyalgia (limited evidence)
• Cancer pain (intrathecal preferred, but SCS used occasionally)

Patient Selection Criteria

Absolute requirements:

Psychological screening (essential):

Contraindications:

Absolute:

• Active infection (systemic or at implant site)
• Uncorrected coagulopathy/bleeding diathesis
• Inability to undergo surgery
• Untreated severe psychiatric disorder
• Inability to operate device or comply with follow-up
• Demand pacemaker/ICD without consultation (electromagnetic interference possible)
• Pregnancy (theoretical risk)
• Life expectancy <6 months (usually)

Relative:

• Severe spinal deformity/scoliosis (technical difficulty)
• Previous spinal surgery with extensive scarring
• Severe epidural fibrosis
• Morbid obesity (infection risk, technical difficulty)
• Immunosuppression
• Diabetes (infection risk)
• Prior radiation to implant site
• MRI requirement (though MRI-conditional systems now available)
• Pacemaker/ICD (requires coordination with cardiology)

Predictors of success:

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Trial Period

Purpose of Trial Stimulation

Rationale:

• Assess efficacy before permanent implant (expensive, invasive)
• Allows patient to experience therapy
• Validates appropriate patient selection
• Predicts long-term success
• Opportunity to optimize lead placement

Duration:

• Traditionally 3-7 days
• Recent evidence supports 24-hour trials (cost-effective, adequate prediction)
• Some centers use extended trials (weeks) for complex cases
• Minimum: Must cover typical pain variability (work, activity, sleep)

Trial Procedure

Pre-trial preparation:

• Informed consent (purpose, limitations, risks)
• Review anticoagulation (stop per guidelines - warfarin INR <1.5, DOACs per clearance)
• Pre-operative antibiotics (cefazolin or vancomycin if allergic)
• Psychological clearance
• Mark pain distribution on body diagram
• Establish baseline pain scores (rest, activity), medication use, function

Trial lead placement:

Technique:

1. Position: Prone or lateral decubitus
2. Sedation: Conscious sedation (midazolam ± fentanyl) - patient must be awake for feedback
3. Access: Tuohy needle insertion into epidural space (paramedian approach)
4. Loss of resistance: To saline or air
5. Lead insertion: Cylindrical lead advanced under fluoroscopy
6. Positioning: Lead tip at appropriate spinal level

Spinal targeting:

Intraoperative testing:

• Connect to external trial stimulator
• Test stimulation at various contacts
• Paresthesia mapping: Patient reports where they feel stimulation
• Goal: Paresthesia overlaps pain distribution
• Adjust amplitude, pulse width, frequency
• Document optimal contacts and parameters

Post-procedure:

• Sterile dressing (tunnel if extended trial)
• Pain management (post-procedure discomfort)
• Activity restrictions (no bending, twisting, lifting)
• Home trial or inpatient observation

Trial Assessment

Outcome measures:

Trial success criteria:

• Traditional: >50% pain relief with improved function
• Some centers accept >30% with significant functional gain
• Consistent response over trial period
• Patient desires permanent implant

Trial failure - reassess:

• Lead malposition (repeat trial with revision)
• Technical issues (generator, connection)
• Unrealistic expectations (counseling)
• Poor patient selection (may be contraindicated)

Trial-to-Permanent Conversion Rate

• 60-80% of trials proceed to permanent implant
• Predictors of conversion: Successful trial, appropriate patient selection, realistic expectations
• Failed trials should prompt re-evaluation before repeat attempt

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Permanent Implant Procedure

Surgical Technique

Pre-operative:

• Confirm trial success
• Pre-operative antibiotics
• Anticoagulation management
• Mark IPG pocket location (buttock, abdomen, flank, chest wall)

Implantation:

Two approaches:

1. Percutaneous leads (most common):

• Epidural needle insertion as per trial
• Lead advanced to target position
• Anchoring suture to prevent migration
• Tunneling to IPG pocket

2. Paddle leads (surgical):

• Laminotomy or partial laminectomy
• Direct visualization of epidural space
• Paddle insertion under direct vision
• Better coverage, lower migration risk
• Longer procedure, more invasive

IPG placement:

• Location options:

  • Gluteal region (most common for lumbar leads)
  • Anterior abdominal wall
  • Lateral chest wall (cervical leads)
  • Infraclavicular
  • Flank

• Pocket creation: Subcutaneous pocket; must accommodate IPG with slack

• Lead tunneling: Tunnel from spinal entry to IPG pocket

• Connection: Lead(s) connected to IPG

• Implantation: IPG placed in pocket; closure in layers

Post-operative care:

• Observation (usually overnight or day case)
• Pain management
• Prophylactic antibiotics (24-48 hours)
• Dressing care (keep dry 7-10 days)
• Activity restrictions (similar to trial)
• Wound check at 7-14 days

Programming and Optimization

Initial programming (post-implant):

Parameters:

Programming approach:

• Identify active contacts providing paresthesia overlap
• Adjust amplitude to comfortable level
• Vary pulse width for best coverage
• Test different frequencies
• Save successful programs
• Teach patient to use programmer

Follow-up schedule:

• 2-4 weeks post-implant: Initial programming, wound check
• 1-3 months: Optimization
• 6 months: Review outcomes
• Annually: Long-term follow-up
• As needed: Troubleshooting, reprogramming

Patient education:

• Charging (rechargeable systems)
• Programmer use
• Activity restrictions initially
• When to contact clinic
• MRI precautions
• Electromagnetic interference (airport security, theft detectors)

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Outcomes and Evidence

Efficacy Data

Failed Back Surgery Syndrome:

CRPS:

Peripheral Neuropathy:

• Growing evidence base
• NNT ~3 for >50% pain relief
• Particularly effective for painful diabetic neuropathy

Angina:

• Multiple RCTs showing benefit
• Reduces angina episodes, improves exercise capacity
• Mechanism: Improved myocardial perfusion
• Does not mask acute coronary syndrome

Limb Ischemia:

• Reduces amputation rates
• Improves microcirculation
• Quality of life improvements

Functional and Quality of Life Outcomes

Cost-Effectiveness

• Initial cost: $20,000-40,000 AUD (device + procedure)
• Cost-effective at 2-3 years compared to ongoing medical management
• Factors: Reduced hospitalizations, reduced opioid costs, improved productivity
• Cost per QALY within acceptable range (varies by jurisdiction)

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Complications

Technical Complications

Lead migration:

• Incidence: 5-15% with cylindrical leads; <5% with paddle leads
• Presentation: Loss of paresthesia coverage, pain recurrence
• Risk factors: Lead placement in mobile spine, inadequate anchoring, body habitus
• Management: Reprogramming (activate different contacts), revision surgery if failed
• Prevention: Paddle leads, secure anchoring, avoiding mobile segments

Lead fracture/breakage:

• Incidence: 5-10% over 5 years
• Causes: Fatigue, micro-movements, trauma
• Diagnosis: Impedance abnormalities on testing, intermittent function
• Management: Surgical revision, lead replacement

Lead dislodgement:

• Pull-out from anchoring or IPG
• Similar presentation to migration

IPG malfunction:

• Battery failure (non-rechargeable)
• Electronic component failure
• Software issues
• Management: IPG replacement surgery

Connection issues:

• Lead-IPG connection failure
• Extension cable issues (if used)
• Often presents as sudden loss of therapy

Biological Complications

Infection:

• Incidence: 2-5% (higher in diabetic patients)
• Types:
  • Superficial incisional (most common)
  • Deep pocket infection
  • Epidural abscess (rare, serious)
  • Meningitis (rare, intrathecal systems)
• Risk factors: Diabetes, obesity, immunosuppression, prolonged procedure, diabetes
• Prevention: Pre-op antibiotics, sterile technique, tight glycemic control
• Management:
  • Superficial: Antibiotics, local care
  • Deep/pocket: Remove hardware (usually), antibiotics, re-implant later
  • Epidural abscess: Urgent decompression, antibiotics

Pain at IPG site:

• Common initially, usually resolves
• May require IPG repositioning
• Rarely indicates infection

CSF leak/dural puncture:

• Risk: 1-2% with percutaneous leads
• Presentation: Postural headache (worse upright, better supine)
• Management:
  • Conservative: Bed rest, hydration, caffeine, analgesics (usually resolves 5-7 days)
  • Epidural blood patch if severe/persistent
  • Surgical repair (rare)

Epidural hematoma:

• Rare (<0.1%) but serious
• Risk factors: Anticoagulation, coagulopathy
• Presentation: Back pain, neurological deficit (urgent)
• Management: Emergency surgical decompression

Seroma:

• Fluid collection at IPG pocket
• Usually self-limiting
• May require aspiration if symptomatic

Clinical Complications

Loss of efficacy:

• Occurs in 10-30% over time
• Causes:
  • Tolerance to stimulation
  • Electrode encapsulation (fibrosis)
  • Disease progression
  • Psychological factors
• Management: Reprogramming, revision surgery, medical optimization, psychological support

Uncomfortable paresthesia:

• Poorly localized stimulation
• Allodynia to paresthesia
• Motor stimulation (unpleasant)
• Management: Reprogramming, lead revision

Inadequate coverage:

• Lead migration, poor initial placement
• Complex pain patterns (axial + extremity)
• Multiple dermatomal involvement

Device-Related Issues

Electromagnetic interference:

• Airport security systems (rarely cause heating if pause over device)
• Theft detection systems (walk through quickly)
• MRI (only with MRI-conditional systems; specific protocols required)
• Diathermy (contraindicated)
• Radiofrequency ablation (caution)
• Lithotripsy (may damage device)

Charging issues (rechargeable):

• Patient non-compliance
• Charging coil misalignment
• Skin irritation from charger

Warranty/expiration:

• Non-rechargeable: 2-5 years
• Rechargeable: 7-10+ years
• Requires replacement surgery

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Special Considerations

MRI and SCS

Traditional systems:

• MRI contraindicated (risk of lead heating, device damage, patient injury)
• CT or alternative imaging required

MRI-conditional systems (modern):

• Specific MR Conditional labeling
• 1.5T or 3T capable
• Strict protocols required:
  • Specific body region only (often exclude IPG pocket)
  • SAR (specific absorption rate) limits
  • Mode: Normal Operating Mode
  • Head transmit/receive coil for cervical imaging
  • Post-scan IPG check

Always:

• Consult manufacturer's guidelines
• Contact implanting center before MRI
• Check device function post-MRI

Cardiac Devices and SCS

Pacemaker/ICD interaction:

• Potential for electromagnetic interference
• Pacemaker may sense SCS signals
• Risk of inappropriate inhibition (pacemaker) or shock (ICD)

Management:

• Cardiology consultation pre-implant
• Testing during trial (paced rhythm)
• Programming adjustments if needed
• Some modern pacemakers/ICDs more resistant to interference
• May be relative contraindication

Pregnancy

• Limited data
• Theoretical risks (lead migration with changing body habitus, electromagnetic effects on fetus)
• Generally avoid if pregnancy anticipated
• Case reports of safe pregnancies with SCS
• Multidisciplinary management if occurs

Pediatric Patients

• Limited data, small case series
• Consider only in refractory cases (CRPS, FBSS)
• Growth considerations (lead length, IPG location)
• Psychological maturity important

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Indigenous Health Considerations

Access Barriers:

• Geographic remoteness - limited access to specialized pain centers
• Travel requirements for trial, implant, programming
• Cost and support for travel/accommodation
• Limited MRI access in remote areas (compatibility issues)

Cultural Considerations:

• Traditional healing may be preferred
• Trust issues with implanted technology
• Family decision-making processes
• Need for culturally safe education about device

Management Approaches:

• Telemedicine for follow-up programming when possible
• Coordinated care with local services for wound care, troubleshooting
• Culturally appropriate education materials
• Support for extended stay near implant center
• Aboriginal Liaison Officer involvement

Māori Considerations:

• Whānau involvement in decision-making
• Integration with traditional healing if requested
• Clear communication about technology

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ANZCA Exam Focus

High-Yield Topics

Written Examination:

• Mechanism of SCS (gate control theory)
• Indications (FBSS, CRPS, neuropathy)
• Patient selection criteria
• Trial procedure and assessment
• Complications and management
• Contraindications

Viva Voce:

• Mechanism of SCS
• Patient selection for SCS
• Trial procedure description
• Complication scenarios (infection, lead migration)
• Case: FBSS patient - is SCS appropriate?

Common Exam Scenarios

Scenario 1: FBSS Patient Selection

• 45-year-old, 2 prior lumbar surgeries
• Persistent radicular pain, no surgical options
• On high-dose oxycodone, limited function

Key points:

• Neuropathic component (radicular) - good candidate
• Trial required
• Psychological screening essential
• Realistic expectations (50% pain reduction, improved function)
• Multimodal approach continues

Scenario 2: Trial Assessment

• Trial performed, day 3
• Patient reports 60% pain reduction
• Able to walk further, sleep better

Key points:

• Successful trial (>50%)
• Functional improvement
• Appropriate for permanent implant
• Discuss expectations for permanent

Scenario 3: Complication Management

• 2 weeks post-implant, fever, IPG site erythema, drainage

Key points:

• Suspected deep infection
• Remove hardware (usually)
• Culture-guided antibiotics
• Re-implant after infection cleared (months)

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Assessment Content

SAQ 1: Spinal Cord Stimulation (20 marks)

Question:

A 48-year-old woman has persistent severe pain following L4-L5 and L5-S1 discectomies performed 3 years ago. She describes burning pain radiating down both legs, worse on the left, with associated numbness and tingling. MRI shows no recurrent disc herniation or spinal stenosis. She has failed extensive conservative management including physical therapy, gabapentin 3600 mg/day, duloxetine 120 mg/day, and oxycodone 60 mg/day with limited benefit and significant side effects. She is unable to work and has difficulty sleeping.

a) Is this patient a candidate for spinal cord stimulation? Justify your answer by outlining the selection criteria for SCS. (8 marks)

b) Describe the trial stimulation process, including the procedure, duration, and criteria for proceeding to permanent implantation. (6 marks)

c) She undergoes successful trial and permanent implant. Six months later, she presents with loss of pain relief and reports the paresthesia is now in her buttocks instead of her legs. What is the likely complication, and how would you manage it? (6 marks)

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Model Answer:

a) SCS candidacy (8 marks):

Yes, she is a candidate.

Diagnosis: Failed back surgery syndrome (FBSS) with predominant neuropathic radicular pain

Why appropriate:

• FBSS with radicular pain is the best-established indication for SCS
• Level I evidence supports superiority over reoperation and conventional management
• Neuropathic pain responds better than pure mechanical/nociceptive pain
• Failed multimodal medical management
• Significant functional impairment

b) Trial stimulation process (6 marks):

Procedure:

1. Psychological screening: Assess expectations, mood, coping, rule out contraindications (active depression, somatization, unrealistic expectations)
2. Preparation: Consent, anticoagulation management, baseline pain/function assessment, mark pain distribution
3. Technique:
   • Tuohy needle insertion into epidural space (paramedian approach)
   • Cylindrical lead advanced under fluoroscopy to T8-T10 level
   • Intraoperative testing with patient awake - map paresthesia coverage
   • Goal: Paresthesia overlaps pain distribution in legs
   • Anchoring suture, sterile dressing
4. Duration: 5-14 days (typically 7-10); home or inpatient
5. Assessment:
   • Pain scores (rest, activity)
   • Function (walking, sleep, ADLs)
   • Medication use
   • Patient satisfaction

Success criteria for permanent implant:

• 50% pain reduction

• Improved function
• Patient desires permanent implant
• No serious complications

c) Complication and management (6 marks):

Likely complication: Lead migration

Why:

• Loss of therapeutic effect
• Change in paresthesia location (buttocks vs. legs)
• Suggests lead has moved cephalad or caudad
• Common technical complication (5-15% with cylindrical leads)

Management approach:

Alternative possibility: Lead fracture (check impedances) or IPG/connection issue (interrogate system)

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References

1. Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965;150(3699):971-979. PMID: 5320816

2. Shealy CN, Mortimer JT, Reswick JB. Electrical inhibition of pain by stimulation of the dorsal columns: preliminary clinical report. Anesth Analg. 1967;46(4):489-491. PMID: 4951846

3. Kumar K, Taylor RS, Jacques L, et al. Spinal cord stimulation versus conventional medical management for neuropathic pain: a multicentre randomised controlled trial in patients with failed back surgery syndrome. Pain. 2007;132(1-2):179-188. PMID: 17900866

4. North RB, Kidd DH, Farrokhi F, Piantadosi SA. Spinal cord stimulation versus repeated lumbosacral spine surgery for chronic pain: a randomized, controlled trial. Neurosurgery. 2005;56(1):98-106. PMID: 15617591

5. Kapural L, Yu C, Doust MW, et al. Comparison of 10-kHz high-frequency and traditional low-frequency spinal cord stimulation for the treatment of chronic back and leg pain: 24-month results from a multicenter, randomized, controlled pivotal trial. Neurosurgery. 2016;79(5):667-677. PMID: 27603799

6. Kemler MA, Barendse GA, van Kleef M, et al. Spinal cord stimulation in patients with chronic reflex sympathetic dystrophy. N Engl J Med. 2000;343(9):618-624. PMID: 10965007

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