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Spinal cord stimulation

Updated: May 22, 2022



What is it?


It is the application of pulsed electrical activity near the spinal cord to manage pain

Electrical leads are placed within the epidural space.

First implantable stimulation device was placed in 1967.


How does it work?


Gate theory:

  • Melzack and Wall proposed the gate theory of pain in 1965.

  • Very simply they posed that pain signals carried by C-fibres and A-delta fibres can be interrupted by stimulating larger A-beta fibres

  • A-beta fibres usually provide touch and vibration signals

However, it is unclear whether the gate theory is as 'clear cut' as originally theorised as the pathways are now understood to be far more complex


Monoamine theory:

  • Alteration of local neurochemistry through electrical stimulation may suppresse hyperexcitability by wide dynamic range neurons by increasing GABA (inhibitory) and serotonin release -- > both reducing glutamate and aspartate (excitatory)


How are they inserted?

Needles are used to access the epidural space. They traverse:

  • Back skin

  • Subcutaneous tissue

  • Supraspinous ligament

  • Interspinous ligament

  • Ligamentum flavum


  • The epidural space is a 'potential' space that contains veins and epidural fat.

  • It varies from L2 at 5-6 mm to 3-4mm in thoracic spine and 1.5-2mm at C7

  • To cover the desired dermatomal area with paresthesia, it is necessary to place electrodes over the dorsal columns several segments cephalic to that level

  • Remembering that the spinal cord ends at L1 in adults

  • Arterial supply for the spinal cord comes from vertebral arteries in the cervical spine, and the intercostal and lumbar arteries in the thoracic and lumbar spine

  • The arteries anastomose with other spinal cord vessels to form the pial plexus.

  • Sensory areas of the spinal cord are somewhat protected from arterial compromise as they anastomose and are not an end artery

  • However, motor supply to the anterior part of the spinal cord is only supplied by the atery of Adamkiewicz which enters the vertebral canal through L1. It supplies the lower two thirds of the spinal cord.

Steps:

  1. Patients are often premeditated with a benzodiazepine agent. Antibiotics have been advocated by some but is not always performed.

  2. A pillow is often placed underneath a persons lumbar region to reduce lumbar lordosis

  3. Site of entry is confirmed under fluoroscopic imaging. Ideally within the dorsal midline at the level of, or below, L1. The spinous processes bisect the pedicles on imaging. The C-arm is then adjusted cephalic or caudal to square off the end plates

  4. Skin entry is typically paramedic - usually two levels below the midline epidural entrance adjacent to the medial border of the ipsilateral pedicle

  5. Shallow angle of entry helps the lead to be advanced

  6. 1% lidocaine with epinephrine is utilised to anaesthetise the skin

  7. SCS percutaneous trial - Leads are placed via an epidural needle and inserted to the right location. Leads are typically cylindered or wire-like and have 4-8 electrode sites separated by >4 mm

  8. Lead location is confirmed both with AP and lateral views. C2-C4 can cover shoulder, C3 and C4 can cover medial forearm and hand, C4-C6 can cover bilateral upper extremity

  9. Lead location to cover the lower torso and extremity neuropathic pain requires placement at T7 and T9 within the midline

  10. Unilateral lower limb extremity stimulation can be produced by lead placement slightly off the midline between T9 and T11. Distal limb often covered by T12 and L1.

  11. A second lead is often placed primarily due to lead migration issues. This is usually placed 1-segment above the first lead's skin-entry or at a contralateral skin-entry site at the same level

  12. Lead is then adhered using a suture or surgical adhesive. Rest of lead is connected to external pulse generator which is also secured to the skin. Device is programmed perioperatively

  13. IF this is successful, the patient can be returned to theatre for creation of a pocket and implantation of more permanent battery.

Lead programming primarily is varied based upon:

  • Frequency or intensity of the signal

  • Voltage height or current

  • Applied pulse width or duration

 

Prior to a permanent implant, some practitioners will request:

  • Urine MCS

  • CBC

  • ESR

  • CXray (if over 45)

  • ECG (if over 45)


What are the indications?

A spinal cord stimulator neuromodulation system should be considered for patients who have failed all reasonable conservative care including appropriate diagnostic, therapeutic, and rehab techniques and have been given a reasonable time for which their body is allowed to recover (e.g. 6-12 mths)


Ideal patient should be motivated, compliant, and free of drug dependence

They should have psychological screening to exclude conditions that predispose to failure of the procedure

  • CRPS

  • Failed back surgery syndrome (post-laminectomy syndrome)

  • Peripheral ischaemia

  • Peripheral neuropathy

  • Angina pectoris (refractory)


Interestingly, factors that do not correlate with outcomes include patient age, duration of pain, intensity, or laterality of pain


Patient social and psychological factors will greatly impact outcome including: depression, anxiety, somatisation, poor coping skills


Positive trial factors include tolerance of paraesthesia, >50-75% pain relief, and overall patient satisfaction. Ideally patients will have improved function, decreased requirements for analgesics.


Prognosis (6):

  • Long term pain benefit (>2yrs and >50%) occurs in ~60% of patients

  • In 50-90% of patients they will have a reduction in opioids

  • Return to full employment in 25-60% of patients (in a population where usual return to work is 1-5%)


What are the contraindications?

  • Infections over surgical sites

  • Aberrant anatomy to make insertion difficult

  • Uncontrolled systemic illness

  • Uncontrolled bleeding diathesis

Anticoagulation is typically held as per the ASRA guidelines


What are the possible complications? (4)

Infection

Infection from implantation varies in studies from 5-10%. A larger review in 2019 suggested 3% infection rate within the US (5). Generator pocket site is the most common site of infection. Risks include diabetes, low nutrition, decubitus ulcers, poor self hygiene, urinary or faecal incontinence, and malabsorption syndromes.


Dural puncture

Occurs in 0-0.5% of cases. Outcomes are usually post-dural headache, diplopia, tinnitus, neck pain, photophobia, and fluid accumulation at the site. Best manangement initially is bed rest otherwise it is a blood patch and/or surgery.


Epidural haematoma

These are more common after placement of a paddle. These have not been reported in the literature on SCS, ONS, and PNFS.


Nerve injury - Very rare


Lead migration or breakage (declining with experience and time)

- Studies vary widely in reporting of lead migration. This is due in part to variability on the definition of 'migration'. E.g. many trials have not differentiated between lateral migration or distal migration, whether revision surgery was required or just reprogramming, how long the leads were in-situ until migration etc. The standard quoted figure from the late 2020's was approximately 10-20% will migrate to some degree though it is unclear if this is the case with different patient selection and experienced practitioners (4).


Battery failure

In old figures battery failure was <1%


Paralysis

Death (though these complications are exceedingly rare)


Outcomes

Up to 70% 0f patients with a SCS implanted will have a positive outcome.


How do you manage potential complications?


What are the companies available in Australia?


Interesting facts:

  • SCS is much cheaper than re-spinal operation ($45,000 vs $105,000)

  • In FBSS, if patients do not receive SCS, costs are approx $38,000/yr versus $29,000/yr

  • The wider the pulse WIDTH the deeper the spinal penetration


References

Statpearls April 2021


Practical Pain Management - 20


Medline - Spinal Cord Stimulation Technique


4. Sam Eldabe, MB ChB, FCRA, FFPMRCA, Eric Buchser, MD, DEAA, Rui V. Duarte, PhD, Complications of Spinal Cord Stimulation and Peripheral Nerve Stimulation Techniques: A Review of the Literature, Pain Medicine, Volume 17, Issue 2, February 2016, Pages 325–336, https://doi.org/10.1093/pm/pnv025


5. Falowski, S. M., Provenzano, D. A., Xia, Y., & Doth, A. H. (2019). Spinal Cord Stimulation Infection Rate and Risk Factors: Results From a United States Payer Database. Neuromodulation : journal of the International Neuromodulation Society, 22(2), 179–189. https://doi.org/10.1111/ner.12843


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