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Introduction

• Spinal Cord Stimulation (SCS) is a technique which has the best results for patients with chronic one sided nerve root radiculopathy (sciatica) pain  which has been resistant to:-
  • Simple Treatments - Acupuncture, TENS
  • Medications - Paracetamol, NSAIDs, Weak Opioids, Strong Opioids, Antidepressants, Anti-convulsants, Anti-arrhythmics
  • Physical Therapy - Exercises, Manipulation, Physiotherapy
  • Injections - Epidural Injections, Nerve Root Blocks
  • Surgical Procedures - Epiduroscopy, IDET, Surgical Decompression
• It can be used for nerve root pain in the cervical, thoracic and lumbar regions.
• SCS is like placing a TENS machine inside the spine, applying the electrical signals directly to the spinal cord. The effect of the stimulator is replace the sciatic pain in the leg with a gentle tingling sensation. By interrupting the pain messages (see Gate Theory), the procedure has shown success in returning some individuals to an active lifestyle.
• Different patterns of stimulation can be achieved as shown in these examples:-
  • Pattern 1
  • Pattern 2
  • Pattern 3
  • Pattern 4
• The equipment has three parts :-
  • Power Source - a small electrical pulse generator is implanted just under the skin just below the ribs.
  • Extension - an electrical lead connects between the power source and the spinal electrode, being tunnelled just under the skin from the power source around the body into the spine, to the epidural space.
  • Lead - a spinal electrode placed in the epidural space which delivers a small electrical current to the spinal cord.
• The SCS pulse generator is battery operated , and can be programmed by an external radiofrequency system attached to a small computer in the outpatient clinic setting. The patient can also have some control of the generator, in that they can switch it on and off using a small hand held magnet. Some generators can also be switched into high mode by this magnet system.
• Battery life is usually 3 - 5 years depending on daily use and the signal intensity required. Further surgery is required to replace the pulse generator with a new one when the batteries have expired. 
• For more information see www.medtronic.com.
• The following publications are available from the British Pain Society:-
  • - Spinal Cord Stimulation for the Management of Pain: Provisional Recommendation for Best Clinical Practice
  • - Spinal Cord Stimulation for Pain: Information for Patients

Surgical Implantation

Implantation usually has two phases :-

1. SCS trial using an external pulse generator, to find out whether >50% pain relief is achievable before spending £10,000 on an implanted system. The purpose of the trial is to achieve stimulation of the correct segment(s) in the spinal cord, which in turn replaces the sciatic pain in the leg with a gentle tingling sensation. After insertion of the trial spinal lead, the lead electrical configuration and stimulation parameters (amplitude, frequency and pulse width) can be adjusted using the external pulse generator to achieve the correct stimulation pattern in the leg(s) and reasonable (>50%) pain relief. Those patients who do not find the nerve stimulation sensation acceptable, or in whom a satisfactory stimulation pattern cannot be achieved, or where the pain relief is <50%, do not progress to definitive implantation.
2. Definitive implantation with two options
   1. The spinal lead from the trial is kept in place, the old extension disconnected and discarded, and a new extension connected to the spinal lead and tunnelled around to the abdomen. This new extension is then connected to the implanted pulse generator, which sits in a pocket of fat below the ribs.
   2. The spinal lead and extension are both removed and the patient sent home. After a period of time, following healing of the wound and exclusion of infection, a whole new system is implanted usually under general anaesthesia.

Lead selection is important in ensuring success in SCS

• Octrode Leads are longer in length and have eight separate stimulation areas, covering approximately 2 segments of the spinal cord during stimulation. Each segment of the octrode can be used together with other segments or independently. Using a longer lead helps to recapture pain relief through reprogramming, should the lead migrate during physical activity - Recapture 1 , Recapture 2 .
• Quadripolar Leads are shorter in length and have four separate stimulation areas, covering approximately 1 segment of the spinal cord during stimulation. Using a shorter lead is more likely to lead to failure of recapture should the lead migrate.
• Multiple Leads are sometimes used to achieve stimulation on both sides of the spinal cord. On the whole SCS is less successful in patients who have bilateral sciatic pains in the legs.

Complications

SCS Trial

• Failure to achieve a satisfactory stimulation pattern in the leg is more likely to occur if the sciatic pain is bilateral or if it is entering the spinal cord in more than 2 segments.
• Unpleasant stimulation sensations - some patients find the tingling sensation in the legs unpleasant, producing a failed trial situation.
• Infection may occur more commonly in the subcutaneous tunnel and exit site, and less commonly in the epidural space around the spinal lead. Infection usually requires the removal of the system and treatment with appropriate antibiotics.
• Lead migration may occur more readily during a trial as fixation is less secure. Migration means that the lead electrode is no longer sitting opposite the correct segments in the spinal cord, and appropriate stimulation can no longer be achieved. The trial may need to be repeated at a later date.

Late Complications

• Lead Migration may occur with some forms of physical activity. Some surgeons prefer to stitch the lead in place to reduce its occurrence. When stimulation has been lost it is sometimes possible to recapture it by reprogramming the pulse generator. Where there has been total loss of stimulation, then the spinal lead will need to be replaced surgically.
• Loss of connection with the pulse generator - with the passage of time the electrical wires in the extension can break causing loss of stimulation. This requires surgical replacement.
• Infection can occur in the pulse generator subcutaneous pocket, extension tunnel, and rarely in the epidural space around the spinal lead. If the infection does not respond to antibiotics, the whole system will need to be removed, and re-implanted at a later date.
• Battery failure produces gradual then total loss of stimulation. Surgical replacement is required.