BurtRepLogo02.gif (3938 bytes)

 

 Spinal Neurostimulation Devices
 For the Relief of Intractable Pain

 
     
Courtesy ANS
The successful "intradural" placement of stimulating electrodes was the single key technical advance to demonstrate that spinal electrodes could be safely placed in stable positions and did not have to reside in the subarachnoid space to be effective.  It then became apparent, from clinical experience, that the most effective pain relief from spinal neurostimulators was primarily that involving the lower extremities and, to a lesser degree,  low back.
The success of the intradural electrode led to the development of multi-contact catheter and plate electrodes designed to be placed directly into the epidural space.  Various designs for epidural neurostimulation have evolved over time. Multicontact electrodes were developed to allow for greater control of the stimulation patterns.
Because the largest manufacturer of neurostimulators was Medtronic, Inc. they decided to focus on marketing internal pulse generators (IPGs).  By turning their back on the more compact and more reliable radiofrequency coupled systems Medtronic allowed other companies the opportunity of further developing this attractive alternative.
 Shown here is a typical bulky neurostimulator IPG which is similar to those used in cardiac pacemakers.  The basic IPGs are powered by internal batteries which require surgery to be replaced.  Typical clinical life before additional surgery is required to change the batteries is 2-3 years.
The present generation of IPGs are now quite compact and rechargeable from an external source.  Shown here is the ANS "Mini Eon" which is presently estimated to have a 8-10 year life expectancy.
Shown here is an example of the compact Radio Frequency (RF) receivers which have been the most reliable systems over the past 30 years.  Because they are activated by an external source the implanted system is inert
        

Courtesy Medtronic
In the illustration to the left a catheter electrode has been inserted through a percutaneously placed needle into the epidural space.  This technique, which is done under local anesthesia with sedation, is attractive  because it is relatively simple to perform.  This ease of implantation has unfortunately made PENS electrodes the definitive implant for many physicians involved in pain management (who are not surgeons).  PENS systems are notorious for their instability and tendency to migrate following implantation. 
           

In the example shown above PENS electrodes have been placed for long-term stimulation (as a definitive implant).  Over a two month period there has been electrode migration causing failure of the neurostimulator requiring revision.  This is not an uncommon circumstance.  In the author's practice PENS electrodes are used only temporarily for screening purposes and are removed after about a week.

    
Courtesy Medtronic

This illustration shows PENS electrodes which have been connected to a IPG.  As noted the early IPGs were typically  associated with the need for multiple battery replacements and, because of this, multiple surgical revisions.  Replacing IPGs may seem to be a simple procedure but, due to local scar tissue buildup, lead wires are not infrequently severed requiring replacement of the entire system.
   

Courtesy Medtronic

Shown here is the surgical placement of a definitive plate electrode into the epidural space.  This procedure is typically performed under general anesthesia.  Unlike PENS electrodes epidural plate electrodes have a much higher degree of stability and much less failure.  Experience has demonstrated that the greatest value of PENS electrodes is as a screening tool to determine if the patient is a good candidate for use of a neurostimulator for pain relief.

    
Courtesy ANS

This illustration shows a radio-frequency (RF) coupled system where the batteries are in an external pulse generator.  The RF receiver, which is about the size of a silver dollar, is placed under the skin and is activated by a small coil placed on the outside of the skin.  Coil usually held in place with an adhesive pad.  Anterior RF receiver placement is preferred so that the patient can properly align the transmitting external disc.

 
Other alternatives exist as means of holding the pad against the skin.  Shown here is a tight fitting "fishnet" style T shirt under which the pad can be placed and held against the skin.

 
Courtesy ANS

The Editor's experience, based on over 1,500 spinal cord neurostimulators implanted for the relief of intractable pain, has indicated that the combination of plate electrodes with RF coupled systems have been, until the present, the most user-friendly. They are also the most reliable as shown by their  long-term success record

As with all medical devices and as with all surgeries there are potential complications.  Fortunately, with neurostimulators the greatest risk is that of failure of the device itself, something which is usually replaceable.