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Glossary of Spinal Neurostimulation: Devices For the Relief of Intractable Pain
Charles V. Burton, M.D., for the Burton Report

 

The "intradural"(or endodural) placement of stimulating electrodes. A microsurgically developed "pocket" has been created within the dura mater. A bipolar electrode is shown in this pocket. Until this advance electrodes had been inserted within the subarachnoid space with serious attendant complications. The intradural technique represented the key step in demonstrating that spinal electrodes could be safely placed and fixed in position.

 

With the intradural demonstration it then became evident that if electrode design were to be improved a epidural placement was the practical next step. Bipolar electrodes were too small to be stable in the epidural space. Development of a multi-contact plate electrode then followed. Shown to the right are catheter-type electrodes which have the advantage of being inserted through a needle.

 

Shown here is the placement of a multi-contact plate electrode into the epidural space. This requires a small surgical incision and often some bone removal. The procedure is typically carried out under local anesthesia with parenteral drug supplementation. Immediately following insertion multi-parameter testing can be carried out.

 

In this x-ray the electrode assembly has been placed in the midline. Positioning can be varied to achieve differing patterns of parasthesia (perceived stimulation) in the body.

 

The greatest attraction of the catheter type electrodes is the fact that they can be inserted through a needle placed in the epidural space. For this reason percutaneous epidural neurostimulating electrodes (PENS) have attracted many physicians to this approach. Not all of these physicians have been skilled in needle placement or in the use of image intensification. Results have often been reminiscent of medicine's past experience with chymopapain.

 

If initial and subsequent ambulatory multi-parameter testing is found to be successful the system is then totally implanted with either a radio-frequency (RF) coupled system or a totally implanted pulse generator system. In the RF model the batteries are in an external unit which the patient controls directly. The "care and feeding" of RF coupled systems is simple which makes them attractive to the user. RF coupled systems have the best long-term success record.

 

This illustration shows a epidural electrode connected to a totally implanted system. The batteries are contained in the implanted pulse generator. Battery change requires additional surgery. Frequency of surgery for battery replacement may be as frequent as less than 2 years. Change in parameters is performed by an external programmer. The system is turned on and off by the placement of a magnet over the pulse generator.

Totally implanted systems require the highest amount of "care and feeding" for both the patient and the physician.

 

The Burton Experience, based on over 1,000 spinal cord neurostimulators implanted for the relief of intractable pain, has indicated that the plate electrodes are the most stable and reliable and that the RF coupled systems are the most user-friendly and most reliable over a period of years. PENS systems, while simpler to use, are much less reliable.

 

Depth brain neurostimulation (DBS), although not presently in use, is presented because it remains an important asset for the very small group of patients with intractable pain for which there is no other humane therapy available. The "death knell" of DBS was sounded when government insurance programs decided to discontinue coverage for it. It is clearly a valuable procedure and needs to continue to be offered to desperate patients by a small group of experienced and skilled neurosurgeons functioning in a tight peer review environment.