1. 2006;9;207-214The Efficacy of a Two Needle Electrode Technique in Percutaneous Radiofrequency Rhizotomy: An Investigational Laboratory Study in an Animal Model
   A Laboratory Investigation
   Richard Derby, MD, and Chang-Hyung Lee, MD.

Background: Radiofrequency neurotomies are used to help reduce pain caused by structures innervated by the medial branch of the dorsal spinal nerve. The duration of effect may vary proportionally to the length of nerve coagulated. Techniques used to maximize the length of nerve within the radius of maximal heat include making multiple lesions, using larger needles, positioning the exposed needle parallel to the target nerve, and attempting more precise placement using 50 hertz test stimulation. A variation of the technique uses two needles that are simultaneously placed to lie parallel to one another and parallel to the probable area the target nerve is known to traverse. Heating both needles at the same time would be a faster method that theoretically might also include more tissue within the heating radius of the needle lengths.

Objective: The purpose of this study was to confirm that two parallel radiofrequency lesions increased the volume of tissue included within the heating radius of the exposed needle tips, to determine optimal heating parameters, and to establish how far apart the needles can be placed and still achieve temperatures between the needles that will coagulate nerves.

Study Design: Investigational laboratory study in an animal model

Methods: Ex-vivo porcine spinal tissue samples were prepared following a standardized protocol and two needle electrodes were connected to the Stryker ® rhizotomy device. A series of tissue samples were prepared with the needles placed 1, 1.5, 2, 3, 4, 5, 6, 7, 8, or 9 mm apart in respective samples. The needles were positioned parallel to the surface, and perpendicular to the tissue.

In one series of samples, two needle electrodes were heated sequentially for each needle placement. Temperature parameters ranged from 60 to 100° C and the time duration ranged from 60 to 90 seconds for each electrode. After each heating, all tissue was dissected and the size of the coagulated area measured. Temperatures at the midpoint between the two needle electrodes were monitored and measured with a Radionics® needle sensor. Using the same study protocol and evaluation, a second set of samples was studied but both needle electrodes were heated simultaneously.

Results: Maximal lesion size was observed when the temperature of the electrode was higher than 70-80°  C and maintained for longer than 70 seconds. When the needles were heated sequentially, the needles could be placed no further than 1.5 to 2 mm apart before areas of incomplete coagulation were visualized at the midpoint between the needles. When both needles were simultaneously heated the needles could be placed 4 mm apart before incomplete coagulation was visualized. With simultaneous heating, the highest peak temperature of the midpoint between two needles (6 mm apart) exceeded 66° C, compared to a temperature of 40°C achieved with sequential heating.

Conclusions: This research confirms the efficacy of utilizing two needle electrodes during lumbar facet rhizotomy in an experimental model. Heating the two electrodes sequentially appears to coagulate a wider area and thus would be more likely to include a longer length of the target nerve and thus potentially could achieve better results in less time.