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Experimental evaluation of the risk of extradiscal thermal damage in intradiscal electrothermal therapy (IDET).

BACKGROUND
In 2000 the intradiscal electrothermal therapy (IDET) procedure for the treatment of discogenic pain was introduced. The technique involves the positioning of an intradiscal catheter with a temperature-controlled thermal resistive heating coil at the inner posterior annulus. The therapeutic mechanism of IDET combines the thermo-coagulation of native nociceptors and in-grown nonmyelinated nerve fibers with collagen shrinkage, stabilizing annular fissures. Thermal nerve root injuries were described with IDET. The temperature in relation to the distance from the catheter tip was investigated. The intradiscal temperature distribution during treatment with IDET was also described.


OBJECTIVE
To examine the temperature distribution outside the disc near neural structures and the risk of thermal damage to nerve tissue during a correctly performed IDET procedure.


STUDY DESIGN
Experimental study.


SETTING
Biomechanical laboratory of an academic orthopedic surgery department.


METHODS
Testing was performed on cadaveric human lumbar spines with 10 intact intervertebral discs in a circulating water bath. Five thermocouples were attached to different locations on the disc. The temperature was recorded for 26 minutes. In addition, surface temperatures were recorded using an infrared camera. For the application of IDET, we used the Electrothermal 20S Spine System by Smith & Nephew and the standard clinical protocol.


RESULTS
The shape of the recorded temperature curves was quite heterogeneous. Inside the spinal canal, temperatures as high as 45.2°C were recorded for a very short time. Temperature monitoring with the infrared camera demonstrated a change in temperature clearly restricted to the nucleus of the disc.


LIMITATIONS
The temperature distribution depends on the exact position of the IDET probe, which will never be 100% identical between individual experiments.


CONCLUSION
This study shows that temperatures generated within the spinal canal during IDET do not appear to be high enough to cause nerve damage.