IN VIVO MEASUREMENT OF PEAK POSTERIOR ANNULAR AND NUCLEAR TEMPERATURES OBTAINED DURING INTRADISCAL ELECTROTHERMAL THERAPY (IDET)

Abstract

Are peak posterior annular and nuclear temperatures obtained during IDET within the temperature range normally associated with nociceptor destruction and contraction of collagen?

Pain relief following intradiscal electrothermal therapy (IDET) has been reported to result from coagulation of annular nociceptors and contraction of collagen. This requires temperatures respectfully of 45°C and 60°C. A cadaveric study using an intradiscal catheter (Spinecath, Oratec Interventions Inc., CA) reported sufficient temperatures for these events to occur. However a human study reported temperatures sufficient only to coagulate nociceptors. This study reports peak posterior annular and nuclear temperatures attained in-vivo with an intradiscal catheter in sheep.

Twenty sheep were anaesthetised and the lumbar spine exposed. In two non-adjacent discs a stab incision was made in the left postero-lateral annulus and the wound closed. Twelve weeks later the animals returned for a second operation. The spine was approached from the right. Under fluoroscopic control the intradiscal catheter was placed into a previously operated disc. One thermocouple sensor needle was placed 2mm posterior to the catheter to record the posterior annular temperature and a second was inserted 2mm anterior to record the nuclear temperature. The process was repeated for a non-operated control disc. Electrothermal energy was delivered according to the recommended heating protocol.

The target temperature of 90°C at the catheter tip was reached in all cases. Data were tabulated with the mean and standard deviation calculated for each site. There was no significant difference between temperatures reached in the ‘degenerate’ discs and those in the control discs. The mean maximum posterior annular temperature was 63.6°C (range 46.8 to 77.7) and the mean maximum nuclear temperature was 67.8°C (Range 51.1 to 81.2).

Intradiscal electrothermal therapy delivered at 90°C in the sheep consistently heats the posterior annulus and the nucleus to a temperature associated both with coagulation of nociceptors and collagen contraction. These findings may contribute to understanding the mechanism of pain relief following IDET.