Intradiscal Electrothermal Therapy (IDET)

Thermal denervation is well-documented and widely used for neural lesioning in facets1, trigeminal nerves2, and the brain3. The majority of these thermal nerve blocks are conducted with RF needle electrodes.

Innervation of the intervertebral disc has been progressively well-documented by researchers since the 1930's. Bogduk's work revealed the sources of lumbar disc innervation4. More recently Coppes et al5 observed nerve fibers "deeper than the outer third of the annulus fibrosis." Freemont et al6 also discovered significant neovascularization with neural expression of substance P and linked that growth to disc degeneration and back pain. They identified nerve fibers as deep as the inner third of the annulus fibrosis and into the nucleus pulposus.

Intradiscal thermal therapy with the Spine CATH can target and destroy nociceptors throughout the annulus from the inner wall to the outer third. Heat produced by the catheter is conducted through the annulus wall. Temperatures produced in the outer third (approximately 45-48 degrees Centigrade)7 are above the threshold required for denervation. Smith et al8 established irreversible nerve blocks occur at 45 degrees Centigrade in all types of nerve fibers.

Collagen contraction, or shrinkage, has been well documented with the use of non-ablative laser energy9, 10, 11, 12 on joint capsular tissue and more recently in RF application in the glenohemeral joint capsule13. Research by Naseef et al has also shown that there is a direct correlation between the temperature and duration of application and resulting collagen contraction14. Their team demonstrated that application of heat via a water bath produced contraction in bovine knee capsule and the phenomena was not dependent on either a laser or RF energy source.

Collagen shrinkage is caused by the disruption of specific heat sensitive bonds of the collagen fibrils. The intervertebral disc is composed of a framework of primarily Types I and II collagen, which have a similar molecular structure15. The tensile strength of these collagen fibrils is derived from the extended conformation of the triple helix molecule. This helix structure is maintained by cross-links of hydrogen bonds, a portion of which have been shown to be reducible or break apart when exposed to specific range of temperatures over time. This disruption of these stabilizing hydrogen bonds releases the strands of the triple helix module which collapse. This collapse, like the release of a spring held taut, results in a new contracted state called the denatured or random coil conformation of the collagen fiber.

From literature, the optimal temperature for collagen contraction is 65 degrees Centigrade. 60 degrees Centigrade is the lowest temperature at which heat sensitive hydrogen bonds will start to break. As the temperature increases more bonds break. Although shrinkage occurs above 75 degrees Centigrade, there is no significant increase in shrinkage rate over 75 degrees Centigrade. In addition thermal shrinkage of collagen is also dependent on the duration of the application of heat. Lower temperatures (within the 60-75 degrees Centigrade range) over a longer period of time result in shrinkage comparable to that achieved with a higher temperature over a shorter period of time.

Intradiscal thermal therapy with the SpineCATH can effectively contract the collagenfibrils of the annulus and nucleus. This phenomena contributes to the overall debulking of the disc7 by decreasing the tissue volume and thereby relieving pressure of a disrupted disc. The tightening of the fibrous structure of the annulus may also enhance the structural integrity of a degenerated or damaged disc and could stabilize annular fissures.

1. Burton C.V., "Percutaneous Radiofrequency Facet Denervation.," Applied Neurophysiology, 1996/97, Vol. 39, pp. 80-86.

2. Apfelbaum R. I., "Technical Considerations for Facilitation of Selective Percutaneous Radiofrequency Neurolysis of the Trigemial Nerve," Neurosurgery, 1978, Vol. 3, No. 3, pp. 396-399.

3. Marchosky J.A ., Moran C.J., Welsh, D.M., Klieforth A.B., Garcia D.M., Deford J.A., Nussbaum G.H., Halverson K., "Thermobrachytherapy Treatment of Malgnant Brain Tumors," Sterotactic Surgery and Radiosurgery, 1993, Medical Physics, pp. 437-450.

4. Boduk N., Towomey L.T., "Nerves of the Lumbar spine," Clinical Anatomy of The Lumbar Spine, 1987, Churchill Livingstone, pp. 92-102.

5. Coppes M.H., Marani E., Thomeer R.T., Groen G.J., "Innervation of 'painful' lumbar discs," Spine, 1997 Oct 15: Vol. 22, No. 20, pp. 2342-2349.

6. Freemont A.J., Peacock T.E., Goupille P., Hoyland J.A., O'Brien J., Jayson M.I., "Nerve Ingrowth into Diseased Intervetrebral Disc in Chronic Back Pain," Lancet, 1997 Jul 19, Vol. 350. No. 9072, pp. 178-181.

7. Saal J.A., Saal J.S., Ashley J., " Thermal Characteristics of the Lumbar Disc: Evaluation of a Novel Approach to Targeted Intradiscal Thermal Therapy," Thirteenth Annual Meeting of the North American Spine Society, october 1998.

8. Smith H.P., McWhorter J.M., Challa V.R., "Radiofrequency Neurolysis in a Clinical Model," Journal of Neurosurgery, Aug 1981, Vol. 55 pp.248-253.

9. Hayasi K., Markel M.D., Thabit G., Bogdanske J.J., Theilke R.J., "Effect of Nonablative Laser Energy on Joint Capsular Prpperties: An In Vitro Mechanical Study Using a Rabbit Model," the American Journal of Sports Medicine, 1995, Vol. 23, No. 4, pp. 482-487.

10. Hayashi K., Thabit G., Vailas A.C., Bogdanske J.J., Cooley A.J., Markel M.D., "The Effect of Nonablative Laser Energy on Joint Capsular Properties: An In Vitro Histologic and Biochemical Study Using a Rabbit Model," The American Journal of Sports Medicine, 1996, Vol. 24, No. 5. pp.640-646.

11. Hayashi K., Thabit G., Bogadanske J.J., Mascio L.N., Markel M.D., "The Effect of nonablative Laser Energy on the Ultrastructure of Joint Capsular Collagen," Arthroscopy: The Journal of Arthroscopic and Related Surgery, Aug. 1996, Vol. 12, No.4, pp. 474-481.

12. Hayashi K., Nieckarz, J.A., Thabit G., Bogdanske J.J., Cooley A.J., Markel M.D., "Effect of Nonablative Laser Energy on the Joint Capsule: An In Vitro Rabbit Study Using a Holmium: YAG laser," Lasers in Surgery and Medicine, 1997, Vol. 20, pp. 164-171.

13. Obrzut S.L., Hecht P., Hayashi K.,Fanton G.S., Thabit G., Markel M.D., "The Effect of Radiofrequency Energy on Length and Temperature Properties of the Glenhumeral Joint Capsule," Arthroscopy: The Journal of Arthroscopic and Related Surgery, June 1998, Vol. 14, No. 4, pp. 395-400.

14. Naseef G.S., Foster T.E., Trauner K., Solhpour S., Anderson R.R., Zarins B., "The Thermal properties of Bovine Joint Capsule: The Basic Science of Laser- and Radiofrequency-Induced Capsular Shrinkage, "The American Journal of Sports Medicine, 1997, Vol. 25, No.5, pp.670-674.

15. Eyre D.R., "Collagens of the Disc," Biology of the Intervertebral Disc, 1988, Gosh P., ed., CRC Press, Inc. Boca Raton, FL Vol. 1, pp. 171-188.