DOES INTRA-DISCAL ELECTROTHERMAL THERAPY (IDET)DENERVATE AND REPAIR EXPERIMENTALLY-INDUCED POSTERO-LATERAL ANNULAR TEARS IN AN ANIMAL MODEL?

Abstract

Objectives: Posterolateral annular lesions were experimentally induced and allowed to mature for 12 weeks in the intervertebral discs of sheep. IDET was performed in an attempt to denervate and repair the annular lesion. The histological and immunohistochemical effects of IDET were studied.

Summary of Background Data: IDET continues to be used as a minimally-invasive treatment for chronic discogenic low back pain, with success rates reported in up to 70% of cases. The mechanism of action by which IDET exerts its effect is poorly understood. Proposed mechanisms include the contraction of collagen and the coagulation of annular nociceptors. An ovine model was used firstly to induce a posterolateral annular lesion, secondly to assess the innervation of such a lesion, and thirdly to assess the effect of IDET on this innervation.

Methods: Posterolateral annular incisions were made in 40 lumbar discs of 20 sheep. Twelve weeks were allowed for each annular lesion to mature. IDET was then performed in the disc with the posterolateral annular tear and in another control level. IDET was performed using a modified intradiscal catheter. Temperatures were recorded in the nucleus (T_N) and the posterior annulus (T_PA). The spines were harvested at predetermined intervals up to eighteen months. Histological sections of the discs were graded for disc morphology to assess degeneration and immunohistochemical staining to assess potential denervation.

Results: Vascular granulation tissue consistent with a healing response was observed in the posterior annular tear of all incised discs from 12 weeks. PGP 9.5 positive nerve fibres were clearly identified in the adjacent periannular tissue and the outer few lamellae of the posterior annulus. During the IDET procedure the mean maximaximum T_PA was 63.6°C and the mean maximaximum T_N was 67.8°C. At sacrifice the number of nerve fibres identified in the posterior annular tear was the same for those specimens that had undergone IDET and those that had not. From six weeks after IDET there was evidence of thermal necrosis in the inner annulus and adjacent nucleus but sparing the periphery of the disc.

Conclusions: IDET delivered at 90°C in the sheep consistently heated the posterior annulus and the nucleus to a temperature normally associated with coagulation of nociceptors and collagen contraction. IDET did not denervate the posterior annular lesion. Thermal necrosis was observed within the inner annulus and adjacent nucleus from six weeks after IDET. The reported benefits from IDET appear to be related to factors other than denervation and repair.