AN ASSESSMENT OF THE POTENTIAL FOR INTRA-DISCAL ELECTROTHERMAL THERAPY (IDET) TO DENERVATE POSTERIOR ANNULAR LESIONS

Abstract

To assess the potential for IDET to ablate nerve fibres in an experimentally induced peripheral annular lesion.

Intradiscal electrothermal therapy (IDET) is being increasingly used as a minimally-invasive treatment for discogenic low back pain, with success reported in up to 70% of cases. One proposed mechanism of IDET is ablation reported in up to 70% of cases. One proposed mechanism of IDET is ablation of nerve fibres in the peripheral annulus. An ovine model was used to assess the innervation of peripheral annular lesions and the potential for IDET to denervate this region of the disc.

Postero-lateral annular incisions were made in 32 lumbar discs of 16 sheep. At twelve weeks the sheep underwent IDET at one level and a sham treatment at the other level. IDET was performed using a modified Intradiscal Catheter (SpineCath, Oratec Interventions Inc., Menlo Park, CA). The spines were harvested at intervals up to six months. Histological sections of the discs were stained with H& E and an antibody to the general neuronal marker PGP 9.5.

Vascular granulation tissue consistent with a healing posterior annular tear was observed in all incised discs from 12 weeks, extending to an average depth of 850 μm at 0 weeks to 690 μm at 6 months. PGP 9.5 positive nerve fibres were clearly identified outside the discs but were scarce within the discs. Nerves were identified up to 300 μm inside the annulus, from the earliest time point, and there was a trend towards less innervation with time. There were no fewer nerve fibres identified in those specimens that had undergone IDET. Specimens obtained six weeks after IDET showed evidence of thermal necrosis in the inner annulus, sparing the periphery of the disc. The reported benefit from IDET appears to be related to factors other than denervation. Thermal necrosis within the annulus six weeks after IDET.