Intradiskal electrothermal therapy: A preliminary histologic study

Objective: To characterize descriptively the histologic and temperature effects of intradiskal electrothermal annuloplasty on human cadaveric lumbar disks. Design: In vitro histologic study. Setting: Hospital-based soft-tissue research laboratory. Cadavers: Six human cadaveric lumbar disks, from 5 cadavers aged 39 to 79 who died from nonspine-related causes. Interventions: Intradiskal electrothermal therapy (IDET) by using a standard high-temperature heating protocol with the temperature of the probe gradually increased from 65 degreesC to 90 degreesC over 16.5 minutes. Disks were stained and examined by light microscopy and electron microscopy. Main Outcome Measures: Temperatures in outer annulus, gross macroscopic changes, and histologic damage. Results: Gross inspection showed a small circumferential area of tissue alteration localized to the posterior annulus but not extending to the endplates. Light microscopy of the posterior aspect of the lumbar disks showed denaturation, shrinkage, and coalescence of annular collagen; the anterior portions, which served as internal controls, showed no evidence of damage. The endplates were structurally preserved and showed no evidence of damage. Electron microscopy showed extensive collagen disorganization, decreased quantity of collagen, collagen fibril shrinkage, and chondrocyte damage when compared with a control portion. The temperature curves showed parallel changes in temperature at the level of the probe and at the posterior portion of the disk. Conclusions: IDET raises temperatures sufficiently to induce collagen denaturation and coalescence. These histologic changes may play a substantial role in the clinical efficacy of IDET.