• Elisa C Bass, William H Nau, Chris J Diederich, Ellen Liebenberg, Richard Shu, Richard Pellegrino, Jeffrey Sutton, Mohamed Attawia, Serena S Hu, William T Ferrier, and Jeffrey C Lotz.
• Orthopaedic Bioengineering Laboratory, Department of Orthopaedic Surgery, University of California at San Francisco, 94143-0514, USA.
• Spine. 2006 Jan 15; 31 (2): 139-45.

Study DesignThermal energy was delivered in vivo to ovine cervical discs and the postheating response was monitored over time.ObjectivesTo determine the effects of two distinctly different thermal exposures on biologic remodeling: a "high-dose" regimen intended to produce both cellular necrosis and collagen denaturation and a "low-dose" regimen intended only to kill cells.Summary Of Background DataThermal therapy is a minimally invasive technique that may ameliorate discogenic back pain. Potential therapeutic mechanisms include shrinkage of collagenous tissues, stimulation of biologic remodeling, and ablation of cytokine-producing cells and nociceptive fibers.MethodsIntradiscal heating was performed using directional interstitial ultrasound applicators. Temperature and thermal dose distributions were characterized. The effects of high (>70 C, 10 minutes) and low (52 C-54 C, 10 minutes) temperature treatments on chronic biomechanical and architectural changes were compared with sham-treated and control discs at 7, 45, and 180 days.ResultsThe high-dose treatment caused both an acute and chronic loss of proteoglycan staining and a degradation of biomechanical properties compared with low-dose and sham groups. Similar amounts of degradation were observed in the low-dose and sham-treated discs relative to the control discs at 180 days after treatment.ConclusionsWhile a high temperature thermal protocol had a detrimental effect on the disc, the effects of low temperature treatment were relatively minor. Thermal therapy did not stimulate significant biologic remodeling. Future studies should focus on the effects of low-dose therapy on tissue innervation and pro-inflammatory factor production.

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