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A Repeated Injury Model of Intervertebral Disc Degeneration and the In-Vivo Effects of Thermal Therapy

  • Author(s): Ulrich, Jill
  • Advisor(s): Lotz, Jeffrey C
  • et al.

Low back pain caused by disc degeneration is a significant health and economic issue. The objective of this research was to advance the understanding of disc degeneration and back pain therapy by developing an animal model of disc degeneration and investigating the effects of thermal therapy on degenerated intervertebral discs. In order to do this, two models of disc degeneration were characterized using rat tail intervertebral discs, and several potential therapeutic mechanisms of thermal therapy were examined using both in vitro and in vivo methods.

A single-stab incision was successful in creating histologic changes consistent with human degenerative discs. Cytokines, primarily located in the wound tract, were transiently elevated following the single-stab injury. A triple-stab injury induced inflammation that continued over the 56-day recovery period and was present throughout the annulus. Features associated with human disc degeneration were also observed following triple-stab injury, including a complete disappearance of normal nuclear matrix.

Both in vitro and in vivo experiments were completed to investigate the effects of thermal therapy on degenerative discs. The in vitro study demonstrated that sublethal heat can induce an HSP70 response and affect cytokine production in disc cells. The cytokine response to thermal therapy was dependent upon thermal dose.

To investigate the in vivo effects of thermal therapy on degenerated discs, a miniature RF heating probe was designed and used to examine the morphological and inflammatory effects of three different thermal exposures on degenerated discs. TNF- levels in the disc were reduced twenty-eight days following treatment with all three thermal exposures. Besides increased proteoglycan production in the tissue surrounding the treatment region, no evidence of disc remodeling was observed in the discs.

This research has implications for the prevention and treatment of disc degeneration. The triple-stab degeneration model induced clinically relevant outcomes including morphological disruption and inflammation and provides a convenient platform to evaluate the impact of anti-inflammatory treatments. The results of the thermal therapy studies suggest that high temperature treatments do not induce a remodeling response and can be harmful to the disc, so future research should focus on the potential therapeutic effects of low thermal exposures.

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