Diagnosis, repair and regeneration of the disc often necessitate needle injection to the nucleus pulposus through the annulus. Discography in which a radio opaque material is injected into the nucleus and electrothermal treatment involving inserting a catheter into the disc requires disruption of the annulus through needle puncture. Annulus puncture may also be required during placement of nucleus implants. Needle puncture is also used to inject growth factors, gene and cell therapy for regeneration of the disc. In animal models, disc degeneration is induced over time by needle puncture of the annulus. The severity of the degeneration depends on the magnitude of the annulus needle puncture. One thing that is not clear is how much of the observed changes in the disc biomechanics and biochemical changes are due to nucleus treatment and how much is due to annular disruption through needle puncture. Animal model studies have shown that significant changes in disc mechanics were noticed within 1 week of needle puncture with a large-gauge needle. Another in-vitro animal study showed that biomechanical changes were observed in the disc when the ratio of needle diameter to disc height is greater than 40%. All these studies were focused on the effect of small number of needle diameters and addressed using animal cadaver models. How these needle puncture injury studies on small and large animal models can be extrapolated to human conditions is still not known. Thus there is need to evaluate effect of range of needle puncture diameters in human lumbar disc biomechanics. The purpose of this study is, with the help of a finite element models, quantify the biomechanical effect due to varying size of needle punctures in a human lumbar intervertebral disc.

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