Needle puncture injury of the rat intervertebral disc affects torsional and compressive biomechanics differently.

Needle puncture is a common method of inducing intervertebral disc (IVD) degeneration in small animal models and may have some similarities to IVD injury conditions such as herniation. Yet, the influence of puncture injuries on IVD biomechanics is not well understood. This study quantified the acute effects of anular injury on the biomechanics of rat caudal IVDs in compression and torsion following puncture with 30, 25 and 21 G needles. In compression, puncture injury reduced elastic stiffness by 20% for all needle sizes, but differences between control and punctured discs did not remain after compressive overload. In contrast, torsional parameters associated with anular fiber tension were affected proportionally with needle size. We conclude that IVD injuries that penetrate through the thickness of the annulus affect IVD biomechanics through different mechanisms for compression and torsion. Anular injuries affect torsional properties in a manner directly related to the amount of fiber disruption and compressive properties in a manner that affects pressurization.