The use of a novel injectable hydrogel nucleus pulposus replacement in restoring the mechanical properties of cyclically fatigued porcine intervertebral discs

Repeated flexion and extension of an intervertebral disc has been shown to affect the angular stiffness of spinal motion segments and is a barometer of the mechanical integrity of the disc. A degenerated disc that loses height causes higher levels of stress on the annulus and facet joints which may increase its level of degeneration; restoring disc height may therefore help to slow this degenerative cascade. Previous research has indicated that nucleus implants have the potential to improve the mechanical characteristics of a disc and an implant that is custom-fit to the intervertebral disc yields the best results with respect to decreasing annular degeneration. Two groups of porcine spinal motion segments were exposed to repeated flexion and extension. One group was then injected with a novel hydrogel while the other group was used as a control. Both groups were then exposed to another round of cyclic flexion and extension to examine the effect that the hydrogel had on restoring the original mechanics to the motion segments. Angular stiffness was restored to the group which received the hydrogel injection in addition to a significant improvement in specimen height. No significant changes were seen in the group which did not receive an injection. It would appear that use of the novel injectable hydrogel is able to restore angular stiffness to cyclically fatigued spinal motion segments. It is also important to note that continued repetition of the event causing specimen fatigue after performing hydrogel injection will result in an eventual return to the same fatigued state.