Novel Total Nucleus Replacement Using Spherical Magnetic Beads: A Biomechanical Study

Objective: Lumbar Degenerative Disc Disease is a potential cause of spinal instability. Surgical techniques such as arthrodesis or arthroplasty are implemented to restore the stability to the spine. Both a fusion and a disc replacement are substantially invasive. A lumbar disk replacement is typically done via retroperitoneal or Trans peritoneal approach. With increasing number of symptomatic levels, the disk replacement becomes incrementally more invasive, with a potential for a significant blood loss, injury to great vessels, injury to abdominal viscera, weakening of abdominal wall, etc. There is no minimally invasive way to perform a disk replacement either at one or multiple levels. Our goal was to evaluate the feasibility of a novel and less invasive total nucleus replacement using magnetic spherical beads in a cadaver-based multidirectional bending flexibility model. We aimed to assess the ability of the beads to restore stability to a spine segment. We hypothesized that the beads would increase stability during flexion and extension motions. Methods: Three fresh-frozen, human cadaveric L2-L3 segments were used. We performed multidirectional flexibility tests in six directions, under intact, nucleotomy and bead insertion conditions. We measured the ranges of motions, the neutral zone and the elastic zone. Results: There was statistically significantly more flexion-extension range of motion, neutral zone and elastic zone observed upon nucleotomy than during intact condition. Bead insertion statistically significantly reduced the neutral zone observed after nucleotomy, during flexion and extension loading. Conclusion: We conclude that our novel total nucleus replacement is capable of restoring the stability to spine motion segments during flexion and extension motions, by means of adjustments to their neutral zones.