Investigation of the stability of two different spondylolysis surgical techniques utilizing finite element simulation

Spondylolysis is defined as a unilateral or bilateral bony defect in the pars interarticularis or isthmus of the vertebra. It is most commonly observed affecting the lumbar vertebrae, manifesting as a fracture that results in low back pain and poor quality of life of the patient. Spondylolysis is frequently treated by spinal fusion, a common surgical procedure, but it can result in a loss of motion at the fused level and potentially increase loading on adjacent segments. As an alternative solution, Gillet introduced a V-shaped rod that demonstrated greater advantages in comparison to the spinal fusion technique. In the context of the aforementioned topic, our previous results highlighted the significance of the lubricity effect of human materials present in the surgical area (blood, fat), which has the potential to markedly reduce the friction coefficient between the spinal rod and the locking screw. The objective of this study was to compare the fracture stability of the two different systems, with and without consideration of the effects of the lubricity of human materials. The spinal fusion and V-rod systems were investigated in Ansys v19 with L1-L4 vertebrae and discs. A fracture was formed on the L2 vertebra and different loads were applied to measure the difference in stability. The simulations were conducted in dry and lubricated conditions. The results demonstrated no significant difference between the two stabilizing methods, but the importance of lubrication effect of human materials was established.