Enhancing Surgical Outcomes in Pars Interarticularis Fracture: An Investigation of Treatment Modalities and Variability in Spondylolysis Surgical Approaches

Author(s): Craig Forsthoefel, Niccolo Galdini, Steven Mardjetko, Nicole Chang, Farid Amirouche

Numerous studies have failed to definitively establish the most stable repair construct for spondylolysis. We seek to clarify this issue through a combination of physical experimentation using SawBones and corresponding finite element analyses (FEA). Using twenty-five SawBones lumbar vertebral body models, we tested four repair techniques: Buck's intralaminar screws, pedicle-screw and hook construct, pars interarticularis plating, and pedicle-screw intralaminar screw construct. Each Sawbones repair construct was secured with a C-clamp to the base of an MTS 858 Bionix test system. The testing frame was programmed to apply axial load to replicate an extension moment on the pars interarticularis and gradually increased until catastrophic failure, gapping of the pars defect exceeded 5 mm, or an obvious yield point was identified on stress-strain curves. The FEA involved creating an L4-L5 vertebrae model from CT scans, simulating fractures, and analyzing stress using SolidWorks and Ansys software. Results showed that while no repair method fully replicated the original stiffness of the intact pars, Buck's technique emerges as the closest approximation. Repair by pedicle screw hook, intralaminar screws, and plates demonstrates enhanced peak load to failure and elastic displacement. In FEA, the Buck technique exhibits superior reliability in comparison to other methods when assessing von Mises stresses, and the novel Implants 1 and 2 showcase the lowest average displacements. While the clinical significance of maintaining greater peak load or elastic displacement remains uncertain, our findings contribute to understanding spondylolysis repair. Additionally, utilizing FEA for novel designs offers promise in enhancing surgical outcomes.