Finite element analysis of the effect of endoscopic lumbar fusion on the biomechanical performance of the lumbar spine

English Keywords:Endoscopy  Interbody fusion  Lumbar  Finite element  Biomechanical

English Abstract:

  【Abstract】 Objectives: To investigate the impact on lumbar spine biomechanical performance of endoscopic lumbar interbody fusion(Endo-LIF) via two approaches, namely endoscopic transforaminal lumbar interbody fusion(Endo-TLIF) and endoscopic posterior lumbar interbody fusion(Endo-PLIF) through finite element analysis. Methods: The L3-L5 CT scan data of a 24-year-old healthy male volunteer was collected to establish a three-dimensional finite element model containing cortical bone, cancellous bone and posterior structure of L3-L5 vertebrae. The validity of the model was verified by comparing with other previous studies. The clinical and radiological data of 40 patients underwent Endo-LIF were analyzed retrospectively, and according to different operational approaches, the patients were divided into Endo-TLIF group(n=19) and Endo-PLIF group(n=21). The cage positions and angles of the patients were measured, and the facet joint preservation ratios were calculated to determine the cage placing positions and angles in constructing finite element surgical models. Finally, four finite element surgical models were constructed as Endo-TLIF+45° cage, Endo-TLIF+60° cage, Endo-PLIF+45° cage, and Endo-PLIF+60° cage. The range of motion(ROM) at the fusion segment and the maximum von Mises stress of endplates, cages, screws, rods, and bone-screw interfaces were calculated. Results: The ROMs of fusion segments in all surgical models reduced significantly compared with the intact model. The maximum von Mises stress of endplates in the surgical segment increased significantly under the flexion conditions in all surgical models. The maximum von Mises stress at the bone-screw interfaces of the Endo-PLIF model was significantly increased compared with the Endo-TLIF model under left and right rotation conditions(23%-84%). The maximum von Mises stress of the endplate and cage in the 60° cage models was higher than that in the 45° cage models. In the Endo-PLIF model, the stress of internal fixations and endplates was significantly increased compared with the Endo-TLIF model under left and right rotation conditions. Conclusions: Comparing with Endo-TLIF, Endo-PLIF has significantly higher maximum von Mises stress around the internal fixations, especially under rotational conditions, with greater risk of internal fixation failure.