Biomechanical Analysis of Lumbar Vertebrae Following Transforaminal Lumbar Interbody Fusion Combined with Bilateral Transpedicular Transdiscal Lumbar Screw Fixation: A Finite Element Study

Abstract

Abstract Background: The use of transpedicular transforaminal screws (TTPs) in lumbar interbody fusion is a novel approach for minimally invasive spinal fixation. In comparison to traditional pedicle screw fixation, the use of a single screw in transpedicular transforaminal fixation allows for the fixation of one segment on one side, providing the advantages of cost-effectiveness, minimally invasive surgery, and convenience. However, there is a limited body of literature on the application of bilateral TTPs in combination with modified transforaminal lumbar interbody fusion (TLIF) surgery. Objective: This study aimed to establish three finite element models: TLIF without internal fixation (cage alone), TLIF combined with bilateral pedicle screw fixation (cage+BPS), and TLIF combined with bilateral transpedicular transdiscal lumbar screws fixation(cage+BTPTDS). The objective was to evaluate the effects of TLIF combined with different internal fixations on the stress distribution of the intervertebral fusion cage, internal fixation, intervertebral disc, lower endplate, and motion range of the lumbar region. Methods: This study collected thin-layer CT scan images of the adult lumbar spine. Three finite element models were created using Mimics, Geomagic, and SolidWorks software: a cage alone model, a cage+BPS model, and a cage+BTPTDS model. Six different motion loads, including flexion, extension, left bending, right bending, left rotation, and right rotation, were simulated using ANSYS Workbench. The stress distribution and motion range of the lumbar region were calculated for the intervertebral fusion cage, internal fixation, lower endplate, and intervertebral disc in the three models. The study also compared the effects of three different surgical plans on the biomechanical characteristics of the lumbar spine. Results: Three finite element models were successfully constructed: cage alone, cage+BPS, and cage+BTPTDS. The maximum stress in the cage+BTPTDS model was lower than that in the cage alone model under flexion and lateral bending loads, and slightly higher than that in the cage+BPS model. Under the extension load, the maximum stress in the cage+BPS model was significantly lower than that in the other two models. Under the rotation load, the maximum stress in the cage+BTPTDS model was similar to that in the cage+BPS model, but lower than that in the cage alone model. Under the flexion and extension loads, the maximum stress of the internal fixation in the cage+BTPTDS model was significantly higher than that in the cage+BPS model. Under the lateral bending load, the maximum stress of the internal fixation in the cage+BTPTDS model was similar to that in the cage+BPS model. However, under the rotation load, the maximum stress of the internal fixation in the cage+BTPTDS model was lower than that in the cage+BPS model. The maximum stress of the lower endplate of the fusion segment in the cage+BPS model was between that of the other two models. The cage+BTPTDS model showed minimal differences in mobility compared to the cage alone model under flexion, extension, lateral bending, and rotation conditions. Conclusions: The combination of modified TLIF and bilateral transpedicular transaminal screw fixation can enhance stability in the fused and fixed segment while preserving lumbar mobility, resulting in favorable biomechanical outcomes.