Application of dual-trajectory screws in revision surgery for lumbar adjacent segment disease: a finite element study

Abstract

Background Advancements in medicine and the popularity of lumbar fusion surgery have made lumbar adjacent segment disease (ASDz) increasingly common, but there is no mature plan for guiding its surgical treatment. Therefore, in this study, four different finite element (FE) ASDz models were designed and their biomechanical characteristics were analysed to provide a theoretical basis for clinical workers to choose the most appropriate revision scheme for ASDz. Methods According to whether internal fixation was retained, different FE models were created to simulate ASDz revision surgery, and flexion, extension, axial rotation and lateral bending were simulated by loading. The biomechanical characteristics of the adjacent segments of the intervertebral disc and the internal fixation system and the range of motion (ROM) of the lumbar vertebrae were analysed. Results The difference in the ROM of the fixed segment between FE models that did or did not retain the original internal fixation was less than 0.1°, and the difference was not significant. However, the stress of the screw–rod system when the original internal fixation was retained and prolonged fixation was performed with dual-trajectory screws was less than that when the original internal fixation was removed and prolonged fixation was performed with a long bar. Especially in axial rotation, the difference between models A and B is the largest, and the difference in peak stress reached 30 MPa. However, for the ASDz revision surgery segment, the endplate stress between the two models was the lowest, and the intradiscal pressure (IDP) of the adjacent segment was not significantly different between different models. Conclusion Although ASDz revision surgery by retaining the original internal fixation and prolonging fixation with dual-trajectory screws led to an increase in stress in the fusion segment endplate, it provides stability similar to ASDz revision surgery by removing the original internal fixation and prolonging fixation with a long bar and does not lead to a significant change in the IDP of the adjacent segment while avoiding a greater risk of rod fracture.

Biomechanical evaluation of different sizes of 3D printed cage in lumbar interbody fusion-a finite element analysis

“…A 64-slice spiral computed tomography scanner (Siemens, Erlangen, Germany) was used to obtain tomographic data in DICOM format with a slice spacing of 0.625 mm, which included imaging data of one sacrum and five vertebral bodies and intervertebral discs. The method of model reconstruction was consistent with the previous study [ 22 ]. The image data were imported into Mimics20.0 (Materialise Inc., Leuven, Belgium), and the 3D geometric surface model of the lumbar spine was reconstructed and saved in STL format [ 23 ].…”

“…We imposed the same conditions on the intact model and surgical models, constrained the base of the sacrum, restricted its movement in all directions, and applied an axial load of 280 N on the L1 vertebral body to simulate part of the human weight [ 27 , 39 ]. A moment of 7.5 N·m was applied to simulate the flexion, extension, lateral bending and rotation of the lumbar spine [ 22 ].…”

Biomechanical differences between two different shapes of oblique lumbar interbody fusion cages on whether to add posterior internal fixation system: a finite element analysis

“…In this study, the minimum MESE was model A2 (kidney-shaped cage + BPSF), which was only 7.91 Mpa at right rotation, the maximum MESE is model B1 (Stand-alone straight cage), and the maximum stress can reach 124.4 Mpa at extension. The previous failure load for cortical bone was 90–200 Mpa [ 21 ]. In this study, the stress generated by model B1 during extension was already in this range, indicating that the risk of CS after surgery was greater when straight cage was applied alone in OLIF surgery.…”

A comparative analysis of using cage acrossing the vertebral ring apophysis in normal and osteoporotic models under endplate injury: a finite element analysis

“…We employed thin-slice CT imaging with a thickness of 0.625 mm to scan patients, capturing comprehensive images of their lumbar vertebrae and sacrum. The model reconstruction process followed the same procedures as an earlier experimental study (Wu et al, 2022). Utilizing mimics20 (Materials, Leuven, Belgium), the lumbar spine's 3D geometric surface model was created and saved in STL format (Kim et al, 2014).…”

“…To simulate the physiological weight borne by the lumbar spine, a 280Nm moment was applied vertically downward to the geometric center of the L1 upper surface (Choi et al, 2017;Takenaka et al, 2020). Then a bending moment of 7.5 N m was applied simultaneously at the points set above to simulate the motion in six directions, as shown in Figure 4 (Wu et al, 2022).…”