Finite Element Analysis of Posterior Rod-Screw Fixation Techniques for Thoracolumbar Endplate Burst Fractures

Finite Element Analysis of Posterior Rod-Screw Fixation Techniques for Thoracolumbar Endplate Burst Fractures | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Finite Element Analysis of Posterior Rod-Screw Fixation Techniques for Thoracolumbar Endplate Burst Fractures Kai He, Wenhua Xing This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6597963/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose To compare the finite element analysis of 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation techniques for the treatment of thoracolumbar burst fractures of the upper or lower endplates. Methods Finite element methods were used to analyze the 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation techniques for treating thoracolumbar upper or lower endplate burst fractures (UM: upper endplate fracture + mono-segment pedicle screw fixation [UEPF + MPSF], US: upper endplate fracture + short-segment pedicle screw fixation [UEPF + SPSF], LM: lower endplate fracture + mono-segment pedicle screw fixation [LEPF + MPSF], LS: lower endplate fracture + short-segment pedicle screw fixation [LEPF + SPSF]). Results For both upper and lower endplate fractures, in the same fracture type, the range of motion (ROM) in all directions was greater for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The von Mises stress of the adjacent intervertebral discs and facet joints was lower for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The maximum displacement of the fixed segment, the mobility of the fixed segment, and the mobility of the injured vertebra were lower for the 6 pedicle screw short-segment fixation than for the 4 pedicle screw mono-segment fixation. The von Mises stress peak values for the screws in the US, UM, LS, and LM models were 386.61 MPa, 397.60 MPa, 302.63 MPa, and 305.59 MPa, respectively, while the von Mises stress peak values for the rods were 416.22 MPa, 446.18 MPa, 329.03 MPa, and 347.47 MPa, respectively. The stress on the injured vertebra was lower for the 6 pedicle screw short-segment fixation than for the 4 pedicle screw mono-segment fixation. For both 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations, the ROM of all movements was greater for lower endplate fractures than for upper endplate fractures. The peak von Mises stress of the adjacent intervertebral discs and facet joints in upper endplate fractures occurred at the proximal end with higher stress on the proximal screws, while in lower endplate fractures, these stresses occurred at the distal end with higher stress on the distal screws. The maximum displacement of the fixed segment, the mobility of the fixed segment, and the mobility of the injured vertebra were lower for lower endplate fractures than for upper endplate fractures. The stress on the screws and rods and the stress on the injured vertebra were lower for lower endplate fractures than for upper endplate fractures. Conclusion From the perspective of the fixation method, 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are both effective methods for treating thoracolumbar burst fractures of the spine. The advantage of 4 pedicle screw mono-segment fixation lies in maintaining the mobility of the spine and reducing the risk of adjacent segment degeneration, while the advantage of 6 pedicle screw short-segment fixation lies in its stability and stress dispersion.From the perspective of the fracture type, there are differences in many aspects between upper endplate fractures and lower endplate fractures. Compared with upper endplate fractures, lower endplate fractures have greater spinal mobility, a lower risk of adjacent segment degeneration, and better stability and stress dispersion. In upper endplate fractures, the adjacent segment at the proximal end is the stress concentration area and the stress on the proximal screws is the greatest, while in lower endplate fractures, the adjacent segment at the distal end is the stress concentration area and the stress on the distal screws is the greatest. The difference in stability between 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for lower endplate fractures is smaller than that for upper endplate fractures. Finite element analysis thoracolumbar spine Endplate burst fracture Posterior fixation techniques biomechanics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Introduction Spinal fractures refer to the interruption of the continuity and integrity of the spinal bones. The thoracolumbar region (T10-L2) is located at the transition zone between the less flexible thoracic spine and the highly flexible lumbar spine. It is also the junction of the physiological kyphosis of the thoracic spine and the physiological lordosis of the lumbar spine. Moreover, this area is connected to the relatively fixed thorax, which restricts its mobility. These factors lead to stress concentration in the thoracolumbar region, making it the most common site for spinal fractures, accounting for about 90%, among which 10–20% are burst fractures( 1 – 4 ). Conservative treatment methods include bed rest, brace therapy, and pain-relief medications. However, delayed conservative treatment may lead to neurological deterioration in 17% of cases( 5 , 6 ). The surgical objectives are to relieve severe pain, decompress the spinal cord and nerves, restore spinal stability, and correct kyphotic deformity( 7 ). However, there is controversy regarding surgical guidelines. First, regarding whether to place screws in the injured vertebra, current clinical evidence suggests that screws placed in the injured vertebra can enhance biomechanical stability, unless the pedicle is destroyed and loses the condition for screw placement, in which case screws are placed across the injured vertebra( 8 – 11 ). Second, the number of screws depends on the degree of spinal injury, with common configurations being 4 screws and 6 screws. When there is a three-column fracture or osteoporotic vertebral compression fracture, more screws are used in long-segment fixation to enhance stability( 12 ). Finally, whether to perform open decompression mainly depends on the size of the bone block entering the spinal canal. Generally, if it is less than 50% of the spinal canal volume, open decompression is not necessary. The fragmented bone can be pushed into the spinal canal through the process of the posterior longitudinal ligament being stretched from its folded state to achieve decompression( 13 , 14 ). With the development of medical standards, we are increasingly focusing on the concept of rapid recovery while pursuing effectiveness. Posterior 4 pedicle screw mono-segment fixation has advantages such as low surgical difficulty, minimal trauma, low risk, and fewer complications, while effectively restoring vertebral height and correcting kyphotic deformity. However, there is currently a lack of relevant research( 15 ). This study compared 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for thoracolumbar burst fractures. More specifically, burst fractures involve the anterior column and the middle column according to the Dennis classification. But for different patients, the injured vertebrae often involve different horizontal planes. Taking the parallel extension line of the lower edge of the pedicle as the boundary, there are fractures that only involve the vertebrae above this extension line, fractures that only involve the vertebrae below this extension line, and fractures that involve both above and below this extension line. Since the pedicle screws enter the vertebrae through the pedicles, when there is a fracture above, the area above the extension line is both the fracture site and the site where the screws are inserted, that is, the screws are involved in the fracture site. When there is a fracture below the extension line, the screws are completely in the normal position. In addition, the vertebra is an irregular structure and does not have symmetry between the upper and lower parts. Therefore, we can assume that there are differences between upper endplate fractures and lower endplate fractures. For lower endplate fractures, the placement of screws in the injured vertebra is equivalent to placing screws in an extended "new segment" separated from the fracture site. Only this extended "new segment" is shorter than the length of one vertebra. It is very likely that it can better reflect the advantages of screw placement compared to upper endplate fractures without extension. Therefore, in this study, thoracolumbar burst fractures are further studied separately according to A3.1 type upper endplate fractures and lower endplate fractures. For A3.1 type fractures involving the middle part, since both the upper and lower parts need to be distracted, 4 pedicle screw mono-segment fixation is suitable for unilateral distraction. Therefore, fractures involving the middle part are not studied in this research.Ultimately, this study analyzed and compared four research objects:US, UM, LS, LM. Materials and Methods Establishment of Normal Model A healthy 35-year-old male volunteer signed an informed consent form. The study was approved by the ethics committee (number: EFY20250094). The geometric details of the T10-L2 vertebrae of a healthy young male were obtained from a 64-slice spiral CT scanner (GE Company, USA). The spinal images from the CT scan were input into Mimics software 20.0 (Materialise, Belgium) in DICOM format to extract the three-dimensional contour tissue contour. Then, the three-dimensional contour was imported into Geomagic 12 (Geomagic, USA) in STL format for reverse engineering reconstruction. The extracted three-dimensional contour was solidified to generate a three-dimensional IGES file format. Based on this model, Solidworks 2015 (Dassault, France) software was used to establish the endplates, annulus fibrosus, nucleus pulposus, cortical bone, cancellous bone, and facet cartilage. The ratio of the annulus fibrosus to the nucleus pulposus was 6:4, with the nucleus pulposus set as incompressible fluid. The intervertebral disc was bound to the vertebra, and the facet joint surfaces were in contact with a friction coefficient of 0.1. The model was then imported into Ansys Workbench 18.0 (Ansys, USA) software to establish various ligaments (anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, supraspinous ligament, interspinous ligament, transverse ligament, and capsular ligament). Node-element: US(326387–1008902), UM(294629–886300), LS(324117–1000149), UM(291995–877833). The material properties assigned are shown in Table 1. Establishment of Fracture Model In accordance with previous studies(16), a V-shaped osteotomy was performed on T12 using Solidworks software to simulate upper and lower endplate fracture models, as shown in Fig. 1. Establishment of Fixation Model Mono-segment or short-segment fixation was performed for upper and lower endplate fractures of the thoracolumbar spine to establish four fixation models: UM model, US model, LM model, and LS model. UM represents upper endplate fracture mono-segment fixation, US represents upper endplate fracture short-segment fixation, LM represents lower endplate fracture mono-segment fixation, and LS represents lower endplate fracture short-segment fixation. Using the modeling function of Solidworks, the screw and rod dimensions (screw diameter 6.0 mm, total screw length 40 mm, rod diameter 5.5 mm, length equal to the fixed segment) were modeled. Then, using the assembly function of Solidworks, the screw and rod assembly was precisely combined with the vertebrae. The fixation model is shown in Fig. 2. The element types, material properties, and ligament cross-sectional areas are shown in Table 1. Boundary Conditions and Loads The lower edge of the L2 vertebra was fixed, restricting the movement of the L2 lower endplate in all directions. A vertical load of 400 N was applied to the upper surface of T10, and a load of 7.5 Nm was applied to the upper surface of the T10 vertebra to simulate flexion, extension, left bending, right bending, left rotation, and right rotation movements. The ROM of all segments, the von Mises stress of the adjacent intervertebral discs, the von Mises stress of the adjacent facet joints, the maximum displacement of the fixed segment, the ROM of the fixed segment, the ROM of the injured vertebra T12, the stress on the injured vertebra T12, and the stress on the pedicle screws and rods were analyzed. Results Validation of the Integrity of the T10-L2 Model To validate the integrity of the T10-L2 model, a vertical pressure load of 150 N and a torque of 10 Nm were applied to the model, as referenced in published literature(17). The ROM of the complete T10-L2 spine model was extracted for flexion, extension, left bending, right bending, left rotation, and right rotation, with values of 5.28°, 4.92°, 2.43°, 2.36°, 4.52°, and 4.68°, respectively. The results were compared and analyzed with the studies of Su et al.(17), Pflugmacher et al.(18), and Li et al.(19). The validation of the model's effectiveness is shown in Table 2. ROM of All Segments Compared with the normal ROM of all segments in humans, the ROM of all segments decreased after fixation. The peak ROM of all segments occurred in the flexion condition, while the minimum ROM of all segments occurred in the rotation condition. The ROM of all segments in the UM model was greater than that in the US model in all six conditions, and the ROM of all segments in the LM model was greater than that in the LS model in all six conditions. The peak ROM of all segments in the UM model was lower than that in the LM model in flexion, extension, left bending, right bending, and left rotation, with decreases of 8.68%, 22.18%, 1.35%, 14.71%, and 19.36%, respectively, compared to the LM model. The ROM of all segments in the US model was lower than that in the LS model in all six conditions, with decreases of 5.54% in flexion, 54.42% in extension, 4.18% in left bending, 20.25% in right bending, 1.84% in left rotation, and 4.71% in right rotation, compared to the LS model. The ROM is shown in Table 3 and Fig. 3. Von Mises Stress of Adjacent Intervertebral Discs The von Mises stress of all adjacent intervertebral discs increased after fixation. The maximum von Mises stress of the adjacent intervertebral discs in each group occurred in the lateral bending condition, while the minimum von Mises stress occurred in the flexion or extension condition. The peak von Mises stress of the adjacent intervertebral discs was 22.102 MPa, which occurred in the left bending condition of the proximal adjacent intervertebral disc in the US model. The average von Mises stress of the proximal adjacent intervertebral discs in the US, UM, LS, and LM models was 15.92 MPa, 14.95 MPa, 14.10 MPa, and 12.35 MPa, respectively, while the average von Mises stress of the distal adjacent intervertebral discs was 12.42 MPa, 8.96 MPa, 12.62 MPa, and 12.17 MPa, respectively. The von Mises stress of the adjacent intervertebral discs in the US model was greater than that in the UM model in all six conditions. Similarly, the von Mises stress of the adjacent intervertebral discs in the LS model was greater than that in the LM model in all six conditions. Compared to the US model, the von Mises stress of the proximal adjacent intervertebral discs in the UM model decreased by 0.69% in flexion, 3.58% in extension, 3.31% in left bending, 0.97% in right bending, 12.42% in left rotation, and 11.30% in right rotation. The von Mises stress of the distal adjacent intervertebral discs in the UM model decreased by 35.31% in flexion, 19.44% in extension, 38.74% in left bending, 49.24% in right bending, 11.46% in left rotation, and 12.18% in right rotation. Compared to the LS model, the von Mises stress of the proximal adjacent intervertebral discs in the LM model decreased by 14.65% in flexion, 7.86% in extension, 16.15% in left bending, 11.94% in right bending, 10.98% in left rotation, and 9.55% in right rotation. The von Mises stress of the distal adjacent intervertebral discs in the LM model decreased by 21.02% in flexion, 0.86% in extension, 1.47% in left bending, 0.47% in right bending, 1.80% in left rotation, and 2.96% in right rotation. The peak von Mises stress of the adjacent intervertebral discs in the UM and US models occurred in the upper intervertebral disc, while the peak von Mises stress in the LM and LS models occurred in the lower intervertebral disc. The peak von Mises stress of the adjacent intervertebral discs in the UM model was greater than that in the LM model, with an increase of 9.17%. Similarly, the peak von Mises stress of the adjacent intervertebral discs in the US model was greater than that in the LS model, with an increase of 12.38%. The peak von Mises stress of the adjacent intervertebral discs in upper endplate fractures occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. The von Mises stress of the adjacent intervertebral discs is shown in Figs. 4, 5, and 6. Von Mises Stress of Adjacent Facet Joints The von Mises stress of all adjacent facet joints increased after fixation. The maximum von Mises stress of the adjacent facet joints in each group occurred in the rotation condition, while the minimum von Mises stress occurred in the flexion condition. The average von Mises stress of the proximal adjacent facet joints in the US, UM, LS, and LM models was 1.2909 MPa, 0.9372 MPa, 0.6168 MPa, and 0.5611 MPa, respectively. The average von Mises stress of the distal adjacent facet joints was 0.9247 MPa, 0.7675 MPa, 0.9776 MPa, and 0.7795 MPa, respectively. The von Mises stress of the adjacent facet joints in the US model was greater than that in the UM model in all six conditions. Similarly, the von Mises stress of the adjacent facet joints in the LS model was greater than that in the LM model in all six conditions. The peak von Mises stress of the adjacent facet joints in the US and UM models occurred at the proximal end, while the peak von Mises stress in the LS and LM models occurred at the distal end. The von Mises stress of the adjacent facet joints in the US model was greater than that in the LS model, and the von Mises stress of the adjacent facet joints in the UM model was greater than that in the LM model. The von Mises stress of the adjacent facet joints is shown in Fig. 7. Maximum Displacement of the Fixed Segment The maximum displacement of the fixed segment was defined as the maximum vertical displacement of the upper vertebra and the lower vertebra at the posterior aspect. The maximum displacement of the fixed segment decreased in all groups, with the peak displacement occurring in the flexion condition and the minimum displacement occurring in the rotation condition. The peak maximum displacement of the fixed segment in the US, UM, LS, and LM models was − 9.985 mm, -11.027 mm, -7.5681 mm, and − 8.7547 mm, respectively. The average maximum displacement of the fixed segment in the US, UM, LS, and LM models was − 3.3395 mm, -3.9784 mm, -3.1379 mm, and − 3.5410 mm, respectively. The maximum displacement of the fixed segment in the US model was lower than that in the UM model in all six conditions, and the maximum displacement of the fixed segment in the LS model was lower than that in the LM model in all six conditions. Compared to the US model, the fixed segment displacement in the UM model increased by 10.44% in flexion, 83.82% in extension, 7.22% in left bending, 10.43% in right bending, 2.02% in left rotation, and 2.78% in right rotation. Compared to the LS model, the fixed segment displacement in the LM model increased by 15.68% in flexion, 14.78% in extension, 7.22% in left bending, 7.00% in right bending, 6.19% in left rotation, and 5.90% in right rotation. The peak maximum displacement of the fixed segment in the UM model was greater than that in the LM model by 20.63%, and the peak maximum displacement of the fixed segment in the US model was greater than that in the LS model by 24.21%. The maximum displacement of the fixed segment is shown in Figs. 8 and 9. ROM of the Fixed Segment and Injured Vertebra T12 The ROM of all fixed segments decreased, with the maximum ROM occurring in flexion. The peak ROM of the fixed segments in the US, UM, LS, and LM models was 5.778°, 6.608°, 4.825°, and 5.016°, respectively. The ROM of the fixed segment in the US model was lower than that in the UM model in all six conditions, and the ROM of the fixed segment in the LS model was lower than that in the LM model in all six conditions. The peak ROM of the fixed segment in the US model was greater than that in the LS model, and the peak ROM of the fixed segment in the UM model was greater than that in the LM model. The ROM of all injured vertebrae T12 decreased, with the maximum ROM occurring in flexion. The peak ROM of the injured vertebra T12 in the US, UM, LS, and LM models was 4.476°, 5.479°, 3.714°, and 4.038°, respectively. The ROM of the injured vertebra T12 in the US model was lower than that in the UM model in all six conditions, and the ROM of the injured vertebra T12 in the LS model was lower than that in the LM model in all six conditions. The peak ROM of the injured vertebra T12 in the US model was greater than that in the LS model, and the peak ROM of the injured vertebra T12 in the UM model was greater than that in the LM model. The instability ratio, defined as the ratio of the ROM of the injured vertebra T12 to the ROM of the fixed segment, was lower in the US model than in the UM model in all six conditions, and lower in the LS model than in the LM model in all six conditions. The average instability ratio in the US, UM, LS, and LM models was 77.66%, 82.59%, 76.17%, and 79.33%, respectively. The average instability ratio in the UM model was 6.35% higher than that in the US model, and the average instability ratio in the LM model was 4.15% higher than that in the LS model. The ROM of the fixed segment and the injured vertebra T12 is shown in Fig. 10. Von Mises Stress of Screws and Rods The peak von Mises stress of the screws in each group occurred in the flexion condition, with values of 386.61 MPa, 397.60 MPa, 302.63 MPa, and 305.59 MPa for the US, UM, LS, and LM models, respectively. Similarly, the peak von Mises stress of the rods occurred in the flexion condition, with values of 416.22 MPa, 446.18 MPa, 329.03 MPa, and 347.47 MPa for the US, UM, LS, and LM models, respectively. The peak von Mises stress of the proximal screws in the UM model was 15.46% higher than that of the distal screws. The peak von Mises stress of the distal screws in the LM model was 13.03% higher than that of the proximal screws. The peak von Mises stress of the proximal screws in the UM model was 36.22% higher than that of the middle screws and 361.57% higher than that of the distal screws. The peak von Mises stress of the distal screws in the LM model was 26.12% higher than that of the middle screws and 402.87% higher than that of the proximal screws. The von Mises stress of the screws and rods is shown in Fig. 11, Fig. 12, Fig. 13, Fig. 14, and Fig. 15. Von Mises Stress of the Injured Vertebra T12 The peak von Mises stress of the injured vertebra T12 in each group occurred in the flexion condition. The peak von Mises stress of the injured vertebra T12 in the US, UM, LS, and LM models was 43.066 MPa, 72.175 MPa, 32.615 MPa, and 49.668 MPa, respectively. The peak von Mises stress of the injured vertebra T12 in the UM model was 67.59% higher than that in the US model, and the peak von Mises stress of the injured vertebra T12 in the LM model was 52.29% higher than that in the LS model. The peak von Mises stress of the injured vertebra T12 in the LM model was 31.18% lower than that in the UM model, and the peak von Mises stress of the injured vertebra T12 in the LS model was 25.66% lower than that in the US model. The von Mises stress distribution after fixation was concentrated in the middle and posterior columns of the injured vertebra, especially at the junction of the pedicle and the vertebral body. In the mono-segment fixation model, the von Mises stress range of the injured vertebra extended more into the anterior column. The stress distribution of the injured vertebra T12 is shown in Fig. 16. Discussion Thoracolumbar burst fractures with spinal cord nerve compression, spinal instability, and kyphotic deformity often require surgical treatment, and posterior screw and rod system fixation is an effective method. However, there is controversy regarding surgical guidelines. Existing studies suggest that fixation through the injured vertebra can enhance the stability of the injured vertebra. The common number of screws used is either 4 or 6, with more screws considered only for particularly severe fractures( 20 ). In most cases, indirect decompression is performed rather than direct decompression, and both 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation can achieve indirect decompression( 21 ). Spinal fractures generally do not require fusion surgery( 22 ). Posterior 4 pedicle screw mono-segment surgery has advantages such as minimal trauma, fewer complications, faster recovery, and lower surgical difficulty and risk, while effectively restoring spinal height( 15 ). Since the upper endplate is parallel to the pedicle and closer to the inserted screw, the screw may involve the fracture site. In contrast, the lower endplate is below the pedicle and farther from the inserted screw, with the screw almost entirely in the normal bone area. To study the impact of this anatomical difference, this study separately investigated thoracolumbar burst fractures classified as upper endplate fractures and lower endplate fractures according to the A3.1 type. Additionally, endplate reduction has an important impact on intervertebral disc degeneration( 23 ). Therefore, this study aims to assess the effects of different fixation methods and the impact of anatomical differences in fracture types on treatment and prognosis through finite element analysis of 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation for treating upper or lower endplate fractures of the thoracolumbar spine. The final research subjects were classified into upper endplate fracture mono-segment fixation (UM), upper endplate fracture short-segment fixation (US), lower endplate fracture mono-segment fixation (LM), and lower endplate fracture short-segment fixation (LS). The outcome indicators observed were the ROM of all segments, the von Mises stress of the adjacent intervertebral discs, the von Mises stress of the adjacent facet joints, the maximum displacement of the fixed segment, the ROM of the fixed segment, the ROM of the injured vertebra T12, the stress on the injured vertebra T12, and the stress on the pedicle screws and rods. In this study, finite element methods were used to calculate and analyze the relevant data. First, the three-dimensional reconstructed CT imaging data of the thoracolumbar spine of a young male without fractures were collected. Then, the data were imported into Mimics software to extract the three-dimensional bony contour. Geomagic software was used to solidify the extracted three-dimensional contour. Solidworks software was employed to establish the intervertebral disc model and two types of internal fixation models. V-shaped osteotomy was performed to create two types of fracture models, which were then assembled with various models. Ansys Workbench software was used to establish ligaments, assign materials, mesh, and calculate solutions. The lower endplate of L2 was restricted, and a vertical load of 150 N and a torque of 10 Nm were applied to the upper endplate of T10 to extract the ROM in flexion, extension, left bending, right bending, left rotation, and right rotation. The results were consistent with those of previous reference models. Since higher gravity is more likely to cause injury and screw breakage, the experimental load used in this study was a vertical load of 400 N and a torque of 7.5 Nm. In this study, for both upper and lower endplate fractures, in the same fracture type, the ROM of all directions was greater for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The 4 pedicle screw mono-segment fixation better preserved the ROM of the spine in all directions. The range of motion affects the quality of life of patients, and some athletes and special groups have high requirements for maintaining the mobility of the spine. The von Mises stress of the adjacent intervertebral discs in the 4 pedicle screw mono-segment fixation was lower than that in the 6 pedicle screw short-segment fixation, indicating a lower risk of adjacent intervertebral disc degeneration in the 4 pedicle screw mono-segment fixation. The peak disc stress was concentrated on the posterior aspect of the annulus fibrosus, and stress concentration in the annulus fibrosus implies the possibility of annulus fibrosus tear and rupture. Similar to the von Mises stress of the adjacent intervertebral discs, the risk of adjacent facet joint degeneration was lower in the 4 pedicle screw mono-segment fixation. The von Mises stress of the adjacent intervertebral discs and facet joints suggested that the 4 pedicle screw mono-segment fixation could reduce the risk of adjacent segment degeneration. The stability index indicates that the 6 pedicle screw short-segment fixation has better stability. Therefore, compared with the 4 pedicle screw mono-segment fixation, the 6 pedicle screw short-segment fixation may have better stability effects for fractures with severe instability. Previous studies have also suggested that 4 pedicle screw mono-segment fixation is suitable for mild and moderate fractures ( 11 , 24 ). The stress peak value of the rod is greater than that of the screw, and the part with the maximum screw stress is at the junction of the screw and the rod. The stress peaks of the screw and rod in both the 4 pedicle screw mono-segment fixation and the 6 pedicle screw short-segment fixation are within the fracture limit of 529 Mpa of titanium alloy ( 25 ). The 4 pedicle screw mono-segment fixation is suitable for patients with normal bone density ( 26 ). Different from patients with osteoporosis, patients with normal bone quality have a stronger ability to withstand the force at the screw-bone junction, which greatly reduces the risk of screw loosening. In addition, some studies have suggested that a longer segment fixation has a greater risk of fatigue fracture ( 27 – 29 ). Wolff's law states that the vertical force on the fracture line can promote bone healing and make the callus thicken continuously. It is not recommended to use excessive fixation techniques that hinder bone growth, which suggests the positive effects of screw force and the stress of the injured vertebra ( 30 ). For all fixations, the Von Mises stress nephogram is concentrated in the middle column and the posterior column of the injured vertebra, especially at the connection part between the pedicle and the vertebral body. The Von Mises stress range of the injured vertebra with mono-segment fixation extends more to the anterior column. Similarly, in this study, for both 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations, the ROM of all directions was greater for lower endplate fractures than for upper endplate fractures. Lower endplate fractures better preserved the ROM of the spine in all directions. The von Mises stress of the adjacent intervertebral discs in upper endplate fractures was greater than that in lower endplate fractures, indicating a lower risk of adjacent intervertebral disc degeneration in lower endplate fractures. The peak von Mises stress of the adjacent intervertebral discs in upper endplate fractures occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. Similar to the von Mises stress of the adjacent intervertebral discs, the risk of adjacent facet joint degeneration was lower in lower endplate fractures. The peak von Mises stress of the adjacent facet joints in upper endplate fractures also occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. The von Mises stress of the adjacent intervertebral discs and facet joints suggested that lower endplate fractures had a lower risk of adjacent segment degeneration compared to upper endplate fractures. The proximal adjacent segment may be the stress concentration area in upper endplate fractures, while the distal adjacent segment may be the stress concentration area in lower endplate fractures. The maximum displacement of the fixed segment in lower endplate fractures was lower than that in upper endplate fractures, indicating better stability in lower endplate fractures. The ROM of the fixed segment and the ROM of the injured vertebra T12 were also similar to the results of the maximum displacement of the fixed segment, further indicating the stability advantage of lower endplate fractures. Moreover, the average instability ratio indicated that the stability gap between 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations was smaller for lower endplate fractures than for upper endplate fractures. The von Mises stress of the screws and rods in lower endplate fractures was lower than that in upper endplate fractures, indicating better stress distribution in lower endplate fractures. The maximum screw stress occurred at the proximal end in upper endplate fractures, while the maximum screw stress occurred at the distal end in lower endplate fractures, which may suggest the use of two additional coarse screws( 31 ). Similar to the results of the screws and rods, lower endplate fractures could better distribute the stress on the injured vertebra. For the above discussion, we can consider two aspects. Firstly, it is difficult to balance the advantages of the fixed segment with those of the adjacent segment. Both posterior 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are effective methods for treating thoracolumbar burst fractures. The minimally invasive 4 pedicle screw mono-segment fixation is suitable for patients with normal bone density and mild to moderate fractures, with the advantage of preserving spinal mobility and reducing the risk of adjacent segment degeneration. The 6 pedicle screw short-segment fixation has a broader application range, with the advantage of stability and stress distribution. However, it sacrifices the range of motion and increases the risk of degeneration of the adjacent segments. Secondly, Indeed, as hypothesized, there are differences between upper endplate fractures and lower endplate fractures. Various factors, such as the irregularity of the vertebra and the "extension effect" of the internal fixation for lower endplate fractures, have an impact on the treatment and prognosis. Upper endplate fractures have a greater impact on the proximal part. Specifically, the adjacent segment at the proximal end is the stress concentration area, and the stress of the proximal screw is the greatest. In contrast, lower endplate fractures have a greater impact on the distal part. Specifically, the adjacent segment at the distal end is the stress concentration area, and the stress of the distal screw is the greatest. This is important for guiding the use of thick screws and focusing on the degenerative parts of adjacent vertebrae to determine the timing of internal fixation removal. Compared with upper endplate fractures, the better prognosis of lower endplate fractures is manifested in many aspects, such as mobility, adjacent segments, stress dispersion, and stability. The gap in stability between the 4 pedicle screw mono-segment fixation and the 6 pedicle screw short-segment fixation for lower endplate fractures is also smaller than that for upper endplate fractures. Limitations of this study. Firstly, similar to most finite element studies, this study also conducted modeling and analysis on a single normal volunteer. Although the cross-repeated verification of the fixation with four screws, six screws and the upper and lower endplates in this study is equivalent to secondary verification, which helps to reduce errors, more research is still needed to expand the sample size and conduct in-depth discussions to further reduce errors. Secondly, soft tissues such as the spinal cord, nerves, muscles, etc. were not included in the model, thus ignoring their biomechanical properties ( 32 ). Thirdly, the mechanical properties were not included in this study, and further biomechanical research through clinical studies and on cadavers is required. Finally, in 4 pedicle screw mono-segment fixation for upper endplate fractures, the normal vertebral body is the upper vertebral body of the injured vertebra and is close to the thoracic vertebra, while in 4 pedicle screw mono-segment fixation for lower endplate fractures, the normal vertebral body is the lower vertebral body of the injured vertebra and is close to the lumbar vertebra. This may have an impact on the research variables of the fracture site, but this situation cannot be avoided. Conclusion From the perspective of the fixation method, 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are both effective methods for treating thoracolumbar burst fractures of the spine. The advantage of 4 pedicle screw mono-segment fixation lies in maintaining the mobility of the spine and reducing the risk of adjacent segment degeneration, while the advantage of 6 pedicle screw short-segment fixation lies in its stability and stress dispersion. From the perspective of the fracture type, there are differences in many aspects between upper endplate fractures and lower endplate fractures. Compared with upper endplate fractures, lower endplate fractures have greater spinal mobility, a lower risk of adjacent segment degeneration, and better stability and stress dispersion. In upper endplate fractures, the adjacent segment at the proximal end is the stress concentration area and the stress on the proximal screws is the greatest, while in lower endplate fractures, the adjacent segment at the distal end is the stress concentration area and the stress on the distal screws is the greatest. The difference in stability between 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for lower endplate fractures is smaller than that for upper endplate fractures. Declarations Ethics approval and consent to participate The study was conducted in accordance to the standards set by the Declaration of Helsinki. This study has been approved：The Ethics Committee of the Second Affiliated Hospital of Inner Mongolia Medical University (number: EFY20250094). Written informed consent has been obtained from the patient for the publication of this case report and accompanying images. Consent for publication Not applicable. Availability of data and material Data and material generated during and/or analyzed during the current study are publicly available, available upon reasonable request. Conflict of interest There is no conflict of interest for any party involved in this study. Fund sources The support of the Fund is appreciated: Central Guided Local Science and Technology Project Fund (grant no. 2022ZY0226); Funding for applied technology research and development in the autonomous regions (grant no. 2019GG076); Special Funds for Science and Technology in the Autonomous Region (grant no. 2023SGGZ092) Clinical Trial Number Not applicable Acknowledgements We would like to thank the funding agencies for their generous support: Central Guided Local Science and Technology Project Fund; Funding for applied technology research and development in the autonomous regions; Special Funds for Science and Technology in the Autonomous Region. Authors' contributions Conceived and designed the experiments: K.H., W.H.X. Funding acquisition: K.H., W.H.X. Software:K.H. Performed the experiments: K.H. Analyzed the data: K.H. Writing – original draft: K.H. Writing – review & editing: K.H., W.H.X. References Dai LY, Jiang SD, Wang XY, Jiang LS. A review of the management of thoracolumbar burst fractures. Surg Neurol. 2007;67(3):221–31. discussion 31. Murphy J, McLoughlin E, Davies AM, James SL, Botchu R. Is T9-11 the true thoracolumbar transition zone? J Clin Orthop trauma. 2020;11(5):891–5. Spiegl UJA, Schnake KJ, Hartmann F, Katscher S, Riehle M, Scheyerer MJ, et al. Traumatic Fractures of the Thoracic Spine. Z fur Orthopadie und Unfallchirurgie. 2021;159(4):373–82. Wood KB, Bohn D, Mehbod A. Anterior versus posterior treatment of stable thoracolumbar burst fractures without neurologic deficit: a prospective, randomized study. J Spin Disord Tech. 2005;18(Suppl):S15–23. Charles YP, Steib JP. Management of thoracolumbar spine fractures with neurologic disorder. Orthop Traumatol Surg research: OTSR. 2015;101(1 Suppl):S31–40. Tan T, Huang MS, Rutges J, Marion TE, Fitzgerald M, Hunn MK, et al. Rate and Predictors of Failure in the Conservative Management of Stable Thoracolumbar Burst Fractures: A Systematic Review and Meta-Analysis. Global spine J. 2022;12(6):1254–66. Li Y, Feng X, Pan J, Yang M, Li L, Su Q, et al. Percutaneous Vertebroplasty Versus Kyphoplasty for Thoracolumbar Osteoporotic Vertebral Compression Fractures in Patients with Distant Lumbosacral Pain. Pain Physician. 2021;24(3):E349–56. Anekstein Y, Brosh T, Mirovsky Y. Intermediate screws in short segment pedicular fixation for thoracic and lumbar fractures: a biomechanical study. J Spin Disord Tech. 2007;20(1):72–7. Baaj AA, Reyes PM, Yaqoobi AS, Uribe JS, Vale FL, Theodore N, et al. Biomechanical advantage of the index-level pedicle screw in unstable thoracolumbar junction fractures. J Neurosurg Spine. 2011;14(2):192–7. Guven O, Kocaoglu B, Bezer M, Aydin N, Nalbantoglu U. The use of screw at the fracture level in the treatment of thoracolumbar burst fractures. J Spin Disord Tech. 2009;22(6):417–21. Mahar A, Kim C, Wedemeyer M, Mitsunaga L, Odell T, Johnson B, et al. Short-segment fixation of lumbar burst fractures using pedicle fixation at the level of the fracture. Spine. 2007;32(14):1503–7. Zhang G, Li J, Zhang L, Song J, Shao J, Lv C, et al. Biomechanical Effect of Different Posterior Fixation Techniques on Stability and Adjacent Segment Degeneration in Treating Thoracolumbar Burst Fracture With Osteoporosis: A Finite Element Analysis. Spine. 2024;49(15):E229–38. Lamichhane S, Chaudhary P, Rijal R, Maharjan R, Kandel K. Outcome of posterior short segment fixation with implanting pedicle screw at the fractured level for treatment of thoracolumbar fracture. J Orthop. 2025;62:106–11. Song Y, Pang X, Zhu F. Finite element analysis of the indirect reduction of posterior pedicle screw fixation for a thoracolumbar burst fracture. Medicine. 2022;101(41):e30965. Wang RY, Hua YJ, Chen JH, Chai JL, Shao LF, Zhao JF. [Single-segment pedicle screw fixation for the treatment of thoracolumbar fractures through the gap of paravertebral muscles]. Zhongguo gu shang = China J Orthop Traumatol. 2012;25(1):42–6. Basaran R, Efendioglu M, Kaksi M, Celik T, Mutlu İ, Ucar M. Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture. World Neurosurg. 2019;128:e1109–17. Su Y, Wang X, Ren D, Liu Y, Liu S, Wang P. A finite element study on posterior short segment fixation combined with unilateral fixation using pedicle screws for stable thoracolumbar fracture. Medicine. 2018;97(34):e12046. Pflugmacher R, Schleicher P, Schaefer J, Scholz M, Ludwig K, Khodadadyan-Klostermann C, et al. Biomechanical comparison of expandable cages for vertebral body replacement in the thoracolumbar spine. Spine. 2004;29(13):1413–9. Li C, Zhou Y, Wang H, Liu J, Xiang L. Treatment of unstable thoracolumbar fractures through short segment pedicle screw fixation techniques using pedicle fixation at the level of the fracture: a finite element analysis. PLoS ONE. 2014;9(6):e99156. Cabrera JP, Guiroy A, Carazzo CA, Yurac R, Valacco M, Vialle E, et al. Unstable Thoracolumbar Injuries: Factors Affecting the Decision for Short-Segment vs Long-Segment Posterior Fixation. Int J spine Surg. 2022;16(5):772–8. Feng D, Duan Y, Chen J, Wu Y, Li T, Wang Y, et al. Posterior Pedicle Screw Fixation With Indirect Decompression Versus Direct Decompression in Treating Thoracolumbar Burst Fracture: A Systematic Review and Meta-Analysis. World Neurosurg. 2024;186:27–34. Lan T, Chen Y, Hu SY, Li AL, Yang XJ. Is fusion superior to non-fusion for the treatment of thoracolumbar burst fracture? A systematic review and meta-analysis. J Orthop science: official J Japanese Orthop Association. 2017;22(5):828–33. Su Y, Ren D, Chen Y, Geng L, Yao S, Wu H, et al. Effect of endplate reduction on endplate healing morphology and intervertebral disc degeneration in patients with thoracolumbar vertebral fracture. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2023;32(1):55–67. Alizadeh M, Kadir MR, Fadhli MM, Fallahiarezoodar A, Azmi B, Murali MR, et al. The use of X-shaped cross-link in posterior spinal constructs improves stability in thoracolumbar burst fracture: a finite element analysis. J Orthop research: official publication Orthop Res Soc. 2013;31(9):1447–54. Wycisk E, Solbach A, Siddique S, Herzog D, Walther F, Emmelmann C. Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties. Physics Procedia. 2014;56:371–8. Akabane T, Suzuki T, Konno Y, Sagae H, Sugita M, Hasegawa H, et al. Bone density as a risk of early loss of correction after percutaneous posterior spinal fixation for traumatic thoracolumbar fracture: a study on the usefulness of Hounsfield unit values on computed tomography scan. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2025;34(2):498–505. Benson DR, Burkus JK, Montesano PX, Sutherland TB, McLain RF. Unstable thoracolumbar and lumbar burst fractures treated with the AO fixateur interne. J Spinal Disord. 1992;5(3):335–43. Soshi S, Shiba R, Kondo H, Murota K. An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine. 1991;16(11):1335–41. Wittenberg RH, Shea M, Swartz DE, Lee KS, White AA 3rd, Hayes WC. Importance of bone mineral density in instrumented spine fusions. Spine. 1991;16(6):647–52. Ma Q, Miri Z, Haugen HJ, Moghanian A, Loca D. Significance of mechanical loading in bone fracture healing, bone regeneration, and vascularization. J tissue Eng. 2023;14:20417314231172573. Lin YC, Fan KF, Liao JC. Two additional augmenting screws with posterior short-segment instrumentation without fusion for unstable thoracolumbar burst fracture - Comparisons with transpedicular grafting techniques. Biomedical J. 2016;39(6):407–13. Sun XY, Kong C, Zhang TT, Lu SB, Wang W, Sun SY, et al. Correlation between multifidus muscle atrophy, spinopelvic parameters, and severity of deformity in patients with adult degenerative scoliosis: the parallelogram effect of LMA on the diagonal through the apical vertebra. J Orthop Surg Res. 2019;14(1):276. Tables Tables 1 to 3 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Tables.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6597963","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":464261794,"identity":"1ffed6f1-3757-4e74-a899-5186815dbb31","order_by":0,"name":"Kai He","email":"","orcid":"","institution":"Inner Mongolia Medical University","correspondingAuthor":false,"prefix":"","firstName":"Kai","middleName":"","lastName":"He","suffix":""},{"id":464261795,"identity":"4ee1d2e4-daa3-46f1-9500-a861ce2a47af","order_by":1,"name":"Wenhua Xing","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIiWNgGAWjYFACHiA2YGDgZ2Y++IA0LZLtbMkGJGgB6TrPYyZAlAaDG7mHPxcU3JEzPsxgxsBQYxNNUIvkjLw06RkGz4zNDjOkPWA4lpbbQEgLv3SOGTOPweHEbYcZjhswNhwmrIVNOsf4M1BL/eZmxjYJorQAbTGQBmpJMGBmZiNOi+T8N2ZAvxw2nHGYjdkggRi/GJw5Y/y54M9hef7+8x8ffKixIawFBJjhrARilKNqGQWjYBSMglGADQAAsW854UgJRJMAAAAASUVORK5CYII=","orcid":"","institution":"Second Affiliated Hospital of Inner Mongolia Medical University","correspondingAuthor":true,"prefix":"","firstName":"Wenhua","middleName":"","lastName":"Xing","suffix":""}],"badges":[],"createdAt":"2025-05-06 01:38:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6597963/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6597963/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":83816515,"identity":"eca49364-13f4-469b-96e9-ceac3bbcc38f","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":223812,"visible":true,"origin":"","legend":"\u003cp\u003eFracture Mode\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/b0b1ceb3f8a34468d36217d8.png"},{"id":83816514,"identity":"bcb6f312-3d7a-4c7f-a63b-53f442d0f3f6","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":343809,"visible":true,"origin":"","legend":"\u003cp\u003eFixation Model\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/8524963068ae10939a14a33e.png"},{"id":83818751,"identity":"616c74ed-9492-449e-b811-71a1bd7e8ad1","added_by":"auto","created_at":"2025-06-03 08:16:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":37971,"visible":true,"origin":"","legend":"\u003cp\u003eROM of All Segments\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/c1e25ce9919005f0c80fa274.png"},{"id":83816516,"identity":"a5e73de7-58f0-4518-bc7a-fbe681a9b7e8","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":100731,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Adjacent Intervertebral Discs\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/ce77baad9dd3d814d3c65c58.png"},{"id":83816527,"identity":"8c445f9c-269f-4765-9a74-dbe490066f59","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":288830,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress Distribution of Adjacent Intervertebral Discs\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/aafad828369cc64f89a3ac9c.png"},{"id":83817671,"identity":"8f5b8cdc-0336-4352-a2cf-ac10fa6d8a85","added_by":"auto","created_at":"2025-06-03 08:00:20","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":526096,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress Distribution of Adjacent Intervertebral Discs\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/a2358a745ce535dc01dbdff1.png"},{"id":83818138,"identity":"cfbb7ea0-1a69-4410-bf0f-86a9acb4ef42","added_by":"auto","created_at":"2025-06-03 08:08:20","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":138682,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Adjacent Facet Joints\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/147245c445983c1eedd26e80.png"},{"id":83818752,"identity":"af8755b7-0f37-4b5a-8350-b85264a612e7","added_by":"auto","created_at":"2025-06-03 08:16:20","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":63527,"visible":true,"origin":"","legend":"\u003cp\u003eMaximum Displacement of the Fixed Segment\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/8b7575146bb77502551eb6b2.png"},{"id":83817670,"identity":"27ea98e8-5201-4183-bff6-94ca629d59db","added_by":"auto","created_at":"2025-06-03 08:00:20","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":695460,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement Distribution of the Fixed Segment\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/d31bb73b760622ede554ceb1.png"},{"id":83816521,"identity":"ba9cbbbb-2831-477b-a387-1c8ffaa666a2","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":99700,"visible":true,"origin":"","legend":"\u003cp\u003eROM of the Fixed Segment and Injured Vertebra T12\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/8825c5764e07c1c0781d5915.png"},{"id":83817666,"identity":"50b1f97c-ef67-4caf-afdc-89dd91970c7d","added_by":"auto","created_at":"2025-06-03 08:00:20","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":75548,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Screws\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/9aed8c4f88727b023cc5eb03.png"},{"id":83817668,"identity":"ecadaaaa-1fde-49bb-9cad-95c198117b24","added_by":"auto","created_at":"2025-06-03 08:00:20","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":73305,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Rods\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/c929a89a876fc643b497897c.png"},{"id":83818135,"identity":"129dfd5a-573e-4a36-b50f-a17bdf58c14d","added_by":"auto","created_at":"2025-06-03 08:08:20","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":95612,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Screws in mono-segment Fixation\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/879191a6985328d36dcf8d36.png"},{"id":83816529,"identity":"df0eb189-8b03-4928-a778-ead95abe838e","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":107877,"visible":true,"origin":"","legend":"\u003cp\u003eVon Mises Stress of Screws in Short-Segment Fixation\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/4ac1ad4d7057e9e7d46283fd.png"},{"id":83816534,"identity":"8e2b91c2-b145-4245-9834-86c2a6dcc801","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":672940,"visible":true,"origin":"","legend":"\u003cp\u003eStress Distribution of Screws and Rods\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/d3f3718793f8d67e4ccd2671.png"},{"id":83816532,"identity":"df68e445-541d-4584-8994-646b0d7f92d2","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":423643,"visible":true,"origin":"","legend":"\u003cp\u003eStress Distribution of the Injured Vertebra T12\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/90dc41d1904829956cdbe2b5.png"},{"id":88397973,"identity":"70ce7479-d9fe-466d-8d07-2af421c5ec85","added_by":"auto","created_at":"2025-08-06 06:32:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4359140,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/104fab38-62d0-4e69-b304-c1c1fb4f9e3f.pdf"},{"id":83816518,"identity":"27344574-fe8a-4cb0-a751-1fa37d6d7a2b","added_by":"auto","created_at":"2025-06-03 07:52:20","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":232221,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-6597963/v1/9f4aee036383a5c689a60404.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Finite Element Analysis of Posterior Rod-Screw Fixation Techniques for Thoracolumbar Endplate Burst Fractures","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSpinal fractures refer to the interruption of the continuity and integrity of the spinal bones. The thoracolumbar region (T10-L2) is located at the transition zone between the less flexible thoracic spine and the highly flexible lumbar spine. It is also the junction of the physiological kyphosis of the thoracic spine and the physiological lordosis of the lumbar spine. Moreover, this area is connected to the relatively fixed thorax, which restricts its mobility. These factors lead to stress concentration in the thoracolumbar region, making it the most common site for spinal fractures, accounting for about 90%, among which 10\u0026ndash;20% are burst fractures(\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). Conservative treatment methods include bed rest, brace therapy, and pain-relief medications. However, delayed conservative treatment may lead to neurological deterioration in 17% of cases(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). The surgical objectives are to relieve severe pain, decompress the spinal cord and nerves, restore spinal stability, and correct kyphotic deformity(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). However, there is controversy regarding surgical guidelines. First, regarding whether to place screws in the injured vertebra, current clinical evidence suggests that screws placed in the injured vertebra can enhance biomechanical stability, unless the pedicle is destroyed and loses the condition for screw placement, in which case screws are placed across the injured vertebra(\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Second, the number of screws depends on the degree of spinal injury, with common configurations being 4 screws and 6 screws. When there is a three-column fracture or osteoporotic vertebral compression fracture, more screws are used in long-segment fixation to enhance stability(\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e). Finally, whether to perform open decompression mainly depends on the size of the bone block entering the spinal canal. Generally, if it is less than 50% of the spinal canal volume, open decompression is not necessary. The fragmented bone can be pushed into the spinal canal through the process of the posterior longitudinal ligament being stretched from its folded state to achieve decompression(\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e). With the development of medical standards, we are increasingly focusing on the concept of rapid recovery while pursuing effectiveness. Posterior 4 pedicle screw mono-segment fixation has advantages such as low surgical difficulty, minimal trauma, low risk, and fewer complications, while effectively restoring vertebral height and correcting kyphotic deformity. However, there is currently a lack of relevant research(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study compared 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for thoracolumbar burst fractures. More specifically, burst fractures involve the anterior column and the middle column according to the Dennis classification. But for different patients, the injured vertebrae often involve different horizontal planes. Taking the parallel extension line of the lower edge of the pedicle as the boundary, there are fractures that only involve the vertebrae above this extension line, fractures that only involve the vertebrae below this extension line, and fractures that involve both above and below this extension line. Since the pedicle screws enter the vertebrae through the pedicles, when there is a fracture above, the area above the extension line is both the fracture site and the site where the screws are inserted, that is, the screws are involved in the fracture site. When there is a fracture below the extension line, the screws are completely in the normal position. In addition, the vertebra is an irregular structure and does not have symmetry between the upper and lower parts. Therefore, we can assume that there are differences between upper endplate fractures and lower endplate fractures. For lower endplate fractures, the placement of screws in the injured vertebra is equivalent to placing screws in an extended \"new segment\" separated from the fracture site. Only this extended \"new segment\" is shorter than the length of one vertebra. It is very likely that it can better reflect the advantages of screw placement compared to upper endplate fractures without extension. Therefore, in this study, thoracolumbar burst fractures are further studied separately according to A3.1 type upper endplate fractures and lower endplate fractures. For A3.1 type fractures involving the middle part, since both the upper and lower parts need to be distracted, 4 pedicle screw mono-segment fixation is suitable for unilateral distraction. Therefore, fractures involving the middle part are not studied in this research.Ultimately, this study analyzed and compared four research objects:US, UM, LS, LM.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\"\u003e\n \u003ch2\u003eEstablishment of Normal Model\u003c/h2\u003e\n \u003cp\u003eA healthy 35-year-old male volunteer signed an informed consent form. The study was approved by the ethics committee (number: EFY20250094).\u003c/p\u003e\n \u003cp\u003eThe geometric details of the T10-L2 vertebrae of a healthy young male were obtained from a 64-slice spiral CT scanner (GE Company, USA). The spinal images from the CT scan were input into Mimics software 20.0 (Materialise, Belgium) in DICOM format to extract the three-dimensional contour tissue contour. Then, the three-dimensional contour was imported into Geomagic 12 (Geomagic, USA) in STL format for reverse engineering reconstruction. The extracted three-dimensional contour was solidified to generate a three-dimensional IGES file format. Based on this model, Solidworks 2015 (Dassault, France) software was used to establish the endplates, annulus fibrosus, nucleus pulposus, cortical bone, cancellous bone, and facet cartilage. The ratio of the annulus fibrosus to the nucleus pulposus was 6:4, with the nucleus pulposus set as incompressible fluid. The intervertebral disc was bound to the vertebra, and the facet joint surfaces were in contact with a friction coefficient of 0.1. The model was then imported into Ansys Workbench 18.0 (Ansys, USA) software to establish various ligaments (anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, supraspinous ligament, interspinous ligament, transverse ligament, and capsular ligament). Node-element: US(326387–1008902), UM(294629–886300), LS(324117–1000149), UM(291995–877833). The material properties assigned are shown in Table\u0026nbsp;1.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eEstablishment of Fracture Model\u003c/h3\u003e\n\u003cp\u003eIn accordance with previous studies(16), a V-shaped osteotomy was performed on T12 using Solidworks software to simulate upper and lower endplate fracture models, as shown in Fig.\u0026nbsp;1.\u003c/p\u003e\n\u003ch3\u003eEstablishment of Fixation Model\u003c/h3\u003e\n\u003cp\u003eMono-segment or short-segment fixation was performed for upper and lower endplate fractures of the thoracolumbar spine to establish four fixation models: UM model, US model, LM model, and LS model. UM represents upper endplate fracture mono-segment fixation, US represents upper endplate fracture short-segment fixation, LM represents lower endplate fracture mono-segment fixation, and LS represents lower endplate fracture short-segment fixation. Using the modeling function of Solidworks, the screw and rod dimensions (screw diameter 6.0 mm, total screw length 40 mm, rod diameter 5.5 mm, length equal to the fixed segment) were modeled. Then, using the assembly function of Solidworks, the screw and rod assembly was precisely combined with the vertebrae. The fixation model is shown in Fig.\u0026nbsp;2. The element types, material properties, and ligament cross-sectional areas are shown in Table\u0026nbsp;1.\u003c/p\u003e\n\u003ch3\u003eBoundary Conditions and Loads\u003c/h3\u003e\n\u003cp\u003eThe lower edge of the L2 vertebra was fixed, restricting the movement of the L2 lower endplate in all directions. A vertical load of 400 N was applied to the upper surface of T10, and a load of 7.5 Nm was applied to the upper surface of the T10 vertebra to simulate flexion, extension, left bending, right bending, left rotation, and right rotation movements. The ROM of all segments, the von Mises stress of the adjacent intervertebral discs, the von Mises stress of the adjacent facet joints, the maximum displacement of the fixed segment, the ROM of the fixed segment, the ROM of the injured vertebra T12, the stress on the injured vertebra T12, and the stress on the pedicle screws and rods were analyzed.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003eValidation of the Integrity of the T10-L2 Model\u003c/h2\u003e\n \u003cp\u003eTo validate the integrity of the T10-L2 model, a vertical pressure load of 150 N and a torque of 10 Nm were applied to the model, as referenced in published literature(17). The ROM of the complete T10-L2 spine model was extracted for flexion, extension, left bending, right bending, left rotation, and right rotation, with values of 5.28°, 4.92°, 2.43°, 2.36°, 4.52°, and 4.68°, respectively. The results were compared and analyzed with the studies of Su et al.(17), Pflugmacher et al.(18), and Li et al.(19). The validation of the model's effectiveness is shown in Table\u0026nbsp;2.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eROM of All Segments\u003c/h3\u003e\n\u003cp\u003eCompared with the normal ROM of all segments in humans, the ROM of all segments decreased after fixation. The peak ROM of all segments occurred in the flexion condition, while the minimum ROM of all segments occurred in the rotation condition.\u003c/p\u003e\n\u003cp\u003eThe ROM of all segments in the UM model was greater than that in the US model in all six conditions, and the ROM of all segments in the LM model was greater than that in the LS model in all six conditions. The peak ROM of all segments in the UM model was lower than that in the LM model in flexion, extension, left bending, right bending, and left rotation, with decreases of 8.68%, 22.18%, 1.35%, 14.71%, and 19.36%, respectively, compared to the LM model. The ROM of all segments in the US model was lower than that in the LS model in all six conditions, with decreases of 5.54% in flexion, 54.42% in extension, 4.18% in left bending, 20.25% in right bending, 1.84% in left rotation, and 4.71% in right rotation, compared to the LS model. The ROM is shown in Table\u0026nbsp;3 and Fig.\u0026nbsp;3.\u003c/p\u003e\n\u003ch3\u003eVon Mises Stress of Adjacent Intervertebral Discs\u003c/h3\u003e\n\u003cp\u003eThe von Mises stress of all adjacent intervertebral discs increased after fixation. The maximum von Mises stress of the adjacent intervertebral discs in each group occurred in the lateral bending condition, while the minimum von Mises stress occurred in the flexion or extension condition.\u003c/p\u003e\n\u003cp\u003eThe peak von Mises stress of the adjacent intervertebral discs was 22.102 MPa, which occurred in the left bending condition of the proximal adjacent intervertebral disc in the US model. The average von Mises stress of the proximal adjacent intervertebral discs in the US, UM, LS, and LM models was 15.92 MPa, 14.95 MPa, 14.10 MPa, and 12.35 MPa, respectively, while the average von Mises stress of the distal adjacent intervertebral discs was 12.42 MPa, 8.96 MPa, 12.62 MPa, and 12.17 MPa, respectively. The von Mises stress of the adjacent intervertebral discs in the US model was greater than that in the UM model in all six conditions. Similarly, the von Mises stress of the adjacent intervertebral discs in the LS model was greater than that in the LM model in all six conditions. Compared to the US model, the von Mises stress of the proximal adjacent intervertebral discs in the UM model decreased by 0.69% in flexion, 3.58% in extension, 3.31% in left bending, 0.97% in right bending, 12.42% in left rotation, and 11.30% in right rotation. The von Mises stress of the distal adjacent intervertebral discs in the UM model decreased by 35.31% in flexion, 19.44% in extension, 38.74% in left bending, 49.24% in right bending, 11.46% in left rotation, and 12.18% in right rotation. Compared to the LS model, the von Mises stress of the proximal adjacent intervertebral discs in the LM model decreased by 14.65% in flexion, 7.86% in extension, 16.15% in left bending, 11.94% in right bending, 10.98% in left rotation, and 9.55% in right rotation. The von Mises stress of the distal adjacent intervertebral discs in the LM model decreased by 21.02% in flexion, 0.86% in extension, 1.47% in left bending, 0.47% in right bending, 1.80% in left rotation, and 2.96% in right rotation.\u003c/p\u003e\n\u003cp\u003eThe peak von Mises stress of the adjacent intervertebral discs in the UM and US models occurred in the upper intervertebral disc, while the peak von Mises stress in the LM and LS models occurred in the lower intervertebral disc. The peak von Mises stress of the adjacent intervertebral discs in the UM model was greater than that in the LM model, with an increase of 9.17%. Similarly, the peak von Mises stress of the adjacent intervertebral discs in the US model was greater than that in the LS model, with an increase of 12.38%. The peak von Mises stress of the adjacent intervertebral discs in upper endplate fractures occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. The von Mises stress of the adjacent intervertebral discs is shown in Figs.\u0026nbsp;4, 5, and 6.\u003c/p\u003e\n\u003cdiv id=\"Sec11\"\u003e\n \u003ch2\u003eVon Mises Stress of Adjacent Facet Joints\u003c/h2\u003e\n \u003cp\u003eThe von Mises stress of all adjacent facet joints increased after fixation. The maximum von Mises stress of the adjacent facet joints in each group occurred in the rotation condition, while the minimum von Mises stress occurred in the flexion condition. The average von Mises stress of the proximal adjacent facet joints in the US, UM, LS, and LM models was 1.2909 MPa, 0.9372 MPa, 0.6168 MPa, and 0.5611 MPa, respectively. The average von Mises stress of the distal adjacent facet joints was 0.9247 MPa, 0.7675 MPa, 0.9776 MPa, and 0.7795 MPa, respectively. The von Mises stress of the adjacent facet joints in the US model was greater than that in the UM model in all six conditions. Similarly, the von Mises stress of the adjacent facet joints in the LS model was greater than that in the LM model in all six conditions. The peak von Mises stress of the adjacent facet joints in the US and UM models occurred at the proximal end, while the peak von Mises stress in the LS and LM models occurred at the distal end. The von Mises stress of the adjacent facet joints in the US model was greater than that in the LS model, and the von Mises stress of the adjacent facet joints in the UM model was greater than that in the LM model. The von Mises stress of the adjacent facet joints is shown in Fig.\u0026nbsp;7.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\"\u003e\n \u003ch2\u003eMaximum Displacement of the Fixed Segment\u003c/h2\u003e\n \u003cp\u003eThe maximum displacement of the fixed segment was defined as the maximum vertical displacement of the upper vertebra and the lower vertebra at the posterior aspect. The maximum displacement of the fixed segment decreased in all groups, with the peak displacement occurring in the flexion condition and the minimum displacement occurring in the rotation condition.\u003c/p\u003e\n \u003cp\u003eThe peak maximum displacement of the fixed segment in the US, UM, LS, and LM models was − 9.985 mm, -11.027 mm, -7.5681 mm, and − 8.7547 mm, respectively. The average maximum displacement of the fixed segment in the US, UM, LS, and LM models was − 3.3395 mm, -3.9784 mm, -3.1379 mm, and − 3.5410 mm, respectively. The maximum displacement of the fixed segment in the US model was lower than that in the UM model in all six conditions, and the maximum displacement of the fixed segment in the LS model was lower than that in the LM model in all six conditions. Compared to the US model, the fixed segment displacement in the UM model increased by 10.44% in flexion, 83.82% in extension, 7.22% in left bending, 10.43% in right bending, 2.02% in left rotation, and 2.78% in right rotation. Compared to the LS model, the fixed segment displacement in the LM model increased by 15.68% in flexion, 14.78% in extension, 7.22% in left bending, 7.00% in right bending, 6.19% in left rotation, and 5.90% in right rotation.\u003c/p\u003e\n \u003cp\u003eThe peak maximum displacement of the fixed segment in the UM model was greater than that in the LM model by 20.63%, and the peak maximum displacement of the fixed segment in the US model was greater than that in the LS model by 24.21%. The maximum displacement of the fixed segment is shown in Figs.\u0026nbsp;8 and 9.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\"\u003e\n \u003ch2\u003eROM of the Fixed Segment and Injured Vertebra T12\u003c/h2\u003e\n \u003cp\u003eThe ROM of all fixed segments decreased, with the maximum ROM occurring in flexion. The peak ROM of the fixed segments in the US, UM, LS, and LM models was 5.778°, 6.608°, 4.825°, and 5.016°, respectively. The ROM of the fixed segment in the US model was lower than that in the UM model in all six conditions, and the ROM of the fixed segment in the LS model was lower than that in the LM model in all six conditions. The peak ROM of the fixed segment in the US model was greater than that in the LS model, and the peak ROM of the fixed segment in the UM model was greater than that in the LM model.\u003c/p\u003e\n \u003cp\u003eThe ROM of all injured vertebrae T12 decreased, with the maximum ROM occurring in flexion. The peak ROM of the injured vertebra T12 in the US, UM, LS, and LM models was 4.476°, 5.479°, 3.714°, and 4.038°, respectively. The ROM of the injured vertebra T12 in the US model was lower than that in the UM model in all six conditions, and the ROM of the injured vertebra T12 in the LS model was lower than that in the LM model in all six conditions. The peak ROM of the injured vertebra T12 in the US model was greater than that in the LS model, and the peak ROM of the injured vertebra T12 in the UM model was greater than that in the LM model.\u003c/p\u003e\n \u003cp\u003eThe instability ratio, defined as the ratio of the ROM of the injured vertebra T12 to the ROM of the fixed segment, was lower in the US model than in the UM model in all six conditions, and lower in the LS model than in the LM model in all six conditions. The average instability ratio in the US, UM, LS, and LM models was 77.66%, 82.59%, 76.17%, and 79.33%, respectively. The average instability ratio in the UM model was 6.35% higher than that in the US model, and the average instability ratio in the LM model was 4.15% higher than that in the LS model. The ROM of the fixed segment and the injured vertebra T12 is shown in Fig.\u0026nbsp;10.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\"\u003e\n \u003ch2\u003eVon Mises Stress of Screws and Rods\u003c/h2\u003e\n \u003cp\u003eThe peak von Mises stress of the screws in each group occurred in the flexion condition, with values of 386.61 MPa, 397.60 MPa, 302.63 MPa, and 305.59 MPa for the US, UM, LS, and LM models, respectively. Similarly, the peak von Mises stress of the rods occurred in the flexion condition, with values of 416.22 MPa, 446.18 MPa, 329.03 MPa, and 347.47 MPa for the US, UM, LS, and LM models, respectively.\u003c/p\u003e\n \u003cp\u003eThe peak von Mises stress of the proximal screws in the UM model was 15.46% higher than that of the distal screws. The peak von Mises stress of the distal screws in the LM model was 13.03% higher than that of the proximal screws. The peak von Mises stress of the proximal screws in the UM model was 36.22% higher than that of the middle screws and 361.57% higher than that of the distal screws. The peak von Mises stress of the distal screws in the LM model was 26.12% higher than that of the middle screws and 402.87% higher than that of the proximal screws. The von Mises stress of the screws and rods is shown in Fig.\u0026nbsp;11, Fig.\u0026nbsp;12, Fig.\u0026nbsp;13, Fig.\u0026nbsp;14, and Fig.\u0026nbsp;15.\u003c/p\u003e\n \u003cp\u003eVon Mises Stress of the Injured Vertebra T12\u003c/p\u003e\n \u003cp\u003eThe peak von Mises stress of the injured vertebra T12 in each group occurred in the flexion condition. The peak von Mises stress of the injured vertebra T12 in the US, UM, LS, and LM models was 43.066 MPa, 72.175 MPa, 32.615 MPa, and 49.668 MPa, respectively. The peak von Mises stress of the injured vertebra T12 in the UM model was 67.59% higher than that in the US model, and the peak von Mises stress of the injured vertebra T12 in the LM model was 52.29% higher than that in the LS model. The peak von Mises stress of the injured vertebra T12 in the LM model was 31.18% lower than that in the UM model, and the peak von Mises stress of the injured vertebra T12 in the LS model was 25.66% lower than that in the US model. The von Mises stress distribution after fixation was concentrated in the middle and posterior columns of the injured vertebra, especially at the junction of the pedicle and the vertebral body. In the mono-segment fixation model, the von Mises stress range of the injured vertebra extended more into the anterior column. The stress distribution of the injured vertebra T12 is shown in Fig.\u0026nbsp;16.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThoracolumbar burst fractures with spinal cord nerve compression, spinal instability, and kyphotic deformity often require surgical treatment, and posterior screw and rod system fixation is an effective method. However, there is controversy regarding surgical guidelines. Existing studies suggest that fixation through the injured vertebra can enhance the stability of the injured vertebra. The common number of screws used is either 4 or 6, with more screws considered only for particularly severe fractures(\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e). In most cases, indirect decompression is performed rather than direct decompression, and both 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation can achieve indirect decompression(\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). Spinal fractures generally do not require fusion surgery(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e). Posterior 4 pedicle screw mono-segment surgery has advantages such as minimal trauma, fewer complications, faster recovery, and lower surgical difficulty and risk, while effectively restoring spinal height(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). Since the upper endplate is parallel to the pedicle and closer to the inserted screw, the screw may involve the fracture site. In contrast, the lower endplate is below the pedicle and farther from the inserted screw, with the screw almost entirely in the normal bone area. To study the impact of this anatomical difference, this study separately investigated thoracolumbar burst fractures classified as upper endplate fractures and lower endplate fractures according to the A3.1 type. Additionally, endplate reduction has an important impact on intervertebral disc degeneration(\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). Therefore, this study aims to assess the effects of different fixation methods and the impact of anatomical differences in fracture types on treatment and prognosis through finite element analysis of 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation for treating upper or lower endplate fractures of the thoracolumbar spine. The final research subjects were classified into upper endplate fracture mono-segment fixation (UM), upper endplate fracture short-segment fixation (US), lower endplate fracture mono-segment fixation (LM), and lower endplate fracture short-segment fixation (LS). The outcome indicators observed were the ROM of all segments, the von Mises stress of the adjacent intervertebral discs, the von Mises stress of the adjacent facet joints, the maximum displacement of the fixed segment, the ROM of the fixed segment, the ROM of the injured vertebra T12, the stress on the injured vertebra T12, and the stress on the pedicle screws and rods.\u003c/p\u003e \u003cp\u003eIn this study, finite element methods were used to calculate and analyze the relevant data. First, the three-dimensional reconstructed CT imaging data of the thoracolumbar spine of a young male without fractures were collected. Then, the data were imported into Mimics software to extract the three-dimensional bony contour. Geomagic software was used to solidify the extracted three-dimensional contour. Solidworks software was employed to establish the intervertebral disc model and two types of internal fixation models. V-shaped osteotomy was performed to create two types of fracture models, which were then assembled with various models. Ansys Workbench software was used to establish ligaments, assign materials, mesh, and calculate solutions. The lower endplate of L2 was restricted, and a vertical load of 150 N and a torque of 10 Nm were applied to the upper endplate of T10 to extract the ROM in flexion, extension, left bending, right bending, left rotation, and right rotation. The results were consistent with those of previous reference models. Since higher gravity is more likely to cause injury and screw breakage, the experimental load used in this study was a vertical load of 400 N and a torque of 7.5 Nm.\u003c/p\u003e \u003cp\u003eIn this study, for both upper and lower endplate fractures, in the same fracture type, the ROM of all directions was greater for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The 4 pedicle screw mono-segment fixation better preserved the ROM of the spine in all directions. The range of motion affects the quality of life of patients, and some athletes and special groups have high requirements for maintaining the mobility of the spine. The von Mises stress of the adjacent intervertebral discs in the 4 pedicle screw mono-segment fixation was lower than that in the 6 pedicle screw short-segment fixation, indicating a lower risk of adjacent intervertebral disc degeneration in the 4 pedicle screw mono-segment fixation. The peak disc stress was concentrated on the posterior aspect of the annulus fibrosus, and stress concentration in the annulus fibrosus implies the possibility of annulus fibrosus tear and rupture. Similar to the von Mises stress of the adjacent intervertebral discs, the risk of adjacent facet joint degeneration was lower in the 4 pedicle screw mono-segment fixation. The von Mises stress of the adjacent intervertebral discs and facet joints suggested that the 4 pedicle screw mono-segment fixation could reduce the risk of adjacent segment degeneration. The stability index indicates that the 6 pedicle screw short-segment fixation has better stability. Therefore, compared with the 4 pedicle screw mono-segment fixation, the 6 pedicle screw short-segment fixation may have better stability effects for fractures with severe instability. Previous studies have also suggested that 4 pedicle screw mono-segment fixation is suitable for mild and moderate fractures (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). The stress peak value of the rod is greater than that of the screw, and the part with the maximum screw stress is at the junction of the screw and the rod. The stress peaks of the screw and rod in both the 4 pedicle screw mono-segment fixation and the 6 pedicle screw short-segment fixation are within the fracture limit of 529 Mpa of titanium alloy (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). The 4 pedicle screw mono-segment fixation is suitable for patients with normal bone density (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e). Different from patients with osteoporosis, patients with normal bone quality have a stronger ability to withstand the force at the screw-bone junction, which greatly reduces the risk of screw loosening. In addition, some studies have suggested that a longer segment fixation has a greater risk of fatigue fracture (\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). Wolff's law states that the vertical force on the fracture line can promote bone healing and make the callus thicken continuously. It is not recommended to use excessive fixation techniques that hinder bone growth, which suggests the positive effects of screw force and the stress of the injured vertebra (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e). For all fixations, the Von Mises stress nephogram is concentrated in the middle column and the posterior column of the injured vertebra, especially at the connection part between the pedicle and the vertebral body. The Von Mises stress range of the injured vertebra with mono-segment fixation extends more to the anterior column.\u003c/p\u003e \u003cp\u003eSimilarly, in this study, for both 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations, the ROM of all directions was greater for lower endplate fractures than for upper endplate fractures. Lower endplate fractures better preserved the ROM of the spine in all directions. The von Mises stress of the adjacent intervertebral discs in upper endplate fractures was greater than that in lower endplate fractures, indicating a lower risk of adjacent intervertebral disc degeneration in lower endplate fractures. The peak von Mises stress of the adjacent intervertebral discs in upper endplate fractures occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. Similar to the von Mises stress of the adjacent intervertebral discs, the risk of adjacent facet joint degeneration was lower in lower endplate fractures. The peak von Mises stress of the adjacent facet joints in upper endplate fractures also occurred at the proximal end, while the peak von Mises stress in lower endplate fractures occurred at the distal end. The von Mises stress of the adjacent intervertebral discs and facet joints suggested that lower endplate fractures had a lower risk of adjacent segment degeneration compared to upper endplate fractures. The proximal adjacent segment may be the stress concentration area in upper endplate fractures, while the distal adjacent segment may be the stress concentration area in lower endplate fractures. The maximum displacement of the fixed segment in lower endplate fractures was lower than that in upper endplate fractures, indicating better stability in lower endplate fractures. The ROM of the fixed segment and the ROM of the injured vertebra T12 were also similar to the results of the maximum displacement of the fixed segment, further indicating the stability advantage of lower endplate fractures. Moreover, the average instability ratio indicated that the stability gap between 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations was smaller for lower endplate fractures than for upper endplate fractures. The von Mises stress of the screws and rods in lower endplate fractures was lower than that in upper endplate fractures, indicating better stress distribution in lower endplate fractures. The maximum screw stress occurred at the proximal end in upper endplate fractures, while the maximum screw stress occurred at the distal end in lower endplate fractures, which may suggest the use of two additional coarse screws(\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e). Similar to the results of the screws and rods, lower endplate fractures could better distribute the stress on the injured vertebra.\u003c/p\u003e \u003cp\u003eFor the above discussion, we can consider two aspects. Firstly, it is difficult to balance the advantages of the fixed segment with those of the adjacent segment. Both posterior 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are effective methods for treating thoracolumbar burst fractures. The minimally invasive 4 pedicle screw mono-segment fixation is suitable for patients with normal bone density and mild to moderate fractures, with the advantage of preserving spinal mobility and reducing the risk of adjacent segment degeneration. The 6 pedicle screw short-segment fixation has a broader application range, with the advantage of stability and stress distribution. However, it sacrifices the range of motion and increases the risk of degeneration of the adjacent segments. Secondly, Indeed, as hypothesized, there are differences between upper endplate fractures and lower endplate fractures. Various factors, such as the irregularity of the vertebra and the \"extension effect\" of the internal fixation for lower endplate fractures, have an impact on the treatment and prognosis. Upper endplate fractures have a greater impact on the proximal part. Specifically, the adjacent segment at the proximal end is the stress concentration area, and the stress of the proximal screw is the greatest. In contrast, lower endplate fractures have a greater impact on the distal part. Specifically, the adjacent segment at the distal end is the stress concentration area, and the stress of the distal screw is the greatest. This is important for guiding the use of thick screws and focusing on the degenerative parts of adjacent vertebrae to determine the timing of internal fixation removal. Compared with upper endplate fractures, the better prognosis of lower endplate fractures is manifested in many aspects, such as mobility, adjacent segments, stress dispersion, and stability. The gap in stability between the 4 pedicle screw mono-segment fixation and the 6 pedicle screw short-segment fixation for lower endplate fractures is also smaller than that for upper endplate fractures.\u003c/p\u003e \u003cp\u003eLimitations of this study. Firstly, similar to most finite element studies, this study also conducted modeling and analysis on a single normal volunteer. Although the cross-repeated verification of the fixation with four screws, six screws and the upper and lower endplates in this study is equivalent to secondary verification, which helps to reduce errors, more research is still needed to expand the sample size and conduct in-depth discussions to further reduce errors. Secondly, soft tissues such as the spinal cord, nerves, muscles, etc. were not included in the model, thus ignoring their biomechanical properties (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). Thirdly, the mechanical properties were not included in this study, and further biomechanical research through clinical studies and on cadavers is required. Finally, in 4 pedicle screw mono-segment fixation for upper endplate fractures, the normal vertebral body is the upper vertebral body of the injured vertebra and is close to the thoracic vertebra, while in 4 pedicle screw mono-segment fixation for lower endplate fractures, the normal vertebral body is the lower vertebral body of the injured vertebra and is close to the lumbar vertebra. This may have an impact on the research variables of the fracture site, but this situation cannot be avoided.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eFrom the perspective of the fixation method, 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are both effective methods for treating thoracolumbar burst fractures of the spine. The advantage of 4 pedicle screw mono-segment fixation lies in maintaining the mobility of the spine and reducing the risk of adjacent segment degeneration, while the advantage of 6 pedicle screw short-segment fixation lies in its stability and stress dispersion.\u003c/p\u003e \u003cp\u003eFrom the perspective of the fracture type, there are differences in many aspects between upper endplate fractures and lower endplate fractures. Compared with upper endplate fractures, lower endplate fractures have greater spinal mobility, a lower risk of adjacent segment degeneration, and better stability and stress dispersion. In upper endplate fractures, the adjacent segment at the proximal end is the stress concentration area and the stress on the proximal screws is the greatest, while in lower endplate fractures, the adjacent segment at the distal end is the stress concentration area and the stress on the distal screws is the greatest. The difference in stability between 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for lower endplate fractures is smaller than that for upper endplate fractures.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in accordance to the standards set by the Declaration of Helsinki. This study has been approved：The Ethics Committee of the Second Affiliated Hospital of Inner Mongolia Medical University (number: EFY20250094). Written informed consent has been obtained from the patient for the publication of this case report and accompanying images.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData and material generated during and/or analyzed during the current study are publicly available, available upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere is no conflict of interest for any party involved in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFund sources\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe support of the Fund is appreciated: Central Guided Local Science and Technology Project Fund (grant no. 2022ZY0226); Funding for applied technology research and development in the autonomous regions (grant no. 2019GG076); Special Funds for Science and Technology in the Autonomous Region (grant no. 2023SGGZ092)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Trial Number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to thank the funding agencies for their generous support: Central Guided Local Science and Technology Project Fund; Funding for applied technology research and development in the autonomous regions; Special Funds for Science and Technology in the Autonomous Region.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors' contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceived and designed the experiments: K.H., W.H.X.\u003c/p\u003e\n\u003cp\u003eFunding acquisition: K.H., W.H.X.\u003c/p\u003e\n\u003cp\u003eSoftware:K.H.\u003c/p\u003e\n\u003cp\u003ePerformed the experiments: K.H.\u003c/p\u003e\n\u003cp\u003eAnalyzed the data: K.H.\u003c/p\u003e\n\u003cp\u003eWriting – original draft: K.H.\u003c/p\u003e\n\u003cp\u003eWriting – review \u0026amp; editing: K.H., W.H.X.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDai LY, Jiang SD, Wang XY, Jiang LS. A review of the management of thoracolumbar burst fractures. Surg Neurol. 2007;67(3):221\u0026ndash;31. discussion 31.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMurphy J, McLoughlin E, Davies AM, James SL, Botchu R. Is T9-11 the true thoracolumbar transition zone? J Clin Orthop trauma. 2020;11(5):891\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSpiegl UJA, Schnake KJ, Hartmann F, Katscher S, Riehle M, Scheyerer MJ, et al. Traumatic Fractures of the Thoracic Spine. Z fur Orthopadie und Unfallchirurgie. 2021;159(4):373\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWood KB, Bohn D, Mehbod A. Anterior versus posterior treatment of stable thoracolumbar burst fractures without neurologic deficit: a prospective, randomized study. J Spin Disord Tech. 2005;18(Suppl):S15\u0026ndash;23.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCharles YP, Steib JP. Management of thoracolumbar spine fractures with neurologic disorder. Orthop Traumatol Surg research: OTSR. 2015;101(1 Suppl):S31\u0026ndash;40.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTan T, Huang MS, Rutges J, Marion TE, Fitzgerald M, Hunn MK, et al. Rate and Predictors of Failure in the Conservative Management of Stable Thoracolumbar Burst Fractures: A Systematic Review and Meta-Analysis. Global spine J. 2022;12(6):1254\u0026ndash;66.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi Y, Feng X, Pan J, Yang M, Li L, Su Q, et al. Percutaneous Vertebroplasty Versus Kyphoplasty for Thoracolumbar Osteoporotic Vertebral Compression Fractures in Patients with Distant Lumbosacral Pain. Pain Physician. 2021;24(3):E349\u0026ndash;56.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnekstein Y, Brosh T, Mirovsky Y. Intermediate screws in short segment pedicular fixation for thoracic and lumbar fractures: a biomechanical study. J Spin Disord Tech. 2007;20(1):72\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaaj AA, Reyes PM, Yaqoobi AS, Uribe JS, Vale FL, Theodore N, et al. Biomechanical advantage of the index-level pedicle screw in unstable thoracolumbar junction fractures. J Neurosurg Spine. 2011;14(2):192\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuven O, Kocaoglu B, Bezer M, Aydin N, Nalbantoglu U. The use of screw at the fracture level in the treatment of thoracolumbar burst fractures. J Spin Disord Tech. 2009;22(6):417\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahar A, Kim C, Wedemeyer M, Mitsunaga L, Odell T, Johnson B, et al. Short-segment fixation of lumbar burst fractures using pedicle fixation at the level of the fracture. Spine. 2007;32(14):1503\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang G, Li J, Zhang L, Song J, Shao J, Lv C, et al. Biomechanical Effect of Different Posterior Fixation Techniques on Stability and Adjacent Segment Degeneration in Treating Thoracolumbar Burst Fracture With Osteoporosis: A Finite Element Analysis. Spine. 2024;49(15):E229\u0026ndash;38.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLamichhane S, Chaudhary P, Rijal R, Maharjan R, Kandel K. Outcome of posterior short segment fixation with implanting pedicle screw at the fractured level for treatment of thoracolumbar fracture. J Orthop. 2025;62:106\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong Y, Pang X, Zhu F. Finite element analysis of the indirect reduction of posterior pedicle screw fixation for a thoracolumbar burst fracture. Medicine. 2022;101(41):e30965.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang RY, Hua YJ, Chen JH, Chai JL, Shao LF, Zhao JF. [Single-segment pedicle screw fixation for the treatment of thoracolumbar fractures through the gap of paravertebral muscles]. Zhongguo gu shang = China J Orthop Traumatol. 2012;25(1):42\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBasaran R, Efendioglu M, Kaksi M, Celik T, Mutlu İ, Ucar M. Finite Element Analysis of Short- Versus Long-Segment Posterior Fixation for Thoracolumbar Burst Fracture. World Neurosurg. 2019;128:e1109\u0026ndash;17.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu Y, Wang X, Ren D, Liu Y, Liu S, Wang P. A finite element study on posterior short segment fixation combined with unilateral fixation using pedicle screws for stable thoracolumbar fracture. Medicine. 2018;97(34):e12046.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePflugmacher R, Schleicher P, Schaefer J, Scholz M, Ludwig K, Khodadadyan-Klostermann C, et al. Biomechanical comparison of expandable cages for vertebral body replacement in the thoracolumbar spine. Spine. 2004;29(13):1413\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi C, Zhou Y, Wang H, Liu J, Xiang L. Treatment of unstable thoracolumbar fractures through short segment pedicle screw fixation techniques using pedicle fixation at the level of the fracture: a finite element analysis. PLoS ONE. 2014;9(6):e99156.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabrera JP, Guiroy A, Carazzo CA, Yurac R, Valacco M, Vialle E, et al. Unstable Thoracolumbar Injuries: Factors Affecting the Decision for Short-Segment vs Long-Segment Posterior Fixation. Int J spine Surg. 2022;16(5):772\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeng D, Duan Y, Chen J, Wu Y, Li T, Wang Y, et al. Posterior Pedicle Screw Fixation With Indirect Decompression Versus Direct Decompression in Treating Thoracolumbar Burst Fracture: A Systematic Review and Meta-Analysis. World Neurosurg. 2024;186:27\u0026ndash;34.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLan T, Chen Y, Hu SY, Li AL, Yang XJ. Is fusion superior to non-fusion for the treatment of thoracolumbar burst fracture? A systematic review and meta-analysis. J Orthop science: official J Japanese Orthop Association. 2017;22(5):828\u0026ndash;33.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSu Y, Ren D, Chen Y, Geng L, Yao S, Wu H, et al. Effect of endplate reduction on endplate healing morphology and intervertebral disc degeneration in patients with thoracolumbar vertebral fracture. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2023;32(1):55\u0026ndash;67.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlizadeh M, Kadir MR, Fadhli MM, Fallahiarezoodar A, Azmi B, Murali MR, et al. The use of X-shaped cross-link in posterior spinal constructs improves stability in thoracolumbar burst fracture: a finite element analysis. J Orthop research: official publication Orthop Res Soc. 2013;31(9):1447\u0026ndash;54.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWycisk E, Solbach A, Siddique S, Herzog D, Walther F, Emmelmann C. Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties. Physics Procedia. 2014;56:371\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAkabane T, Suzuki T, Konno Y, Sagae H, Sugita M, Hasegawa H, et al. Bone density as a risk of early loss of correction after percutaneous posterior spinal fixation for traumatic thoracolumbar fracture: a study on the usefulness of Hounsfield unit values on computed tomography scan. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical. Spine Res Soc. 2025;34(2):498\u0026ndash;505.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBenson DR, Burkus JK, Montesano PX, Sutherland TB, McLain RF. Unstable thoracolumbar and lumbar burst fractures treated with the AO fixateur interne. J Spinal Disord. 1992;5(3):335\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSoshi S, Shiba R, Kondo H, Murota K. An experimental study on transpedicular screw fixation in relation to osteoporosis of the lumbar spine. Spine. 1991;16(11):1335\u0026ndash;41.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWittenberg RH, Shea M, Swartz DE, Lee KS, White AA 3rd, Hayes WC. Importance of bone mineral density in instrumented spine fusions. Spine. 1991;16(6):647\u0026ndash;52.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa Q, Miri Z, Haugen HJ, Moghanian A, Loca D. Significance of mechanical loading in bone fracture healing, bone regeneration, and vascularization. J tissue Eng. 2023;14:20417314231172573.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLin YC, Fan KF, Liao JC. Two additional augmenting screws with posterior short-segment instrumentation without fusion for unstable thoracolumbar burst fracture - Comparisons with transpedicular grafting techniques. Biomedical J. 2016;39(6):407\u0026ndash;13.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun XY, Kong C, Zhang TT, Lu SB, Wang W, Sun SY, et al. Correlation between multifidus muscle atrophy, spinopelvic parameters, and severity of deformity in patients with adult degenerative scoliosis: the parallelogram effect of LMA on the diagonal through the apical vertebra. J Orthop Surg Res. 2019;14(1):276.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Finite element analysis, thoracolumbar spine, Endplate burst fracture, Posterior fixation techniques, biomechanics","lastPublishedDoi":"10.21203/rs.3.rs-6597963/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6597963/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eTo compare the finite element analysis of 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation techniques for the treatment of thoracolumbar burst fractures of the upper or lower endplates.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eFinite element methods were used to analyze the 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixation techniques for treating thoracolumbar upper or lower endplate burst fractures (UM: upper endplate fracture\u0026thinsp;+\u0026thinsp;mono-segment pedicle screw fixation [UEPF\u0026thinsp;+\u0026thinsp;MPSF], US: upper endplate fracture\u0026thinsp;+\u0026thinsp;short-segment pedicle screw fixation [UEPF\u0026thinsp;+\u0026thinsp;SPSF], LM: lower endplate fracture\u0026thinsp;+\u0026thinsp;mono-segment pedicle screw fixation [LEPF\u0026thinsp;+\u0026thinsp;MPSF], LS: lower endplate fracture\u0026thinsp;+\u0026thinsp;short-segment pedicle screw fixation [LEPF\u0026thinsp;+\u0026thinsp;SPSF]).\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eFor both upper and lower endplate fractures, in the same fracture type, the range of motion (ROM) in all directions was greater for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The von Mises stress of the adjacent intervertebral discs and facet joints was lower for the 4 pedicle screw mono-segment fixation than for the 6 pedicle screw short-segment fixation. The maximum displacement of the fixed segment, the mobility of the fixed segment, and the mobility of the injured vertebra were lower for the 6 pedicle screw short-segment fixation than for the 4 pedicle screw mono-segment fixation. The von Mises stress peak values for the screws in the US, UM, LS, and LM models were 386.61 MPa, 397.60 MPa, 302.63 MPa, and 305.59 MPa, respectively, while the von Mises stress peak values for the rods were 416.22 MPa, 446.18 MPa, 329.03 MPa, and 347.47 MPa, respectively. The stress on the injured vertebra was lower for the 6 pedicle screw short-segment fixation than for the 4 pedicle screw mono-segment fixation. For both 4 pedicle screw mono-segment and 6 pedicle screw short-segment fixations, the ROM of all movements was greater for lower endplate fractures than for upper endplate fractures. The peak von Mises stress of the adjacent intervertebral discs and facet joints in upper endplate fractures occurred at the proximal end with higher stress on the proximal screws, while in lower endplate fractures, these stresses occurred at the distal end with higher stress on the distal screws. The maximum displacement of the fixed segment, the mobility of the fixed segment, and the mobility of the injured vertebra were lower for lower endplate fractures than for upper endplate fractures. The stress on the screws and rods and the stress on the injured vertebra were lower for lower endplate fractures than for upper endplate fractures.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eFrom the perspective of the fixation method, 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation are both effective methods for treating thoracolumbar burst fractures of the spine. The advantage of 4 pedicle screw mono-segment fixation lies in maintaining the mobility of the spine and reducing the risk of adjacent segment degeneration, while the advantage of 6 pedicle screw short-segment fixation lies in its stability and stress dispersion.From the perspective of the fracture type, there are differences in many aspects between upper endplate fractures and lower endplate fractures. Compared with upper endplate fractures, lower endplate fractures have greater spinal mobility, a lower risk of adjacent segment degeneration, and better stability and stress dispersion. In upper endplate fractures, the adjacent segment at the proximal end is the stress concentration area and the stress on the proximal screws is the greatest, while in lower endplate fractures, the adjacent segment at the distal end is the stress concentration area and the stress on the distal screws is the greatest. The difference in stability between 4 pedicle screw mono-segment fixation and 6 pedicle screw short-segment fixation for lower endplate fractures is smaller than that for upper endplate fractures.\u003c/p\u003e","manuscriptTitle":"Finite Element Analysis of Posterior Rod-Screw Fixation Techniques for Thoracolumbar Endplate Burst Fractures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-03 07:52:15","doi":"10.21203/rs.3.rs-6597963/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3d944b88-76f0-4f8f-9eb2-865cf82ee1e6","owner":[],"postedDate":"June 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-06T06:24:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-03 07:52:15","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6597963","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6597963","identity":"rs-6597963","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}