Finite Element Analysis and Comparative Study of 4 Kinds of Internal Fixation Systems for Anterior Cervical Discectomy and Fusion in Children

Background: Spinal injury in children usually occurs in the cervical spine region. Anterior fixation of lower cervical spine has been applied in the treatment of pediatric cervical spine injury and disease due to its stable and firm mechanical properties. This study performed finite element analysis and comparison of 4 different anterior cervical internal fixation systems for children, and explored more stable methods of anterior cervical internal fixation in children. Methods: A finite element model of 6-year-old children with lower cervical spine C4/5 discectomy was established, and the self-designed lower cervical spine anterior locking internal fixation system ACBLP and the children’s anterior cervical internal fixation system ACOP, ACVLP, ACSLP plate screws were fixed and loaded on the model. 27.42N•m torque load was applied to each internal fixation model under 6 working conditions of anteflexion, backward flexion, left flexion, right flexion, left rotation and right rotation, to simulate the movement of the cervical spine. The activity and stress distribution cloud diagram of each finite element model was obtained. Results: In the four internal fixation models of ACOP, ACVLP, ACSLP, and ACBLP, the mobility of C4/5 segment basically showed a decreasing relationship, and the mobility of adjacent segments increased significantly. In the Mises stress cloud diagram of the cervical spine of the four models, the vertebral body and accessories of the ACBLP model born the least stress, followed by ACSLP; The steel plate and screws in the ACVLP internal fixation model were the most stressed; The stress of the internal fixation system (plate/screw) in all models increased in the order of ACBLP, ACSLP, ACVLP, and ACOP.Conclusions: ACBLP internal fixation system had obvious advantages in anterior internal fixation of lower cervical spine in children, C4/5 had the smallest degree of movement, relative displacement was minimal, the stress on the pedicle was the least while the stress on the plate screw was relatively the smallest.

A Finite Element Analysis of the Effects of Different Internal Fixation Strategies and Cage Implantation Methods on the Biomechanics of the Lumbar Spine

Objective: Providing the biomechanical evidences to the surgeons on the internal fixation strategy and Cage implantation method in minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) by the finite element analysis (FEA).Methods: Firstly, based on the common MIS-TLIF surgical methods, three surgical models with different internal fixation strategies and Cage implantation methods were established. The surgical models simulated the physiological activities of the lumbar spine to evaluate the range of motion (ROM) of lumbar spine, the peak stress and the overall stress of the internal fixation system and Cage.Results: The results of the study show that the ROM of the surgical model has decreased significantly under all working conditions, and the decrease range is between 71.07-97.53%. The peak stress of the internal fixation system range was 48.56 to 100.09 MPa in Model-A, 58.10 to 136.05 MPa in Model-B, and 83.26 to 189.81 MPa in Model-C. Especially in the three working conditions of left lateral bending (LLB), left rotation (LR), and right rotation (RR), the peak stress of the internal fixation system of Model-C is 1.80 , 2.07, 1.79 times of Model-A and 2.05 , 1.64, 2.28 times of Model-B. The peak stress of Model-C Cage is significantly lower than Model-A and Model-B under all working conditions.Conclusion: Although the strategy of unilateral pedicle screw + lamina articular process screw + Cage horizontal implantation has the least Cage stress, there is a higher risk of internal fixation fail. Comprehensive evaluation, the surgical strategy of bilateral pedicle screw + Cage horizontal implantation has the best performance, and has the potential to become the standard implantation strategy of MIS-TLIF.

Finite element analysis of the optimal configuration of bridging combined internal fixation system in the treatment of vancouver B1 periprosthetic femoral fractures.

Background and Objective: The incidence of periprosthetic fracture increases with the increase of total hip arthroplasty. The treatment of periprosthetic fracture is always a difficult point. The bridged combined internal fixation system (Ortho-bridge System, OBS) is well adapted to the characteristics of periprosthetic fractures.In this study, finite element analysis was used to evaluate the optimal configuration of OBS for fixation of Vancouver B1 periprosthetic femoral fractures.Methods: A three-rod combination OBS fixation model was established to evaluate the optimal position of the third rod, the cross Angle of proximal screws, the diameter of the connecting rod, and the number of screws. Femoral displacement and the maximum Von Mises (equivalent) stress of OBS were used as evaluation indexes.Results: The third rod is located at 35mm below the lateral fovea of the femur and the minimum Von Mises peak stress of OBS, which is the best location for placing the third rod. It is feasible for proximal screw intersection Angle to be about 71° and 84°.To fix the strength, the 6mm connecting rod is better. Considering the number of screws scheme comprehensively, scheme D is the best number of screws scheme.Conclusion: The personalized and diversified fixation mode of OBS is well adapted to the characteristics of periprosthetic fracture and provides an effective means for the treatment of periprosthetic femoral fracture.Statement : I confirm that this manuscript has not been published or presented elsewhere in part or entirety and is not under consideration by another journal. However, you may notice that a preprint has been published in research square https://www.researchsquare.com/article/rs-661745/v1, “Finite element analysis of the optimal configuration of bridging combined internal fixation system in the treatment of Vancouver B1 periprosthetic femoral fractures”. But it's not published or under consideration by any journal.

Finite Element Analysis of the Optimal Configuration of Bridging Combined Internal Fixation System in The Treatment of Vancouver B1 Periprosthetic Femoral Fractures

Background and Objective: The incidence of periprosthetic fracture increases with the increase of total hip arthroplasty. The treatment of periprosthetic fracture is always a difficult point. The bridged combined internal fixation system (Ortho-bridge System, OBS) is well adapted to the characteristics of periprosthetic fractures.In this study, finite element analysis was used to evaluate the optimal configuration of OBS for fixation of Vancouver B1 periprosthetic femoral fractures.Methods: A three-rod combination OBS fixation model was established to evaluate the optimal position of the third rod, the cross Angle of proximal screws, the diameter of the connecting rod, and the number of screws. Femoral displacement and the maximum Von Mises (equivalent) stress of OBS were used as evaluation indexes.Results: The third rod is located at 35mm below the lateral fovea of the femur and the minimum Von Mises peak stress of OBS, which is the best location for placing the third rod. It is feasible for proximal screw intersection Angle to be about 71° and 84°.To fix the strength, the 6mm connecting rod is better. Considering the number of screws scheme comprehensively, scheme D is the best number of screws scheme.Conclusion: The personalized and diversified fixation mode of OBS is well adapted to the characteristics of periprosthetic fracture and provides an effective means for the treatment of periprosthetic femoral fracture.

A Finite Element Study on the Treatment of Thoracolumbar Fracture with a New Spinal Fixation System

Objective. In this study, the mechanical properties of the new spinal fixation system (NSFS) in the treatment of thoracolumbar fractures were evaluated by the finite element analysis method, so as to provide a mechanical theoretical basis for the later biomechanical experiments and clinical experiments. Methods. T12-L2 bone model was constructed to simulate L1 vertebral fracture, and three models of internal fixation systems were established on the basis of universal spinal system (USS): Model A: posterior short-segment fixation including the fractured vertebra (PSFFV); Model B: short-segment pedicle screw fixation (SSPF); Model C: new spinal fixation system (NSFS). After assembling the internal fixation system and fracture model, the finite element analysis was carried out in the ANSYS Workbench 18.0 software, and the stress of nail rod system, fracture vertebral body stress, vertebral body mobility, and vertebral body displacement were recorded in the three models. Results. The peak values of internal fixation stress, vertebral body stress, vertebral body maximum displacement, and vertebral body maximum activity in Model C were slightly smaller than those in Model B. Conclusions. Compared with the traditional internal fixation system, the new spinal internal fixation system may have the mechanical advantage and can provide sufficient mechanical stability for thoracolumbar fractures.

RESEARCH ON THE STRATEGY OF REDUCTION OPERATION OF BASILAR INVAGINATION COMBINED WITH ATLANTOAXIAL DISLOCATION

Background: The complicated basilar invagination and atlantoaxial dislocation (BI-AAD) can cause a variety of neurological symptoms. Active treatment should be given. The main method of surgical treatment is to relieve the compression of the ventral bone of the brain stem and to fix the unstable spinal segments for fusion. At present, more surgical methods choose modified posterior cervical reduction and internal fixation fusion. Objective: The clinician has preliminarily designed an internal occipital fixation system capable of restoring both horizontal and vertical AADs, and proposed a new compression and distraction reduction (CDR) technique. The feasibility and effectiveness of posterior AAD reduction surgery using CDR techniques for different types of patients were studied in this paper. Methods: First, according to the CT scan sequence images of the congenital BI-AAD patient’s cervical vertebra, the software Materialize Mimics 13.1 was imported to reconstruct 3D geometric model of cervical spine (C0-C7). Then the geometric topology model was carried out in Geomagic2012 software, and surrounding soft tissue was established using SpaceClaim 14.0. The 3D finite element model (FEM) of cervical vertebra for congenital BI-AAD patients was obtained by assigning material attributes, setting contacts and mesh in ANSYS 14.0. To simulate the physiological activities of the spine under two conditions of forward flexion and backward extension, preoperative verification was carried out with the maximum displacement parameter. According to the postoperative CT data of the patient, the position and degree of freedom (DOF) of the occipitocervical internal fixation system were determined. The FEM of the occipitocervical internal fixation system was established by dividing unit grid in ANSYS. Using multiple loading step of statics analysis method, the CDR technology of posterior AAD reduction surgery was simulated. When the atlantoaxial horizontal and vertical reductions were satisfactory, the displacement data were obtained and verified using the post-operative data. Results: The cervical spine (C0-C7) FEM of congenital BI-AAD patients was established. For some lateral atlantoaxial articulation abnormal ossification II, we simulated the CDR technique for the AAD reduction surgery and proposed using the vertical traction instead of vertical reduction. Conclusion: This study confirms the feasibility and effectiveness of posterior AAD reduction surgery using CDR techniques and proposes the different reduction optimization scheme for the patients with lateral atlantoaxial articulation abnormal ossification II of congenital BI-AAD. The results of this study provide a biomechanical theoretical basis for improving the reliability of simple posterior reduction surgery and optimizing the surgical treatment of BI-AAD.

Finite Element- and Design of Experiment-Derived Optimization of Screw Configurations and a Locking Plate for Internal Fixation System

Objectives. The optimization for the screw configurations and bone plate parameters was studied to improve the biomechanical performances such as reliable internal fixation and beneficial callus growth for the clinical treatment of femoral shaft fracture. Methods. The finite element analysis (FEA) of internal fixation system under different screw configurations based on the orthogonal design was performed and so was for the different structural parameters of the locking plate based on the combination of uniform and orthogonal design. Moreover, orthogonal experiment weight matrixes for four evaluation indexes with FEA were analyzed. Results. The analytical results showed the optimal scheme of screw configuration was that screws are omitted in the thread holes near the fracture site, and single cortical screws are used in the following holes to the distal end, while the double cortical screws are fixed in thread holes that are distal to the fracture; in the other words, the length of the screws showed an increasing trend from the fracture site to the distal end in the optimized configuration. The plate structure was optimized when thread holes gap reached 13 mm, with a width of 11 mm and 4.6 mm and 5 mm for thickness and diameter of the screw, respectively. The biomechanical performance of the internal fixation construct was further improved by about 10% based on the optimal strain range and lower stress in the internal fixation system. Conclusions. The proposed orthogonal design and uniform design can be used in a more efficient way for the optimization of internal fixation system, which can reduce the simulation runs to about 10% compared with comprehensive test, and the methodology can be also used for other types of fractures to achieve better internal fixation stability and optimal healing efficiency, which may provide a method for an orthopedist in choosing the screw configurations and parameters for internal fixation system in a more efficient way.