“…The 3D-printed prosthesis is a porous structure made of titanium alloy (Ti6Al4V). The effective Young's modulus was used to characterize the material property of the porous structure for simplification [17,18]. The material properties used in the finite element model (Table 1) are based on previous reports [19,20].…”
Section: Finite Element Postoperative Modelmentioning
Objective
To analyse and compare the biomechanical differences between 3D-printed prostheses, titanium mesh cages and poorly matched titanium mesh cages in total en bloc spondylectomy (TES).
Methods
The finite element model of T10-L2 for healthy adults was modified to make three models after T12 total spondylectomy. These models were a 3D-printed prosthesis, titanium mesh cage and prosthesis-endplate mismatched titanium mesh cage for reconstruction. The range of motion (ROM), stress distribution of the endplate and internal fixation system of three models in flexion and extension, lateral bending and axial rotation were simulated and analysed by ABAQUS.
Result
In flexion, due to the support of the anterior prosthesis, the fixation system showed the maximum fixation strength. The fixation strength of the 3D-printed prosthesis model was 26.73 N·m /°, that of the TMC support model was 27.20 N·m /°, and that of the poorly matched TMC model was 24.16 N·m /°. In flexion, the L1 upper endplate stress of the poorly matched TMC model was 35.5% and 49.6% higher than that of the TMC and 3D-printed prosthesis, respectively. It was 17% and 28.1% higher in extension, 39.3% and 42.5% higher in lateral bending, and 82.9% and 91.2% higher in axial rotation, respectively. The lower endplate of T11 showed a similar trend, but the magnitude of the stress change was reduced. In the stress analysis of the 3D-printed prosthesis and TMC, it was found that the maximum stress was in flexion and axial rotation, followed by left and right bending, and the least stress was in extension. However, the mismatched TMC withstood the maximum von Mises stress of 418.7 MPa (almost twice as much as the buckling state) in rotation, 3 times and 5.83 times in extension, and 1.29 and 2.85 times in lateral bending, respectively.
Conclusion
Different prostheses with good endplate matching after total spondylectomy can obtain effective postoperative stable support, and the reduction in contact area caused by mismatch will affect the biomechanical properties and increase the probability of internal fixation failure.
“…The 3D-printed prosthesis is a porous structure made of titanium alloy (Ti6Al4V). The effective Young's modulus was used to characterize the material property of the porous structure for simplification [17,18]. The material properties used in the finite element model (Table 1) are based on previous reports [19,20].…”
Section: Finite Element Postoperative Modelmentioning
Objective
To analyse and compare the biomechanical differences between 3D-printed prostheses, titanium mesh cages and poorly matched titanium mesh cages in total en bloc spondylectomy (TES).
Methods
The finite element model of T10-L2 for healthy adults was modified to make three models after T12 total spondylectomy. These models were a 3D-printed prosthesis, titanium mesh cage and prosthesis-endplate mismatched titanium mesh cage for reconstruction. The range of motion (ROM), stress distribution of the endplate and internal fixation system of three models in flexion and extension, lateral bending and axial rotation were simulated and analysed by ABAQUS.
Result
In flexion, due to the support of the anterior prosthesis, the fixation system showed the maximum fixation strength. The fixation strength of the 3D-printed prosthesis model was 26.73 N·m /°, that of the TMC support model was 27.20 N·m /°, and that of the poorly matched TMC model was 24.16 N·m /°. In flexion, the L1 upper endplate stress of the poorly matched TMC model was 35.5% and 49.6% higher than that of the TMC and 3D-printed prosthesis, respectively. It was 17% and 28.1% higher in extension, 39.3% and 42.5% higher in lateral bending, and 82.9% and 91.2% higher in axial rotation, respectively. The lower endplate of T11 showed a similar trend, but the magnitude of the stress change was reduced. In the stress analysis of the 3D-printed prosthesis and TMC, it was found that the maximum stress was in flexion and axial rotation, followed by left and right bending, and the least stress was in extension. However, the mismatched TMC withstood the maximum von Mises stress of 418.7 MPa (almost twice as much as the buckling state) in rotation, 3 times and 5.83 times in extension, and 1.29 and 2.85 times in lateral bending, respectively.
Conclusion
Different prostheses with good endplate matching after total spondylectomy can obtain effective postoperative stable support, and the reduction in contact area caused by mismatch will affect the biomechanical properties and increase the probability of internal fixation failure.
“…And the interface assigns a friction coefficient of 0.2 to simplify the effect of the teeth of cage [ 40 ]. In order to simplify the analysis and reduce the calculation cost, referring to the previous experimental method, we adopted small Young’s modulus to simulate the porous part of cage [ 41 ]. Fig.…”
Objective
To study the biomechanical characteristics of various tissue structures of different sizes of 3D printed Cage in lumbar interbody fusion.
Methods
A finite element model of normal spine was reconstructed and verified. Pedicle screws and Cage of different sizes were implanted in the L4/5 segment to simulate lumbar interbody fusion. The range of motion of the fixed and cephalic adjacent segment, the stress of the screw-rod system, the stress at the interface between cage and L5 endplate, and intervertebral disc pressure of the adjacent segment were calculated and analyzed.
Results
The range of motion and intervertebral disc pressure of the adjacent segment of each postoperative model were larger than those of the intact model, but there was not much difference between them. The stress of cage-endplate interface was also larger than that of the intact model. However, the difference is that the stress of the endplate and the screw-rod system has a tendency to decrease with the increase of the axial area of cage.
Conclusions
Cage with larger axial area in lumbar interbody fusion can reduce the stress of internal fixation system and endplate, but will not increase the range of motion and intervertebral disc pressure of adjacent segment. It has a certain effect in preventing the cage subsidence, internal fixation system failure and screw rod fracture.
“…In terms of FEM models, many approaches have been developed for the lumbar ( Xu et al, 2017 ; Finley et al, 2018 ; Dong et al, 2020 ), thoracic ( Aroeira et al, 2017 ; Aroeira et al, 2018 ) or the cervical spine ( Lasswell et al, 2017 ). Furthermore, Dicko et al, (2015) developed a hybrid lumbar spine model containing rigid bodies, FEM and contact mechanics, while Clin et al, (2011) developed a novel method to include gravitational forces in an FE model.…”
This work describes a computational methodology for the design of braces for adolescent idiopathic scoliosis. The proposed methodology relies on a personalized simulation model of the patient’s trunk, and automatically searches for the brace geometry that optimizes the trade-off between clinical improvement and patient comfort. To do this, we introduce a formulation of differentiable biomechanics of the patient’s trunk, the brace, and their interaction. We design a simulation model that is differentiable with respect to both the deformation state and the brace design parameters, and we show how this differentiable model is used for the efficient update of brace design parameters within a numerical optimization algorithm. To evaluate the proposed methodology, we have obtained trunk models with personalized geometry for five patients of adolescent idiopathic scoliosis, and we have designed Boston-type braces. In a simulation setting, the designed braces improve clinical metrics by 45% on average, under acceptable comfort conditions. In the future, the methodology can be extended beyond synthetic validation, and tested with physical braces on the actual patients.
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