Improvement in determining the risk of damage to the human lumbar functional spinal unit considering age, height, weight and sex using a combination of FEM and RSM

Finite element models of intervertebral disc: recent advances and prospects

OBJECTIVES

The incidence rate of intervertebral disc degeneration (IVDD) is increasing year by year, which brings great harm to our health. The change of biomechanical factors is an important reason for IVDD. Therefore, more and more studies use finite element (FE) models to analyze the biomechanics of spine.

METHODS

In this review, literatures which reported the FE model of intervertebral disc (IVD) were reviewed. We summarized the types and constructional methods of the FE models and analyzed the applications of some representative FE models.

RESULTS

The most widely used model was the nonlinear model which considers the behavior of porous elastic materials. As more advanced methods, More and more models which involve penetration parameters were used to simulate the biological behavior and biomechanical properties of IVD.

CONCLUSIONS

Personalized modeling should be carried out in order to better provide accurate basis for the diagnosis and treatment of the disease. In addition, microstructure, cell behavior and complex load should be considered in the process of model construction to build a more realistic model.

Finite element analysis of neck sports injury based on a whole cervical spine model with muscles

Cervical atlantoaxial subluxation injuries, often resulting from high-intensity external forces or improper posture during high-speed, rotational sports, pose significant risks to athletes' health and careers. This study aims to investigate the biomechanical effects of atlantoaxial subluxation on the cervical spine. Models representing Model 1 (healthy bone model), Model 2 (healthy muscle model), and atlantoaxial subluxation diseased model were developed using CT and MRI data. A 30 N gravitational force and a 1.5 Nm torque were applied to the C0 node. The study simulated changes in range of motion (ROM), disc stress, and muscle stress under six motion states-flexion-extension, lateral flexion, and axial rotation-to evaluate the post-injury movement limitations of the cervical spine. The validity and consistency of this study with cadaver data from the literature were verified through range of motion (ROM) comparison and Bland-Altman analysis. Compared to the healthy model, the diseased model showed a reduction in ROM, with a 10°-30° decrease in C0-C1 ROM across all six movements. The distribution of stress shifted from the bones to the damaged atlantoaxial joint and muscles, while the stress on the intervertebral discs decreased. This study, through the establishment of a finite element model of the cervical spine, reveals the biomechanical effects of atlantoaxial subluxation on the cervical spine, including reduced ROM, altered stress distribution, and increased muscle load. The findings provide a theoretical basis for the prevention of sports injuries, the development of rehabilitation programs, and personalized treatments, emphasizing the importance of muscle recovery and proper management of movement loads. Future work will further validate and expand the application by integrating clinical data.

Comparative Analysis of Three Vertebral Screw Placement Directions in Anterior Thoracolumbar Fracture Surgery: A Finite Element Study

BACKGROUND

Thoracolumbar fractures, especially burst fractures, are common severe spinal injuries requiring surgery. The main goals are to restore spinal stability and normal curvature, relieve nerve compression, and prevent further neurological damage. Minimally invasive techniques are increasingly used in spinal surgery. This study aims to use finite element analysis to compare two new thoracolumbar anterior fixation systems: Hybrid cross-thoracolumbar fixation system and new hybrid cross-thoracolumbar fixation system (HXTL and NHXTL) with Medtronic's ANTERIOR system, providing a theoretical reference for surgeries.

METHOD

A finite element model of the T12-L2 vertebrae of a 27-year-old healthy male was built based on CT images. The model was processed, optimized, meshed, and analyzed using software. In vitro biomechanical tests were compared with the finite element model results to verify the model's validity. A 500 N compressive load and a 10 N m bending moment were applied to the upper surface of T12. The stress and displacement of the vertebral body and the stress state of the support body of the two models under various conditions like forward flexion and backward extension were observed and analyzed.

RESULTS

The study compared the biomechanical performance of the HXTL, NHXTL, and ANTERIOR systems under six physiological conditions. The vertebral body displacement of the three systems was maximum under forward flexion. During right flexion, the HXTL displacement was significantly greater than that of the ANTERIOR and NHXTL systems, while during extension, the HXTL and NHXTL displacements were significantly less than those of the ANTERIOR system. Under other motion conditions, the displacements were relatively small. In terms of vertebral body stress, the ANTERIOR model had the maximum stress during left flexion, significantly greater than that of the other two. In terms of titanium mesh stress, the HXTL system had significantly higher stress during extension and left rotation compared to the other two systems. In terms of nail-rod stress, the ANTERIOR system had higher stress in all directions than the HXTL and NHXTL systems.

CONCLUSION

Compared with the ANTERIOR system, the HXTL system reduces the surgical incision through oblique nail placement, can reduce the risk of nail-rod failure, and increase the stability of the titanium mesh between vertebral bodies, but it also brings a higher risk of subsidence. The NHXTL model not only reduces the surgical incision and the risk of accidental injury to contralateral blood vessels but also reduces the risk of nail-rod failure and does not increase the risk of titanium mesh subsidence. It is a more optimized choice.

Biomechanical effects of upper articular process resection proportion on lumbar after transforaminal endoscopic spine system surgery

Transforaminal endoscopic spine system resection of upper articular process with different proportions often has different effects on lumbar spine biomechanics. Therefore, finite element method was used to explore this problem in this study. The Finite Element (FE) model constructed and validated in this study was a 3D heterogeneous model of the L1-S1 lumbar spine. Nine groups of models with different resect proportions were constructed and compared in six physiological movements. Following the experiment, we reached the following main results. The peak Von Mises stress of the left upper articular process of L5 increased most significantly when the resection proportion increased from 40% to 50% under flexion-extension and bending conditions, with an increase value of 6.04-11.47 MPa. When the resection proportion increased from 70% to 80% under rotation conditions, the peak Von Mises stress of the left articular process of L5 increased most significantly, with an increase value of 26.89 and 37.43 MPa. When the resection proportion increased from 70% to 80% under rotation conditions, the peak Von Mises stress of L4-L5 disc increased by 0.69 and 1.84 MPa. The stress concentration area was mainly located in the junction area of articular process and articular cartilage. Based on the above results, we draw the following conclusions. The resection of 50% of the upper articular process is the critical value of lumbar spine biomechanical change. Especially when the proportion of upper articular process resection exceeds 80%, lumbar instability and postoperative pain may occur during rotation. The postoperative pain is related to the stress concentration stimulation of the articular process and articular cartilage junction.

Appropriate sagittal positioning of femoral components in total knee arthroplasty to prevent fracture and loosening

Aims

This study aimed to investigate the optimal sagittal positioning of the uncemented femoral component in total knee arthroplasty to minimize the risk of aseptic loosening and periprosthetic fracture.

Methods

Ten different sagittal placements of the femoral component, ranging from -5 mm (causing anterior notch) to +4 mm (causing anterior gap), were analyzed using finite element analysis. Both gait and squat loading conditions were simulated, and Von Mises stress and interface micromotion were evaluated to assess fracture and loosening risk.

Results

During gait, varied sagittal positioning did not lead to excessive Von Mises stress or micromotion. However, under squat conditions, posterior positioning (-4 and -5 mm) resulted in stress exceeding 150 MPa at the femoral notch, indicating potential fracture risk. Conversely, +1 mm and 0 mm sagittal positions demonstrated minimal interface micromotion.

Conclusion

Slightly anterior sagittal positioning (+1 mm) or neutral positioning (0 mm) effectively reduced stress concentration at the femoral notch and minimized interface micromotion. Thus, these positions are deemed suitable to decrease the risk of aseptic loosening and periprosthetic femoral fracture.

Do lateral ankle ligaments contribute to syndesmotic stability: a finite element analysis study

Whether the lateral ankle ligaments contribute to syndesmotic stability is still controversial and has been the subject of frequent research recently. In our study, we tried to elucidate this situation using the finite element analysis method. Intact model and thirteen different injury models were created to simulate injuries of the lateral ankle ligaments (ATFL, CFL, PTFL), injuries of the syndesmotic ligaments (AITFL, IOL, PITFL) and their combined injuries. The models were compared in terms of LFT, PFT and EFR. It was observed that 0.537 mm LFT, 0.626 mm PFT and 1.25° EFR occurred in the intact model (M#1), 0.539 mm LFT, 0.761 mm PFT and 2.31° EFR occurred in the isolated ATFL injury (M#2), 0.547 mm LFT, 0.791 mm PFT and 2.50° EFR occurred in the isolated AITFL injury (M#8). The LFT, PFT and EFR amounts were higher in the both M#2 and M#8 compared to the M#1. LFT, PFT and EFR amounts in M#2 and M#8 were found to be extremely close. In terms of LFT and PFT, when we compare models with (LFT: 0.650 mm, PFT: 1.104) and without (LFT: 0.457 mm, PFT: 1.150) IOL injury, it is seen that the amount of LFT increases and the amount of PFT decreases with IOL injury. We also observed that injuries to the CFL, PTFL and PITFL did not cause significant changes in fibular translations and PFT and EFR values show an almost linear correlation. Our results suggest that ATFL injury plays a crucial role in syndesmotic stability.

The biomechanical evaluation of metacarpal fractures fixation methods during finger movements: a finite element study

Objective

This study used finite element analysis to simulate four commonly used fixation methods for metacarpal shaft oblique fractures during finger motion and evaluate their biomechanical performance. The aim was to provide evidence for clinically selecting the optimal fixation method, guiding early rehabilitation treatment, and reducing the risk of complications.

Methods

Finite element analysis simulated dynamic proximal phalanx motion (60° flexion, 20° extension, 20° adduction, and 20° abduction). We analysed stress, displacement, and distributions for dorsal plates, intramedullary nails, Kirschner wire, and screw fixation methods.

Results

At 60° of finger flexion and 20° of abduction, plate fixation demonstrated greater stability and minimal displacement, with a peak displacement of 0.19 mm; however, it showed higher stress levels in all motion states, increasing the risk of failure. The stability of the intramedullary nail was similar to that of the dorsal plate, with a maximum displacement difference of 0.04 mm, and it performed better than the dorsal plate during adduction of 20°. Kirschner wire showed the highest stress levels of 81.6 Mpa during finger flexion of 60°, indicating a greater risk of failure and unstable displacement. Screws had lower stress levels in all finger motion states, reducing the risk of failure, but had poorer stability. Stress and displacement distributions showed that the dorsal plate, intramedullary nail, and Kirschner wire mainly bore stress on the implants, concentrating near the fracture line and the proximal metacarpal. In contrast, the screws partially bore stress in the screw group. The anterior end of the metacarpal mainly hosted the maximum displacement.

Conclusion

This study demonstrates that under simulated finger motion states, the dorsal plate fixation method provides the best stability in most cases, especially during finger flexion and abduction. However, high stress levels also indicate a higher risk of failure. The intramedullary nail is similar to the dorsal plate in stability and performs better in certain motion states. Kirschner wire exhibits the highest risk of failure during flexion. Although screws have poorer stability in some motion states, they offer a lower risk of failure. These findings provide important reference and surgical selection strategies for treating metacarpal fractures.

Effect of anteroposterior vibration frequency on the risk of lumbar injury in seated individuals

Few studies investigate the impact of anterior-posterior excitation frequency on the time-domain vibrational response and injury risk of the lumbar spine in seated individuals. Firstly, this study utilised a previously developed finite element model of an upright seated human body on a rigid chair without a backrest to investigate the modes that affect the anterior-posterior vibrations of the seated body. Subsequently, transient dynamic analysis was employed to calculate the lumbar spine's time-domain responses (displacement, stress, and pressure) and risk factors under anteroposterior sinusoidal excitation at varying frequencies (1-8 Hz). Modal analysis suggested the frequencies significantly affecting the lumbar spine's vibration were notably at 4.7 Hz and 5.5 Hz. The transient analysis results and risk factor assessment indicated that the lumbar responses were most pronounced at 5 Hz. In addition, risk factor assessment showed that long-term exposure to 8 Hz vibration was associated with a greater risk of lumbar injury.

Computational assessment of carbon fabric reinforced polymer made prosthetic knee: Mechanics, finite element simulations and experimental evaluation

A prosthetic knee is designed to replace the functionality of an anatomical knee in transfemoral amputees. The purpose of a prosthetic knee is to restore mobility and compensate amputees for their impairment. In the present research numerical modelling and simulation of a carbon fabric reinforced polymer made polycentric prosthetic knee with four-bar mechanism was performed. Virtual prototyping with computer-aided design and computer-aided engineering software ensured geometric and structural stability of the knee design. The linkage mechanism, instantaneous centre's location and trajectory were investigated using multibody dynamics and analytical formulations. Computational simulations with a non-linear finite element model were employed with joints, contact formulations and an orthotropic material model to predict the displacement, stress formulated and life of the knee prosthesis under static and cyclic loading conditions. Finite element analysis assessed the strength and durability of knee in accordance to standards. Maximum Principal stress of 155 MPa and life expectancy of 3.1 × 106 cycles were determined for the composite knee through numerical simulations ensuring a safe design. Experimental testing was also conducted as per standards and the percentage error was estimated to be 2.52%, thereby establishing the validity of the finite element model deployed. This type of simulation-based approach can be implemented to efficiently and affordably design and prototype a prosthetic knee with desired functioning criteria.

Validation and Estimation of Obesity-Induced Intervertebral Disc Degeneration through Subject-Specific Finite Element Modelling of Functional Spinal Units

(1) Background: Intervertebral disc degeneration has been linked to obesity; its potential mechanical effects on the intervertebral disc remain unknown. This study aimed to develop and validate a patient-specific model of L3-L4 vertebrae and then use the model to estimate the impact of increasing body weight on disc degeneration. (2) Methods: A three-dimensional model of the functional spinal unit of L3-L4 vertebrae and its components were developed and validated. Validation was achieved by comparing the range of motions (RoM) and intradiscal pressures with the previous literature. Subsequently, the validated model was loaded according to the body mass index and estimated stress, deformation, and RoM to assess disc degeneration. (3) Results: During validation, L3-L4 RoM and intradiscal pressures: flexion 5.17° and 1.04 MPa, extension 1.54° and 0.22 MPa, lateral bending 3.36° and 0.54 MPa, axial rotation 1.14° and 0.52 MPa, respectively. When investigating the impact of weight on disc degeneration, escalating from normal weight to obesity reveals an increased RoM, by 3.44% during flexion, 22.7% during extension, 29.71% during lateral bending, and 33.2% during axial rotation, respectively. Also, stress and disc deformation elevated with increasing weight across all RoM. (4) Conclusions: The predicted mechanical responses of the developed model closely matched the validation dataset. The validated model predicts disc degeneration under increased weight and could lay the foundation for future recommendations aimed at identifying predictors of lower back pain due to disc degeneration.

A 3D finite element model of uterus support to evaluate mechanisms underlying uterine prolapse formation

Uterine prolapse (UP) seriously affects the quality of life and physical and mental health of elderly women, which can easily be caused by ligament injury or intra-abdominal pressure (IAP) increasing. The objective of this manuscript was to study the influence of IAP and ligament injury on uterus and its surrounding ligaments using the finite element method. First, the three-dimensional (3D) models of retroverted uterus and its surrounding ligaments were established, and loads and constraints were set in ABAQUS software, then the stress and deformation of uterine ligaments and uterine displacement were calculated. The study found that the uterine displacement and the stress and deformation of the ligaments increased when IAP and ligament injury increased alone or simultaneously. Then, the stress and sensitivity of the ligaments to the changes of IAP or ligament injury were in the order of uterosacral ligament (USL), broad ligament (BL), cardinal ligament (CL) and round ligament (RL), while the deformation and sensitivity the changes of the ligaments were in the order of BL > RL > USL > CL. Moreover, the ligament injury had a greater influence on the uterus and uterine ligaments than IAP. The results of this study can provide guidance for optimization of surgical scheme of uterus prolapsed in clinic and exploration of pathogenesis.

Modelling of Intervertebral Disc (IVD) with Structured Mesh and Crosswise Collagen Fibers

The highly organized collagen network of human lumbar annulus fibrosus (AF) is fundamental to preserve the mechanical integrity of the intervertebral discs. In the healthy AF, fibers are embedded in a hydrated matrix and arranged in a crosswise fashion, giving an anisotropic structure capable to undergo large strains. For finite element analysis (FEA) of spine, modelling a realistic intervertebral disc geometry has always been a challenge. This paper proposes a simple yet efficient workflow details for generating structured mesh of the ground substance of the AF and the method for generating collagen fibers with controllable angles that are embedded in AF.Clinical Relevance- The biomechanical response of spine is usually studied by finite element analysis (FEA) of the assembly of vertebra and IVD and other components. The FEA results are always dependent on the correct generation of the geometry and the material of the components. For IVD, creating structured mesh with crosswise collagen fibers with adjustable angles will provide a better control over the anisotropic property definitions of the IVD and approaching a more realistic simulation.

Modeling of the PHEMA-gelatin scaffold enriched with graphene oxide utilizing finite element method for bone tissue engineering

The development of computer-aided facilities has contributed to the optimization of tissue engineering techniques due to the reduction in necessary practical assessments and the removal of animal or human-related ethical issues. Herein, a bone scaffold based on poly (2-hydroxyethyl methacrylate) (PHEMA), gelatin and graphene oxide (GO), was simulated by SOLIDWORKS and ABAQUS under a normal compression force using finite element method (FEM). Concerning the mechanotransduction impact, GO could support the stability of the structure and reduce the possibility of the failure resulting in the integrity and durability of the scaffold efficiency which would be beneficial for osteogenic differentiation.

Analysis of stress and stabilization in adolescent with osteoporotic idiopathic scoliosis: finite element method

Objective: To explore the effect of osteoporosis on the stress, stability, and lumbar intervertebral disc of AIS lumbar vertebrae by finite element method. Better understand the biomechanical characteristics of osteoporotic scoliosis.Methods: Based on the CT images of normal lumbar vertebrae and lumbar vertebrae with AIS, the finite element models were established to simulate the estimated osteoporosis by changing the Young's modulus of cortical bone, cancellous bone, and endplate. Four finite element models of normal lumbar, osteoporotic lumbar, normal AIS lumbar and osteoporotic AIS lumbar were established, and the same load and boundary conditions were applied respectively. The displacement, stress, and intervertebral disc strain of the four models were compared to explore the effect of osteoporosis on the stability and injury risk of AIS.Results: After suffering from osteoporosis, under the same load, the displacement of lumbar spine increases, the stability decreases, and the stability of AIS lumbar spine decrease more obviously, especially under extension load. Suffering from osteoporosis will increase the stress of lumbar spine, AIS lumbar spine increases more obviously, and the stress is more concentrated, Osteoporotic lumbar spine only affects the strain of intervertebral disc when AIS lumbar spine bends on the concave side, resulting in greater strain behind the concave side of intervertebral disc.Conclusions: AIS patients with OP have lower lumbar stability, a higher risk of fracture of lumbar vertebrae, and spinal nerves are more likely to be compressed by intervertebral discs. OP can aggravate the scoliosis of lumbar vertebrae.

Geometrical model establishment and preoperative evaluation on A-T flap design: Finite element method-based computer-aided simulation on surgical operation processes

Objective

A-T flap has been extensively applied to repair dermal soft tissue defects. The flap design completely depends on the experience of doctors. Herein, we explored the approach of analyzing the reasonability of A-T flap design and performed a simulation of operation processes by computer-aided technology. Afterward, the finite element analysis software (MSC.Marc/Mentat) was used to establish the simulation model, based on which the computer simulation of flap suturing and release state in A-T flap surgery was performed.

Methods

A geometrical model of the A-T flap was established, and the length-width ratio of the flap, maximum suture distance, and suture area that could influence the postoperative suture effects of the flap were analyzed. The reasonable surgical planning for A-T flap design based on the crossing constraint relationship was achieved. The simulation model was established by the finite element analysis software (MSC.Marc/Mentat), based on which computer simulation of flap suture and release state of A-T flap in surgery processes were performed. The flap's stress and deformation distribution results confirmed the applicability of the A-T flap design method proposed in the present study.

Results

When the apex angle of the A-T flap was 60 degrees, the suture area was the smallest, and the flap design had the highest practicability.

Conclusion

Computer-assisted preoperative assessment, which has high clinical value, could provide a theoretical basis for A-T flap design in clinical practice.

Finite Element Analysis of Elbow Joint Stability by Different Flexion Angles of the Annular Ligament

Objective

The injury of the annular ligament can change the stress distribution and affect the stability of the elbow joint, but its biomechanical mechanism is unclear. The present study investigated the biomechanical effects of different flexion angles of the annular ligament on elbow joint stability.

Methods

A cartilage and ligament model was constructed using SolidWorks software according to the magnetic resonance imaging results to simulate the annular ligament during normal, loosened, and ruptured conditions at different buckling angles (0°, 30°, 60°, 90°, and 120°). The fixed muscle strengths were 40 N (F1), 20 N (F2), 20 N (F3), 20 N (F4), and 20 N (F5) for the triceps, biceps, and brachial tendons and the base of the medial collateral ligament and lateral collateral ligament. The different elbow three‐dimensional (3D) finite element models were imported into ABAQUS software to calculate and analyze the load, contact area, contact stress, and stress of the medial collateral ligament of the olecranon cartilage.

Results

The results showed that the stress value of olecranon cartilage increased under different conditions (normal, loosened, and ruptured annular ligament) with elbow extension, and the maximum stress value of olecranon cartilage was 2.91 ± 0.24 MPa when the annular ligament was ruptured. The maximum contact area of olecranon cartilage was 254  mm² with normal annular ligament when the elbow joint was flexed to 30°, while the maximum contact area of loosened and ruptured annular ligament was 283 and 312 mm² at 60° of elbow flexion, and then decreased gradually. The maximum stress of the medial collateral ligament was 6.52 ± 0.23, 11.51 ± 0.78, and 18.74 ± 0.94 MPa under the different conditions, respectively.

Conclusion

When the annular ligament ruptures, it should be reconstructed as much as possible to avoid the elevation of stress on the surface of the medial collateral ligament of the elbow and the annular cartilage, which may cause clinical symptoms.

Sacrospinous and sacrotuberous ligaments influence in pelvis kinematics

The alteration in mechanical properties of posterior pelvis ligaments may cause a biased pelvis deformation which, in turn, may contribute to hip and spine instability and malfunction. Here, the effect of different mechanical properties of ligaments on lumbopelvic deformation is analyzed via the finite element method. First, the improved finite element model was validated using experimental data from previous studies and then used to calculate the sensitivity of lumbopelvic deformation to changes in ligament mechanical properties, load magnitude, and unilateral ligament resection. The deformation of the lumbopelvic complex relative to a given load was predominant in the medial plane. The effect of unilateral resection on deformation appeared to be counterintuitive, suggesting that ligaments have the ability to redistribute load and that they play an important role in the mechanics of the lumbopelvic complex.

Patient-Specific Finite Element Modeling of the Whole Lumbar Spine Using Clinical Routine Multi-Detector Computed Tomography (MDCT) Data-A Pilot Study

(1) Background: To study the feasibility of developing finite element (FE) models of the whole lumbar spine using clinical routine multi-detector computed tomography (MDCT) scans to predict failure load (FL) and range of motion (ROM) parameters. (2) Methods: MDCT scans of 12 subjects (6 healthy controls (HC), mean age ± standard deviation (SD): 62.16 ± 10.24 years, and 6 osteoporotic patients (OP), mean age ± SD: 65.83 ± 11.19 years) were included in the current study. Comprehensive FE models of the lumbar spine (5 vertebrae + 4 intervertebral discs (IVDs) + ligaments) were generated (L1−L5) and simulated. The coefficients of correlation (ρ) were calculated to investigate the relationship between FE-based FL and ROM parameters and bone mineral density (BMD) values of L1−L3 derived from MDCT (BMDQCT-L1-3). Finally, Mann−Whitney U tests were performed to analyze differences in FL and ROM parameters between HC and OP cohorts. (3) Results: Mean FE-based FL value of the HC cohort was significantly higher than that of the OP cohort (1471.50 ± 275.69 N (HC) vs. 763.33 ± 166.70 N (OP), p < 0.01). A strong correlation of 0.8 (p < 0.01) was observed between FE-based FL and BMDQCT-L1-L3 values. However, no significant differences were observed between ROM parameters of HC and OP cohorts (p = 0.69 for flexion; p = 0.69 for extension; p = 0.47 for lateral bending; p = 0.13 for twisting). In addition, no statistically significant correlations were observed between ROM parameters and BMDQCT- L1-3. (4) Conclusions: Clinical routine MDCT data can be used for patient-specific FE modeling of the whole lumbar spine. ROM parameters do not seem to be significantly altered between HC and OP. In contrast, FE-derived FL may help identify patients with increased osteoporotic fracture risk in the future.

Effect of the In Situ Screw Implantation Region and Angle on the Stability of Lateral Lumbar Interbody Fusion: A Finite Element Study

Objective

To investigate the effect of the in situ screw implantation region and angle on the stability of lateral lumbar interbody fusion (LLIF) from a biomechanical perspective.

Methods

A validated L2‐4 finite element (FE) model was modified for simulation. The L3‐4 fused segment undergoing LLIF surgery was modeled. The area between the superior and inferior edges and the anterior and posterior edges of the vertebral body (VB) is divided into four zones by three parallel lines in coronal and horizontal planes. In situ screw implantation methods with different angles based on the three parallel lines in coronal plane were applied in Models A, B, and C (A: parallel to inferior line; B: from inferior line to midline; C: from inferior line to superior line). In addition, four implantation methods with different regions based on the three parallel lines in horizontal plane were simulated as types 1–2, 1–3, 2–2, and 2–3 (1–2: from anterior line to midline; 1–3: from anterior line to posterior line; 2–2: parallel to midline; 2–3: from midline to posterior line). L3‐4 ROM, interbody cage stress, screw‐bone interface stress, and L4 superior endplate stress were tracked and calculated for comparisons among these models.

Results

The L3‐4 ROM of Models A, B, and C decreased with the extent ranging from 47.9% (flexion‐extension) to 62.4% (lateral bending) with no significant differences under any loading condition. Types 2–2 and 2–3 had 45% restriction, while types 1–2 and 1–3 had 51% restriction in ROM under flexion‐extension conditions. Under lateral bending, types 2–2 and 2–3 had 70.6% restriction, while types 1–2 and 1–3 had 61.2% restriction in ROM. Under axial rotation, types 2–2 and 2–3 had 65.2% restriction, while types 1–2 and 1–3 had 59.3% restriction in ROM. The stress of the cage in types 2–2 and 2–3 was approximately 20% lower than that in types 1–2 and 1–3 under all loading conditions in all models. The peak stresses at the screw‐bone interface in types 2–2 and 2–3 were much lower (approximately 35%) than those in types 1–2 and 1–3 under lateral bending, while no significant differences were observed under flexion‐extension and axial rotation. The peak stress on the L4 superior endplate was approximately 30 MPa and was not significantly different in all models under any loading condition.

Conclusions

Different regions of entry‐exit screws induced multiple screw trajectories and influenced the stability and mechanical responses. However, different implantation angles did not. Considering the difficulty of implantation, the ipsilateral‐contralateral trajectory in the lateral middle region of the VB can be optimal for in situ screw implantation in LLIF surgery.

The Use of Customized Three-Dimensionally Printed Mandible Prostheses with a Pressure-Reducing Device: A Finite Element Analysis in Different Chewing Positions, Biomechanical Testing, and In Vivo Animal Study Using Lanyu Pigs

Segmental bony defects of the mandible constitute a complete loss of the regional part of the mandible. Although several types of customized three-dimension-printed mandible prostheses (CMPs) have been developed, this technique has yet to be widely used. We used CMP with a pressure-reducing device (PRD) to investigate its clinical applicability. First, we used the finite element analysis (FEA). We designed four models of CMP (P1 to P4), and the result showed that CMP with posterior PRD deployment (P4 group) had the maximum total deformation in the protrusion and right excursion positions, and in clenching and left excursion positions, posterior screws had the minimum von Mises stress. Second, the P4 CMP-PRD was produced using LaserCUSING from titanium alloy (Ti-6Al-4V). The fracture test result revealed that the maximum static pressure that could be withstood was 189 N, and a fatigue test was conducted for 5,000,000 cycles. Third, animal study was conducted on five male 4-month-old Lanyu pigs. Four animals completed the experiment. Two animals had CMP exposure in the oral cavity, but there was no significant inflammation, and one animal had a rear wing fracture. According to a CT scan, the lingual cortex of the mandible crawled along the CMP surface, and a bony front-to-back connection was noted in one animal. A histological examination indicated that CMP was significantly less reactive than control materials (p = 0.0170). Adequate PRD deployment in CMP may solve a challenge associated with CMP, thus promoting its use in clinical practice.

A comparative finite element analysis of artificial intervertebral disc replacement and pedicle screw fixation of the lumbar spine

Titanium alloy-based Pedicle screw-rod fusion is a very common technique to provide higher fusion regularity than other methods. In recent times, Carbon-fibre-reinforced (CFR)-PEEK rod is used to better reduce the fusion rate. Alternatively, total disc replacement (TDR) is also very common for the non-fusion treatment method for degenerative disc disease (DDD). This study aims to investigate flexibility (ROM), stability, stress condition in implant, implant adjacent bone of the implanted lumbar spine during different physiological movements and loading environments. The finite element (FE) intact model of the lumbar spine (L2-L5) with two-level pedicle screw-rod fusion at L3-L4-L5 and two-level artificial disc replacement was developed. CFR-PEEK was taken for rod for semi-rigid fusion. UHMWPE was taken as core part of the artificial disc. The FE models were simulated under 6, 8 and 10 Nm moments in left right lateral bending, flexion and extension movements. The total ROM was reduced for two-level pedicle screw fixation and increased for the artificial disc replacement model during flexion extension compared to the intact spine. The total ROM was reduced by around 54% and 25% for two-level fixation and increased by 30% and 19.5% for artificial disc replacement spine, under flexion-extension and left-right lateral bending respectively. For screw fixation, the ROM increased by 15% and 18% reduced by 4.5% and 14% for disc replacement at the adjacent segments for flexion-extension and left-right lateral bending.

Is There Any Relationship between Plasma IL-6 and TNF-α Levels and Lumbar Disc Degeneration? A Retrospective Single-Center Study

Intervertebral disc degeneration (IDD) is one of the most common degenerative diseases all over the world. A growing number of studies have proved that large amounts of cytokines are produced during the development of IDD, and the inflammatory responses induced by these cytokines aggravate the occurrence and development of the disc degeneration. In this retrospective single-center study, a total of 182 lumbar spine cases were retrospectively reviewed between July 2020 and October 2021. An appropriate cutoff value was found for discriminating severity of IDD by William rank-sum test and locally weighted scatterplot smoothing algorithm. The cumulative grade was also calculated by summing Pfirrmann grades for all lumbar spine intervertebral discs. It was found that high-score group (total score > 18) plasma interleukin-6 (IL-6) concentration was significantly higher than that of the low-score group (total score ≤ 18) (9.6 ± 1.75 vs. 5.40 ± 0.61 pg/ml, p = 0.002), tumor necrosis factor-α (TNF-α) following the same trend (5.27 ± 1.48 vs. 2.97 ± 0.23, p = 0.006), which was most pronounced in the upper lumbar intervertebral discs (L1-3). In the entire sample, preoperative IL-6 concentration was significantly higher than that of the postoperation (p < 0.001), while the TNF-α was the opposite (p = 0.039). It was also found that there were significant differences in the two groups with respect to age and hypertension (p < 0.001 and p = 0.037). In conclusion, this study preliminarily indicated the relationship between IL-6 and TNF-α and the severity of lumbar disc degeneration.

Prevailing treatment methods for lumbar spondylolysis: A systematic review

Background:

Aim of this study was to systematically review the prevailing treatment methods for lumbar spondylolysis.

Methods:

Manuscripts published between 1951 and 2020 were searched by using PubMed, Medline, Scopus, Springer, Web of Science databases. The study protocol was registered with PROSPERO (CRD42020218651). The inclusion criteria for all articles of prevailing treatment methods for spondylolysis were:

Standards have been independently applied by using 2 reviewers and another author resolved disagreements.

Results:

Data extraction screened 12 full-length articles. Description, treatment, outcome, and findings were individually extracted and cross-referenced.

Discussion:

Current review has suggested that the noninvasive treatment method specifically low intensity pulsed ultrasound, electro acupuncture and pulsed electromagnetic filed is effective for bone union while operative treatment specifically pedicle screw fixation +/- interbody fusion depending the extent of disk degeneration and craniocaudal foraminal stenosis is effective for minimizing pain and functional disability in patients with spondylolysis. This review concluded that the noninvasive treatment method specifically low intensity pulsed ultrasound is effective for bone union.

Review Registration:

PROSPERO (CRD42020218651).

Longitudinally centered embossed structure in the locking compression plate for biodegradable bone implant plate: a finite element analysis

In the current revolution of internal fixation implant in orthopaedics, a biodegradable implant is the most awaited and exceptional medical device where biodegradable material has paid more attention to the success of a biodegradable implant than the design of a biodegradable bone implant plate. By far, LCP is the most traditionally used implant plate (using non-biodegradable material) because of its experimental success, but not with qualified biodegradable material (Mg-alloy). This lack of mechanical performance is a major drawback that can be rectified by better structural design. This will help avoid few other problems as well. Therefore, with proper consideration, the LCP has been added to a semicircular filleted longitudinally centered embossed (LCE) structure to enhance overall mechanical performance that can help emphasize mechanical support even after continuous degradation when applied in a physiological environment. For mechanical verification of this advanced design of biodegradable bone implant plate, four-point bending test (4PBT) and axial compression test (ACT) have been performed using FEM on LCELCP, LCP, continuously degraded (CD)-LCELCP, and CD-LCP. LCELCP showed reduced stress of about 22% and 10% in 4PBT and ACT, respectively, compared to LCP. CD-LCELCP is safe during ACT over 6 months of continuous degradation when the degradation rate is assumed to be 4 mm/year. These results also ensured accuracy using mesh convergence and also mesh checked for quality assurance. Overall, LCELCP can be considered as a biodegradable bone implant plate because of its superior performance, if its ultimate validation is carried out through animal/human trials as future work.

Prediction of biomechanical responses of human lumbar discs - a stochastic finite element model analysis

BACKGROUND

Accurate biomechanical investigation of human intervertebral discs (IVDs) is difficult because of their complicated structural and material features.

AIM

To investigate probabilistic distributions of the biomechanical responses of the IVD by considering varying nonlinear structural and material properties using a stochastic finite element (FE) model.

METHODS

A FE model of a L3-4 disc was reconstructed, including the nucleus pulposus (NP), annular matrix and fibers. A Monte Carlo method was used to randomly generate 500 sets of the nonlinear material properties and fiber orientations of the disc that were implemented into the FE model. The FE model was analyzed under seven loading conditions: a 500 N compressive force, a 7.5Nm moment simulating flexion, extension, left-right lateral bending, and left-right axial rotation, respectively. The distributions of the ranges of motion (ROMs), intradiscal pressures (IDP), fiber stresses and matrix strains of the disc were analyzed.

RESULTS

Under the compressive load, the displacement varied between 0.29 mm and 0.76 mm. Under the 7.5Nm moment, the ROMs varied between 3.0° and 6.0° in primary rotations. The IDPs varied within 0.3 MPa under all the loading conditions. The maximal fiber stress (3.22 ± 0.64 MPa) and matrix strain (0.27 ± 0.12%) were observed under the flexion and extension moments, respectively.

CONCLUSION

The IVD biomechanics could be dramatically affected by the structural and material parameters used to construct the FE model. The stochastic FE model that includes the probabilistic distributions of the structural and material parameters provides a useful approach to analyze the statistical ranges of the biomechanical responses of the IVDs.

A novel material point method (MPM) based needle-tissue interaction model

Needle-tissue interaction model is essential to tissue deformation prediction, interaction force analysis and needle path planning system. Traditional FEM based needle-tissue interaction model would encounter mesh distortion or continuous mesh subdivision in dealing with penetration, in which the computational instability and poor accuracy could be introduced. In this work, a novel material point method (MPM) is applied to establish the needle-tissue interaction model which is suitable to handle the discontinuous penetration problem. By integrating a hyperelastic material model, the tissue deformation and interaction force can be solved simultaneously and independently. A testbed of needle insertion into a Polyvinyl alcohol (PVA) hydrogel phantom was constructed to validate both tissue deformation and interaction force. The results showed the experimental data agrees well with the simulation results of the proposed model.

Developing a Quantifying Device for Soft Tissue Material Prop-Erties around Lumbar Spines

Knowing the material properties of the musculoskeletal soft tissue could be important to develop rehabilitation therapy and surgical procedures. However, there is a lack of devices and information on the viscoelastic properties of soft tissues around the lumbar spine. The goal of this study was to develop a portable quantifying device for providing strain and stress curves of muscles and ligaments around the lumbar spine at various stretching speeds. Each sample was conditioned and applied for 20 repeatable cyclic 5 mm stretch-and-relax trials in the direction and perpendicular direction of the fiber at 2, 3 and 5 mm/s. Our device successfully provided the stress and strain curve of the samples and our results showed that there were significant effects of speed on the young's modulus of the samples (p < 0.05). Compared to the expensive commercial device, our lower-cost device provided comparable stress and strain curves of the sample. Based on our device and findings, various sizes of samples can be measured and viscoelastic properties of the soft tissues can be obtained. Our portable device and approach can help to investigate young's modulus of musculoskeletal soft tissues conveniently, and can be a basis for developing a material testing device in a surgical room or various lab environments.

A Theoretical Model with Which to Safely Optimize the Configuration of Hydraulic Suspension of Modular Trailers in Special Road Transport

The dimensions and weight of machines, structures, and components that need to be transported safely by road are growing constantly. One of the safest and most widely used transport systems on the road today due to their versatility and configuration are modular trailers. These trailers have hydraulic pendulum axles that are that are attached in pairs to the rigid platform above. In turn, these modular trailers are subject to limitations on the load that each axle carries, the tipping angle, and the oil pressure of the suspension system in order to guarantee safe transport by road. Optimizing the configuration of these modular trailers accurately and safely is a complex task. Factors to be considered include the load’s characteristics, the trailer’s mechanical properties, and road route conditions including the road’s slope and camber, precipitation and direction, and force of the wind. This paper presents a theoretical model that can be used for the optimal configuration of hydraulic cylinder suspension of special transport by road using modular trailers. It considers the previously mentioned factors and guarantees the safe stability of road transport. The proposed model was validated experimentally by placing a nacelle wind turbine at different points within a modular trailer. The weight of the wind turbine was 42,500 kg and its dimensions were 5133 × 2650 × 2975 mm. Once the proposed model was validated, an optimization algorithm was employed to find the optimal center of gravity for load, number of trailers, number of axles, oil pressures, and hydraulic configuration. The optimization algorithm was based on the iterative and automatic testing of the proposed model for different positions on the trailer and different hydraulic configurations. The optimization algorithm was tested with a cylindrical tank that weighed 108,500 kg and had dimensions of 19,500 × 3200 × 2500 mm. The results showed that the proposed model and optimization algorithm could safely optimize the configuration of the hydraulic suspension of modular trailers in special road transport, increase the accuracy and reliability of the calculation of the load configuration, save time, simplify the calculation process, and be easily implemented.

Accurate simulation of the herniated cervical intervertebral disc using controllable expansion: a finite element study

Expansions were carried out in finite element (FE) models of disc hernia including symmetric (median, lateral, paramedian) and asymmetric types. In all models, lubricous disk bulging that applied a linear compression to the anterior part of the cord was observed at the posterior surfaces of the expansion zone, respectively. The shape and position of protrusions varyed with the temperature, magnitude, and location of expanding elements. The geometric deformation and stress distribution of the spinal cord increased as the extent of compression grew. This method is in possession of enormous potential in promoting further individualized research of cervical spondylotic myelopathy.