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

The influence of cement-bone composite material on the biomechanical properties of cervical partial vertebral osteotomy fusion surgery

By establishing micro finite element models of cement-bone composite materials and fusion surgery models (C4-C7), the mechanical properties of cement-bone composite materials (Polymethyl methacrylate (PMMA) and a mixture of PMMA and calcium phosphate bone cement (PMMA/CPC)) were analyzed, and the influence of bone cement on the biomechanical properties of anterior cervical discectomy fusion surgery with partial vertebral osteotomy was evaluated. The results revealed that compared with bone cement, the elastic modulus of cement-bone composite material decreased, the PMMA/CPC+bone (osteoporosis) decreased by 73.65% compared to PMMA/CPC. Furthermore, compared with the PMMA/CPC+bone (osteoporosis), the mechanical properties of the PMMA/CPC+bone (osteoporosis) composite material are closer to those of healthy cancellous bone, exhibiting a lower elastic modulus and higher strain compatibility. This study suggests that choosing PMMA/CPC as a reinforcement material may be more beneficial for cervical fusion surgery in patients with osteoporosis.

Predicting the biomechanical behavior of lumbar intervertebral Discs: A comparative finite element analysis of a novel artificial disc design

Osseointegration along with better mimicry of natural bone behaviour addresses the long-term performance of artificial intervertebral disc prosthesis. Here the effect of a novel artificial intervertebral disc geometry on stress, deformation and strain on lumbar segments to restore movement of the spine was investigated. The process involved, using CT image data, and solid modelling, simulation-driven design and finite element (FE) analysis, hexahedral mesh sensitivity analysis, implant placements. The range of motion (ROM) was calculated using an ANSYS deformation probe. The intact lumbar spine model established was compared with two implants, replacement at segment L4-L5 level, and biomechanical results were compared using axial loads of 500 N, 800 N, 1000 N and 10Nm moment. The two lumbosacral FE models, a novel implant Titanium Conix (TIC) and another FDA approved SB Charite™ (SBC) implant were considered. Novel TIC implant geometry exhibited comparable ROM values in four physiological motions, which were comparable to as required for restoring natural motion. The result shows that the proposed TIC observed the deformation during flexion, extension, bending and twist as 3.43 mm, 3.19 mm, 3.33 mm and 3.48 mm respectively. Similarly strain of 0.01 during flexion, 0.02 during extension, 0.01 during bending and 0.02 during twist. The implants designed in this study demonstrate the suitability of titanium alloy in endplates and annulus. The FE models in the study with their biomechanical parameters can be considered before clinical implementation of any implants, pre-surgery evaluations, implant placement simulations, postsurgical response, follow-up revisions, implant customization and manufacturing.

Quantitative relationships between elastic modulus of rod and biomechanical properties of transforaminal lumbar interbody fusion: a finite element analysis

Background

Currently, some novel rods with lower elastic modulus have the potential as alternatives to traditional titanium alloy rods in lumbar fusion. However, how the elastic modulus of the rod (rod-E) influences the biomechanical performance of lumbar interbody fusion remains unclear. This study aimed to explore the quantitative relationships between rod-E and the biomechanical performance of transforaminal lumbar interbody fusion (TLIF).

Methods

The intact finite element model of L1-S1 was constructed and validated. Then 12 TLIF models with rods of different elastic moduli (ranging from 1 GPa to 110 GPa with an interval of 10 GPa) were developed. The range of motion (ROM) of the fixed segment, mean strain of the bone graft, and maximum von Mises stresses on the cage, endplate, and posterior fixation system models were calculated. Finally, regression analysis was performed to establish functional relationships between rod-E and these indexes.

Results

Increasing rod-E decreased ROM of the fixed segment, mean strain of the bone grafts, and peak stresses on the cage and endplate, while increasing peak stress on the screw-rod system. When rod-E increased from 1 GPa to 10 GPa, ROM decreased by 10.4%-39.4%. Further increasing rod-E from 10 GPa to 110 GPa resulted in a 9.3%-17.4% reduction in ROM. The peak stresses on the posterior fixation system showed a nonlinear increase as the rod-E increased from 1 GPa to 110 GPa under most loading conditions. The R 2 values for all fitting curves ranged from 0.76 to 1.00.

Conclusion

The functional relationships between rod-E and the biomechanical properties of TLIF were constructed comprehensively. When the rod-E exceeds 10 GPa, further increases may not significantly improve stability, however, it may increase the risk of fixation failure. Therefore, a rod with an elastic modulus of approximately 10 GPa may provide optimal biomechanical properties for TLIF.

Biomechanical analysis of single and multi-level artificial disc replacement (ADR) in cervical spine using multi-scale loadings: A finite element study

Artificial disc replacement (ADR) is a clinical procedure used to diagnose cervical degenerative disc disease, preserving range of motion (ROM) at the fixation level and preventing adjacent segment degeneration (ASD). This study analyzed the biomechanics of ADR by examining range of motion (ROM), stress levels in bone and implants, and strain in the bone-implant interface using multi-scale loadings. The study focused on single- and double-level patients across various loading scales during physiological motions within the cervical spine. Results showed increased ROM in single-level and double-level fixations during physiological loadings, while ROM decreased at the adjacent level of fixation with the intact cervical spine model. The Prodisc-Implant metal endplate experienced a maximum von Mises stress of 432 MPa during axial rotation, confirming the long durability and biomechanical performance of the bone-implant interface.

Structural modification and biomechanical analysis of lumbar disc prosthesis: A finite element study

BACKGROUND

Most ball-in-socket artificial lumbar disc implanted in the spine result in increased hypermobility of the operative level and overloading of the facet joint.

METHODS

A finite element model was established and validated for the lumbar spine (L1-L5). The structure of the Mobidisc prosthesis was modified, resulting in the development of two new intervertebral disc prostheses, Movcore and Mcopro. The prostheses were implanted into the L3/L4 level to simulate total disc replacement, and the biomechanical properties of the lumbar spine model were analyzed after the operation.

FINDINGS

Following the implantation of the prostheses, the mobility of operative level, peak stress of lumbar spine models, and peak stress of facet joint increased. The performance of mobility was found to be more similar between Movcore and Mobidisc. The mobility and facet joint peak stress of the Mcopro model decreased progressively with an increase in the Young's modulus of the artificial annulus during flexion, extension, and lateral bending. Among all the models, the Mcopro50 model had the mobility closest to the intact model. It showed a 3% decrease in flexion, equal range of motion in extension, a 9% increase in left lateral bending, a 7% increase in right lateral bending, and a 3% decrease in axial rotation.

INTERPRETATION

The feasibility of the new intervertebral disc prostheses, Movcore and Mcopro, has been established. The Mcopro prosthesis, which features an artificial annular structure, offers significant advantages in terms of reduced mobility of the operative level and peak stress of facet joint.

Biomechanical analysis of cervical spine (C2-C7) at different flexed postures

Musculoskeletal diseases are often related with postural changes in the neck region that can be caused by prolonged cervical flexion. This is one of the contributing factors. When determining the prevalence, causes, and related risks of neck discomfort, having a solid understanding of the biomechanics of the cervical spine (C1-C7) is absolutely necessary. The objective of this study is to make predictions regarding the intervertebral disc (IVD) stress values across C2-C7 IVD, the ligament stress, and the variation at 0°, 15°, 30°, 45°, and 60° of cervical neck angle using finite element analysis (FEA). In order to evaluate the mechanical properties of the cervical spine (particularly, C2-C7), this investigation makes use of computed tomography (CT) scans to develop a three-dimensional FEA model of the cervical spine. A preload of 50 N compression force was applied at the apex of the C2 vertebra, and all degrees of freedom below the C7 level were constrained. The primary objective of this investigation is to assess the distribution of von Mises stress within the IVDs and ligaments spanning C2-C7 at various flexion angles: 0°, 15°, 30°, 45°, and 60°, utilizing FEA. The outcomes derived from this analysis were subsequently compared to previously published experimental and FEA data to validate the model's ability to replicate the physiological motion of the cervical spine across different flexion angles.

[Mathematical modeling of the fracture along the length of the femur diaphysis]

THE AIM OF THE STUDY

Was to establish a pattern of femur diaphysis fracture with impact force over the entire front surface in an increments of 25 mm. Transverse, oblique and comminuted femur fractures were studied as a result of mathematical modeling. The application of mathematical modeling using the finite element analysis made it possible to visualize and predict the tension arising in the transient material during the impact force of blunt object, as well as the features of fractures' morphology in different sections of femur diaphysis. Modelled data about the mechanism and morphology of femur fracture were confirmed by the results of original full-scale experiments.

Biomechanical Analysis of Two-Level Novel Cage-Type Implant for Anterior Cervical Discectomy and Fusion: A Finite Element Analysis

One of the standard treatments for spinal diseases is anterior cervical discectomy and fusion (ACDF). ACDF is a secure and successful operation that prevents patients to improve their pain and function. The mechanical goal of the ACDF is to prevent motion between adjoining vertebrae by a novel cage-screw implant. The objective of this study is to analyze the biomechanical flexibility in terms of the range of motion (ROM) of two-level ACDF fixation using the finite element method (FEM). A CT scan-based FEM model of the cervical spine (C2-C7) is used and two-level cage is implanted at C4-C6 segments. A 50-N compressive force and 1-Nm moment are applied on C2 vertebrae and C7 is fixed in all directions. The ROM at two-level fixation (C4-C5-C6) is reduced by 55 to 88% compared with intact spine during all physiological movement. The ROM slightly increase (3-9%) at the adjacent segment. The maximum von Mises stress variations are 25-65 MPa during flexion-extension, lateral bending, and axial rotations under given loading. The maximum von Mises stress found in cage and screw is below the yield stress during all physiological movement.

[Mathematical modeling of femoral diaphyseal fracture at an acute angle]

The aim of the work is to establish the regularity of the formation femoral diaphysis fracture under an impact action on the anterior surface of the femur at an acute angle. As a result of mathematical modeling, transverse and short oblique, comminuted fractures of the femoral diaphysis were studied. Application of mathematical modeling with final element analysis made it possible to visualize and predict the stresses arising in the trace-perceiving material under the impact action of a blunt solid object. The data obtained in modeling of the mechanism and morphology of the femoral diaphysis fracture are confirmed by the results of the original full-scale experiments. Absence of experiments and practical observations of femoral fractures with the above described conditions does not enable us to fully validate the mathematical model of femoral fracture and indicates the need for scientific research on biomannequins.