A lattice topology optimization of cervical interbody fusion cage and finite element comparison with ZK60 and Ti-6Al-4V cages

Biomechanical analysis of a newly designed and 3D printed plate-locking interbody cage: an observational study of finite element analysis

Anterior cervical interbody fusion (ACDF) has become a classic surgical procedure for the treatment of cervical degenerative diseases, and various interbody cages are widely used in this procedure. We used 3D printing technology to produce a new type of plate-locking cage, anticipating to achieve high fusion rate with the high biomechanical stability. This study is to compare the biomechanical characteristics between a newly designed interbody cage and a conventional Zero-profile cage during ACDF using finite element analysis. The CT images of a 35-year-old healthy male were extracted and saved in DICOM format. Mimics Research 19.0, Geomagic Wrap 2017, NX12. 0, Abaqus 6.14 were used to construct the finite element models, then, titanium plate, titanium screw, cages, and the residual parts of both groups were assembled with reference to the surgical approach of ACDF (C4/5), following the successful establishment of both surgical models, a total of six boundary and loading conditions were tested, including flexion, extension, left and right bending, and left and right axial torsion. It is found that the plate stress peak of the new cage group decreased 73.78 MPa, 70.00%; 77.17 MPa, 70.67%; 59.77 MPa, 64.97%; 49.94 MPa, 58.28%; 44.55 MPa, 68.38%; 46.14 MPa, 68.00% in flexion, extension, left bending, right bending, left axial torsion and right axial torsion, respectively. There were no obvious increases of C5 upper endoplate stress peak between these two surgical models (< 50%), except 11.68 MPa, 153.08%; 6.55 MPa, 51.45%; in flexion and extension. The 3D-printed porous plate-locking cage was shown to be biomechanically stable compared to the conventional Zero-profile cage, and it is worth noticing that the stress on the plate of the new cage is less than that on screw of the conventional cage, which indicates that the risk of fracture, loosening, and prolapse of the new cage is less likely to occur.

Human head-neck model and its application thresholds: a narrative review

There have been many studies on human head-neck biomechanical models in the last two decades, and the associated modelling techniques were constantly evolving at the same time. Computational approaches have been widely leveraged, in parallel to conventional physical tests, to investigate biomechanics and injuries of the head-neck system in fields like the automotive industry, orthopedic, sports medicine, etc. The purpose of this manuscript is to provide a global review of the existing knowledge related to the modelling approaches, structural and biomechanical characteristics, validation, and application of the present head-neck models. This endeavor aims to support further enhancements and validations in modelling practices, particularly addressing the lack of data for model validation, as well as to prospect future advances in terms of the topics. Seventy-four models subject to the proposed selection criteria are considered. Based on previously established and validated head-neck computational models, most of the studies performed in-depth investigations of included cases, which revolved around four specific subjects: physiopathology, treatment evaluation, collision condition, and sports injury. Through the review of the recent 20 years of research, the summarized modelling information indicated existing deficiencies and future research topics, as well as provided references for subsequent head-neck model development and application.

Cervical Vertebra Bone Quality Score Predicts Zero-Profile Anchored Spacer Interbody Fusion Cage Subsidence after Anterior Cervical Diskectomy and Fusion: A Retrospective Study

STUDY DESIGN

Retrospective study.

OBJECTIVE

This retrospective study primary focus is to investigate the relationship between the C-VBQ score and the occurrence of postoperative zero-profile anchored spacer (ROI-C) interbody fusion cage subsidence. Additionally, we aim to evaluate the predictive efficacy of the C-VBQ scoring system for subsidence in the context of ACDF with the ROI-C.

METHODS

Patients who underwent ACDF with the ROI-C cage at our hospital between January 2016 and December 2022 were included in this study. Univariate analysis and multivariate logistic regression were employed to identify independent risk factors associated with ROI-C cage subsidence after ACDF. Pearson correlation analysis was utilized to assess the correlation between the C-VBQ score and the height of ROI-C cage subsidence.

RESULTS

A total of 102 patients underwent ACDF with ROI-C in our hospital were included in this study. Univariate analysis showed that age (P = 0.021) and C-VBQ score (P < 0.001) were the influencing factors of cage subsidence. Pearson correlation analysis showed that there was a significant positive correlation between the subsidence height of ROI-C cage and C-VBQ (r = 0.55, P < 0.01). Multivariate binary logistic regression analysis showed that C-VBQ score was the only variable that could significantly predict the subsidence of ROI-C cage after ACDF. Higher C-VBQ score was significantly associated with cage subsidence (P < 0.001).The AUC was 0.89, and the cutoff value for C-VBQ was 2.70.

CONCLUSION

The findings indicate a significant correlation between a higher C-VBQ score before surgery and ROI-C cage subsidence after ACDF. The preoperative assessment of C-VBQ proves valuable for clinicians, enabling them to identify patients with low bone mineral density and predict the risk of zero-profile anchored spacer interbody fusion cage subsidence following ACDF.

Does the novel artificial cervical joint complex resolve the conflict between stability and mobility after anterior cervical surgery? a finite element study

Background and objective

Our group has developed a novel artificial cervical joint complex (ACJC) as a motion preservation instrument for cervical corpectomy procedures. Through finite element analysis (FEA), this study aims to assess this prosthesis's mobility and stability in the context of physiological reconstruction of the cervical spine.

Materials and methods

A finite element (FE)model of the subaxial cervical spine (C3-C7) was established and validated. ACJC arthroplasty, anterior cervical corpectomy and fusion (ACCF), and two-level cervical disc arthroplasty (CDA) were performed at C4-C6. Range of motion (ROM), intervertebral disc pressure (IDP), facet joint stress (FJS), and maximum von Mises stress on the prosthesis and vertebrae during loading were compared.

Results

Compared to the intact model, the ROM in all three surgical groups demonstrated a decline, with the ACCF group exhibiting the most significant mobility loss, and the highest compensatory motion in adjacent segments. ACJC and artificial cervical disc prosthesis (ACDP) well-preserved cervical mobility. In the ACCF model, IDP and FJS in adjacent segments increased notably, whereas the index segments experienced the most significant FJS elevation in the CDA model. The ROM, IDP, and FJS in both index and adjacent segments of the ACJC model were intermediate between the other two. Stress distribution of ACCF instruments and ACJC prosthesis during the loading process was more dispersed, resulting in less impact on the adjacent vertebrae than in the CDA model.

Conclusion

The biomechanical properties of the novel ACJC were comparable to the ACCF in constructing postoperative stability and equally preserved physiological mobility of the cervical spine as CDA without much impact on adjacent segments and facet joints. Thus, the novel ACJC effectively balanced postoperative stability with cervical motion preservation.

A Review of Finite Element Modeling for Anterior Cervical Discectomy and Fusion

The cervical spine poses many complex challenges that require complex solutions. Anterior cervical discectomy and fusion (ACDF) has been one such technique often employed to address such issues. In order to address the problems with ACDF and assess the modifications that have been made to the technique over time, finite element analyses (FEA) have proven to be an effective tool. The variations of cervical spine FEA models that have been produced over the past couple of decades, particularly more recent representations of more complex geometries, have not yet been identified and characterized in any literature. Our objective was to present material property models and cervical spine models for various simulation purposes. The outlining and refinement of the FEA process will yield more reliable outcomes and provide a stable basis for the modeling protocols of the cervical spine.

Finite element analysis of lattice designed lumbar interbody cage based on the additive manufacturing

Additive manufacturing (AM) methods, which facilitate the production of complex structures with different geometries, have been used in producing interbody cages in recent years. In this study, the effects of Ti6Al4V alloy interbody lattice designed fusion cages between the third and fourth lumbar vertebrae where degenerative disc diseases occur were investigated using the finite element method. Face centered cubic (FCC), body centered cubic (BCC), and diamond structures were selected as the lattice structure suitable for the interbody cage. A kidney shaped interbody lumbar cage was designed. The designated lattice structures were selected by adjusting the cell sizes suitable for the designed geometry, and the mesh configuration was made by the lumbar lattice structure. 400 N Axial force and 7.5 N.m moments were applied to the spine according to lateral bending, flexion, and torsion. 400 N axial force and 7.5 N.m flexion moment is shown high strain and total deformation then lateral bending and torsion on BCC FCC and diamond lattice structured interbody cages. In addition, the effects of lattice structures under high compression forces were investigated by applying 1000 N force to the lattice structures. When von Mises stresses were examined, lower von Mises stress and strains were observed in the BCC structure. However, a lower total deformation was observed in the FCC. Due to the design of the BCC and the diamond structure, it is assumed that bone implant adhesion will increase. In the finite element analysis (FEA), the best results were shown in BCC structures.

Interbody Fusion Cage Design Driven by Topology Optimization

OBJECTIVE

We used topology optimization technology to explore the new theory and method of interbody fusion cage design and realized an innovative design of interbody cages.

METHODS

The lumbar spine of a normal healthy volunteer was scanned to perform reverse modeling. Based on the scan data for the L1-L2 segments of the lumbar spine, a three dimensional model was reconstructed to obtain the complete simulation model of the L1-L2 segment. The boundary inversion method was used to obtain approximately isotropic material parameters that can effectively characterize the mechanical behavior of vertebrae, thereby reducing the computational complexity. The topology description function was used to model the clinically used traditional fusion cage to obtain Cage A. The moving morphable void-based topology optimization method was used for the integrated design of size, shape, and topology to obtain the optimized fusion cage, Cage B.

RESULTS

The volume fraction of the bone graft window in Cage B was 74.02%, which was 60.67% higher than that (46.07%) in Cage A. Additionally, the structural strain energy in the design domain of Cage B was 1.48 mJ, which was lower than that of Cage A (satisfying the constraints). The maximum stress in the design domain of Cage B was 5.336 Mpa, which was 35.6% lower than that (8.286 Mpa) of Cage A. In addition, the surface stress distribution of Cage B was more uniform than that of Cage A.

CONCLUSIONS

This study proposed a new innovative design method for interbody fusion cages, which not only provides new insights into the innovative design of interbody fusion cages but may also guide the customized design of interbody fusion cages in different pathological environments.

Resisting subsidence with a truss Implant: Application of the "Snowshoe" principle for interbody fusion devices

The primary objective was to compare the subsidence resistance properties of a novel 3D-printed spinal interbody titanium implant versus a predicate polymeric annular cage. We evaluated a 3D-printed spinal interbody fusion device that employs truss-based bio-architectural features to apply the snowshoe principle of line length contact to provide efficient load distribution across the implant/endplate interface as means of resisting implant subsidence. Devices were tested mechanically using synthetic bone blocks of differing densities (osteoporotic to normal) to determine the corresponding resistance to subsidence under compressive load. Statistical analyses were performed to compare the subsidence loads and evaluate the effect of cage length on subsidence resistance. The truss implant demonstrated a marked rectilinear increase in resistance to subsidence associated with increase in the line length contact interface that corresponds with implant length irrespective of subsidence rate or bone density. In blocks simulating osteoporotic bone, comparing the shortest with the longest length truss cage (40 vs. 60 mm), the average compressive load necessary to induce subsidence of the implant increased by 46.4% (383.2 to 561.0 N) and 49.3% (567.4 to 847.2 N) for 1 and 2 mm of subsidence, respectively. In contrast, for annular cages, there was only a modest increase in compressive load when comparing the shortest with the longest length cage at a 1 mm subsidence rate. The Snowshoe truss cages demonstrated substantially more resistance to subsidence than corresponding annular cages. Clinical studies are required to support the biomechanical findings in this work.

Biomechanical performance of the novel assembled uncovertebral joint fusion cage in single-level anterior cervical discectomy and fusion: A finite element analysis

Introduction: Anterior cervical discectomy and fusion (ACDF) is widely accepted as the gold standard surgical procedure for treating cervical radiculopathy and myelopathy. However, there is concern about the low fusion rate in the early period after ACDF surgery using the Zero-P fusion cage. We creatively designed an assembled uncoupled joint fusion device to improve the fusion rate and solve the implantation difficulties. This study aimed to assess the biomechanical performance of the assembled uncovertebral joint fusion cage in single-level ACDF and compare it with the Zero-P device.

Methods: A three-dimensional finite element (FE) of a healthy cervical spine (C2−C7) was constructed and validated. In the one-level surgery model, either an assembled uncovertebral joint fusion cage or a zero-profile device was implanted at the C5–C6 segment of the model. A pure moment of 1.0 Nm combined with a follower load of 75 N was imposed at C2 to determine flexion, extension, lateral bending, and axial rotation. The segmental range of motion (ROM), facet contact force (FCF), maximum intradiscal pressure (IDP), and screw−bone stress were determined and compared with those of the zero-profile device.

Results: The results showed that the ROMs of the fused levels in both models were nearly zero, while the motions of the unfused segments were unevenly increased. The FCF at adjacent segments in the assembled uncovertebral joint fusion cage group was less than that that of the Zero-P group. The IDP at the adjacent segments and screw–bone stress were slightly higher in the assembled uncovertebral joint fusion cage group than in those of the Zero-P group. Stress on the cage was mainly concentrated on both sides of the wings, reaching 13.4–20.4 Mpa in the assembled uncovertebral joint fusion cage group.

Conclusion: The assembled uncovertebral joint fusion cage provided strong immobilization, similar to the Zero-P device. When compared with the Zero-P group, the assembled uncovertebral joint fusion cage achieved similar resultant values regarding FCF, IDP, and screw–bone stress. Moreover, the assembled uncovertebral joint fusion cage effectively achieved early bone formation and fusion, probably due to proper stress distributions in the wings of both sides.

Factors influencing cage subsidence in anterior cervical corpectomy and discectomy: a systematic review

PURPOSE

Various factors have been examined in relation to cage subsidence risk, including cage material, cage geometry, bone mineral density, device type, surgical level, bone graft, and patient age. The present study aims to compare and synthesize the literature of both clinical and biomechanical studies to evaluate and present the factors associated with cage subsidence.

METHODS

A comprehensive search of the literature from January 2003 to December 2021 was conducted using the PubMed and ScienceDirect databases by following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Following the screening for inclusion and exclusion criteria, a total of 49 clinical studies were included. Correlations between clinical and biomechanical studies are also discussed.

RESULTS

Patients treated with the cage and plate combination had a lower subsidence rate than patients with the stand-alone cage. Overall, Polyetheretherketone material was shown to have a lower subsidence rate than titanium and other materials. The subsidence rate was also higher when the surgery was performed at levels C5-C7 than at levels C2-C5. No significant correlation was found between age and cage subsidence clinically.

CONCLUSIONS

Cage subsidence increases the stress on the anterior fixation system and may cause biomechanical instability. Severe cage subsidence decreases the Cobb angle and intervertebral height, which may cause destabilization of the implant system, such as screw/plate loosening or breakage of the screw/plate. Various factors have been shown to influence the risk of cage subsidence. Examining clinical research alongside biomechanical studies offers a more comprehensive understanding of the subject.

Titanium Lattice Structures Produced via Additive Manufacturing for a Bone Scaffold: A Review

The progress in additive manufacturing has remarkably increased the application of lattice materials in the biomedical field for the fabrication of scaffolds used as bone substitutes. Ti6Al4V alloy is widely adopted for bone implant application as it combines both biological and mechanical properties. Recent breakthroughs in biomaterials and tissue engineering have allowed the regeneration of massive bone defects, which require external intervention to be bridged. However, the repair of such critical bone defects remains a challenge. The present review collected the most significant findings in the literature of the last ten years on Ti6Al4V porous scaffolds to provide a comprehensive summary of the mechanical and morphological requirements for the osteointegration process. Particular attention was given on the effects of pore size, surface roughness and the elastic modulus on bone scaffold performances. The application of the Gibson–Ashby model allowed for a comparison of the mechanical performance of the lattice materials with that of human bone. This allows for an evaluation of the suitability of different lattice materials for biomedical applications.

Mechanical performance of porous biomimetic intervertebral body fusion devices: an in vitro biomechanical study

BACKGROUND

Degenerative disc disease is one of the most common ailments severely affecting the quality of life in elderly population. Cervical intervertebral body fusion devices are utilized to provide stability after surgical intervention for cervical pathology. In this study, we design a biomimetic porous spinal cage, and perform mechanical simulations to study its performances following American Society for Testing and Materials International (ASTM) standards before manufacturing to improve design process and decrease cost and consumption of material.

METHODS

The biomimetic porous Ti-6Al-4 V interbody fusion devices were manufactured by selective laser melting (laser powder bed fusion: LPBF in ISO/ASTM 52900 standard) and subsequently post-processed by using hot isostatic pressing (HIP). Chemical composition, microstructure and the surface morphology were studied. Finite element analysis and in vitro biomechanical test were performed.

FINDINGS

The post heat treatment can optimize its mechanical properties, as the stiffness of the cage decreases to reduce the stress shielding effect between two instrumented bodies. After the HIP treatment, the ductility and the fatigue performance are substantially improved. The use of HIP post-processing can be a necessity to improve the physical properties of customized additive manufacturing processed implants.

INTERPRETATION

In conclusion, we have successfully designed a biomimetic porous intervertebral device. HIP post-treatment can improve the bulk material properties, optimize the device with reduced stiffness, decreased stress shielding effect, while still provide appropriate space for bone growth.

CLINICAL SIGNIFICANCE

The biomechanical performance of 3-D printed biomimetic porous intervertebral device can be optimized. The ductility and the fatigue performance were substantially improved, the simultaneously decreased stiffness reduces the stress shielding effect between two instrumented bodies; while the biomimetic porous structures provide appropriate space for bone growth, which is important in the patients with osteoporosis.

Biomechanical analysis of customized cage conforming to the endplate morphology in anterior cervical discectomy fusion: A finite element analysis

In anterior cervical discectomy and fusion (ACDF), an interbody fusion device is an essential implant. An unsuitable interbody fusion device can cause postoperative complications, including subsidence and nonunion. We designed a customized intervertebral fusion device to reduce postoperative complications and validated it by finite element analysis. Herein, we built a non-homogeneous model of the C3-7 cervical spine. Three implant models (customized cage, commercial cage, and bone graft cage) were constructed and placed in the C45 cervical segment after ACDF surgery. The simulated range of motion (ROM), stress at the cage-bone interface, and stress on the cage and implants were compared under different conditions. The commercial cage showed maximum stress peaks at 40.3 MPa and 43.2 MPa in the inferior endplate of C4 and superior endplate of C5 under rotational conditions, higher compared to 29.7 MPa and 26.4 MPa, respectively, in the customized cage. The ROM was not significantly different between the three cages placed after ACDF. The stresses on the commercial cage were higher compared to the other two cages under all conditions. The bone graft in the customized cage was subject to higher stress than the commercial cage under all conditions, particularly lateral bending, wherein the maximum stress was 5.5 MPa. These results showed that a customized cage that better conformed to the vertebral anatomy was promising for reducing the risk of stress shielding and the occurrence of subsidence.

Recent advancement in finite element analysis of spinal interbody cages: A review

Finite element analysis (FEA) is a widely used tool in a variety of industries and research endeavors. With its application to spine biomechanics, FEA has contributed to a better understanding of the spine, its components, and its behavior in physiological and pathological conditions, as well as assisting in the design and application of spinal instrumentation, particularly spinal interbody cages (ICs). IC is a highly effective instrumentation for achieving spinal fusion that has been used to treat a variety of spinal disorders, including degenerative disc disease, trauma, tumor reconstruction, and scoliosis. The application of FEA lets new designs be thoroughly "tested" before a cage is even manufactured, allowing bio-mechanical responses and spinal fusion processes that cannot easily be experimented upon in vivo to be examined and "diagnosis" to be performed, which is an important addition to clinical and in vitro experimental studies. This paper reviews the recent progress of FEA in spinal ICs over the last six years. It demonstrates how modeling can aid in evaluating the biomechanical response of cage materials, cage design, and fixation devices, understanding bone formation mechanisms, comparing the benefits of various fusion techniques, and investigating the impact of pathological structures. It also summarizes the various limitations brought about by modeling simplification and looks forward to the significant advancement of spine FEA research as computing efficiency and software capabilities increase. In conclusion, in such a fast-paced field, the FEA is critical for spinal IC studies. It helps in quantitatively and visually demonstrating the cage characteristics after implanting, lowering surgeons' learning costs for new cage products, and probably assisting them in determining the best IC for patients.

Porous interbody fusion cage design via topology optimization and biomechanical performance analysis

The porous interbody fusion cage could provide space and stable mechanical conditions for postoperative intervertebral bone ingrowth. It is considered to be an important implant in anterior cervical discectomy and internal fixation. In this study, two types of unit cells were designed using topology optimization method and introduced to the interbody fusion cage to improve the biomechanical performances of the cage. Topology optimization under two typically loading conditions was first conducted to obtain two unit cells (O-unit cell and D-unit cell) with the same volume fraction. Porous structures were developed by stacking the obtained unit cells in space, respectively. Then, porous interbody fusion cages were obtained by the Boolean intersection between the global structural layout and the porous structures. Finite element models of cervical spine were created that C5-C6 segment was fused by the designed porous cages. The range of motion (ROM) of the cervical spine, the maximum stress on the cage and the bone graft, and the stress and displacement distributions of the cage were analyzed. The results showed the ROMs of C5-C6 segment in D-unit cell and O-unit cell models were range from 0.14° to 0.25° under different loading conditions; the cage composed of the D-unit cells had a more uniform stress distribution, smaller displacement on cage, a more reasonable internal stress transfer mode (transmission along struts of the unit cell), and higher stress on the internal bone graft (0.617 MPa). In conclusion, the optimized porous cage is a promising candidate for fusion surgery, which would avoid the cage subsidence, and promote the fusion of adjacent endplates.

Three-Dimensional Biomechanical Finite Element Analysis of Lumbar Disc Herniation in Middle Aged and Elderly

Lumbar intervertebral disc protrusion disease refers to the degeneration of intervertebral disc, rupture of fibrous ring, nucleus pulpous protrusion and stimulation or compression of nerve root. The import command in Mimics medical 3D reconstruction software was used to erase the irrelevant image data and obtain vertebral body images. The original 3D model of each vertebral body was built by 3D computing function. A three-dimensional finite element model was established to analyze the effect of different surgical methods on the mechanical distribution of the spine after disentomb. The stress distribution of the spine, intervertebral disc, and left and right articular cartilage at L4/L5 stage and the position shift of the fourth lumbar vertebra were analyzed under 7 working conditions of vertical, forward flexion, extension, left and right flexion, and left and right rotation. The results showed that the established model was effective, and the smaller the area of posterior laminar decompression was, the lesser the impact on spinal stability was. The PELD treatment of lumbar disc herniation had little impact on spinal biomechanics and could achieve good long-term biomechanical stability. Combining the clinical experiment method and finite element simulation, using the advantages of finite element software to optimize the design function can provide guidance for the design and improvement of medical devices and has important significance for the study of clinical mechanical properties and biomechanics.