Biomechanical analysis of 3D printed porous extremely-low modulus Ti-24Nb-4Zr-8Sn lumbar interbody fusion cage-A finite element study

ABSTRACT

This study aimed to design and assess the biomechanical properties of a 3D-printed porous titanium alloy lumbar fusion cage, comparing it to traditional PEEK cages in lumbar PLIF surgery using finite element modelling. Employing Ti-24Nb-4Zr-8Sn (Ti2448) and Ti-6Al-4 V (Ti64) materials via EBM-3D printing, the fabricated cage exhibited enhanced mechanical stability when paired with the same internal fixation system. Biomechanical analysis revealed superior performance of both Ti2448 and Ti64 porous models over PEEK, notably Ti2448. These porous titanium cages effectively mitigate maximum stress at the cage-endplate interface, ensuring uniform stress distribution and minimizing subsidence risk. Additionally, their porous structure fosters osteogenesis, while the low modulus titanium alloy, resembling human cancellous bone, enhances interbody fusion and diminishes the probability of cage subsidence.

KEYWORDS:

• Finite element analysis
• interbody fusion cage
• porous titanium alloy
• stress shielding
• cage subsidence

Introduction

In the late 1990s, spinal fusion cages made of titanium (Ti) and polyetheretherketone (PEEK) materials were first experimentally applied in lumbar spinal fusion surgery [1]. Since then, various spinal fusion cages have rapidly developed and have been utilized to maintain the physiological curvature of the spine and promote interbody fusion in lumbar spinal fusion surgeries. Given the excellent biocompatibility of Ti and PEEK, they remain the most commonly used materials for spinal fusion cages. Notably, PEEK’s excellent X-ray transparency facilitates postoperative imaging assessment of fusion, and its elastic modulus is closer to that of bone, promoting bone fusion and preventing implant subsidence. These characteristics have made PEEK fusion cages widely applied in clinical surgery [2,3]. However, PEEK’s chemical inertness and hydrophobic nature, indicative of its biocompatibility, limit direct cell adhesion on the implant surface. Animal experiments have shown the presence of fibrous tissue around the surface of PEEK implants after insertion into bone [4,5]. Furthermore, in vitro studies have demonstrated that osteogenic differentiation of mesenchymal stem cells on PEEK surfaces is inhibited compared to titanium surfaces, and inflammatory responses are activated [6,7].

Clinically, Nemoto et al. reported that pseudoarthrosis formation after lumbar spinal fusion surgery with PEEK fusion cages leads to poorer radiological outcomes than titanium fusion cages [8]. Consequently, titanium is gaining increasing attention as a material for spinal fusion cages due to its superior bone bioactivity compared to PEEK [9].

The Ti-6Al-4 V (Ti64) material is widely employed in clinical surgery due to its excellent biocompatibility, superior mechanical properties, and corrosion resistance [10]. Ti64 fusion cages, through the TiO₂ thin layer formed on their surfaces, facilitate the formation of new bone between vertebrae. (TiO₂ generates hydroxyl ions that can combine with Ca²⁺ and PO₄³⁻ to create a structure similar to bone apatite, promoting osteogenic activity) [11,12]. However, the high elastic modulus of Ti64 material, far exceeding that of human cortical bone, makes it prone to stress shielding effects, hindering new bone growth [13]. This, in turn, can lead to implant subsidence. Previous studies have suggested that introducing a porous structure into implants is an effective method to reduce the elastic modulus of implants further and mitigate stress shielding [14,15].

With continuous improvements and innovations in additive manufacturing processes, current 3D printing technology can effectively produce highly interconnected porous metal structures. Currently, 3D-printed porous Ti64 lumbar fusion cages have been applied in clinical practice. The micro-interconnected porous structure created by 3D printing not only lowers the overall elastic modulus of the fusion cage but also allows for the infiltration of stem cells or osteoblasts into the porous scaffold, further promoting osteogenesis.

However, despite these advancements, cases of fusion cage subsidence are still reported. Therefore, searching for ‘softer’ implants or those with an elastic modulus closer to bone tissue is a crucial breakthrough in enhancing implant-bone integration [16]. Ti-24Nb-4Zr-8Sn (Ti2448), as an emerging β-titanium alloy in recent years, possesses a comprehensive performance with high strength (800–900 MPa) and low elastic modulus (~42GPa), making it highly suitable for bone implantation [17]. However, there is limited biomechanical research on the Ti2448 porous interbody fusion cage.

In recent years, finite element analysis (FEA) has been widely used to evaluate the biomechanical behaviour of different fusion cages in lumbar spinal fusion surgeries [3,18]. The computational complexity of finite element analysis for porous fusion cage models is substantial. In existing studies, most finite element models for porous fusion cages are regular-shaped cuboids or cubes, and there is scarce literature on the finite element modelling of clinically relevant porous fusion cages. With the rapid development of medical imaging technology and continuous improvement in computer simulation software, the accuracy of finite element models and the reliability of simulation algorithms have greatly improved. Therefore, this study is based entirely on the actual specifications of porous fusion cages, using finite element analysis to investigate the biomechanical behaviour of a novel 3D-printed porous Ti2448 low elastic modulus interbody fusion cage. A comparison is made with porous Ti64 and PEEK fusion cages, and specific values such as range of motion (ROM), stress in the pedicle-screw system, stress at the fusion cage-endplate interface, and micro-movements at the fusion cage-endplate interface are recorded. These values will be extensively elaborated and discussed.

Material and methods

CT image acquisition

For finite element analysis, a single healthy adult male volunteer aged 35 was selected. Relevant examinations, including X-rays (DigitalDiagnost 4, Siemens, Germany) and CT scans (Spectral CT, Siemens, Germany)were conducted to rule out spinal deformities, fractures, infections, tumours, rheumatic diseases, or other relevant medical history. The volunteer signed an informed consent form before participating in the study. Subsequently, lumbar spine CT images were acquired from the volunteer and saved in DICOM format. The CT images were taken with a slice thickness of 0.625 mm.

Lumbar PLIF finite element Model establishment

1. Import the lumbar spine CT data (in DICOM format) into Mimics 19.0 software. Firstly, use the threshold command to separate the bone tissue into a Mask. Then, separate the L4 and L5 vertebrae using the Edit Mask command. Finally, the Calculate 3D command is used to reconstruct the L4 and L5 vertebrae individually in three dimensions and export them one by one in STL format.

2. Import the STL data exported from Mimics into Geomagic Wrap 2017. Firstly, use Mesh Doctor to repair surface roughness, noise, etc automatically. Draw the outlines of the vertebral bodies to facilitate further meshing. Upon successful meshing, create a lattice structure and fit the surfaces. In this step, use the ‘Global Offset’ command to separate the cortical and cancellous bone of L4 and L5 vertebrae, with a cortical bone thickness set to 2 mm. Finally, output the cortical and cancellous bone models of L4 and L5 vertebrae in STP format.

3. Import the processed cortical and cancellous bone models of L4 and L5 vertebrae into SolidWorks 2018. Assemble the models according to the original anatomical structure. Then, sketch tools, surface tools, Boolean operations, etc., can be used to create structures such as joint cartilage, annulus fibrosus, nucleus pulposus, and endplates. Proceed to assemble the fusion cage model and internal fixation system components according to the PLIF surgical method (refer to Figure 1).

   Figure 1. Schematic representation of finite element models. The intact L4-L5 model (left), PLIF model of PEEK interbody fusion cage (middle), and PLIF model of porous interbody fusion cage (right).

   

4. Import the assembled models from SolidWorks into ANSYS Workbench 2022 R2 software and use Transient Structure for analysis. Refer to Table 1 for the elastic moduli and Poisson’s ratios of various materials. Define seven major ligaments, such as the anterior longitudinal ligament, posterior longitudinal ligament, ligamentum flavum, capsule ligament, supraspinous ligament, interspinous ligament, and intertransverse ligament as nonlinear springs, connected with specified stiffness values at their attachment points (refer to Table 2). Define frictional contact between the fusion cage and endplate interface and facet joint contact with a Coulomb friction coefficient of 0.2; other contact types are defined as bonded. Subsequently, mesh the model, controlling mesh size and type to ensure accuracy meets analysis requirements. After convergence analysis < 5% of the finite element model, set the mesh size for joint cartilage and internal implants to 1.0 mm and 2.0 mm for others, with tetrahedral mesh type.

   Table 1. Material parameters for various components in the finite element models.

   Structure	Young’s Modulus (MPa)	Poisson’s Ratio	Cross-Section (mm2)
   Cortical Bone	12,000	0.3	N/A
   Trabecular Bone	100	0.3	N/A
   Nucleus Pulposus	1	0.45	N/A
   Annulus Fibrosus	4.2	0.3	N/A
   Endplate	12,000	0.3	N/A
   Articular Cartilage	10	0.3	N/A
   Anterior Longitudinal Ligament	Nonlinear Spring, 8	N/A	63.7
   Posterior Longitudinal Ligament	Nonlinear Spring, 10	N/A	20
   ligamentum flavum	Nonlinear Spring, 15	N/A	40
   Interspinous Ligament	Nonlinear Spring, 10	N/A	40
   Supraspinous Ligament	Nonlinear Spring, 8	N/A	30
   Capsular Ligament	Nonlinear Spring, 7.5	N/A	30
   intertransverse ligament	Nonlinear Spring, 10	N/A	1.8
   Rod-Screw System	110,000	0.3	N/A
   PEEK fusion cage	4,000	0.4	N/A
   Ti2448 fusion cage	42,000	0.14	N/A
   Ti64 fusion cage	114,000	0.3	N/A

   Table 2. Comparison of range of motion (ROM) for the Complete L4-L5 Model with previous studies.

   L4-L5	Yueh Wu^[Citation19] et al	Schilling^[Citation20] et al	Current Study
   Flexion	5.1°	5.62° (±2.17)	5.32°
   Extension	3.1°	3.32° (±1.12)	3.47°
   Lateral Bending	4.8°	7.76° (±1.85)	5.48°
   Axial Rotation	3.9°	5.16° (±1.30)	4.74°

Boundary and loading conditions

All degrees of the nodes on the lower surface of the L5 vertebra were constrained. A fixed load of 500N was applied to the upper surface of the L4 vertebra, oriented in the negative Z-axis direction, simulating the gravitational force of the upper body in the human body. Additionally, different moments of 10 N·m were applied to the upper surface of the L4 vertebra in various directions, simulating six motion conditions, including flexion, extension, left/right bending, and left/right rotation of the human spine.

Materials preparation

The novel 3D-printed porous Ti2448 and Ti64 interbody fusion cages were fabricated by an EBM system (Arcam A1, Sweden). The designed device is based on a diamond lattice unit with a pore size of 600 μm and a porosity of 70% [21,22] (Figure 2). Ti64 cages were fabricated layer-by-layer using the medical-graded Ti-6Al-4 V (ELI) powders with an average particle diameter of ~50 μm. Each powder layer was created by raking powder gravity fed from two cassettes, and then heated to ~ 730°C by multiple pre-heat scans, followed by melting the selected areas controlled by a CAD program [23]. Ti2448 cages were built layer-by-layer using a spherical Ti2448 powder with an average particle size of 80 μm. Each layer of powder with thickness of 0.07 mm was laid by raking powder gravity fed from two cassettes, and preheated to 450°C, then electron beam melted the selected areas controlled by a CAD program [24]. The as-fabricated interbody fusion Ti2448 and Ti64 cages are shown in Figure 3.

Figure 2. Model of Porous Interbody fusion cage: 14.00 × 10.00 * 26.00 mm, a diamond lattice unit with a pore size of 600 μm and a porosity of 70%.

Figure 3. 1# Ti64 interbody fusion cage, 2# Ti2448 interbody fusion cage.

Result

Finite element model validation

In the intact model, the experiment recorded the range of motion (ROM) for L4-L5 under various conditions, including flexion, extension, lateral bending, and left/right rotation. The obtained ROM data were compared with previous research [19,20], as presented in Table 2. Based on the ROM data derived from finite element analysis, the results fell within the reference range in the literature. Consequently, it is considered that the model meets the requirements of finite element analysis.

Range of motion (ROM)

Under six conditions, including flexion, extension, lateral bending, and left/right rotation, the ROM values for the PEEK fusion cage model were 4.99 mm, 2.84 mm, 2.42 mm, 1.86 mm, 2.73 mm, and 2.75 mm, respectively. The ROM values for the Ti64 fusion cage model were 3.74 mm, 3.16 mm, 1.50 mm, 1.91 mm, 1.90 mm, and 1.42 mm, respectively. The Ti2448 fusion cage model’s ROM values were 3.86 mm, 3.16 mm, 1.52 mm, 1.92 mm, 1.93 mm, and 1.43 mm, respectively. The overall trend is compared in Figure 4. In conditions such as flexion, lateral bending, and left/right rotation, the ROM of both sets of porous titanium alloy models showed a varying degree of reduction compared to the traditional PEEK model. However, there was no significant difference between the two porous titanium alloy models with different materials. This suggests that, with the support of the pedicle screw-rod system, porous titanium alloy interbody fusion cages exhibit good mechanical stability and can better restrict vertebral movement in the operated segment compared to PEEK fusion cages.

Figure 4. Range of motion (ROM) for different finite element models.

The maximum pedicle-screw system stress

Under six conditions, including flexion, extension, lateral bending, and left/right rotation, the PEEK fusion cage model’s stress in the pedicle-screw system were 149.33 MPa, 154.67 MPa, 190.97 MPa, 177.26 MPa, 158.55 MPa, and 182.28 MPa, respectively. For the Ti64 fusion cage model, the stress in the pedicle-screw system was 56.49 MPa, 41.14 MPa, 73.11 MPa, 85.90 MPa, 58.61 MPa, and 64.08 MPa, respectively. In the Ti2448 fusion cage model, the stress in the pedicle-screw system was 71.61 MPa, 41.72 MPa, 84.36 MPa, 93.11 MPa, 69.71 MPa, and 70.48 MPa, respectively. The overall trend of stress is compared in Figure 5, and the distribution of stress is illustrated in Figure 6. In all conditions, the PEEK fusion cage model exhibited significantly higher stress in the pedicle-screw system compared to the other two sets of porous titanium alloy fusion cage models. There was no significant difference between the two porous titanium alloy models with different materials, indicating that porous titanium alloy fusion cages are more effective in reducing the stress of the internal fixation system than PEEK fusion cages.

Figure 5. Maximum stress in the fixation system for different finite element models.

Figure 6. Stress distribution in the fixation system for different finite element models. PEEK fusion cage Model (left), Porous Ti64 fusion cage Model (middle), Porous Ti2448 fusion cage Model (right).

The maximum fusion cage-endplate interface stress

Under six conditions, including flexion, extension, lateral bending, and left/right rotation, the PEEK fusion cage model’s interface stress were 85.44 MPa, 51.33 MPa, 83.20 MPa, 76.53 MPa, 77.48 MPa, and 80.79 MPa, respectively. For the Ti64 fusion cage model, the interface stress was 71.79 MPa, 17.79 MPa, 43.98 MPa, 54.16 MPa, 59.76 MPa, and 44.34 MPa, respectively. In the Ti2448 fusion cage model, the interface stress was 78.24 MPa, 13.09 MPa, 47.47 MPa, 43.73 MPa, 32.40 MPa, and 37.62 MPa, respectively. The stress at the fusion cage-endplate interface is a crucial factor influencing postoperative fusion cage settling in PLIF. Compared to the tensile strength of cortical bone (approximately 126 MPa) [25], the experimental results for all three groups of models were below 126 MPa. Both sets of porous titanium alloy fusion cage models exhibited lower interface stress in various conditions, with the Ti2448 fusion cage model showing a clear advantage over the Ti64 fusion cage model, especially in right flexion and left/right rotation. The overall trend is illustrated in Figure 7, and detailed stress distribution at the interface is shown in Figure 8.

Figure 7. Maximum stress on fusion cage-endplate interface for different finite element model.

Figure 8. Stress distribution on fusion cage-endplate interface for different finite element model. (left: PEEK fusion cage model, middle: porous Ti64 fusion cage model, right: porous Ti2448 fusion cage model).

Fusion cage-endplate interface micro-motions

The overall trend of micro-motions at the fusion cage-endplate interface for each group is compared in Figure 9. The results show that the micro-motions for the PEEK fusion cage model were significantly higher than the other two porous models. However, there was no significant difference between the two porous models. Under six conditions, including flexion, extension, lateral bending, and left/right rotation, the micro-motions at the fusion cage-endplate interface for the PEEK fusion cage model were 94.13 μm, 91.20 μm, 89.56 μm, 90.17 μm, 97.16 μm, and 90.71 μm, respectively. For the Ti64 fusion cage model, the micro-motions were 10.74 μm, 35.29 μm, 5.65 μm, 9.75 μm, 13.38 μm, and 38.61 μm, respectively. In the Ti2448 fusion cage model, the micro-motions were 14.82 μm, 36.68 μm, 9.49 μm, 14.30 μm, 11.14 μm, and 38.38 μm, respectively. The specific distribution is illustrated in Figure 10.

Figure 9. Maximum value of micromotion on fusion cage-endplate interface for different finite element model.

Figure 10. Micromotion on fusion cage-endplate interface for different finite element model. PEEK fusion cage Model (left), porous Ti64 fusion cage Model (middle), porous Ti2448 fusion cage Model (right).

Discussion

Lumbar interbody fusion surgery is a widely utilized and highly effective procedure in the clinical management of degenerative lumbar diseases [26]. Following the implantation of interbody fusion cages into the lumbar spine, there is a significant enhancement in the load-bearing capacity of the anterior column of the vertebrae. Subsequent osseous fusion between vertebral bodies effectively reduces the load on internal fixation, thereby reconstructing the biomechanical stability of the lumbar spine and mitigating the risk of internal fixation loosening or fractures [27].

Various materials with different moduli, such as PEEK, CFRP, titanium, stainless steel, and cobalt-chromium alloys, have been employed in the fabrication of spinal interbody fusion cages. Nevertheless, the occurrence of pseudoarthrosis, fusion cage subsidence, and adjacent segment diseases remain three major complications post lumbar interbody fusion surgery, typically manifesting several months after the procedure. The influence of interbody fusion cages’ structure, rigidity, and elastic modulus on long-term osseous integration outcomes is not yet clearly understood. Consequently, understanding how to minimize the incidence of postoperative complications and thereby enhance the long-term effectiveness of spinal fusion surgery holds crucial clinical significance.

Research on porous structures of titanium alloy materials has recently become a focus [28,29]. The ability of porous metal structures to induce bone ingrowth has been widely studied and acknowledged. Porous structures can effectively reduce the overall stiffness of implants, thereby reducing stress-shielding effects and further promoting bone integration [30]. Additionally, during the 3D printing process, the titanium alloy powder is sintered into a metal mesh after being melted by a high-energy electron beam or laser, resulting in a surface with micrometre-scale roughness, which serves as an ideal substrate for bone cell adhesion. Porous scaffolds with interconnected microchannel structures facilitate bone ingrowth and promote new blood vessel formation, ensuring efficient bone formation [31].

After the interbody fusion cage is implanted between the vertebrae, successful bone integration at the interface is crucial for achieving the long-term stability of the fusion cage. It is a critical factor in the success of spinal fusion surgery, which aims to promote a robust bony fusion of the treated segment. Elastic modulus data is essentially additional information that can assist surgeons in selecting the material and structure of the fusion cage.

A mismatch in elastic modulus between the implant and the host bone can impede bone integration at the implant-bone interface. Implants with higher stiffness and complete restriction are more likely to cause stress shielding, hindering bone integration and potentially leading to pseudoarthrosis [32,33].

Implants with stiffness significantly greater than the surrounding bone, such as metallic implants, have been demonstrated to accelerate degeneration in untreated adjacent segments [34]. Using metallic implants with a very high elastic modulus, placed between bone surfaces with much lower moduli, may result in implant subsidence. From a surgical perspective, excessive removal of the bone endplate may also cause even lower modulus pillars to subside into the subjacent vertebra [35].

The Ti-24Nb-4Zr-8Sn material selected for the porous Ti2448 fusion cage designed in this study has an elastic modulus of approximately 42 GPa, closely matching that of the human cortical bone (18 GPa). In comparison, Ti64 has an elastic modulus of about 110 GPa, while PEEK has an elastic modulus of approximately 4 GPa.

There is a relative scarcity of biomechanical studies on porous vertebral interbody fusion implants made of β titanium alloys domestically and internationally. This study introduces a novel 3D-printed porous Ti2448 lumbar interbody fusion cage. Through precise modelling of the porous structure, three fusion cage models with the same specifications but different materials were established for posterior lumbar interbody fusion (PLIF), and their biomechanical characteristics were analysed through finite element simulation.

Based on the Range of Motion (ROM) analysis results, all three interbody cage models, through coordination with the pedicle screw-rod system, demonstrated excellent overall stability. Adequate fixation is crucial for the success of spinal fusion. The stress in the rod system revealed that the stress in the porous structure group was significantly lower than that in the traditional PEEK model. The main reason for this is that the relatively loose structure of the porous fusion cage, compared to the overall rigidity of the conventional PEEK fusion cage, leads to a decrease in the overall stiffness. This, in turn, allows better elastic release of energy in the anterior and middle columns of the surgical segment during spinal movement, consequently reducing stress distribution in the posterior rod system. Therefore, it can be inferred that 3D-printed porous Ti2448 and Ti64 lumbar interbody fusion cages exhibit biomechanical stability comparable to traditional PEEK fusion cages. Simultaneously, they reduce the burden on the rod system, contributing to the prolonged lifespan of the rod system.

The magnitude of forces at the fusion cage – endplate interface indicates that, owing to the design of the porous structure, the interface stress of both porous titanium alloy fusion cages with the endplate is lower than that of the solid PEEK fusion cage. Moreover, the Ti2448 fusion cage exhibits a significant advantage in maximum interface stress under certain conditions. Studies [36,37] have suggested that a certain level of stress stimulation can effectively promote bone integration between the implant and the bone interface. However, excessive interface stress may lead to localized bone absorption, further hindering the bone integration between the implant and the bone interface. Bone tissue is mechanically sensitive tissue with strong adaptive capabilities capable of maintaining a specific mechanical environment. The mechanical environment in which the vertebral bodies reside is constantly changing and highly complex. Bone tissue adjusts and updates its internal structure and external morphology in response to changes in the local mechanical environment. This ensures that the bone adapts optimally to the continuously changing mechanical conditions [38]. The results of this study suggest that compared to Ti64, the low-modulus Ti2448 interbody fusion cage can better facilitate the mechanical stress conditions of surrounding bone tissue.

After lumbar interbody fusion surgery, subsidence of the endplates and sinking of the fusion cage can significantly reduce the effectiveness of interbody fusion. In addition to endplate damage caused by surgical procedures, stress shielding effects generated by high elastic modulus are important factors leading to fusion cage subsidence [39,40]. Excessive interface stress leading to stress concentration can cause endplate fractures, resulting in fusion cage subsidence and affecting the long-term effectiveness of interbody fusion. The results of this study suggest that the 3D-printed Ti2448 porous structure can reduce the overall stiffness of the fusion cage, thereby decreasing the interface stress between the fusion cage and the endplate. This may help reduce the occurrence of fusion cage subsidence in interbody fusion procedures.

The porous fusion cage prevents excessive stress at the implant-bone interface and reduces micro-movements of the fusion cage within the vertebral bodies. Traditional fusion cages are designed with a serrated structure to prevent slippage. In contrast, the surface of porous fusion cages is rougher, with a significantly increased contact area with the endplate. As seen in Figure 9, the relative micro-movements of both groups of porous Ti metal fusion cages are noticeably smaller than those of the traditional PEEK fusion cage. This aligns with practical observations: the rough surface of porous fusion cages offers both mechanical and biological advantages. The rough surface generates more friction, reducing the likelihood of implant displacement [41]. This friction helps minimize micro-motions, as excessive micro-movement at the surgical site (≥150 µm) has been demonstrated to induce the formation of fibrous tissue on the implant surface [42].

In summary, the novel porous Ti2448 fusion cage exhibits excellent mechanical performance in maintaining stability at the operative segment and effectively reduces the contact stress and relative sliding at the interface between the fusion cage and the upper/lower endplates. The reduction in contact interface stress can decrease the risk of postoperative subsidence of the fusion cage, and preventing excessive movement of the fusion cage between the vertebrae is also more favourable for bone integration. Additionally, compared to Ti64 fusion cages, the elements in the Ti2448 alloy do not exhibit significant toxicity in the body, nor do they induce immune reactions or allergies [24]. Experiments conducted by K.C. Nune et al. in vitro have demonstrated that Ti2448 alloy possesses good biocompatibility and osteogenic activity, suggesting promising potential for its use in implants [43].

It is important to note that, due to the complexity of the spinal structure and significant variations among individuals, coupled with the inherent limitations of three-dimensional finite element analysis, the biomechanical simulation results presented here may not fully reflect the actual clinical scenarios. Further validation through in vitro biomechanical testing and animal experiments is essential to verify the biomechanical performance and bone integration capability of the low-modulus 3D-printed porous interbody fusion cages.Additional experiments will provide more comprehensive theoretical support for further clinical research.

Conclusion

In posterior lumbar interbody fusion (PLIF) procedures, 3D-printed porous Ti64 and Ti2448 interbody fusion cage demonstrate superior biomechanical performance compared to traditional PEEK cage. They effectively reduce stress concentration on the upper and lower endplates, mitigating the risk of implant subsidence. The effects are particularly pronounced with the low modulus Ti2448 interbody fusion cage. The excellent biomechanical characteristics of 3D-printed porous interbody fusion cages and their unique porous structure contribute to a more favourable environment for new bone growth, promoting long-term bone integration.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The Natural Science Foundation of Liaoning Province, China (No.2022-YGJC-42) Liaoning Provincial Department of science and technology (No.2022JH1/10800073) Aeronautical Science Foundation of China (2022Z053092001) the Opening Project of National Key Laboratory of Shock Wave and Detonation Physics (2022JCJQLB05702)