Subsidence and fusion performance of a 3D-printed porous interbody cage with stress-optimized body lattice and microporous endplates - a comprehensive mechanical and biological analysis

Lumbar Fusion With Micro- & Nano-Textured, 3D Printed Porous Titanium Versus PEEK Interbody Cages in TLIF: A Single-Blinded, Randomized Controlled Trial

Study DesignProspective, randomized controlled study.ObjectiveAssess early radiological outcomes in transforaminal lumbar interbody fusion (TLIF) with 3D-printed porous titanium (3DPPT) compared to PEEK.MethodsSingle-blinded prospective, randomized controlled trial comparing 1-2 level TLIF with micro- & nano-textured, 3DPPT vs PEEK cages from 11/2021 to 5/2023. Interbody fusion was assessed on CT at 6 months according to Brantigan and Steffee method, modified to describe the Fraser definition of locked pseudoarthrosis [(BSF) scale]. Primary outcome was radiographic fusion at 6 months. ResultsInitial study protocol included 70 total patients but was ended early given the significance on interim analysis. Amongst 17 patients with 25 interbody levels implanted, 10 3DPPT and 15 PEEK cages were implanted. 3DPPT levels had a significantly higher rate of successful fusion (BSF-3) at 6 months compared with PEEK (100% vs 0.0%, P < 0.001). The posterior probability that 3DPPT increased the odds of fusion versus PEEK was > 99.9%, indicating a near-certain beneficial effect. Using a Bayesian mixed-effects model, the predicted probability of 6-month BSF-3 fusion was 9.0% for PEEK and 91.2% for 3DPPT. There were no significant differences in lumbar pathologies, level of fusion, number of fused levels, cage height, length of hospital stay, surgery duration, postoperative complications, subsidence, or reoperations.ConclusionsThe rate of successful lumbar interbody fusion at 6 months was significantly higher in 3DPPT levels compared to PEEK. 3DPPT may accelerate the rate and quality of bony fusion. Additional studies are needed to further delineate the impact of these radiographical findings on long-term clinical outcomes.

Optimization of 3D-printed titanium interbody cage design. Part 2: An in vivo study of spinal fusion in sheep

BACKGROUND CONTEXT

3D-printed titanium cage designs can incorporate complex, porous features for bone ingrowth and a greater surface area for minimizing subsidence. In a companion study (Part 1), we determined that increased surface area leads to decreased subsidence; however, it remains unclear how increasing the cage surface area, resulting in a smaller graft aperture, influences fusion.

PURPOSE

We evaluated the effects of surface area of 3D-printed titanium cages and the use of autologous bone grafts on spinal fusion in sheep.

STUDY DESIGN

In vivo large animal study in 12 sheep.

METHODS

Interbody fusion was performed in 12 adult sheep at 24 levels (L2-3 and L4-5) using 3D-printed titanium cages with bilateral pedicle screw fixation. The cage designs varied in aperture: standard (low endplate surface area), small (medium endplate surface area), or none (high endplate surface area). These cages were packed with autologous iliac crest bone grafts (ICBG). A fourth group was implanted without bone grafts, using the no-aperture cage. Fusion was evaluated at 16 weeks via manual palpation, microcomputed tomography (microCT), histology, and histomorphometry.

RESULTS

Standard, small, and no-aperture cages packed with ICBG resulted in high fusion rates (80%, 100%, and 83%, respectively) at 16 weeks by manual palpation, and these results were not significantly different. Implantation without ICBG was associated with a significantly lower fusion rate (33%, p<.05). Histological, histomorphometry, and microCT results supported the findings obtained by manual palpation; findings from these modalities showed new bone spanning the vertebral endplates in the spines graded as fused by manual palpation.

CONCLUSIONS

Similar fusion results for standard, small, and no-aperture cage designs packed with ICBG suggest that aperture size does not influence fusion results in the sheep model. However, without ICBG grafting, fusion was significantly decreased, suggesting that graft material is necessary to predictably obtain fusion in this model. When the in vitro subsidence data (companion study, Part 1) is considered with the in vivo fusion data described here, porous 3D-printed titanium cages with maximal surface endplate contact and bone grafting perform favorably, resulting in low subsidence and high fusion rates.

CLINICAL SIGNIFICANCE

3D-printed porous titanium interbody cages are novel devices with increasing clinical use. The study results show that the aperture size of the interbody cage did not influence fusion in a large animal (sheep) model. The use of bone graft material was the most important variable affecting fusion. These data suggest that the clinical use of 3D Ti cages without graft material should be avoided.

Radiographic and Clinical Comparison of Polyetheretherketone Versus 3D-Printed Titanium Cages in Lumbar Interbody Fusion-A Single Institution's Experience

Background/Objectives: Spinal fusion surgery is an accepted form of management for select patients who suffer from degenerative lumbar disease. The need for cost-effective durable techniques is paramount as our population ages. This study compares the radiographic and clinical outcomes of PEEK and 3D-printed titanium interbody cages. Methods: This study compared two cohorts which underwent either PEEK or 3D-printed titanium (3DPT) interbody fusion at a single institution between 2013 and 2022. The PEEK cohort was a retrospective analysis of a prospectively collected registry. The 3DPT data were prospectively collected. The inclusion criteria were adults >18 years who underwent 1 or 2 level lumbar interbody fusion for degenerative spine disease with at least 6 months follow-up. Patient demographics, radiographs, and PROMs were collected. The cohorts were compared using ANOVA for continuous variables and Fisher's exact test for categorical variables, with significance set to 0.05. Results: The final study included 91 patients, 49 PEEK and 42 3DPT. The 3DPT patients were older (p = 0.047) with increased incidence of hypertension (p < 0.001). The 3DPT patients had less bone morphogenetic protein (BMP) usage (80.9% vs. 54.8%; p = 0.012), but more cellular allograft (p < 0.001). Fusion rate was high for both cohorts, with PEEK at 95.9% and 3DPT at 97.6%. There was no significant difference in reoperation rate. Both the PEEK and 3DPT cohorts demonstrated an improvement in the Oswestry Disability Index (ODI) and EuroQol 5 Dimension (EQ-5D) at 1 and 2 years compared to preoperative baseline. More patients in the 3DPT group met the MCID for EQ-5D at 1 and 2 years compared to PEEK; however, this was not significant (p = 0.350; p = 1.000). Conclusions: The 3DPT interbody provided comparable if not superior fusion properties to the PEEK interbody given the decreased use of BMP. Both cohorts demonstrated similar improvements in ODI and EQ-5D compared to preoperative baseline. These results suggest that 3DPT cages may be a cost-effective alternative in spinal fusion. Further studies utilizing a larger population with higher follow-up rates are indicated to determine the economic and clinical benefits of 3DPT compared to PEEK cages in lumbar fusion surgery.

The rational design, biofunctionalization and biological properties of orthopedic porous titanium implants: a review

Porous titanium implants are becoming an important tool in orthopedic clinical applications. This review provides a comprehensive survey of recent advances in porous titanium implants for orthopedic use. First, the review briefly describes the characteristics of bone and the design requirements of orthopedic implants. Subsequently, the pore size and structural design of porous titanium alloy materials are presented, then we introduce the application of porous titanium alloy implants in orthopedic clinical practice, including spine surgery, joint surgery, and the treatment of bone tumors. Following that, we describe the surface modifications applied to porous titanium implants to obtain better biological functions. Finally, we discuss incorporating environmental responsive mechanisms into porous titanium alloy materials to achieve additional functionalities.

3D-printed porous titanium versus polyetheretherketone cages in lateral lumbar interbody fusion: a systematic review and meta-analysis of subsidence

Background

Cage subsidence frequently complicates lumbar fusion procedures, including lateral lumbar interbody fusion (LLIF), potentially leading to recurrent pain, impaired fusion, and accelerated degeneration of adjacent segments. A critical factor influencing cage subsidence is the selection of material. Polyetheretherketone (PEEK) and three-dimensional printed titanium (3D-Ti) cages are commonly used in LLIF procedures, each offering distinct advantages. However, these materials possess inherent property differences that may translate into divergent settling rates. To contribute to this discourse and offer insights, this systematic review and meta-analysis aims to compare the rates of cage subsidence between 3D-Ti and PEEK cages in LLIF.

Methods

A meticulous systematic search that employs distinct MeSH terms was conducted in major electronic databases (MEDLINE, PubMed, Embase, Scopus, Web of Science, and Cochrane) up to December 20, 2023. The quality of inclusion was measured using the Newcastle-Ottawa Scale (NOS) for non-randomized trials. The primary outcome measure was cage subsidence, while the secondary outcome involved evaluating subsidence within each treatment segment using the Marchi classification.

Results

The review included 265 patients (441 segments) from three studies. All with NOS ratings exceeding 5 stars. In the analysis, 189 segments (42.9%) underwent LLIF with 3D-Ti cages, while 252 segments (57.1%) participated in LLIF with PEEK cages. Overall, the cage subsidence rate was significantly lower with 3D-Ti compared to PEEK (p < 0.00001, OR = 0.25; 95% CI 0.14 to 0.44). Specifically, the 3D-Ti group exhibited a markedly lower subsidence rate, categorized by grade I, II, and III, compared to the PEEK group (p < 0.05). Furthermore, the incidence of severe subsidence was significantly reduced in the 3D-Ti group compared to the PEEK group (p = 0.0004, OR = 0.17; 95% CI 0.07 to 0.46).

Conclusion

The study concludes that the subsidence rate associated with 3D-Ti cages in LLIF is notably lower than that observed with PEEK cages, underscoring the potential advantages of 3D-Ti cages in mitigating cage subsidence.

How to improve the mechanical safety of a novel spinal implant while saving costs and time

Background

Spinal implant failure is associated with prolonged patient suffering, high costs for the medical device industry, and a high economic burden for the health care system. Pre-clinical mechanical testing has great potential to reduce the risk of such failure. However, there are no binding regulations for planning and interpretation of mechanical testing. Therefore, different strategies exist. Mainly for novel implants an option is to start with a structured scientific literature search that forms an objective background for the definition of an implant-specific test plan, the derivation of acceptance criteria and interpretation of the test results.

Methods

This paper describes, how a literature-based approach can look like from the initial literature search through the derivation of the test plan and the acceptance criteria, to the final test result evaluation and how this approach can support the proof that the device meets all necessary safety and performance standards.

Results

The main advantage of this literature-based approach is that testing and test result interpretation are linked with the loads acting on the individual implant in vivo. In an ideal case, testing is focused on the individual implant in a way that ensures maximum efficiency during the development and approval process combined with maximum insight in safety and effectiveness of the implant. Even comparative implant testing may become obsolete, which is a big advantage if comparative implant and related data are not available.

Conclusion

This approach to pre-clinical mechanical testing offers the potential to create a chain of arguments, from literature review through testing to the interpretation of test results. This methodology can significantly enhance testing efficiency, reduce risk of failure, and ultimately prevent unnecessary patient suffering and healthcare costs. By synthesizing scientific insights with regulatory requirements, this review aims to guide clinicians and researchers in improving patient care and advancing device technologies.

A novel porous interbody fusion cage modified by microarc oxidation and hydrothermal treatment technology accelerate osseointegration and spinal fusion in sheep

The clinical outcome of spinal fusion surgery is closely related to the success of bone fusion. Nowadays, the interbody cage which is used to replace the disc for spinal fusion is expected to have biological activity to improve osseointegration, especially for the aging and osteoporotic patients. Here, through micro-arc oxidation and hydrothermal treatment (MAO + HT), a bioactive CaP coating with micro/nano multilevel morphology was developed on 3D printed Ti6Al4V alloy then verified in vitro and in sheep anterior cervical decompression fusion model systematically. In vitro studies have confirmed the positive effects of characteristic micro/nano morphology and hydrophilicity of the coating formed after surface treatment on the adhesion, proliferation, and osteogenic differentiation of osteoblast precursor cells. Furthermore, the MAO + HT treated interbody cage showed a closer integration with the surrounding bone tissue, improved kinetic stability of the implanted segment, and significantly reduced incidence of fusion failure during the early postoperative period, which indicated that such a surface modification strategy is applicable to the biomechanical and biological microenvironment of the intervertebral space.

In vivo Assessment of AMP2, a Novel Ceramic-Binding BMP-2, in Ovine Lumbar Interbody Fusion

STUDY DESIGN

Assessment of bone formation in an ovine interbody fusion study.

OBJECTIVE

To compare OsteoAdapt SP, which consists of AMP-2, a modified variant of recombinant human bone morphogenetic protein (rhBMP-2) bound to a tricalcium phosphate-containing carrier, to autologous iliac crest bone graft (ICBG) in a lumbar interbody fusion model.

SUMMARY OF BACKGROUND DATA

Treatment of lumbar disk degeneration often involves spinal fusion to reduce pain and motion at the affected spinal segment by insertion of a cage containing bone graft material. Three graft materials were compared in this study-ICBG and OsteoAdapt SP (low or high dose).

METHODS

The sheep underwent lateral lumbar fusion surgery with PEEK or Titanium interbody cages packed with OsteoAdapt SP (low or high dose) or ICBG. Outcomes were evaluated at 8-, 16- and 26- weeks. Newly formed bone quality, bone mineralization, and fusion were assessed by manual palpation, qualitative and semi-quantitative histopathology, histomorphometry, computed tomography (CT), and micro-CT (mCT) analysis.

RESULTS

OsteoAdapt SP was implanted into 43 animals and ICBG into 21 animals (L3-L4). No group showed evidence of systemic toxicity by multiple assessments. All levels were fused by manual palpation at 26 weeks. Serial CT scans showed increasing fusion scores over time. Both doses of OsteoAdapt SP resulted in robust new bone formation and progression of fusion in the interbody cage. Range of motion tests for treatment groups was lower compared with ICBG at 8- and 16 weeks. Similarly, histology at eight weeks demonstrated more robust new bone formation for both OsteoAdapt SP groups compared to autograft.

CONCLUSION

We have demonstrated the preclinical safety and efficacy of OsteoAdapt SP in a clinically relevant large animal model, supporting faster and more robust new bone formation within the interbody cage, comparable to or better than the gold standard, ICBG, in all measures.

Subsidence Rates Associated With Porous 3D-Printed Versus Solid Titanium Cages in Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective Cohort Study.

OBJECTIVE

To determine whether 3D-printed porous titanium (3DPT) interbody cages offer any clinical or radiographic advantage over standard solid titanium (ST) interbody cages in transforaminal lumbar interbody fusions (TLIF).

METHODS

A consecutive series of adult patients undergoing one- or two-level TLIF with either 3DPT or ST "banana" cages were analyzed for patient reported outcome measures (PROMs), radiographic complications, and clinical complications. Exclusion criteria included clinical or radiographic follow-up less than 1 year.

RESULTS

The final cohort included 90 ST interbody levels from 74 patients, and 73 3DPT interbody levels from 50 patients for a total of 124 patients. Baseline demographic variables and comorbidity rates were similar between groups (P > .05). Subsidence of any grade occurred more frequently in the ST group compared with the 3DPT group (24.4% vs 5.5%, respectively, P = .001). Further, the ST group was more likely to have higher grades of subsidence than the 3DPT group (P = .009). All PROMs improved similarly after surgery and revision rates did not differ between groups (both P > .05). On multivariate analysis, significant positive correlators with increasing subsidence grade included greater age (P = .015), greater body mass index (P = .043), osteoporosis/osteopenia (P < .027), and ST cage type (P = .019).

CONCLUSIONS

When considering interbody material for TLIF, both ST and 3DPT cages performed well; however, 3DPT cages were associated with lower rates of subsidence. The clinical relevance of these findings deserves further randomized, prospective investigation.

Advancements in Custom 3D-Printed Titanium Interbody Spinal Fusion Cages and Their Relevance in Personalized Spine Care

3D-printing technology has revolutionized spinal implant manufacturing, particularly in developing personalized and custom-fit titanium interbody fusion cages. These cages are pivotal in supporting inter-vertebral stability, promoting bone growth, and restoring spinal alignment. This article reviews the latest advancements in 3D-printed titanium interbody fusion cages, emphasizing their relevance in modern personalized surgical spine care protocols applied to common clinical scenarios. Furthermore, the authors review the various printing and post-printing processing technologies and discuss how engineering and design are deployed to tailor each type of implant to its patient-specific clinical application, highlighting how anatomical and biomechanical considerations impact their development and manufacturing processes to achieve optimum osteoinductive and osteoconductive properties. The article further examines the benefits of 3D printing, such as customizable geometry and porosity, that enhance osteointegration and mechanical compatibility, offering a leap forward in patient-specific solutions. The comparative analysis provided by the authors underscores the unique challenges and solutions in designing cervical, and lumbar spine implants, including load-bearing requirements and bioactivity with surrounding bony tissue to promote cell attachment. Additionally, the authors discuss the clinical outcomes associated with these implants, including the implications of improvements in surgical precision on patient outcomes. Lastly, they address strategies to overcome implementation challenges in healthcare facilities, which often resist new technology acquisitions due to perceived cost overruns and preconceived notions that hinder potential savings by providing customized surgical implants with the potential for lower complication and revision rates. This comprehensive review aims to provide insights into how modern 3D-printed titanium interbody fusion cages are made, explain quality standards, and how they may impact personalized surgical spine care.

Application of 3D‑printed porous titanium interbody fusion cage vs. polyether ether ketone interbody fusion cage in anterior cervical discectomy and fusion: A systematic review and meta‑analysis update

The present study aimed to compare the differences between 3D-printed porous titanium and polyether ether ketone (PEEK) interbody fusion cages for anterior cervical discectomy and fusion (ACDF). Literature on the application of 3D-printed porous titanium and PEEK interbody fusion cages for ACDF was searched in the PubMed, Web of Science, Embase, China National Knowledge Infrastructure, Wanfang and VIP databases. A total of 1,181 articles were retrieved and 12 were finally included. The Cochrane bias risk assessment criteria and Newcastle-Ottawa scale were used for quality evaluation and Review Manager 5.4 was used for data analysis. The 3D cage group was superior to the PEEK cage group in terms of operative time [mean difference (MD): -7.68; 95% confidence interval (CI): -11.08, -4.29; P<0.00001], intraoperative blood loss (MD: -6.17; 95%CI: -10.56, -1.78; P=0.006), hospitalization time (MD: -0.57; 95%CI: -0.86, -0.28: P=0.0001), postoperative complications [odds ratio (OR): 0.35; 95%CI: 0.15, 0.80; P=0.01], C2-7 Cobb angle (MD: 2.85; 95%CI: 1.45, 4.24; P<0.0001), intervertebral space height (MD: 1.20; 95%CI: 0.54, 1.87; P=0.0004), Japanese Orthopaedic Association Assessment of Treatment (MD: 0.69; 95%CI: 0.24, 1.15; P=0.003) and visual analogue scale score (MD: -0.43; 95%CI: -0.78, -0.07; P=0.02). The difference was statistically significant, while there was no significant difference between the two groups in terms of fusion rate (OR: 1.74; 95%CI: 0.71, 4.27; P=0.23). The use of 3D-printed porous titanium interbody fusion cage in ACDF has the advantages of short operation time, less bleeding loss, shorter hospitalization time and fewer postoperative complications. It can better maintain the cervical curvature and intervertebral height, relieve pain and accelerate postoperative functional recovery.

Innovative Developments in Lumbar Interbody Cage Materials and Design: A Comprehensive Narrative Review

This review comprehensively examines the evolution and current state of interbody cage technology for lumbar interbody fusion (LIF). This review highlights the biomechanical and clinical implications of the transition from traditional static cage designs to advanced expandable variants for spinal surgery. The review begins by exploring the early developments in cage materials, highlighting the roles of titanium and polyetheretherketone in the advancement of LIF techniques. This review also discusses the strengths and limitations of these materials, leading to innovations in surface modifications and the introduction of novel materials, such as tantalum, as alternative materials. Advancements in three-dimensional printing and surface modification technologies form a significant part of this review, emphasizing the role of these technologies in enhancing the biomechanical compatibility and osseointegration of interbody cages. In addition, this review explores the increase in biodegradable and composite materials such as polylactic acid and polycaprolactone, addressing their potential to mitigate long-term implant-related complications. A critical evaluation of static and expandable cages is presented, including their respective clinical and radiological outcomes. While static cages have been a mainstay of LIF, expandable cages are noted for their adaptability to the patient's anatomy, reducing complications such as cage subsidence. However, this review highlights the ongoing debate and the lack of conclusive evidence regarding the superiority of either cage type in terms of clinical outcomes. Finally, this review proposes future directions for cage technology, focusing on the integration of bioactive substances and multifunctional coatings and the development of patient-specific implants. These advancements aim to further enhance the efficacy, safety, and personalized approach of spinal fusion surgeries. Moreover, this review offers a nuanced understanding of the evolving landscape of cage technology in LIF and provides insights into current practices and future possibilities in spinal surgery.

Biomechanical Analysis of a Newly Proposed Surgical Combination (MIS Screw-Rod System for Indirect Decompression+ Interspinous Fusion System for long Term Spinal Stability) in Treatment of Lumbar Degenerative Diseases

OBJECTIVE

The aim of this study is to analyze the biomechanical stability of a newly proposed surgical combination (minimally invasive surgery of screw-rod system for indirect decompression + interspinous fusion system for long term spinal stability) in treatment of lumbar degenerative diseases.

METHODS

The three-dimensional (3D) computed tomography (CT) image data of an adult healthy male volunteer were selected. An intact model of L4/5 was further established and validated by using Mimic and 3-matic, 3D slicer, abaqus, Python. Four surgical models were constructed. The biomechanical stability among these surgical modes was compared and analyzed using finite element analysis.

RESULTS

The maximum von mises on fixation system in surgical models 2 and 3 exhibited comparable values. This finding suggested that the increase in interspinous fusion did not result in a significant elevation in maximum von mises on fixation system. Compared with the third surgical model, the fourth model, which received less average von mises experienced by the screw in contact with both cancellous and cortical bone. The findings indicated that the inclusion of facet joint fusion in surgical procedures might not be necessary to increase the average von Mises stress experienced by the screw in contact with both cancellous and cortical bone.

CONCLUSIONS

The biomechanical stability of the newly proposed surgical combination (MIS screw-rod for indirect decompression + interspinous fusion for long term spinal stability technique) was not lower than that of the other surgical combination groups, and it might not be necessary to perform facet joint fusion during the surgery.

Advances in Implant Technologies for Spine Surgery

Spine implants are becoming increasingly diversified. Taking inspiration from other industries, three-dimensional modeling of the spinal column has helped meet the custom needs of individual patients as both en bloc replacements and pedicle screw designs. Intraoperative tailoring of devices, a common need in the operating room, has led to expandable versions of cages and interbody spacers.

Porous Cage Macro-Topography Improves Early Fusion Rates in Anterior Cervical Discectomy and Fusion

Objectives

Anterior cervical discectomy and fusion (ACDF) aims to improve pain, relieve neural compression, achieve rapid solid bony arthrodesis, and restore cervical alignment. Bony fusion occurs as early as 3 months and up to 24 months after ACDF. The correlations between bony fusion and clinical outcomes after ACDF remain unclear. Macro-topographic and porous features have been introduced to interbody cage technology, aiming to improve the strength of the bone-implant interface to promote early fusion. In this study, we aimed to compare clinical outcomes and CT-evaluated fusion rates in patients undergoing ACDF using one of two different interbody cages: traditional NanoMetalene™ (NM) cages and NM cages with machined porous features (NMRT).

Methods

This was a prospective, observational, nonrandomised, cohort study of consecutive patients undergoing ACDF. The NM cage cohort was enrolled first, then the NMRT cohort second. The visual analogue scale, neck disability index, and 12-item Short Form Survey scores were evaluated preoperatively and at 6 weeks, 3 months, and 6 months. The minimum clinical follow-up period was 12 months. Plain radiographs were obtained on postoperative day 2 to assess instrumentation positioning, and computed tomography (CT) was performed at 3 and 6 months postoperatively to assess interbody fusion (Bridwell grade).

Results

Eighty-nine (52% male) patients with a mean age of 62 ± 10.5 years were included in this study. Forty-one patients received NM cages, and 48 received NMRT cages. All clinical outcomes improved significantly from baseline to 6 months. By 3 months, the NMRT group had significantly higher CT fusion rates than the NM group (79% vs 56%, p=0.02). By 6 months, there were no significant differences in fusion rates between the NMRT and NM groups (83% vs 78%, p=0.69). The mean Bridwell grade at 6 months was 1.4 ± 0.7 in the NMRT group and 1.8 ± 1.0 in the NM group (p=0.08).

Conclusions

With both NM and NMRT cages, serial improvements in postoperative clinical outcomes were associated with fusion progression on CT. NMRT cages demonstrated significantly better fusion at 3 months and a trend toward higher quality of fusion at 6 months compared with NM cages, suggesting earlier cage integration with NMRT. An early 3-month postoperative CT is adequate for fusion assessment in almost 80% of patients undergoing ACDF with an NMRT cage, permitting an earlier return to activity.

Evaluating the effect of pore size for 3d-printed bone scaffolds

The present study investigated the influence of pore size of strut-based Diamond and surface-based Gyroid structures for their suitability as medical implants. Samples were made additively from laser powder bed fusion process with a relative density of 0.3 and pore sizes ranging from 300 to 1300 μm. They were subsequently examined for their manufacturability and mechanical properties. In addition, non-Newtonian computational fluid dynamics and discrete phase models were conducted to assess pressure drop and cell seeding efficiency. The results showed that both Diamond and Gyroid had higher as-built densities with smaller pore sizes. However, Gyroid demonstrated better manufacturability as its relative density was closer to the as-designed one. In addition, based on mechanical testing, the elastic modulus was largely unaffected by pore size, but post-yielding behaviors differed, especially in Diamond. High mechanical sensitivity in Diamond could be explained partly by Finite Element simulations, which revealed stress localization in Diamond and more uniform stress distribution in Gyroid. Furthermore, we defined the product of the normalized specific surface, normalized pressure drop, and cell seeding efficiency as the indicator of an optimal pore size, in which this factor identified an optimal pore size of approximately 500 μm for both Diamond and Gyroid. Besides, based on such criterion, Gyroid exhibited greater applicability as bone scaffolds. In summary, this study provides comprehensive assessment of the effect of pore size and demonstrates the efficient estimation of an in-silico framework for evaluating lattice structures as medical implants, which could be applied to other lattice architectures.

Comparison between Three-Dimensional Printed Titanium and PEEK Cages for Cervical and Lumbar Interbody Fusion: A Prospective Controlled Trial

OBJECTIVES

The three-dimensional printing titanium (3DPT) cage with excellent biomechanical properties and osseointegration capabilities has been initially used in spinal fusion, while the polyetheretherketone (PEEK) cage, a bioinert material device, has been a widely used for decades with relatively excellent clinical outcomes. This study was performed to investigate the early radiographic and clinical outcomes of 3DPT cage versus PEEK cage in patients undergoing anterior cervical discectomy and fusion (ACDF) and transforaminal lumbar interbody fusion (TLIF).

METHODS

This prospective controlled trial, from December 2019 to June 2022, included patients undergoing ACDF and TLIF with 3DPT cages and compared them to patients using PEEK cages for treating spinal degenerative disorders. The outcome measures included radiographic parameters (intervertebral height [IH], subsidence, fusion status, and bone-cage interface contact) and clinical outcomes (Japanese Orthopaedic Association [JOA], Neck Disability Index [NDI], Oswestry Disability Index [ODI], Short Form 12-Item Survey [SF-12], Visual Analog Scale [VAS], and Odom's criteria). Student's independent samples t test and Pearson's chi-square test were used to compare the outcome measures between the two groups before surgery and at 1 week, 3 and 6 months after surgery.

RESULTS

For the patients undergoing ACDF, the 3DPT (18 patients/[26 segments]) and PEEK groups (18 patients/[26 segments]) had similar fusion rates at 3 months and 6 months follow-up (3 months: 96.2% vs. 83.3%, p = 0.182; 6 months: 100% vs. 91.7%, p = 0.225). The subsidence in the 3DPT group was significantly lower than that in the PEEK group (3 months: 0.4 ± 0.2 mm vs. 0.9 ± 0.7 mm p = 0.004; 6 months: 0.7 ± 0.3 mm vs. 1.5 ± 0.8 mm, p < 0.001). 3DPT and PEEK cage all achieved sufficient contact with the cervical endplates. For the patients undergoing TLIF, the 3DPT (20 patients/[26 segments]) and PEEK groups (20 patients/[24 segments]) had no statistical difference in fusion rate (3 months: 84.6% vs. 58.3%, p = 0.059; 6 months: 92.3% vs. 75%, p = 0.132). The subsidence was lower than that in the PEEK group without significantly difference (3 months: 0.9 ± 0.7 mm vs.1.2 ± 0.9 mm p = 0.136; 6 months: 1.6 ± 1.0 mm vs. 2.0 ± 1.0 mm, p = 0.200). At the 3-month follow-up, the bone-cage interface contact of the 3DPT cage was significantly better than that of the PEEK cage (poor contact: 15.4% vs. 75%, p < 0.001). The values of UAR were higher in the 3DPT group than in the PEEK group during the follow-up in cervical and lumbar fusion, there were more statistical differences in lumbar fusion. There were no significant differences in the clinical assessment between 3DPT or PEEK cage in spinal fusion.

CONCLUSION

The 3DPT cage and PEEK cage can achieve excellent clinical outcomes in cervical and lumbar fusion. The 3DPT cage has advantage in fusion quality, subsidence severity, and bone-cage interface contact than PEEK cage.

Implant failure and revision strategies after total spondylectomy for spinal tumors

Background

Although there have been several risk factors reported for implant failure (IF), little consensus exists. Potential applicable measures to protect patients from IF are relatively few. This study aimed to discover new risk factors for IF and explore potential protective measures from IF after total spondylectomy for spinal tumors.

Methods

A total of 145 patients undergoing total spondylectomy for thoracic and lumbar spinal tumors between 2010 and 2021 were included from three tertiary university hospitals. Patient demographic and surgical characteristics and follow-up outcomes were collected.

Results

During a mean follow-up of 53.77 months (range, 12 to 149 months), 22 of 145 patients (15.17%) developed IF. Patients undergoing thoracolumbar junctional region (T12/L1) resection were more likely to develop IF compared to those undergoing surgery at other vertebral levels (HR = 21.622, 95% CI = 3.567-131.084, P = 0.001). Patients undergoing titanium mesh cage reconstruction were more likely to develop IF compared to patients undergoing expandable titanium cage reconstruction (HR = 8.315, 95% CI = 1.482-46.645, P = 0.016). Patients with bone cement augmentation around the cage were less likely to develop IF compared to those not receiving bone cement augmentation (HR = 0.015, 95% CI = 0.002-0.107, P < 0.001). Of the 22 patients with IF, 14 (63.63%) accepted personalized revision surgery.

Conclusion

The use of an expandable cage and the use of bone cement augmentation around the anterior column support cage are protective measures against IF after total spondylectomy.

Novel 3D printed lattice structure titanium cages evaluated in an ovine model of interbody fusion

Background

The use of intervertebral cages within the interbody fusion setting is ubiquitous. Synthetic cages are predominantly manufactured using materials such as Ti and PEEK. With the advent of additive manufacturing techniques, it is now possible to spatially vary complex 3D geometric features within interbody devices, enabling the devices to match the stiffness of native tissue and better promote bony integration. To date, the impact of surface porosity of additively manufactured Ti interbody cages on fusion outcomes has not been investigated. Thus, the objective of this work was to determine the effect of implant endplate surface and implant body architecture of additive manufactured lattice structure titanium interbody cages on bony fusion.

Methods

Biomechanical, microcomputed tomography, static and dynamic histomorphometry, and histopathology analyses were performed on twelve functional spine units obtained from six sheep randomly allocated to body lattice or surface lattice groups.

Results

Nondestructive kinematic testing, microcomputed tomography analysis, and histomorphometry analyses of the functional spine units revealed positive fusion outcomes in both groups. These data revealed similar results in both groups, with the exception of bone-in-contact analysis, which revealed significantly improved bone-in-contact values in the body lattice group compared to the surface lattice group.

Conclusion

Both additively manufactured porous titanium cage designs resulted in increased fusion outcomes as compared to PEEK interbody cage designs as illustrated by the nondestructive kinematic motion testing, static and dynamic histomorphometry, microcomputed tomography, and histopathology analyses. While both cages provided for similar functional outcomes, these data suggest boney contact with an interbody cage may be impacted by the nature of implant porosity adjacent to the vertebral endplates.

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.

Three-Dimensional-Printed Titanium Versus Polyetheretherketone Cages for Lumbar Interbody Fusion: A Systematic Review of Comparative In Vitro, Animal, and Human Studies

Interbody fusion is a workhorse technique in lumbar spine surgery that facilities indirect decompression, sagittal plane realignment, and successful bony fusion. The 2 most commonly employed cage materials are titanium (Ti) alloy and polyetheretherketone (PEEK). While Ti alloy implants have superior osteoinductive properties they more poorly match the biomechanical properties of cancellous bones. Newly developed 3-dimensional (3D)-printed porous titanium (3D-pTi) address this disadvantage and are proposed as a new standard for lumbar interbody fusion (LIF) devices. In the present study, the literature directly comparing 3D-pTi and PEEK interbody devices is systematically reviewed with a focus on fusion outcomes and subsidence rates reported in the in vitro, animal, and human literature. A systematic review directly comparing outcomes of PEEK and 3D-pTi interbody spinal cages was performed. PubMed, Embase, and Cochrane Library databases were searched according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines. Mean Newcastle-Ottawa Scale score for cohort studies was 6.4. A total of 7 eligible studies were included, comprising a combination of clinical series, ovine animal data, and in vitro biomechanical studies. There was a total population of 299 human and 59 ovine subjects, with 134 human (44.8%) and 38 (64.4%) ovine models implanted with 3D-pTi cages. Of the 7 studies, 6 reported overall outcomes in favor of 3D-pTi compared to PEEK, including subsidence and osseointegration, while 1 study reported neutral outcomes for device related revision and reoperation rate. Though limited data are available, the current literature supports 3D-pTi interbodies as offering superior fusion outcomes relative to PEEK interbodies for LIF without increasing subsidence or reoperation risk. Histologic evidence suggests 3D-Ti to have superior osteoinductive properties that may underlie these superior outcomes, but additional clinical investigation is merited.

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.

Research relating to three-dimensional (3D) printing in spine surgery: a bibliometric analysis

PURPOSE

Although numerous publications on three-dimensional printing (3DP) in spine surgery have been published, bibliometric analysis studies are scarce. Thus, this study aimed to present a bibliometric analysis of the status, hot spots, and frontiers of 3DP in spine surgery and associated research disciplines.

METHODS

All publications relating to the utilization of 3DP in spine surgery from 1999 to May 9, 2022, were retrieved from the Web of Science. The bibliometric analysis was performed using CiteSpace software, and information on the country, institution, author, journal, and keywords for each publication was collected.

RESULTS

A total of 270 articles were identified. From 2016 onward, a significant increase in publications on spinal surgery was observed. China was the most productive and influential country (98 publications) and H-index (22), followed by the USA and Australia. The most productive institution was Capital Medical University (9 publications). P. S. D'urso (8 publications, 46 citations) and R. J. Mobbs (8 publications, 39 citations) were the most prolific authors. European Spine Journal contributed the highest number of publications. The eight main clusters were: "rapid prototyping" #0, "3D printed" #1, "spine fusion" #2, "scoliosis" #3, "spine surgery" #4, "patient-specific" #5, "nervous system" #6, and "neuronavigation" #7. The strongest keyword bursts in 3DP in spine surgery were "fixation," "drill template," "instrumentation," "fusion," "complication," and "atlantoaxial instability."

CONCLUSION

This analysis provides information on research trends and frontiers in the application of 3DP in spine surgery, as well as research and collaboration partners, institutions, and countries.

3D printing in spine care: A review of current applications

3D printing (3DP) has been brought to medical use since the early part of this century- but it has been widely researched on and publicized only in the last few years. Amongst patients with spinal disorders, 3DP has been utilized in various facets of patient care. These include pre-operative aspects - such as patient education, resident training, pre-operative planning and simulations, intra-operative assistance in the form of customized jigs for pedicle screw insertion, patient specific interbody cages and vertebral body substitutes in complex malignancies and spinal infections. It has also been utilized in deformity surgeries and has opened new avenues in minimally invasive spine care. Guidelines have now been drafted by various organizations including the FDA with a prime focus on quality control measures applicable to this new technology. There has been a recent surge in publications supporting the use of 3DP in spinal disorders, reporting an improvement in various aspects of patient care. As the technology spreads out its wings further, more innovations and applications are expected to unfold in the coming years. Considering the rapid advances that 3DP has made, having a basic understanding of this technology is imperative for all spine surgeons. Despite promising preliminary results, there still exist a few pitfalls of the technology which have hindered the universal application of 3DP. Most importantly, there is a dearth of data related to long term outcomes supporting its clinical use. The prohibitive cost of 3D models, the specialized manpower it necessitates and the need for specific instrumentation are major deterrents to widespread use of this technology, particularly in small-scale healthcare setups. With further advancements in technology, the goal must be to make it more accurate and affordable to hospitals and patients so that the benefits of the technology can reach a wider patient population.

Biomechanical comparison of subsidence performance among three modern porous lateral cage designs

BACKGROUND

Cage subsidence remains a major complication after spinal surgery. The goal of this study was to compare the subsidence performance of three modern porous cage designs.

METHODS

Three porous cages were evaluated: a porous titanium cage, a porous polyetheretherketone cage and a truss titanium cage. Mechanical testing was performed for each cage per the American Society for Testing and Materials F2077 and F2267 standards to evaluate cage stiffness and block stiffness, and per a novel clinically relevant dynamic subsidence testing method simulating cyclic spine loading during 3-months postoperatively to evaluate the subsidence displacement.

FINDINGS

The porous polyetheretherketone cage demonstrated the lowest cage stiffness (21.0 ± 1.1 kN/mm), less than half of both titanium cages (truss titanium cage, 49.1 kN/mm; porous titanium cage, 43.6 kN/mm). The block stiffness was greatest for the porous titanium cage (2867.7 ± 105.3 N/mm), followed by the porous polyetheretherketone (2563.4 ± 72.9 N/mm) and truss titanium cages (2213.7 ± 21.8 N/mm). The dynamic subsidence displacement was greatest for the truss titanium cage, which was 1.5 and 2.5 times the subsidence displacement as the porous polyetheretherketone and porous titanium cages respectively.

INTERPRETATIONS

Specific porous cage design plays a crucial role in the cage subsidence performance, to a greater degree than the selection of cage materials. A porous titanium cage with body lattice and microporous endplates significantly outperformed a truss titanium cage with a similar cage stiffness in subsidence performance, and a porous polyetheretherketone cage with half of its stiffness.

[Application of three-dimensional printed porous titanium alloy cage and poly-ether-ether-ketone cage in posterior lumbar interbody fusion]

Objective

To compare the effectiveness between three-dimensional (3D) printed porous titanium alloy cage (3D Cage) and poly-ether-ether-ketone cage (PEEK Cage) in the posterior lumbar interbody fusion (PLIF).

Methods

A total of 66 patients who were scheduled to undergo PLIF between January 2018 and June 2019 were selected as the research subjects, and were divided into the trial group (implantation of 3D Cage, n=33) and the control group (implantation of PEEK Cage, n=33) according to the random number table method. Among them, 1 case in the trial group did not complete the follow-up exclusion study, and finally 32 cases in the trial group and 33 cases in the control group were included in the statistical analysis. There was no significant difference in gender, age, etiology, disease duration, surgical segment, and preoperative Japanese Orthopaedic Association (JOA) score between the two groups (P>0.05). The operation time, intraoperative blood loss, complications, JOA score, intervertebral height loss, and interbody fusion were recorded and compared between the two groups.

Results

The operations of two groups were completed successfully. There was 1 case of dural rupture complicated with cerebrospinal fluid leakage during operation in the trial group, and no complication occurred in the other patients of the two groups. All incisions healed by first intention. There was no significant difference in operation time and intraoperative blood loss between groups (P>0.05). All patients were followed up 12-24 months (mean, 16.7 months). The JOA scores at 1 year after operation in both groups significantly improved when compared with those before operation (P<0.05); there was no significant difference between groups (P>0.05) in the difference between pre- and post-operation and the improvement rate of JOA score at 1 year after operation. X-ray film reexamination showed that there was no screw loosening, screw rod fracture, Cage collapse, or immune rejection in the two groups during follow-up. At 3 months and 1 year after operation, the rate of intervertebral height loss was significantly lower in the trial group than in the control group (P<0.05). At 3 and 6 months after operation, the interbody fusion rating of trial group was significantly better in the trial group than in the control group (P<0.05); and at 1 year after operation, there was no significant difference between groups (P>0.05).

Conclusion

There is no significant difference between 3D Cage and PEEK Cage in PLIF, in terms of operation time, intraoperative blood loss, complications, postoperative neurological recovery, and final intervertebral fusion. But the former can effectively reduce vertebral body subsidence and accelerate intervertebral fusion.