Evaluation of cage subsidence in standalone lateral lumbar interbody fusion: novel 3D-printed titanium versus polyetheretherketone (PEEK) cage

3D printed titanium banana interbody cages versus titanium-coated PEEK bullet cages for TLIF

INTRODUCTION

Lumbar degenerative spinal disease is a common, major cause of pain and disability. Titanium and polyetheretherketone (PEEK) are popular materials for interbody implants although evidence is mixed on which material is superior in terms of fusion and subsidence. The purpose of this study was to evaluate the clinical outcome of 3D printed titanium (3DPT) cages in patients undergoing TLIFs, as well as complication profiles based on widely used outcome metrics and reoperation events.

METHODS

A retrospective review was conducted for patients receiving 1- or 2-level TLIF at an academic medical center between January 2018 and May 2022. Patients were divided into two cohorts according to the material of interbody cage(s), either 3DPT banana or titanium-coated PEEK bullet. Radiographs, patient-reported outcome measures (PROMs), and complications were analyzed and compared. All included patients had radiographic and clinical follow-up of at least one year.

RESULTS

200 patients with 277 interbody cage-implanted levels were included. Patients received either 3DPT (n = 140) or PEEK (n = 60) interbody cages with 202 and 75 instrumented vertebral levels per cohort, respectively. At one year, the 3DPT cohort demonstrated a higher fusion rate of 93.3 % compared to the PEEK cohort's fusion rate of 73.2 % (p < 0.0001). Subsidence rates were 6.0 % and 25.0 % for the 3DPT and PEEK groups, respectively (p < 0.0001).

CONCLUSION

While 3DPT and PEEK interbody cages demonstrated few adverse events at short- and long-term follow-up, 3DPT exhibited a higher rate of fusion and lower rate of subsidence at one year.

A comprehensive review on the State of the Art in the research and development of poly-ether-ether-ketone (PEEK) biomaterial-based implants

Polyetheretherketone (PEEK) is a preferred high-performance polymer in the spine, orthopedic, and craniomaxillofacial implant industry. However, despite its commendable mechanical properties, its bioinert nature limits the implants from integrating with neighboring tissues, impacting the implant's long-term performance. To address this limitation, various kinds of surface functionalization techniques have been developed over the years. Noteworthy efforts have been made to incorporate bioactive fillers in the PEEK matrix to develop standalone bioactive composites. In personalized medicine, significant advances have been made in the 3D Printing of PEEK implants. 3D-printed PEEK implants are now being developed at Point-of-Care, significantly reducing manufacturing and logistic time. Given the recent clinical follow-up updates and advancements in PEEK-based implants, PEEK implants are witnessing an important phase in its history. Recognizing this vital phase, this paper aims to comprehensively review the advancements of PEEK implants over the past decade. The review starts with an overview of the clinical impact of varying PEEK implants, followed by PEEK's surface functionalization techniques and engineering of PEEK-based bioactive composites. Next, this review describes the advancements made in the 3D printing of PEEK implants and points out the essential considerations that should be considered when developing 3D-printed PEEK-based implants. Finally, the review ends with an estimated projection about the future of PEEK-based implants. Readers are expected to gain an all-encompassing and in-depth understanding of PEEK biomedical implants' past, present, and future, enabling researchers to advance the research and development of PEEK-based implants in the required direction. STATEMENT OF SIGNIFICANCE: PEEK is a preferred high-performance polymer in the implant industry, with notable benefits over metallic and ceramic implants, such as bone-matching stiffness and durability. Significant strides have been made in the last decade to make PEEK implants bioactive and utilize 3D Printing to develop patient-specific implants. Given the recent advancements in PEEK-based implants, this review aims to provide an all-encompassing and in-depth understanding of PEEK biomedical implants' past, present, and future. It will comprehensively discuss the know-how gained from the clinical follow-up, the strategies to address the limitations of PEEK implants, and the essential considerations in 3D Printing of PEEK implants. This review will enable researchers to advance the research and development of PEEK implants in the required direction.

Biomimetic Porous Ti6Al4V Implants: A Novel Interbody Fusion Cage via Gel-Casting Technique to Promote Spine Fusion

An interbody fusion cage (Cage) is crucial in spinal decompression and fusion procedures for restoring normal vertebral curvature and rebuilding spinal stability. Currently, these Cages suffer from issues related to mismatched elastic modulus and insufficient bone integration capability. Therefore, a gel-casting technique is utilized to fabricate a biomimetic porous titanium alloy material from Ti6Al4V powder. The biomimetic porous Ti6Al4V is compared with polyetheretherketone (PEEK) and 3D-printed Ti6Al4V materials and their respective Cages. Systematic validation is performed through mechanical testing, in vitro cell, in vivo rabbit bone defect implantation, and ovine anterior cervical discectomy and fusion experiments to evaluate the mechanical and biological performance of the materials. Although all three materials demonstrate good biocompatibility and osseointegration properties, the biomimetic porous Ti6Al4V, with its excellent mechanical properties and a structure closely resembling bone trabecular tissue, exhibited superior bone ingrowth and osseointegration performance. Compared to the PEEK and 3D-printed Ti6Al4V Cages, the biomimetic porous Ti6Al4V Cage outperforms in terms of intervertebral fusion performance, achieving excellent intervertebral fusion without the need for bone grafting, thereby enhancing cervical vertebra stability. This biomimetic porous Ti6Al4V Cage offers cost-effectiveness, presenting significant potential for clinical applications in spinal surgery.

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.

Evolution of Titanium Interbody Cages and Current Uses of 3D Printed Titanium in Spine Fusion Surgery

PURPOSE OF REVIEW

To summarize the history of titanium implants in spine fusion surgery and its evolution over time.

RECENT FINDINGS

Titanium interbody cages used in spine fusion surgery have evolved from solid metal blocks to porous structures with varying shapes and sizes in order to provide stability while minimizing adverse side effects. Advancements in technology, especially 3D printing, have allowed for the creation of highly customizable spinal implants to fit patient specific needs. Recent evidence suggests that customizing shape and density of the implants may improve patient outcomes compared to current industry standards. Future work is warranted to determine the practical feasibility and long-term clinical outcomes of patients using 3D printed spine fusion implants. Outcomes in spine fusion surgery have improved greatly due to technological advancements. 3D printed spinal implants, in particular, may improve outcomes in patients undergoing spine fusion surgery when compared to current industry standards. Long term follow up and direct comparison between implant characteristics is required for the adoption of 3D printed implants as the standard of care.

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.

Comparison of Lumbar Interbody Fusion with 3D-Printed Porous Titanium Cage Versus Polyetheretherketone Cage in Treating Lumbar Degenerative Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

To compare the safety and radiological effectiveness of lumbar interbody fusion with a 3D-printed porous titanium (3D-PPT) cage versus a polyetheretherketone (PEEK) cage for the treatment of lumbar degenerative disease.

METHODS

This study was registered at PROSPERO (CRD42023461511). We systematically searched the PubMed, Embase, and Web of Science databases for related studies from inception to September 3, 2023. Review Manager 5.3 was used to conduct this meta-analysis. The reoperation rate, complication rate, fusion rate, and subsidence rate were assessed using relative risk and 95% confidence intervals.

RESULTS

Ten articles reporting 9 studies comparing lumbar interbody fusion with 3D-PPT cages versus PEEK cages for the treatment of lumbar degenerative disease were included. The subsidence rate at the 1-year follow-up in the 3D-PPT cage was significantly lower than that in the PEEK cage. The fusion rate in the 3D-PPT cage was significantly higher than that in the PEEK cage at the 6-month follow-up. No significant difference was identified between the 2 groups at the 12-month follow-up. No significant difference was identified between the 2 groups in terms of the complication rate and reoperation rate. There was a trend toward a lower complication rate and reoperation rate with the 3D-PPT cage.

CONCLUSIONS

Compared with the PEEK cage, the 3D-PPT cage may be a safer implant. The 3D-PPT cage was associated with a higher fusion rate and lower subsidence rate. The 3D-PPT cage may accelerate the intervertebral fusion process, improve the quality of fusion and prevent the occurrence of subsidence.

Comparison of Long-term Follow-Up of n-HA PA66 Cage and PEEK Cage of Lumbar Interbody Fusion in Multi-level Degenerative Lumbar Diseases: A Stepwise Propensity Score Matching Analysis

OBJECTIVE

Previous studies have confirmed that the nanohydroxyapatite/polyamide-66 (n-HA/PA66) cage is an ideal alternative material for degenerative lumbar disease (DLD) comparable to the polyether ether ketone (PEEK) cage due to its similar radiographic fusion, subsidence rate, and clinical results. However, these studies were restricted to one-level surgery. The aim of this study was to analyze the long-term clinical and radiologic outcomes between n-HA PA66 cage and PEEK cage for patients with multi-level degenerative lumbar diseases (DLDs).

METHODS

We retrospectively reviewed all patients who underwent multi-level transforaminal lumbar interbody fusion (TLIF) from June 2010 to December 2016 with a minimum 6-year follow-up. Matched-pair analysis was performed using a 1-to-1 closest neighbor approach to match patients who received an n-HA PA66 cage with those who received a PEEK cage. Clinical outcomes and radiographic evaluations were compared between the two groups. The independent student's t-test and χ2 -test were applied to compare the differences between groups.

RESULTS

At the end of the propensity score matching (PSM) analysis, 48 patients from n-HA/PA66 group were matched to 48 patients in the PEEK group. No significant difference was observed in cage subsidence and bony fusion except for adjacent segment degeneration (ASD). The occurrence of ASD was 14.58% (7/48) in the n-HA/PA 66 group, which was significantly less than that in the PEEK group (33.33% [16/48]) (p = 0.031). Although the intervertebral space height (IH), segmental angle (SA) and lumbar lordosis (LL) significantly increased after surgery in both groups, there was no significant difference at any time point after surgery (p > 0.05). The visual analogue scale (VAS) and Oswestry disability index (ODI) scores significantly improved in both groups at 3m postoperative, 1y postoperative and at final follow-up. However, there were no significant differences in the VAS and ODI score at any time point (p > 0.05). The total complications and re-admission rate were not different between the two groups.

CONCLUSION

Overall, our data suggest that the outcomes of n-HA/PA66 cage group are comparable to those of the PEEK cage group, with a similar high fusion rate and low cage subsidence rate as PEEK cages, except its lower rate of ASD occurrence.

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.

Comparative Analysis of Radiologic Outcomes Between Polyetheretherketone and Three-Dimensional-Printed Titanium Cages After Transforaminal Lumbar Interbody Fusion

OBJECTIVE

Transforaminal lumbar interbody fusion (TLIF) is performed worldwide with polyetheretherketone (PEEK) and titanium (Ti) cages for the treatment of degenerative lumbar diseases. The aim of this study was to compare radiologic outcomes between a PEEK and three-dimensional-printed titanium (3DP-Ti) cage after TLIF with >1 year of follow-up.

METHODS

A total of 140 patients with degenerative lumbar diseases who underwent TLIF operation were included in this study. Intervertebral disc height and whole lumbar lordosis were measured and evaluated from the preoperative stage to the final follow-up. Subsidence of the cage was indicated if the cage sunk into the adjacent vertebral body or if there was a reduction in height of the fused segment by ≥3 mm during the postoperative follow-up. Migration of the cage was determined as the displacement of the interbody cage by ≥2 mm during the postoperative period. Fusion status was assessed at the 1 year and final follow-up using standard methods.

RESULTS

Both disc height and lumbar lordosis were well maintained throughout the study period, and no significant differences were observed between PEEK and 3DP-Ti groups. Both PEEK and 3DP-Ti cages demonstrated low rates of cage subsidence, with no significant difference was noted. A significant cage migration rate was observed in the PEEK group and the revision operation was required for 2 patients. The fusion rate of this study was not found to be statistically significant, although the 3DP-Ti cage was known to have an improved fusion rate than PEEK cage after lumbar interbody fusion.

CONCLUSIONS

Radiologic results suggest that the 3DP-Ti cage may be a better interbody cage for TLIF than is the PEEK cage.

Optimizing Spinal Fusion Cage Design to Improve Bone Substitute Filling on Varying Disc Heights: A 3D Printing Study

The success of spinal fusion surgery relies on the precise placement of bone grafts and minimizing scatter. This study aims to optimize cage design and bone substitute filling methods to enhance surgical outcomes. A 3D printed lumbar spine model was utilized to implant 3D printed cages of different heights (8 mm, 10 mm, 12 mm, and 14 mm) filled with BICERA® Bone Graft Substitute mixed with saline. Two filling methods, SG cage (side hole for grafting group, a specially designed innovative cage with side hole, post-implantation filling) and FP cage (finger-packing group, pre-implantation finger packing, traditional cage), were compared based on the weight of the implanted bone substitute. The results showed a significantly higher amount of bone substitute implanted in the SG cage group compared to the FP cage group. The quantity of bone substitute filled in the SG cage group increased with the height of the cage. However, in the FP cage group, no significant difference was observed between the 12 mm and 14 mm subgroups. Utilizing oblique lumbar interbody fusion cages with side holes for bone substitute filling after implantation offers several advantages. It reduces scatter and increases the amount of implanted bone substitute. Additionally, it effectively addresses the challenge of insufficient fusion surface area caused by gaps between the cage and endplates. The use of cages with side holes facilitates greater bone substitute implantation, ultimately enhancing the success of fusion. This study provides valuable insights for future advancements in oblique lumbar interbody fusion cage design, highlighting the effectiveness of using cages with side holes for bone substitute filling after implantation.

Subsidence of Interbody Cage Following Oblique Lateral Interbody Fusion: An Analysis and Potential Risk Factors

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

This study aimed to report the incidence and potential risk factors of polyetheretherketone (PEEK) cage subsidence following oblique lateral interbody fusion (OLIF) for lumbar degenerative diseases. We proposed also an algorithm to minimize subsidence following OLIF surgery.

METHODS

The study included a retrospective cohort of 107 consecutive patients (48 men and 59 women; mean age, 67.4 years) who had received either single- or multi-level OLIF between 2012 and 2019. Patients were classified into subsidence and non-subsidence groups. PEEK cage subsidence was defined as any violation of either endplate from the computed tomography scan in both sagittal and coronal views. Preoperative variables such as age, sex, body mass index, bone mineral density (BMD) measured by preoperative dual-energy X-ray absorptiometry, smoking status, corticosteroid use, diagnosis, operative level, multifidus muscle cross-sectional area, and multifidus muscle fatty degeneration were collected. Age-related variables (height and length) were also documented. Univariate and multivariate logistic regression analyses were used to analyze the risk factors of subsidence.

RESULTS

Of the 107 patients (137 levels), 50 (46.7%) met the subsidence criteria. Higher PEEK cage height had the strongest association with subsidence (OR = 9.59, P < .001). Other factors significantly associated with cage subsistence included age >60 years (OR = 3.15, P = .018), BMD <-2.5 (OR = 2.78, P = .006), and severe multifidus muscle fatty degeneration (OR = 1.97, P = .023).

CONCLUSIONS

Risk factors for subsidence in OLIF were age >60 years, BMD < -2.5, higher cage height, and severe multifidus muscle fatty degeneration. Patients who had subsidence had worse early (3 months) postoperative back and leg pain.

Polyetheretherketone development in bone tissue engineering and orthopedic surgery

Polyetheretherketone (PEEK) has been widely used in the medical field as an implant material, especially in bone tissue engineering and orthopedic surgery, in recent years. This material exhibits superior stability at high temperatures and is biosecured without harmful reactions. However, the chemical and biological inertness of PEEK still limits its applications. Recently, many approaches have been applied to improve its performance, including the modulation of physical morphology, chemical composition and antimicrobial agents, which advanced the osteointegration as well as antibacterial properties of PEEK materials. Based on the evolution of PEEK biomedical devices, many studies on the use of PEEK implants in spine surgery, joint surgery and trauma repair have been performed in the past few years, in most of which PEEK implants show better outcomes than traditional metal implants. This paper summarizes recent studies on the modification and application of biomedical PEEK materials, which provides further research directions for PEEK implants.

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.

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.

Changes in psoas and posterior paraspinal muscle morphology after standalone lateral lumbar interbody fusion: a quantitative MRI-based analysis

PURPOSE

Standalone lateral lumbar interbody fusion (SA-LLIF) without posterior instrumentation can be an alternative to 360° fusion in selected cases. This study aimed to investigate quantitative changes in psoas and paraspinal muscle morphology that occur on index levels after SA-LLIF.

METHODS

Patients undergoing single- or multi-level SA-LLIF at L2/3 to L4/5 who had preoperative and postoperative lumbar MRI scans, the latter performed between 3 and 18 months after surgery for any reason, were retrospectively included. Muscle measurements were performed of the psoas and posterior paraspinal muscles (PPM; erector spinae and multifidus) on index levels using manual segmentation and an automated pixel intensity threshold method to differentiate muscle from fat signal. Changes in the total cross-sectional area (TCSA), the functional cross-sectional area (FCSA), and the percentage of fat infiltration (FI) of these muscles were assessed.

RESULTS

A total of 67 patients (55.2% female, age 64.3 ± 10.6 years, BMI 26.9 ± 5.0 kg/m2) with 125 operated levels were included. Follow-up MRI scans were performed after an average of 8.7 ± 4.6 months, primarily for low back pain. Psoas muscle parameters did not change significantly, irrespective of the approach side. Among PPM parameters, the mean TCSA at L4/5 (+ 4.8 ± 12.4%; p = 0.013), and mean FI at L3/4 (+ 3.1 ± 6.5%; p = 0.002) and L4/5 (+ 3.0 ± 7.0%; p = 0.002) significantly increased.

CONCLUSION

Our study demonstrated that SA-LLIF did not alter psoas muscle morphology, underlining its minimally invasive nature. However, FI of PPM significantly increased over time despite the lack of direct tissue damage to posterior structures, suggesting a pain-mediated response and/or the result of segmental immobilization.

Biportal endoscopic extraforaminal lumbar interbody fusion using a 3D-printed porous titanium cage with large footprints: technical note and preliminary results

PURPOSE

The aim of this study was to introduce biportal endoscopic extraforaminal lumbar interbody fusion (BE-EFLIF), which involves insertion of a cage through a more lateral side as compared to the conventional corridor of transforaminal lumbar interbody fusion. We described the advantages and surgical steps of 3D-printed porous titanium cage with large footprints insertion through multi-portal approach, and preliminary results of this technique.

METHODS

This retrospective study included 12 consecutive patients who underwent BE-EFLIF for symptomatic single-level lumbar degenerative disease. Clinical outcomes, including a visual analog scale (VAS) for back and leg pain and the Oswestry disability index (ODI), were collected at preoperative months 1 and 3, and 6 months postoperatively. In addition, perioperative data and radiographic parameters were analyzed.

RESULTS

The mean patient age, follow-up period, operation time, and volume of surgical drainage were 68.3 ± 8.4 years, 7.6 ± 2.8 months, 188.3 ± 42.4 min, 92.5 ± 49.6 mL, respectively. There were no transfusion cases. All patients showed significant improvement in VAS and ODI postoperatively, and these were maintained for 6 months after surgery (P < 0.001). The anterior and posterior disc heights significantly increased after surgery (P < 0.001), and the cage was ideally positioned in all patients. There were no incidences of early cage subsidence or other complications.

CONCLUSIONS

BE-EFLIF using a 3D-printed porous titanium cage with large footprints is a feasible option for minimally invasive lumbar interbody fusion. This technique is expected to reduce the risk of cage subsidence and improve the fusion rate.

Vertebral Endplate Concavity in Lateral Lumbar Interbody Fusion: Tapered 3D-Printed Porous Titanium Cage versus Squared PEEK Cage

Background and Objectives: To prevent postoperative problems in extreme lateral interbody fusion (XLIF), it is critical that the vertebral endplate not be injured. Unintentional endplate injuries may depend on the cage. A novel porous titanium cage for XLIF has improved geometry with a tapered tip and smooth surface. We hypothesized that this new cage should lead to fewer endplate injuries. Materials and Methods: This retrospective study included 32 patients (mean 74.1 ± 6.7 years, 22 females) who underwent anterior and posterior combined surgery with XLIF for lumbar degenerative disease or adult spinal deformity from January 2018 to June 2022. A tapered 3D porous titanium cage (3DTi; 11 patients) and a squared PEEK cage (sPEEK; 21 patients) were used. Spinal alignment values were measured on X-ray images. Vertebral endplate concavity (VEC) was defined as concavity ≥ 1 mm of the endplate on computed tomography (CT) images, which were evaluated preoperatively and at 1 week and 3 months postoperatively. Results: There were no significant differences in the patient demographic data and preoperative and 3-month postoperative spinal alignments between the groups. A 3DTi was used for 25 levels and an sPEEK was used for 38 levels. Preoperative local lordotic angles were 4.3° for 3DTi vs. 4.7° for sPEEK (p = 0.90), which were corrected to 12.3° and 9.1° (p = 0.029), respectively. At 3 months postoperatively, the angles were 11.6° for 3DTi and 8.2° for sPEEK (p = 0.013). VEC was present in 2 levels (8.0%) for 3DTi vs. 17 levels (45%) for sPEEK (p = 0.002). After 3 months postoperatively, none of the 3DTi had VEC progression; however, eight (21%) levels in sPEEK showed VEC progression (p = 0.019). Conclusions: The novel 3DTi cage reduced endplate injuries by reducing the endplate load during cage insertion.

Biomechanical evaluation of two-level oblique lumbar interbody fusion combined with posterior four-screw fixation：A finite element analysis

OBJECTIVE

By constructing the three-dimensional finite element model of two-level OLIF lumbar spine, the aim of this study was to demonstrate the feasibility and effectiveness of posterior four-screw fixation for treatment of two-level lumbar degenerative diseases from the perspective of biomechanics.

METHODS

An intact L3-S1 segment nonlinear lumbar finite element model (M0) was constructed from the CT scanning data of a healthy adult. After verification, two-level OLIF procedure were simulated, and three patterns of finite element analysis models were constructed: two-level stand-alone OLIF group (M1), two-level OLIF + four-screw fixation group (M2) and two-level OLIF + six-screw fixation group (M3). Range of motion, stress of the cage, and stress of fixation were evaluated in the different models.

RESULTS

Under various motion modes，the ROM of M2 and M3 were significantly lower than those of M1. The ROM reduction of M2 relative to M1 was much greater than that of M3 relative to M2. Moreover, the peak von Mises stresses of endplates in M2 were almost the same as those in M3. In terms of the maximum stresses of cages, M2 and M3 were essentially identical. Besides, the maximum stresses of posterior instrumentation in M2 and M3 were similar, which were mainly concentrated at the root of pedicle screws.

CONCLUSION

There were no significant differences between M2 and M3 from the biomechanical analysis. In two-level OLIF, posterior four-screw fixation can replace six-screw fixation, which reduces surgical trauma and decreases economic burden of patients, and will be a cost-effective alternative.

The predictive value of psoas and paraspinal muscle parameters measured on MRI for severe cage subsidence after standalone lateral lumbar interbody fusion

BACKGROUND CONTEXT

The effect of psoas and paraspinal muscle parameters on cage subsidence after minimally invasive techniques, such as standalone lateral lumbar interbody fusion (SA-LLIF), is unknown.

PURPOSE

This study aimed to determine whether the functional cross-sectional area (FCSA) of psoas and lumbar spine extensor muscles (multifidus and erector spinae), and psoas FCSA normalized to the vertebral body area (FCSA/VBA) differ among levels with severe cage subsidence after SA-LLIF when compared to levels without severe cage subsidence.

STUDY DESIGN

Retrospective single center cohort study.

PATIENT SAMPLE

Patients who underwent SA-LLIF between 2008 and 2020 for degenerative conditions using exclusively polyetheretherketone (PEEK) cages, had a lumbar magnetic resonance imaging (MRI) scan within 12 months, a lumbar computed tomography (CT) scan within 6 months prior to surgery, and a postoperative clinical and radiographic follow-up at a minimum of 6 months were included.

OUTCOME MEASURES

Severe cage subsidence.

METHODS

MRI measurements included psoas and combined multifidus and erector spinae (paraspinal) FCSA and FCSA/VBA at the L3-L5 pedicles. Following manual segmentation of muscles on axial T2-weighted images using ITK-SNAP (version 3.8.0), the FCSA was calculated using a custom written program on Matlab (version R2019a, The MathWorks, Inc.) that used an automated pixel intensity threshold method to differentiate between fat and muscle. Mean volumetric bone mineral density (vBMD) at L1/2 was measured by quantitative CT. The primary endpoint was severe cage subsidence per level according to the classification by Marchi et al. Multivariable logistic regression analysis was performed using generalized linear mixed models. All analyses were stratified by biological sex.

RESULTS

95 patients (45.3% female) with a total of 188 operated levels were included in the analysis. The patient population was 92.6% Caucasian with a median age at surgery of 65 years. Overall subsidence (Grades 0-III) was 49.5% (53/107 levels) in men versus 58.0% (47/81 levels) in women (p=.302), and severe subsidence (Grades II-III) was 22.4% (24/107 levels) in men versus 25.9% (21/81 levels) in women (p=.608). In men, median psoas FCSA and psoas FCSA/VBA at L3 and L4 were significantly greater in the severe subsidence group when compared to the non-severe subsidence group. No such difference was observed in women. Paraspinal muscle parameters did not differ significantly between non-severe and severe subsidence groups for both sexes. In the multivariable logistic regression analysis with adjustments for vBMD and cage length, psoas FCSA at L3 (OR 1.002; p=.020) and psoas FCSA/VBA at L3 (OR 8.655; p=.029) and L4 (OR 4.273; p=.043) were found to be independent risk factors for severe cage subsidence in men.

CONCLUSIONS

Our study demonstrated that greater psoas FCSA at L3 and psoas FCSA/VBA at L3 and L4 were independent risk factors for severe cage subsidence in men after SA-LLIF with PEEK cages. The higher compressive forces the psoas exerts on lumbar segments as a potential stabilizer might explain these findings. Additional pedicle screw fixation might be warranted in these patients to avoid severe cage subsidence.

Endplate volumetric bone mineral density biomechanically matched interbody cage

Disc degenerative problems affect the aging population, globally, and interbody fusion is a crucial surgical treatment. The interbody cage is the critical implant in interbody fusion surgery; however, its subsidence risk becomes a remarkable clinical complication. Cage subsidence is caused due to a mismatch of material properties between the bone and implant, specifically, the higher elastic modulus of the cage relative to that of the spinal segments, inducing subsidence. Our recent observation has demonstrated that endplate volumetric bone mineral density (EP-vBMD) measured through the greatest cortex-occupied 1.25-mm height region of interest, using automatic phantomless quantitative computed tomography scanning, could be an independent cage subsidence predictor and a tool for cage selection instruction. Porous design on the metallic cage is a trend in interbody fusion devices as it provides a solution to the subsidence problem. Moreover, the superior osseointegration effect of the metallic cage, like the titanium alloy cage, is retained. Patient-specific customization of porous metallic cages based on the greatest subsidence-related EP-vBMD may be a good modification for the cage design as it can achieve biomechanical matching with the contacting bone tissue. We proposed a novel perspective on porous metallic cages by customizing the elastic modulus of porous metallic cages by modifying its porosity according to endplate elastic modulus calculated from EP-vBMD. A three-grade porosity customization strategy was introduced, and direct porosity-modulus customization was also available depending on the patient's or doctor's discretion.

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.

Subsidence after lateral lumbar interbody fusion using a 3D-printed porous titanium interbody cage: single-institution case series

OBJECTIVE

Cage subsidence is a well-known phenomenon after lateral lumbar interbody fusion (LLIF), occurring in 10%-20% of cases. A 3D-printed porous titanium (pTi) cage has a stiffness that mimics the modulus of elasticity of native vertebrae, which reduces stress at the bone-hardware interface, lowering the risk of subsidence. In this study, the authors evaluated their institutional rate of subsidence and resultant reoperation in patients who underwent LLIF using a 3D-printed pTi interbody cage.

METHODS

This is a retrospective case series of consecutive adult patients who underwent LLIF using pTi cages from 2018 to 2020. Demographic and clinical characteristics including age, sex, bone mineral density, smoking status, diabetes, steroid use, number of fusion levels, posterior instrumentation, and graft size were collected. The Marchi subsidence grade was determined at the time of last follow-up. Outcome measures of interest were subsidence and resultant reoperation. Univariable logistic regression analysis was performed to assess the extent to which clinical and operative characteristics were associated with Marchi grade I-III subsidence. Significance was assessed at p < 0.05.

RESULTS

Fifty-five patients (38 with degenerative disc disease and 17 with adult spinal deformity) were treated with 97 pTi interbody cages with a mean follow-up of 18 months. The mean age was 63.6 ± 10.1 years, 60% of patients were female, and 36% of patients had osteopenia or osteoporosis. Patients most commonly underwent single-level LLIF (58.2%). Sixteen patients (29.1%) had posterior instrumentation. The subsidence grade distribution was as follows: 89 (92%) grade 0, 5 (5%) grade I, 2 (2%) grade II, and 1 (1%) grade III. No patients who were active or prior smokers and no patients with posterior instrumentation experienced graft subsidence. No clinical or operative characteristics were significantly associated with graft subsidence. One patient (1.8%) required reoperation because of subsidence.

CONCLUSIONS

In this institutional case series, subsidence of pTi intervertebral cages after LLIF occurred in 8% of operated levels, 3% of which were grade II or III. Only 1 patient required reoperation. These reported rates are lower than those reported for polyetheretherketone implants. Further studies are necessary to compare the impact of these cage materials on subsidence after LLIF.

[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.

Early Outcomes of 3D-printed Porous Titanium versus Polyetheretherketone (PEEK) Cage Implantation for Standalone Lateral Lumbar Interbody Fusion in the Treatment of Symptomatic Adjacent Segment Degeneration

OBJECTIVE

This study compared outcomes of 3D-printed porous titanium (Ti) versus polyetheretherketone (PEEK) cage implantation for standalone lateral lumbar interbody fusion (SA-LLIF) in the treatment of symptomatic adjacent segment degeneration (ASD).

METHODS

44 patients (59 levels) underwent SA-LLIF with Ti or PEEK cages between 10/2016 and 07/2020. The primary outcome was cage subsidence according to Marchi et al. Secondary outcomes included revision/recommendations for revision surgery, back/leg pain severity, changes in disc/foraminal height and global/segmental lumbar lordosis.

RESULTS

44 patients (21 female) were included with a mean age at surgery of 61.8±11.5 years, average radiological follow-up of 12.5±8.2 and clinical follow-up of 11.0±7.1 months. The overall subsidence rate was significantly less in the Ti versus PEEK group (20% vs. 58.8%; p=0.004). Revision was recommended to none of the patients in the Ti and 3 in the PEEK group (p=0.239). Furthermore, patients in the Ti group showed significantly better improvement in back pain NRS score (p=0.001). Disc height (p<0.001) and foraminal height restoration (p=0.011) were statistically significant in the Ti group, whereas only disc height restoration was significant in the PEEK group (p=0.003).

CONCLUSION

In patients undergoing SA-LLIF for ASD treatment, 3D-printed Ti cages had significantly lower overall subsidence rate compared to PEEK cages. Furthermore, Ti cages resulted in fewer recommendations for revision surgery. Whether greater pain reduction in the Ti group is associated with earlier or higher fusion rates needs to be further elucidated.

Development of a decision-making pathway for utilizing standalone lateral lumbar interbody fusion

PURPOSE

To develop a decision-making pathway for primary SA-LLIF. Furthermore, we analyzed the agreement of this pathway and compared outcomes of patients undergoing either SA-LLIF or 360-LLIF.

METHOD

A decision-making pathway for SA-LLIF was created based on the results of interviews/surveys of senior spine surgeons with over 10 years of experience. Internal validity was retrospectively evaluated using consecutive patients undergoing either SA-LLIF or 360-LLIF between 01/2018 and 07/2020 with 3D-printed Titanium cages. An outcome assessment looking primarily at revision surgery and secondary at cage subsidence, changes in disk and foraminal height, global and segmental lumbar lordosis, duration of surgery, estimated blood loss, and length of stay was carried out.

RESULTS

78 patients with 124 treated levels (37 SA-LLIF, 41 360-LLIF) were retrospectively analyzed. The pathway showed a direct agreement (SA-LLIF) of 100.0% and an indirect agreement (360-LLIF) of 95.1%. Clinical follow-up averaged 13.5 ± 6.5 months including 4 revision surgeries in the 360-LLIF group and none in the SA-LLIF group (p = 0.117). Radiographic follow-up averaged 9.5 ± 4.3 months, with no statistically significant difference in cage subsidence rate between the groups (p = 0.440). Compared to preoperative images, patients in both groups showed statistically significant changes in disk height (p < 0.001), foraminal height (p < 0.001), as well as restoration of segmental lordosis (p < 0.001 and p = 0.018). The SA-LLIF group showed shorter duration of surgery, less estimated blood loss and shorter LOS (p < 0.001).

CONCLUSION

The proposed decision-making pathway provides a guide to adequately select patients for SA-LLIF. Further studies are needed to assess the external applicability and validity.

LEVEL OF EVIDENCE III

Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.