Outcome of Ti/PEEK Versus PEEK Cages in Minimally Invasive Transforaminal Lumbar Interbody Fusion

Definition of cage subsidence in transforaminal lumbar interbody fusion (TLIF) approach and posterior lumbar interbody fusion (PLIF) approach - A systematic review

BACKGROUND

Although cage subsidence is one of the most common phenomenona associated with interbody fusions and was characterized more than 70 years ago, a standardized method for its measurement, detection, and reporting among different lumbar fusion procedures does not exist. Here, we review previously published literature on cage subsidence to present the most common methods for defining subsidence in the posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) techniques.

METHODS

A search was completed in PubMed and Embase with inclusion criteria focused on identifying any study that provided descriptions of the method, imaging modality, and subsidence threshold used to define the presence of cage subsidence in study articles published between January 1, 2001 and December 31, 2022.

RESULTS

A total of 54 studies were included in the final analysis. Among them, 32 (59.2 %) reported on TLIF, 20 (37.1 %) reported on PLIF, and 2 studies (3.7 %) reported on both approaches. For TLIF and PLIF procedures, the preferred method to determine subsidence was cage migration into the vertebral bodies rather than changes in disc height. In the TLIF group, the predominant criteria for defining subsidence were thresholds of ≥ 2 mm and > 2 mm utilized in each of 10 of the 34 studies (58.8 %). Similarly, in the PLIF group, the common criterion for defining subsidence was also ≥ 2 mm, observed in 5 of 22 studies (22.7 %), with > 2 mm observed in 4 studies (18.2 %). The methods for assessing cage migration or disc height change varied substantially among studies, with none of the measurements being consistently applied in more than 50 % of the studies.

CONCLUSIONS

Inconsistency persists in the methods used to determine, report, or measure the degree of subsidence. Surgeons and researchers should standardize these methods to ensure consistency and generalizability in reporting and studying subsidence.

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.

Retrospective analysis of medium-term outcomes following anterior lumbar interbody fusion surgery performed in a tertiary spinal surgical centre

INTRODUCTION

Anterior lumbar interbody fusion (ALIF) can treat spondylolisthesis, degenerative disc disease and pseudoarthrosis. This approach facilitates complete discectomy, disc space distraction, indirect decompression of neural foramina and placement of large interbody devices. Several intra- and postoperative complications can be attributed to the anterior approach: vascular/visceral injury, hypogastric plexus injury and urogenital consequences. Spine-specific complications include implant migration, graft failure, pseudoarthrosis and persistent symptomology.

METHODS

This retrospective study reviewed patient demographics, medium-term outcomes and complication rates following ALIF surgery performed over a 5-year period. A total of 110 consecutive patients had undergone ALIF surgery at a single tertiary spinal centre. The database was reviewed with a primary outcome of identifying postoperative 90-day complications and whether a revision anterior operation was required after primary ALIF.

RESULTS

No patients required revision anterior operation after their primary ALIF surgery by final follow-up. Out of 110 patients, 11 (10%) recorded a complication attributed to the anterior stage of their operation within 90 days.

CONCLUSIONS

Our 90-day complication rate of 10% lies within the 2.6% acute complication and 40% overall complications rates described in previous literature. The risk of vascular/visceral injury is significant (3%) and we recommend that ALIF be performed as a dual surgeon procedure with a vascular-trained access surgeon accompanying the spinal surgeon. ALIF is a valid revision surgical option for failed posterior approaches leading to complications such as pseudoarthrosis. In our sample, 89% of patients were managed with posterior fixation to augment the anterior fusion as, biomechanically, this is a proven construct.

Synergistic Effect of Nano Strontium Titanate Coating and Ultraviolet C Photofunctionalization on Osteogenic Performance and Soft Tissue Sealing of poly(ether-ether-ketone)

This study aimed to evaluate the bioactivity of poly(ether ether ketone) (PEEK) after surface modification by persistent photoconductive strontium titanate (SrTiO3) magnetron sputtering and ultraviolet (UV) C irradiation. According to the different modifications, the PEEK specimens were randomly divided into five groups (n = 38/group): PEEK, Sr100-PEEK, Sr200-PEEK, UV/PEEK, and UV/Sr200-PEEK. Then, the specimens of Sr100-PEEK and Sr200-PEEK groups were, respectively, coated with 100 and 200 nm thickness photocatalyst SrTiO3 on the PEEK surface by magnetron sputtering. Subsequently, UV-C light photofunctionalized the specimens of PEEK and Sr200-PEEK groups to form UV/PEEK and UV/Sr200-PEEK groups. The specimens were characterized by a step meter, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), and a water contact angle meter. The release test of the Sr ion was performed by inductively coupled plasma mass spectrometry (ICP-MS). In vitro study, osteogenic activity (MC3T3-E1 osteoblast-like cells) and epithelial and connective tissue attachment (gingival epithelial cells GE1 and fibroblasts NIH3T3) were analyzed in five groups. Surface morphology of the specimens was changed after coating, and the Sr content on the Sr-PEEK surface was increased with increasing coating thickness. In addition, the contact angle was increased significantly after magnetron sputtering. After UV-C photofunctionalization, the content of surface elements changed and the contact angle was decreased. The release of Sr ion was sustained, and the final cumulative release amount did not exceed the safety limit. In vitro experiments showed that SrTiO3 improved the cell activity of MC3T3-E1 and UV-C irradiation further enhanced the osteogenic performance of PEEK. Besides, UV-C irradiation also significantly promoted the cell viability, development, and expression of adhesion proteins of GE1 and NIH3T3 on PEEK. The present investigation demonstrated that nano SrTiO3 coating with UV-C photofunctionalization synergistically enhanced the osteogenic properties and soft tissue sealing function of PEEK in vitro.

Clinical and radiological results of TLIF surgery with titanium-coated PEEK or uncoated PEEK cages: a prospective single-centre randomised study

BACKGROUND

A comparison of fusion rates and clinical outcomes of instrumented transforaminal interbody fusion (TLIF) between polyetheretherketone (PEEK) and titanium-coated PEEK (Ti-PEEK) cages is not well documented.

METHODS

A single-centre, prospective, randomised study included patients who underwent one-level TLIF between L3-S1 segments. Patients were randomised into one of two groups: TLIF surgery with the PEEK cage and TLIF surgery with the Ti-PEEK cage. Clinical results were measured. All patients were assessed by repeated X-rays and 3D CT scans. Cage integration was assessed using a modified Bridwell classification. The impact of obesity and smoking on fusion quality was also analysed. Patients in both groups were followed up for 2 years.

RESULTS

Altogether 87 patients were included in the study: of these 87 patients, 81 (93.1%) completed the 2-year follow-up. A significant improvement in clinical outcome was found in the two measurements scales in both groups (RM: p = 0.257, VAS: p = 0.229). There was an increase in CobbS and CobbL angle in both groups (p = 0.172 for CobbS and p = 0.403for CobbL). Bony fusion was achieved in 37 of 40 (92.5%) patients in the TiPEEK group and 35 of 41 (85.4%) in the PEEK group (p = 0.157). Cage subsided in 2 of 40 patients (5%) in the TiPEEK group and 11 of 41 (26.8%) in the PEEK group (p = 0.007). Body mass index > 30 and smoking were not predictive factors of bony fusion achievement.

CONCLUSION

There is no significant advantage of TiPEEK cages over PEEK cages in clinical outcome and fusion rate 2 years after surgery.

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.

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.

Research and Application of Medical Polyetheretherketone as Bone Repair Material

Polyetheretherketone (PEEK) can potentially be used for bone repair because its elastic modulus is similar to that of human natural bone and good biocompatibility and chemical stability. However, its hydrophobicity and biological inertness limit its application in the biomedical field. Inspired by the composition, structure, and function of bone tissue, many strategies are proposed to change the structure and functionality of the PEEK surface. In this review, the applications of PEEK in bone repair and the optimization strategy for PEEK's biological activity are reviewed, which provides a direction for the development of multifunctional bone repair materials in the future.

Titanium‑coated polyetheretherketone cages vs. polyetheretherketone cages in lumbar interbody fusion: A systematic review and meta‑analysis

Fusion material is one of the key factors in the success of lumbar interbody fusion surgery. The present meta-analysis compared the safety and efficacy of titanium-coated (Ti) polyetheretherketone (PEEK) and PEEK cages. Published literature on the use of Ti-PEEK and PEEK cages in lumbar interbody fusion was systematically searched on Embase, PubMed, Central, Cochrane Library, China National Knowledge Infrastructure and Wanfang databases. A total of 84 studies were retrieved and seven were included in the present meta-analysis. Literature quality was assessed using the Cochrane systematic review methodology. After data extraction, meta-analysis was performed using the ReviewManager 5.4 software. Meta-analysis showed that, compared with that in the PEEK cage group, the Ti-PEEK cage group showed a higher interbody fusion rate at 6 months postoperatively (95% CI, 1.09-5.60; P=0.03) and improved Oswestry Disability Index (ODI) scores at 3 months postoperatively [95% CI, -7.80-(-0.62); P=0.02] and visual analog scale (VAS) scores of back pain at 6 months postoperatively [95% CI, -0.8-(-0.23); P=0.0008]. However, there were no significant differences in intervertebral bone fusion rate (12 months after surgery), cage subsidence rate, ODI score (6 and 12 months after surgery) or VAS score (3 and 12 months after surgery) between the two groups. The results of the meta-analysis showed that the Ti-PEEK group had an improved interbody fusion rate and higher postoperative ODI score in the early postoperative period (≤6 months).

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

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

An update of interbody cages for spine fusion surgeries: from shape design to materials

INTRODUCTION

Discectomy and interbody fusion are widely used in the treatment of intervertebral disc-related diseases. Among them, the interbody cage plays a significant role. However, the complications related to the interbody cage, such as nonunion or pseudoarthrosis, subsidence, loosening, and prolapse of the cage, cannot be ignored. By changing the design and material of the interbody fusion cage, a better fusion effect can be obtained, the incidence of appeal complications can be reduced, and the quality of life of patients after interbody fusion can be improved.

AREAS COVERED

This study reviewed the research progress of cage design and material and discussed the methods of cage design and material to promote intervertebral fusion.

EXPERT OPINION

Current treatment of cervical and lumbar degenerative disease requires interbody fusion to maintain decompression and to promote fusion and reduce the incidence of fusion failure through improvements in implant material, design, internal structure, and function. However, interbody fusion is not an optimal solution for treating vertebral instability.Abbreviations: ACDF, Anterior cervical discectomy and fusion; ALIF, anterior lumbar interbody fusion; Axi-aLIF, axial lumbar interbody fusion; BAK fusion cage, Bagby and Kuslich fusion cage; CADR, cervical artificial disc replacement; DBM, decalcified bone matrix; HA, hydroxyapatite; LLIF/XLIF, lateral or extreme lateral interbody fusion; MIS-TLIF, minimally invasive transforaminal lumbar interbody fusion; OLIF/ATP, oblique lumbar interbody fusion/anterior to psoas; PEEK, Poly-ether-ether-ketone; PLIF, posterior lumbar interbody fusion; ROI-C, Zero-profile Anchored Spacer; ROM, range of motion; SLM, selective melting forming; TLIF, transforaminal lumbar interbody fusion or.

Evolution of polyetheretherketone (PEEK) and titanium interbody devices for spinal procedures: a comprehensive review of the literature

INTRODUCTION

Interbody fusion is commonly utilized for arthrodesis and stability among patients undergoing spine surgery. Over the last few decades, interbody device materials, such as titanium and polyetheretherketone (PEEK), have been replacing traditional autografts and allografts for interbody fusion. As such, with the exponential growth of bioengineering, a large variety cage surface technologies exist. Different combinations of cage component materials and surface modifications have been created to optimize interbody constructs for surgical use. This review aims to provide a comprehensive overview of common surface technologies, their performance in the clinical setting, and recent modifications and material combinations.

MATERIALS AND METHODS

We performed a comprehensive review of the literature on titanium and PEEK as medical devices between 1964 and 2021. We searched five major databases, resulting in 4974 records. Articles were screened for inclusion manually by two independent reviewers, resulting in 237 articles included for review.

CONCLUSION

Interbody devices have rapidly evolved over the last few decades. Biomaterial and biomechanical modifications have allowed for continued design optimization. While titanium has a high osseointegrative capacity, it also has a high elastic modulus and is radio-opaque. PEEK, on the other hand, has a lower elastic modulus and is radiolucent, though PEEK has poor osseointegrative capacity. Surface modifications, material development advancements, and hybrid material devices have been utilized in search of an optimal spinal implant which maximizes the advantages and minimizes the disadvantages of each interbody material.