Polyetheretherketone (PEEK) cages in cervical applications: a systematic review

Biomechanical Comparison of a Novel PEEK Tibial Cortical Suspension Device With 6 Metallic Femoral Cortical Suspension Devices Used in Anterior Cruciate Ligament Reconstruction

Background

Conventional cortical suspensory fixation devices (CSFDs) are made of metal. Most adjustable-loop CSFDs originally intended for femoral-side fixation are also used on the tibial side during "all-inside" anterior cruciate ligament (ACL) reconstruction. The T-Button-A is a novel adjustable-loop polyether ether ketone (PEEK) CSFD intended specifically for tibial-side fixation during ACL reconstruction using the "full-tunnel" technique.

Purpose/Hypothesis

The purpose of this study was to compare the biomechanical characteristics of the T-Button-A with those of 6 commercially available fixed- or adjustable-loop CSFDs. It was hypothesized that the T-Button-A would be comparable with conventional metallic CSFDs intended for femoral-side fixation in terms of its biomechanical properties.

Study Design

Controlled laboratory study.

Methods

Ten implants each, of T-Button-A, Tightrope RT, Proloop Ultra, Procinch RT, Infinity, Infiloop, and Endobutton CL Ultra were biomechanically tested using an axial and torsion testing machine, and an incremental load-based testing protocol comprising 3500 cycles. Elongation and load to failure on cyclic and pull-to-failure loading, respectively, were recorded for each implant and compared across all devices. The consistency of implants in completing the 3500 test cycles, and demonstrating cyclic elongation <3 mm as well as load to failure >650 N, was compared across the tested devices.

Results

The T-Button-A demonstrated a mean elongation of 2.09 ± 0.43 mm, which was less than that of Infinity (P = .007), but comparable with the rest of the devices. Its mean load to failure was 1370.02 N ± 110.11 N, which was greater than that of Tightrope RT (P = .02), Infinity (P < .001), and Endobutton CL Ultra (P = .03), less than that of Procinch RT (P = .002), and comparable with that of Proloop Ultra and Infiloop. All 10 T-Button-A, Tightrope RT, Proloop Ultra, Infiloop, and Endobutton CL Ultra consistently completed the testing protocol and delivered elongation and load-to-failure values <3 mm and >650 N, respectively.

Conclusion

The biomechanical performance of the T-Button-A is comparable with most fixed- and adjustable-loop metallic CSFDs and is beyond what is considered acceptable to support ACL reconstruction grafts during early postoperative rehabilitation.

Clinical Relevance

The PEEK T-Button-A is a viable alternative to conventional metallic CSFDs, for tibial-side fixation during ACL reconstruction.

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

Bone Regeneration and Polyetheretherketone Implants in Maxillo-Facial Surgery and Neurosurgery: A Multidisciplinary Study

Polyetheretherketone (PEEK) in the last few years has emerged as an exceedingly promising material for craniofacial defects due to its biocompatibility and mechanical properties. However, its utilization remains controversial due to its inertness and low osteoinductivity. This study aimed to investigate the postoperative outcomes of patients undergoing maxillo-facial and neurosurgical procedures with PEEK implants. The focus is on evaluating bone regrowth on the surface and edges of the implant, periosteal reactions, and implant positioning. A retrospective analysis of 12 maxillo-facial surgery patients and 10 neurosurgery patients who received PEEK implants was conducted. CT scans performed at least one year post operation were examined for bone regrowth, periosteal reactions, and implant positioning. In maxillo-facial cases, the analysis included mandibular angle and fronto-orbital reconstruction, while neurosurgical cases involved cranioplasty. In maxillofacial surgery, 11 out of 12 patients showed radiological evidence of bone regrowth around PEEK implants, with favorable outcomes observed in craniofacial reconstruction. In neurosurgery, 9 out of 10 patients exhibited minimal or none bone regrowth, while one case demonstrated notable bone regeneration beneath the PEEK implant interface. The study highlights the importance of implant design and patient-specific factors in achieving successful outcomes, providing valuable insights for future implant-based procedures.

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.

Mechano-driven intervertebral bone bridging via oriented mechanical stimulus in a twist metamaterial cage: An in silico study

Stiffer cages provide sufficient mechanical support but fail to promote bone ingrowth due to stress shielding. It remains challenging for fusion cage to satisfy both bone bridging and mechanical stability. Here we designed a fusion cage based on twist metamaterial for improved bone ingrowth, and proved its superiority to the conventional diagonal-based cage in silico. The fusion process was numerically reproduced via an injury-induced osteogenesis model and the mechano-driven bone remodeling algorithm, and the outcomes fusion effects were evaluated by the morphological features of the newly-formed bone and the biomechanical behaviors of the bone-cage composite. The twist-based cages exhibited oriented bone formation in the depth direction, in comparison to the diagonal-based cages. The axial stiffness of the bone-cage composites with twist-based cages was notably higher than that with diagonal-based cages; meanwhile, the ranges of motion of the twist-based fusion segment were lower. It was concluded that the twist metamaterial cages led to oriented bone ingrowth, superior mechanical stability of the bone-cage composite, and less detrimental impacts on the adjacent bones. More generally, metamaterials with a tunable displacement mode of struts might provide more design freedom in implant designs to offer customized mechanical stimulus for osseointegration.

Clinical and radiological outcomes of non-window-type bioactive glass-ceramic cage in single-level ACDF versus PEEK cage filled with autologous bone

Bioactive glass-ceramic (BGC) cage is a substitute for polyether ether ketone (PEEK) cages in anterior cervical discectomy and fusion (ACDF). Only a few comparative studies exist using PEEK and non-window-type BGC cages (CaO-SiO2-P2O5-B2O3) in single-level ACDF. This study compared PEEK cages filled with autologous iliac bone grafts and BGC cages regarding clinical safety and effectiveness. A retrospective case series was performed on 40 patients who underwent single-level ACDF between October 2020 and July 2021 by a single orthopedic spine surgeon. The spacers used in each ACDF were a PEEK cage with a void filled with an autologous iliac bone graft and a non-window-type BGC cage in 20 cases. The grafts were compared pre-operatively and post-operatively at 6 weeks and 3, 6, and 12 months. Post-operative complications were investigated in each group. Clinical outcome was measured, including Visual Analog Scale (VAS) scores of neck and arm pains, Japanese Orthopedic Association score (JOA), and Neck Disability Index (NDI). Dynamic lateral radiographs were used to assess the inter-spinous motion (ISM) between the fusion segment and subsidence. The fusion status was evaluated using a computed tomography (CT) scan. Overall, 39 patients (19 and 20 patients in the PEEK and BGC groups, respectively) were recruited. Eighteen (94.7%) and 19 (95.0%) patients in the PEEK and BGC groups, respectively, were fused 12 months post-operatively, as assessed by ISM in dynamic lateral radiograph and bone bridging formation proven in CT scan. The PEEK and BGC groups showed substantial improvement in neck and arm VAS, JOA, and NDI scores. No substantial difference was found in clinical and radiological outcomes between the PEEK and BGC groups. However, the operation time was considerably shorter in the BGC group than in the PEEK group. In conclusion, a non-window-type BCG cage is a feasible substitute for a PEEK cage with an autologous iliac bone graft in single-level ACDF.

A Comparison between Structural Allografts and Polyetheretherketone Interbody Spacers Used in Anterior Cervical Discectomy and Fusion: A Systematic Review and Meta-analysis

Among interbody implants used during anterior cervical discectomy and fusion (ACDF), structural allografts and polyetheretherketone (PEEK) are the most used spacers. Currently, no consensus has been established regarding the superiority of either implant, with US surgeons preferring structural allografts, whereas UK surgeons preferring PEEK. The purpose of this systematic review (level of evidence, 4) was to compare postoperative and patient-reported outcomes between the use of structural allografts PEEK interbody spacers during ACDF. Five electronic databases (PubMed, Embase, Scopus, Web of Science, and Cochrane) were searched for articles comparing the usage of structural allograft and PEEK interbody spacers during ACDF procedures from inception to April 10, 2023. The searches were conducted using the keywords "Spine," "Allograft," and "PEEK" and were performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines. Subsequent quality and sensitivity analyses were performed on the included studies. Nine studies involving 1,074 patients were included. Compared with the PEEK group, the structural allograft group had comparable rates of postoperative pseudoarthrosis (p=0.58). However, when stratified according to the number of levels treated, the 3-level ACDF PEEK group was 3.45 times more likely to have postoperative pseudoarthrosis than the structural allograft group (p=0.01). Subsequent postoperative outcomes (rate of subsidence and change in the preoperative and postoperative segmental disc heights) were comparable between the PEEK and structural allograft groups. Patient-reported outcomes (Visual Analog Scale [VAS] of neck pain and Neck Disability Index [NDI]) were comparable. This study showed that for 3-level ACDFs, the use of structural allografts may confer higher fusion rates. However, VAS neck pain, NDI, and subsidence rates were comparable between structural allografts and PEEK cages. In addition, no significant difference in pseudoarthrosis rates was found between PEEK cages and structural allografts in patients undergoing 1- and 2-level ACDFs.

Mapping Subchondral Bone Density Distribution in the Canine C6-C7 Vertebral Endplates: A CT-OAM Study

Intervertebral cage subsidence is a common complication in treating disc-associated cervical spondylomyelopathy in dogs. The mechanical stability of the vertebral endplate in contact with the cage is crucial to preventing subsidence. This study aims to assess subchondral bone mineral density (sBMD) in the canine vertebral endplate (specifically, the C6-C7 vertebral motion unit) as a measure of its mechanical stability. The sBMD distribution was mapped for the C6 caudal and C7 cranial vertebral endplates in 15 middle- to large-breed dogs using computed tomography osteoabsorptiometry. The sBMD distribution in the canine C6 and C7 vertebral endplates exhibited a heterogeneous pattern, with lower density observed in the central and dorsal contact areas of the nucleus pulposus, where common subsidence occurs. Our results suggest a potential need to redesign intervertebral cages to ensure that contact areas align with regions of higher bone density. A broad-based design extending toward the lateral and dorsal aspects of the annulus fibrosus contact area may enhance stability.

3D-Printed PEEK/Silicon Nitride Scaffolds with a Triply Periodic Minimal Surface Structure for Spinal Fusion Implants

The issue of spine-related disorders is a global healthcare concern that requires effective solutions to restore normal spine functioning. Spinal fusion implants have become a standard approach for this purpose, making it crucial to develop biomaterials and structures that possess high osteogenic capacities and exhibit mechanical properties and dynamic responses similar to those of the host bone. This study focused on the fabrication of 3D-printed polyether ether ketone/silicon nitride (PEEK/SiN) scaffolds with a triply periodic minimal surface (TPMS) structure, which offers several advantages, such as a large surface area and uniform stress distribution under load. The mechanical properties and dynamic response of PEEK/SiN scaffolds with varying porosities were evaluated through mechanical testing and finite element analysis. The scaffold with 30% porosity exhibited a compressive strength (34.56 ± 1.91 MPa) and elastic modulus (734 ± 64 MPa) similar to those of trabecular bone. In addition, the scaffold demonstrated favorable damping properties. The biological data revealed that incorporating silicon nitride into the PEEK scaffold stimulated osteogenic differentiation. In light of these findings, it can be inferred that PEEK/SiN TPMS scaffolds exhibit significant potential for use in bone tissue engineering and represent a promising option as candidates for spinal fusion implants.

Anterior Cervical Discectomy and Fusion Performed Using a CaO-SiO2-P2O5-B2O3 Bioactive Glass Ceramic or Polyetheretherketone Cage Filled with Hydroxyapatite/β-Tricalcium Phosphate: A Prospective Randomized Controlled Trial

A CaO-SiO₂-P₂O₅-B₂O₃ bioactive glass-ceramic (BGS-7) spacer provides high mechanical stability, produces a chemical bond to the adjacent endplate, and facilitates fusion after spine surgery. This prospective, randomized, single-blind, non-inferiority trial aimed to evaluate the radiographic outcomes and clinical efficacy of anterior cervical discectomy and fusion (ACDF) using a BGS-7 spacer for treating cervical degenerative disorders. Thirty-six patients underwent ACDF using a BGS-7 spacer (Group N), and 40 patients underwent ACDF using polyetheretherketone (PEEK) cages filled with a mixture of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) for the treatment of cervical degenerative disorders. The spinal fusion rate was assessed 12 months postoperatively using three-dimensional computed tomography (CT) and dynamic radiographs. Clinical outcomes included patient-reported outcome measures, visual analog scale scores for neck and arm pain, and scores from the neck disability index (NDI), European Quality of Life-5 Dimensions (EQ-5D), and 12-item Short Form Survey (SF-12v2). All participants were randomly assigned to undergo ACDF using either a BGS-7 spacer or PEEK cage filled with HA and β-TCP. The primary outcome was the fusion rate on CT scan image at 12 months after ACDF surgery based on a per-protocol strategy. Clinical outcomes and adverse events were also assessed. The 12-month fusion rates for the BGS-7 and PEEK groups based on CT scans were 81.8% and 74.4%, respectively, while those based on dynamic radiographs were 78.1% and 73.7%, respectively, with no significant difference between the groups. There were no significant differences in the clinical outcomes between the two groups. Neck pain, arm pain, NDI, EQ-5D, and SF-12v2 scores significantly improved postoperatively, with no significant differences between the groups. No adverse events were observed in either group. In ACDF surgery, the BGS-7 spacer showed similar fusion rates and clinical outcomes as PEEK cages filled with HA and β-TCP.

Does titanium cage subsidence affect clinical outcomes in ACDF surgery? A tertiary centre experience

BACKGROUND

Cage subsidence after anterior cervical discectomy and fusion (ACDF) surgery has been well documented with rates of up to 40%. Cages fill the void after cervical discectomy and promote fusion. These materials have different biomechanical profiles with differing rates of subsidence. This retrospective cohort study aimed to determine subsidence rates specifically associated with the novel Emerging Implant Technologies (EIT) titanium cage, identify risk factors associated with subsidence, and evaluate whether subsidence affects clinical outcomes.

METHODS

ACDF with insertion of stand-alone EIT cage was performed in 39 patients (64 levels) between December 2016 and February 2019 with a median follow-up of 11 months. Patients were classified into two groups; subsidence and non-subsidence, and were compared in terms of the resultant clinical outcomes as well as presence of risk factors. Health-related quality of life (HRQOL) outcomes were assessed using Visual Analogue Scale (VAS) for neck and arm pain, EuroQol 5-Dimension 5-Level (EQ-5D-5L), EuroQol Visual Analogue Scale (EQ VAS) and Neck Disability Index (NDI) scores.

RESULTS

Cage subsidence (>3mm) was present in nine patients (23%), which corresponded to ten levels treated (16%). Development of subsidence was not associated with gender (p = 0.12), age (p = 0.27), smoking (p = 0.13), number of treatment levels (p = 0.10) or cage size used (p = 0.34). It had no effect on any of the HRQOL outcomes, namely VAS Neck (p = 0.07), VAS Arms (p = 0.08), EQ-5D-5L (p = 0.36), EQ VAS (p = 0.85) and NDI (p = 0.80).

CONCLUSIONS

The EIT cage seems to be associated with lower rates of subsidence compared with other cage types. Cage subsidence was not associated with HRQOL outcomes or risk factors.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

3D-printed polyether-ether-ketone/n-TiO2 composite enhances the cytocompatibility and osteogenic differentiation of MC3T3-E1 cells by downregulating miR-154-5p

The object was to enhance the bioactivity of pure polyether-ether-ketone (PEEK) by incorporating nano-TiO2 (n-TiO2) and investigate its potential mechanism. PEEK/n-TiO2 composite was manufactured using a 3D PEEK printer and characterized by scanning electron microscopy (SEM), 3D profiler, energy-dispersive spectroscopy, and Fourier-transform infrared (FT-IR) analyses. Cytocompatibility was tested using SEM, fluorescence, and cell counting kit-8 assays. Osteogenic differentiation was evaluated by osteogenic gene and mineralized nodule levels. The expression of the candidate miRNAs were detected in composite group, and its role in osteogenic differentiation was studied. As a results the 3D-printed PEEK/n-TiO2 composite (Φ = 25 mm, H = 2 mm) was successfully fabricated, and the TiO2 nanoparticles were well distributed and retained the nanoscale size of the powder. The Ra value of the composite surface was 2.69 ± 0.29, and Ti accounted for 22.29 ± 12.09% (in weight), and FT-IR analysis confirmed the characteristic peaks of TiO2. The cells in the composite group possessed better proliferation and osteogenic differentiation abilities than those in the PEEK group. miR-154-5p expression was decreased in the composite group, and the inhibition of miR-154-5p significantly enhanced the proliferation and osteogenic differentiation abilities. In conclusion, 3D-printed PEEK/n-TiO2 composite enhanced cytocompatibility and osteogenic induction ability by downregulating miR-154-5p, which provides a promising solution for improving the osteointegration of PEEK.

Biocompatibility and osteointegration capability of β-TCP manufactured by stereolithography 3D printing: In vitro study

Beta-tricalcium phosphate (β-TCP) bioceramics have an inorganic composition similar to the human bone. While conventional methods can only produce ceramic scaffolds with poor controllability, the advancement of 3D-printing, especially stereolithography, made it possible to manufacture controllable, highly precise, micropore ceramic scaffolds. In this study, the stereolithography was applied to produce β-TCP bioceramics, while ZrO₂, Al₂O₃, Ti6Al4V, and polyetheretherketone (PEEK) were used as controls. Phase analysis, water contact angle tests, and Micro-CT were applied to evaluate the surface properties and scaffold. Hemolytic toxicity, cell proliferation, and morphological assessment were performed to evaluate the biocompatibility. Alkaline phosphatase (ALP) level, mineralization, and qRT-PCR were measured to evaluate the osteointegration. During the manufacturing of β-TCP, no evident impurity substance and hemolytic toxicity was found. Cells on β-TCP had good morphologies, and their proliferation capability was similar to Ti6Al4V, which was higher than the other materials. Cells on β-TCP had higher ALP levels than PEEK. The degree of mineralization was significantly higher on β-TCP. The expression of osteogenesis-related genes on β-TCP was similar to Ti6Al4V and higher than the other materials. In this study, the β-TCP produced by stereolithography had no toxicity, high accuracy, and excellent osteointegration capability, thus resulting as a good choice for bone implants.

Bio-Activated PEEK: Promising Platforms for Improving Osteogenesis through Modulating Macrophage Polarization

The attention on orthopedic biomaterials has shifted from their direct osteogenic properties to their osteoimmunomodulation, especially the modulation of macrophage polarization. Presently, advanced technologies endow polyetheretherketone (PEEK) with good osteoimmunomodulation by modifying PEEK surface characteristics or incorporating bioactive substances with regulating macrophage polarization. Recent studies have demonstrated that the fabrication of a hydrophilic surface and the incorporation of bioactive substances into PEEK (e.g., zinc, calcium, and phosphate) are good strategies to promote osteogenesis by enhancing the polarization of M2 macrophages. Furthermore, the modification by other osteoimmunomodulatory composites (e.g., lncRNA-MM2P, IL-4, IL-10, and chitosan) and their controlled and desired release may make PEEK an optimal bio-activated implant for regulating and balancing the osteogenic system and immune system. The purpose of this review is to comprehensively evaluate the potential of bio-activated PEEK in polarizing macrophages into M2 phenotype to improve osteogenesis. For this objective, we retrieved and discussed different kinds of bio-activated PEEK regarding improving osteogenesis through modulating macrophage polarization. Meanwhile, the relevant challenges and outlook were presented. We hope that this review can shed light on the development of bio-activated PEEK with more favorable osteoimmunomodulation.

Sterilization of Polymeric Implants: Challenges and Opportunities

Degradable and environmentally responsive polymers have been actively developed for drug delivery and regenerative medicine applications, yet inadequate consideration of their compatibility with terminal sterilization presents notable barriers to clinical translation. This Review discusses industry-established terminal sterilization methods and aseptic processing and contrasts them with innovative approaches aimed at preserving the integrity of polymeric implants. Regulatory guidelines, fiscal considerations, and potential pitfalls are discussed to encourage early integration of sterility regulatory considerations in material designs.

Comparison of Long-Term Outcomes between the n-HA/PA66 Cage and the PEEK Cage Used in Transforaminal Lumbar Interbody Fusion for Lumbar Degenerative Disease: A Matched-Pair Case Control Study

OBJECTIVE

The nanohydroxyapatite/polyamide-66 (n-HA/PA66) cage is a novel bioactive nonmetal cage that is now used in some medical centers, while the polyetheretherketone (PEEK) cage is a typical device that has been widely used for decades with excellent clinical outcomes. This study was performed to compare the long-term radiographic and clinical outcomes of these two different cages used in transforaminal lumbar interbody fusion (TLIF).

METHODS

In this retrospective and matched-pair case control study, we included 200 patients who underwent TLIF from January 2010 to December 2014 with a minimum 7-year follow-up. One hundred patients who used n-HA/PA66 cages were matched with 100 patients who used PEEK cages for age, sex, diagnosis, and fusion level. The independent student's t-test and Pearson's chi-square test were used to compare the two groups regarding radiographic (fusion status, cage subsidence rate, segmental angle [SA], and interbody space height [IH]) and clinical (Oswestry Disability Index [ODI], and Visual Analog Scale [VAS] for back and leg) parameters preoperatively, postoperatively, and at the final follow-up.

RESULTS

The n-HA/PA66 and PEEK groups had similar fusion rates of bone inside and outside the cage at the final follow-up (95.3% vs 91.8%, p = 0.181, 92.4% vs 90.1%, p = 0.435). The cage union ratios exposed to the upper and lower endplates of the n-HA/PA66 group were significantly larger than those of the PEEK group (p < 0.05). The respective cage subsidence rates in the n-HA/PA66 and PEEK groups were 10.5% and 17.5% (p = 0.059). There were no significant differences between the two groups in the SA, IH, ODI scores, or VAS scores at any time point. The n-HA/PA66 group showed high fusion and low subsidence rates during long-term follow-up.

CONCLUSION

Both n-HA/PA66 and PEEK cages can achieve satisfactory long-term clinical and radiographic outcomes in TLIF. However, the n-HA/PA66 group showed significantly larger cage union ratios than the PEEK group. Therefore, the results indicated that the n-HA/PA66 cage is an ideal alternative material comparable to the PEEK cage in TLIF.

Separation Surgery, Fixation With Carbon-Fiber Implants, and Stereotactic Body Radiotherapy for Oligometastatic Spinal Disease

The management of spinal metastases focuses on reducing symptoms and protecting the spinal cord, historically involving extracorporeal radiotherapy alone. The use of separation surgery techniques alongside high-dose radiotherapy to treat spinal metastases is a novel concept and has changed the treatment paradigm. Additionally, titanium implants have been increasingly used in cases of metastatic spinal tumours requiring adjuvant stereotactic radiotherapy (SBRT). We present the case of a 48-year-old female patient who was diagnosed with a metastatic deposit of breast cancer within L1 with an Epidural Spinal Cord Compression score greater than 1a. At the time of the diagnosis, her prognosis was estimated to be more than two years. She underwent a posterior instrumented fusion of T11-L3 vertebrae with a carbon-fibre fixation system and separation surgery (debulking of the tumour around the spinal cord). The patient was discharged on the second postoperative day achieving complete resolution of the mechanical back pain. SBRT was performed 12 weeks after the surgery. The patient regained ECOG status of 1 shortly after but sadly passed away due to multiple brain metastases 36 months following posterior fixation. Her spinal disease remained well-controlled throughout the follow-up. Carbon-fibre implants appear to be safe and relatively easy to apply. Their use, due to limited artefacts in both computed tomography and magnetic resonance imaging, makes SBRT much more straightforward and follow-up imaging easier to be interpreted. Our experience demonstrates that, in conjunction with separation surgery, the translucent, low perturbing properties of these implants can improve SBRT intervention and detection of recurrence on follow-up imaging.

Complications in Spinal Fusion Surgery: A Systematic Review of Clinically Used Cages

Spinal fusion (SF) comprises surgical procedures for several pathologies that affect different spinal levels, and different cages are employed in SF surgery. Few clinical studies highlight the role of cages in complications beyond the outcomes. The aim of this systematic review is to collect the last 10 years' worth of clinical studies that include cages in SF surgery, focusing on complications. Three databases are employed, and 21 clinical studies are included. The most-performed SF procedure was anterior cervical discectomy and fusion (ACDF), followed by lumbar SF. The polyetheretherketone (PEEK) cage was the most-used, and it was usually associated with autograft or calcium phosphate ceramics (hydroxyapatite (HA) and tricalcium phosphate (βTCP)). For lumbar SF procedures, the highest percentages of subsidence and pseudoarthrosis were observed with PEEK filled with bone morphogenetic protein 2 (BMP2) and βTCP. For ACDF procedures, PEEK filled with autograft showed the highest percentages of subsidence and pseudoarthrosis. Most studies highlighted the role of surgical techniques in patient complications. There are many interacting events that contextually affect the rate of clinical success or failure. Therefore, in future clinical studies, attention should focus on cages to improve knowledge of chemical, biological and topographical characteristics to improve bone growth and to counteract complications such as cage loosening or breaking and infections.

Optimization of cervical cage and analysis of its base material: A finite element study

Nowadays, cervical disorders are common due to human lifestyles. Accordingly, the cage design should be optimized as an essential issue. For an optimal design, an objective function is utilized to calculate the proper geometrical parameters. Additionally, the base material of the cage plays a key role in its functionality and final cost. Novel materials are currently introduced with more compatibility with the bone in terms of mechanical and chemical properties. In this study, a cervical cage was modeled based on PEEK material with three types of tooth designs on its surface. The cervical cage is assumed to be implanted between C6 and C7 vertebrae. The geometric parameters of the cage were optimized to minimize the mass by determining allowable stress and subsidence. The effect of complete cortical removal was investigated as a surgical mistake. Finally, a new composition of PEEK/titanium was introduced as the base material of the cage. Ansys 18.2 was used for FEA. The cage with a straight tooth was chosen due to its lower stress and subsidence compared with other designs. Furthermore, the optimized structures of all three tooth designs were determined. The mass and volume of the optimal cages were reduced by 41.47% and 41.52% respectively. Besides, complete cortical resection should not be carried out during fusion surgery, since it may lead to higher subsidence. The composition of PEEK/titanium was chosen as an appropriate base material due to its better performance compared with PEEK or titanium alone.

A unique biomimetic modification endows polyetherketoneketone scaffold with osteoinductivity by activating cAMP/PKA signaling pathway

Osteoinductivity of a biomaterial scaffold can notably enhance the bone healing performance. In this study, we developed a biomimetic and hierarchically porous polyetherketoneketone (PEKK) scaffold with unique osteoinductivity using a combined surface treatment strategy of a sulfonated process and a nano bone-like apatite deposition. In a beagle intramuscular model, the scaffold induced bone formation ectopically after 12-week implantation. The better bone healing ability of the scaffold than the original PEKK was also confirmed in orthotopic sites. After culturing with bone marrow-derived mesenchymal stem cells (BMSCs), the scaffold induced osteogenic differentiation of BMSCs, and the new bone formation could be mainly depending on cell signaling through adenylate cyclase 9, which activates the cyclic adenosine monophosphate/protein kinase A signaling cascade pathways. The current work reports a new osteoinductive synthetic polymeric scaffold with its detailed molecular mechanism of action for bone repair and regeneration.

Comparison of the Postoperative Motion Stabilization Between Anterior Cervical Decompression and Fusion with a Zero-Profile Implant System and a Plate-Cage Construct

OBJECTIVE

Due to the lack of an additional anterior plate, the motion stability of a zero-profile device with an anchored cage (AC) may be inferior to that of a traditional plate-cage construct (PCC). However, the impact of this difference in motion stability on various outcomes has not been fully explored. Therefore, the aim of this study was to compare the motion stabilization features of an AC and a PCC and analyze their impact on postoperative outcomes and complications.

METHODS

A retrospective study of patients treated with single-level anterior cervical discectomy and fusion from January 2008 to May 2016 was performed. First, clinical and radiological outcomes, postoperative complications and time to achieve motion stabilization were compared between the AC and PCC groups. Then, based on the time to achieve motion stabilization, all patients were divided into group A (time to achieve motion stabilization <3 months), group B (time to achieve motion stabilization from 3-6 months), and group C (time to achieve motion stabilization >6 months). The early postoperative complications were compared across the 3 groups. Motion stabilization was measured on dynamic cervical radiographs using the interspinous process method and Cobb angle method according to previously published methods.

RESULTS

A total of 160 patients met the inclusion criteria, including 90 patients in the AC group and 70 patients in the PCC group. There were no significant differences between the AC and PCC groups in the clinical outcomes, C2-7 angle change, segmental angle change, final fusion rate or adjacent-level degeneration (P > 0.05). The disc height loss was 2.26 ± 1.00 mm in the AC group and 1.76 ± 1.13 mm in the PCC group (P = 0.004), and the incidence of implant subsidence was 24.44% in the AC group and 11.43% in the PCC group (P = 0.036). In addition, the PCC was more dynamically stable than the AC at 3 months post-surgery (P < 0.001), and at this time, the disc height loss and implant subsidence in motion-stable patients were significantly lower than those in motion-unstable patients (P < 0.05). Furthermore, our results also showed that when the arrival time of motion stabilization was prolonged, the loss of disc height and occurrence of subsidence gradually increased.

CONCLUSIONS

More attention should be given to minimizing the adverse impact of poor motion stability in the design and development of future zero-profile cervical implants, although this has little impact on clinical efficacy.

The SNAP Trial: 2-Year Results of a Double-Blind Multicenter Randomized Controlled Trial of a Silicon Nitride Versus a PEEK Cage in Patients After Lumbar Fusion Surgery

STUDY DESIGN

Randomized controlled trial.

OBJECTIVES

Lumbar interbody fusion with cages is performed to provide vertebral stability, restore alignment, and maintain disc and foraminal height. Polyetheretherketone (PEEK) is commonly used. Silicon nitride (Si₃N₄) is an alternative material with good osteointegrative properties. This study was designed to assess if Si₃N₄ cages perform similar to PEEK.

METHODS

A non-inferiority double-blind multicenter RCT was designed. Patients presenting with chronic low-back pain with or without leg pain were included. Single- or double-level instrumented transforaminal lumbar interbody fusion (TLIF) using an oblique PEEK or Si₃N₄ cage was performed. The primary outcome was the Roland-Morris Disability Questionnaire (RMDQ). The non-inferiority margin for the RMDQ was 2.6 points on a scale of 24. Secondary outcomes included the Oswestry Disability Questionnaire (ODI), Visual Analogue Scales (VAS), SF-36 Physical Function, patient and surgeon Likert scores, radiographic evaluations for subsidence, segmental motion, and fusion. Follow-up was planned at 3, 6, 12, and 24-months.

RESULTS

Ninety-two patients were randomized (i.e. 48 to PEEK and 44 to Si₃N₄). Both groups showed good clinical improvements on the RMDQ scores of up to 5-8 points during follow-up. No statistically significant differences were observed in clinical and radiographic outcomes. Mean operative time and blood loss were statistically significantly higher for the Si₃N₄ cohort. Although not statistically significant, there was a higher incidence of complications and revisions associated with the Si₃N₄ cage.

CONCLUSIONS

There was insufficient evidence to conclude that Si₃N₄ was non-inferior to PEEK.

Evaluation of interbody fusion efficacy and biocompatibility of a polyetheretherketone/calcium silicate/porous tantalum cage in a goat model

Objective

To evaluate the interbody fusion efficacy and biocompatibility of a graft-free cage made of polyetheretherketone/calcium silicate composite/porous tantalum (PEEK/CS/pTa cage) compared with a PEEK/CS cage with an autogenous bone graft in a goat model.

Methods

PEEK/CS/pTa and PEEK/CS cages were prepared through an injection-moulding method. The PEEK/CS composites and porous tantalum were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) mapping. Then, adult goats were chosen for C2/C3 and C3/C4 discectomy via the anterior cervical approach and randomly implanted with PEEK/CS/pTa and PEEK/CS/cages with autogenous bone grafts. The fusion performance and osseointegration of the cages were evaluated by X-ray imaging, magnetic resonance imaging (MRI) scanning, and bone histomorphometry analysis. Moreover, the concentrations of Ca and Si in urine, serum, tissue around the fusion segments and major organs of the goats were determined by inductively coupled plasma–optical emission spectrometry (ICP–OES). Histological observation of major organs of the goats was used to evaluate the biosafety of PEEK/CS/pTa and PEEK/CS cages.

Results

X-ray and MRI imaging suggested that both PEEK/CS/pTa cages and PEEK/CS cages maintained similar average intervertebral space heights. The tissue volumes in the fusion area were comparable between the two groups of cages at 26 weeks after surgery. Histological morphometric data showed that PEEK/CS/pTa cages and PEEK/CS cages with autogenous bone grafts had similar bone contact and osseointegration at 12 and 26 weeks. Element determination of serum, urine, spinal cord, dura matter, bone and organs showed that the CS/PEEK cages did not cause abnormal systemic metabolism or accumulation of calcium and silicon in local tissues and major organs of goats after implantation. No obvious pathological changes were found in the heart, liver, spleen, liver or kidney tissues.

Conclusion

Overall, these results suggested that the graft-free PEEK/CS/pTa cage showed similar bony fusion performance to the PEEK/CS cages with autogenous bone grafts. The cages releasing calcium and silicon had good biological safety in vivo.

The translational potential of this article: This study provided a new graft-free interbody fusion solution to patients with degenerative disc diseases, which could avert potential donor-site complications. This study also provided a detailed assessment of element excretion and accumulation of Ca and Si in vivo, which validated the biosafety of this new type of bioactive interbody fusion cage.

[Application of three-dimensional printing technology in treatment of limb bone tumors]

With the developing of three-dimensional (3D) printing technology, it is widely used in the treatment of bone tumors in the clinical orthopedics. Because of the great individual differences in the location of bone tumor, resection and reconstruction are difficult. Based on 3D printing technology, the 3D models can be prepared to show the anatomical part of the disease, so that the surgeons can create a patient-specific operational plans based on better understand the local conditions. At the same time, preoperative simulation can also be carried out for complex operations and patient-specific prostheses can be further designed and prepared according to the location and size of tumor, which may have more advantages in adaptability. In this paper, the domestic and international research progress of 3D printing technology in the treatment of limb bone tumors in recent years were reviewed and summarized.

Morphologic Change of CorticoCancellous Allograft Used for Anterior Cervical Discectomy and Fusion

STUDY DESIGN

Retrospective cohort study.

OBJECTIVE

The aim of this study was to evaluate the incidence and clinical implications of graft morphologic changes in corticocancellous allografts used for anterior cervical discectomy and fusion (ACDF), such as graft resorption or fracture.

SUMMARY OF BACKGROUND DATA

Although cortico-cancellous allograft is one of the most commonly used interbody spacer for ACDF, clinical implications of allograft resorption or fracture is unclear.

METHODS

One-hundred and thirty-eight consecutive patients who underwent ACDF for degenerative cervical myelopathy or radiculopathy were retrospectively reviewed. Patients with allograft morphologic changes, including graft resorption and fracture (morphologic change group), were compared with patients without morphologic changes (unchanged group). Furthermore, operated segments with morphologic changes were compared with unchanged segments. Patient characteristics, cervical lordosis, segmental lordosis, fusion, subsidence, neck pain visual analogue scale (VAS), arm pain VAS, and neck disability index (NDi) scores were evaluated.

RESULTS

Ninety patients (149 segments) were included in the study. Allograft resorption or fracture was detected in 46 (51.1%) patients and 81 (54.3%) segments, respectively. The fusion rate of morphologic change segments was significantly lower than that of the unchanged segments (P < 0.001). Furthermore, segments with morphologic changes had significantly higher rates of subsidence compared to unchanged segments ( P < 0.001). Segmental lordosis at the final follow-up was significantly smaller in the morphologic change segments ( P < 0.001). Neck pain VAS, arm pain VAS, and NDI scores did not demonstrate significant intergroup differences.

CONCLUSION

Corticocancellous allograft demonstrated a high rate of graft morphologic change (54.3%). Graft resorption or fracture was associated with increased pseudarthrosis, subsidence, and decreased postoperative segmental lordosis; however, the clinical results were not significantly affected. Caution is needed when choosing to use corticocancellous allografts for ACDF due to the high rate of graft resorption or fracture and the negative implications of these risks.

Transforaminal Fusion Using Physiologically Integrated Titanium Cages with a Novel Design in Patients with Degenerative Spinal Disorders: A Pilot Study

More contemporary options have been presented in the last few years as surgical methods and materials have improved in patients with degenerative spine illnesses. The use of biologically integrated titanium cages of a unique design based on computer 3D modeling for the surgical treatment of patients with degenerative illnesses of the spine’s intervertebral discs has been proposed and experimentally tested. The goal of this study is to compare the radiographic and clinical outcomes of lumbar posterior interbody fusion with a 3D porous titanium alloy cage versus a titanium-coated polyetheretherketone (PEEK) cage, including fusion quality, time to fusion, preoperative and postoperative patient assessments, and the presence, severity, and other side effect characteristics. (1) Methods: According to the preceding technique, patients who were operated on with physiologically integrated titanium cages of a unique design based on 3D computer modeling were included in the study group. This post-surveillance study was conducted as a randomized, prospective, interventional, single-blind, center study to look at the difference in infusion rates and the difference compared to PEEK cages. The patients were evaluated using CT scans, Oswestry questionnaires (every 3, 6, and 12 months), and VAS scales. (2) Results: Six months following surgery, the symptoms of fusion and the degree of cage deflation in the group utilizing the porous titanium 3D cage were considerably lower than in the group using the PEEK cage (spinal fusion sign, p = 0.044; cage subsidence, p = 0.043). The control group had one case of cage migration into the spinal canal with screw instability, one case of screw instability without migration but with pseudoarthrosis formation and two surrounding segment syndromes with surgical revisions compared with the 3D porous titanium alloy cage group. (3) Conclusions: The technique for treating patients with degenerative disorders or lumbar spine instability with aspects of neural compression utilizing biologically integrated titanium cages of a unique design based on computer 3D printing from CT scans has been proven. This allows a new approach of spinal fusion to be used in practice, restoring the local sagittal equilibrium of the spinal motion segment and lowering the risk of pseudarthrosis and revision surgery.

PEEK versus titanium-coated PEEK cervical cages: fusion rate

BACKGROUND

Anterior cervical discectomy and fusion (ACDF) is one of the most commonly performed procedures for degenerative cervical disease. The evaluation of fusion status is still not fully standardized, and a variety of measurement methods are used. This study presents our own evaluation of fusion by comparing two types of implants.

METHODS

A total of 170 disc spaces were operated on in 104 patients using PEEK (polyetheretherketone) cages and titanium-coated (TC) PEEK cages. Patients were assigned to a specific implant using a randomisation table. Fusion status was evaluated based on functional radiographs and CT scans obtained at 12 months post-surgery. Multivariate mixed-effects logistic regression models were performed to assess the association of type of implant with different fusion rates.

RESULTS

At 12 months post-surgery, CT scans were performed in 86 patients (a total of 144 disc spaces) and conventional radiographs were obtained in 102 (a total of 166 disc spaces). Complete fusion was demonstrated in 101 cases (71.1%), partial fusion in 43 cases (29.9%). There were no cases of absence of fusion. A total of 85 PEEK cages (59%) and 59 TC-PEEK cages (41%) were implanted. For PEEK cages, complete fusion was seen in 75 (88.2%) disc spaces, compared to 26 (44.1%) achieved with TC-PEEK cages. A significantly higher proportion of complete fusions (B = 15.58; P < 0.0001) after 12 months was observed with PEEK implants compared to TC-PEEK implants.

CONCLUSION

Complete fusion was noted at 12 months post-surgery significantly more frequently with PEEK implants compared to TC-PEEK implants.

Feasibility of postoperative spine stereotactic body radiation therapy in proximity of carbon and titanium hybrid implants using a robotic radiotherapy device

BACKGROUND AND PURPOSE

To assess the feasibility of postoperative stereotactic body radiation therapy (SBRT) for patients with hybrid implants consisting of carbon fiber reinforced polyetheretherketone and titanium (CFP-T) using CyberKnife.

MATERIALS AND METHODS

All essential steps within a radiation therapy (RT) workflow were evaluated. First, the contouring process of target volumes and organs at risk (OAR) was done for patients with CFP-T implants. Second, after RT-planning, the accuracy of the calculated dose distributions was tested in a slab phantom and an anthropomorphic phantom using film dosimetry. As a third step, the accuracy of the mandatory image guided radiation therapy (IGRT) including automatic matching was assessed using the anthropomorphic phantom. For this goal, a standard quality assurance (QA) test was modified to carry out its IGRT part in presence of CFP-T implants.

RESULTS

Using CFP-T implants, target volumes could precisely delineated. There was no need for compromising the contours to overcome artifact obstacles. Differences between measured and calculated dose values were below 11% for the slab phantom, and at least 95% of the voxels were within 5% dose difference. The comparisons for the anthropomorphic phantom showed a gamma-passing rate (5%, 1 mm) of at least 97%. Additionally the test results with and without CFP-T implants were comparable. No issues concerning the IGRT were detected. The modified machine QA test resulted in a targeting error of 0.71 mm, which corresponds to the results of the unmodified standard tests.

CONCLUSION

Dose calculation and delivery of postoperative spine SBRT is feasible in proximity of CFP-T implants using a CyberKnife system.

Radiological and Clinical Outcomes after Anterior Cervical Discectomy and Fusion (ACDF) with an Innovative 3D Printed Cellular Titanium Cage Filled with Vertebral Bone Marrow

Objectives

To assess the clinical and radiological outcomes after ACDF with 3D printed cellular titanium cages filled with bone marrow and to compare the clinical and radiological results with the current scientific literature.

Methods

ACDF was performed monosegmentally under standardized conditions. X-rays were analyzed to determine the range of motion, fusion rates, and subsidence preoperatively and 3 and 12 months postoperatively. Clinical outcome measurements included neck disability index (NDI), visual analogue scale (VAS) for brachialgia and cervicalgia, and patient satisfaction.

Results

18 patients were included in the study. The mean RoM decreased from 7.7° ± 2.6 preoperatively to 1.7° ± 1.1° after 3 months and 1.8° ± 1.2° 12 months after surgery. The fusion rates were at 94.4% after 3 and 12 months. The mean subsidence was 0.9 mm ± 0.5 mm 3 months postoperatively and 1.1 mm ± 0.5 mm 12 months after surgery. The mean NDI improved significantly from preoperatively to 12 months postoperatively (34.6 ± 6.2 and 3.4 ± 4.1, respectively). The VAS-neck also showed a large improvement from 5.8 ± 2.2 before and 1.3 ± 1.4 12 months after surgery, as did the VAS-arm (6.4 ± 1.5 and 0.9 ± 1.6, respectively). Patient satisfaction was high throughout the follow-up period.

Conclusion

ACDF with a 3D printed titanium cage resulted in fast fusion without pathological subsidence. In comparison to other cage materials such as PEEK, the 3D printed titanium cage was noninferior in regard to its fusion rate and clinical results.

Quality assessment of systematic reviews of surgical treatment of cervical spine degenerative diseases: an overview

OBJECTIVE

To gather all systematic reviews of surgical treatment of degenerative cervical diseases and assess their quality, conclusions and outcomes.

METHODS

A literature search for systematic reviews of surgical treatment of degenerative cervical diseases was conducted. Studies should have at least one surgical procedure as an intervention. Included studies were assessed for quality through Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) and Assessment of Multiple Systematic Reviews (AMSTAR) questionnaires. Quality of studies was rated accordingly to their final score as very poor (<30%), poor (30%-50%), fair (50%-70%), good (70%-90%), and excellent (>90%). If an article reported a conclusion addressing its primary objective with supportive statistical evidence for it, they were deemed to have an evidence-based conclusion.

RESULTS

A total of 65 systematic reviews were included. According to AMSTAR and PRISMA, 1.5% to 6.2% of studies were rated as excellent, while good studies counted for 21.5% to 47.7%. According to AMSTAR, most studies were of fair quality (46.2%), and 6.2% of very poor quality. Mean PRISMA score was 70.2%, meaning studies of good quality. For both tools, performing a meta-analysis significantly increased studies scores and quality. Cervical spondylosis studies reached highest scores among diseases analyzed. Authors stated conclusions for interventions compared in 70.7% of studies, and only two of them were not supported by statistical evidence.

CONCLUSION

Systematic reviews of surgical treatment of cervical degenerative diseases present "fair" to "good" quality in their majority, and most of the reported conclusions are supported by statistical evidence. Including a meta-analysis significantly increases the quality of a systematic review.

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Accelerated Neutral Atom Beam (ANAB) Modified Poly-Ether-Ether-Ketone for Increasing In Vitro Bone Cell Functions and Reducing Bacteria Colonization Without Drugs or Antibiotics

Poly-ether-ether-ketone (PEEK) has become the spinal implant material of choice due to its radiolucency, low elastic modulus, manufacturability, and mechanical durability. However, studies have highlighted less that optimal cytocompatibility properties of conventional PEEK leading to decreased bone growth and/or extensive bacteria infection. In order to improve the surface properties of PEEK for orthopedic applications, here, Accelerated Neutral Atom Beam (ANAB) technology was used to modify PEEK and such samples were tested In Vitro for osteoblast (bone-forming cell) functions and bacterial colonization. Results showed significantly improved osteoblast responses (such as deposition of calcium containing mineral as well as alkaline phosphatase, osteocalcin, osteopontin, and osteonectin synthesis) on ANAB modified PEEK compared to controls due to optimized surface energy from nanostructured features and greater exposure of PEEK chemistry. ANAB treatment enhanced protein absorption (specifically, mucin, casein, and lubricin) to the PEEK surface and consequently significantly reduced bacterial (including methicillin resistant Staph. aureus (or MRSA), E. coli, and Staph. epidermidis) colonization. Collectively, this study introduces ANAB treated PEEK as a novel material that should be further studied for a wide range of improved orthopedic applications.

Endowing Polyetheretherketone Implants with Osseointegration Properties: In Situ Construction of Patterned Nanorod Arrays

Polyetheretherketone (PEEK) is widely used in orthopedic and craniomaxillofacial surgeries as it exhibits excellent biocompatibility, mechanical property, and chemical stability. However, its clinical application is limited by the biological inertness of PEEK. Numerous efforts have been made to improve the bioactivity of this polymer over the years. However, modification methods that can not only promote osteogenesis but also maintain excellent properties are still limited. Hence, a facile hot die formation technique is developed for establishing patterned nanorod arrays on the PEEK surface in situ. This method can maintain the excellent properties of PEEK and can be used in implantation as it can facilitate osteogenic activity in the absence of any organic/inorganic differentiation-inducing factors. PEEK with 200-nm patterned nanorod arrays on the surface exhibits excellent osteogenic properties. This result is obtained by assessing the osteogenic differentiation properties of rat adipose-derived stem cells at the gene and protein levels in vitro. In vivo experimental results reveal that the surface-modified cylindrical PEEK 200 implants present with excellent osseointegration properties. Moreover, they can tightly bind with the surrounding bone tissue. A practical method for manufacturing single-component PEEK implants with excellent osseointegration properties is reported, and the materials can be possibly used as orthopedic implants.

Comparison of Outcomes Between Cage Materials Used for Patients Undergoing Anterior Cervical Discectomy and Fusion with Standalone Cages: A Systematic Review and Meta-Analysis

INTRODUCTION

Interbody cages are currently being used to address diseases of the vertebra requiring surgical stabilization. Titanium cages were first introduced in 1988. Polyetheretherketone (PEEK) cages are used frequently as one of the alternatives to titanium cages in current practice. This study aimed to compare available cage materials by reviewing the surgical and radiographic outcomes following anterior cervical discectomy and fusion.

METHODS

A comprehensive search of several electronic databases was conducted following the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines. Baseline characteristics, operative outcomes, arthrodesis rates, subsidence rates, and complications were collected from included studies. Collected outcomes were further stratified according to the procedure type, the number of levels operated, and graft used to compare cage materials.

RESULTS

Following the screening for inclusion criteria, a total of 37 studies with 2363 patients were included. The median age was 49.5 years and the median follow-up was 26 months. Overall, no significant differences were found between PEEK and titanium cages regarding fusion, neurologic deficit, subsidence rates, or "good and excellent" outcome according to Odom criteria. However, the standalone comparison between PEEK, titanium, and poly-methyl-methacrylate (PMMA) cages showed a significantly lower fusion rate for PMMA (PEEK: 94%, PMMA: 56%, titanium: 95%, P < 0.01).

CONCLUSIONS

In the present systematic review and meta-analysis, a comparison of the long-term patient-reported and the radiographic outcomes associated with the use of titanium and PEEK, intervertebral body cages showed similar findings. However, there were significantly lower fusion rates for PMMA cages when using a standalone cage without graft material.

Carbon fibre reinforced PEEK versus traditional metallic implants for orthopaedic trauma surgery: A systematic review

INTRODUCTION

There is no literature review comparing outcomes of fixation using carbon-fibre-reinforced polyetheretherketone (CFR PEEK) compared to metal implants used in orthopaedic extremity trauma surgery. A systematic review was performed to compare CFR PEEK to metal implants for clinically-important fracture outcomes.

METHODS

A search of the online databases of PubMed/Medline, EMBASE and Cochrane Database was conducted. A systematic review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A meta-analyses was performed for functional outcomes in proximal humerus fractures converting the score differences to standard mean difference units. GRADE approach was used to determine the level of certainty of the estimates.

RESULTS

Two prospective randomised controlled trials and seven comparative observational studies with a total of 431 patients were included. Of the nine studies included, four compared the use of CFR PEEK against metal plates in proximal humerus fractures. Aggregated functional scores across the proximal humerus studies, there was a small signal of better improvement with CFR PEEK (SMD 0.22, 95% CI -0.03 to 0.47, p = 0.08, low certainty). Greater odds of adverse events occurred in the metal group (OR 2.34, 95% CI 0.73 to 7.55, p = 0.15, low certainty).

CONCLUSIONS

Low to very low certainty evidence suggests a small improvement in functional recovery with CFR PEEK in proximal humerus fractures. This may be mediated through a small reduction in major adverse events related to fracture healing and stability. There is currently insufficient evidence to support the widespread use of CFR PEEK implants in fracture fixation.

LEVEL OF EVIDENCE

Level IV.

Structural Allograft Versus Synthetic Interbody Cage for Anterior Cervical Discectomy and Fusion: A Comparison of 1-Year Outcomes From a National Database

STUDY DESIGN

Observational cohort study.

OBJECTIVE

To compare 1-year perioperative complications between structural allograft (SA) and synthetic cage (SC) for anterior cervical discectomy and fusion (ACDF) using a national database.

METHODS

The TriNetX Research Network was retrospectively queried. Patients undergoing initial single or multilevel ACDF surgery between October 1, 2015 and April 30, 2019 were propensity score matched based on age and comorbidities. The rates of 1-year revision ACDF surgery and reported diagnoses of pseudoarthrosis, surgical site infection (SSI), and dysphagia were compared between structural allograft and synthetic cage techniques.

RESULTS

A comparison of 1-year outcomes between propensity score matched cohorts was conducted on 3056 patients undergoing single-level ACDF and 3510 patients undergoing multilevel ACDF. In single-level ACDF patients, there was no difference in 1-year revision ACDF surgery (P = .573), reported diagnoses of pseudoarthrosis (P = .413), SSI (P = .620), or dysphagia (P = .529) between SA and SC groups. In multilevel ACDF patients, there was a higher rate of revision surgery (SA 3.8% vs SC 7.3%, odds ratio = 1.982, P < .001) in the SC group, and a higher rate of dysphagia in the SA group (SA 15.9% vs SC 12.9%).

CONCLUSION

While the overall revision and complication rate for single-level ACDF remains low despite interbody graft selection, SC implant selection may result in higher rates of revision surgery in multilevel procedures despite yielding lower rates of dysphagia. Further prospective study is warranted.

Mechanical, Chemical, and Processing Properties of Specimens Manufactured from Poly-Ether-Ether-Ketone (PEEK) Using 3D Printing

As part of the experiments herein, the mechanical properties of specimens made of poly-ether-ether-ketone (PEEK) material using 3D printing technology were determined. Two populations of specimens were investigated, the first of which contained an amorphous structure, while the other held a crystal structure. The studies also investigated the influence of the print directionality on the mechanical properties obtained. Static tensile, three-point bending, and impact tests were carried out. The results for the effect of the structure type on the tensile properties showed that the modulus of elasticity was approximately 20% higher for the crystal than for the amorphous PEEK form. The Poisson’s ratios were similar, but the ratio was slightly higher for the amorphous samples than the crystalline ones. Furthermore, the studies included a chemical PEEK modification to increase the hydrophilicity. For this purpose, nitrite and hydroxyl groups were introduced into the chain by chemical reactions. The results demonstrate that the modified PEEK specimens had worse thermoplastic properties than the unmodified specimens.

Understanding the Future Prospects of Synergizing Minimally Invasive Transforaminal Lumbar Interbody Fusion Surgery with Ceramics and Regenerative Cellular Therapies

Transforaminal lumber interbody fusion (TLIF) is the last resort to address the lumber degenerative disorders such as spondylolisthesis, causing lower back pain. The current surgical intervention for these abnormalities includes open TLIF. However, in recent years, minimally invasive TLIF (MIS-TLIF) has gained a high momentum, as it could minimize the risk of infection, blood loss, and post-operative complications pertaining to fusion surgery. Further advancement in visualizing and guiding techniques along with grafting cage and materials are continuously improving the safety and efficacy of MIS-TLIF. These assistive techniques are also playing a crucial role to increase and improve the learning curve of surgeons. However, achieving an appropriate output through TLIF still remains a challenge, which might be synergized through 3D-printing and tissue engineering-based regenerative therapy. Owing to their differentiation potential, biomaterials such as stem/progenitor cells may contribute to restructuring lost or damaged tissues during MIS-TLIF, and this therapeutic efficacy could be further supplemented by platelet-derived biomaterials, leading to improved clinical outcomes. Thus, based on the above-mentioned strategies, we have comprehensively summarized recent developments in MIS-TLIF and its possible combinatorial regenerative therapies for rapid and long-term relief.

Nonunion Rates After Anterior Cervical Discectomy and Fusion: Comparison of Polyetheretherketone vs Structural Allograft Implants

BACKGROUND

Although advances in implant materials, such as polyetheretherketone (PEEK), have been developed aimed to improve outcome after anterior cervical discectomy and fusion (ACDF), it is essential to confirm whether these changes translate into clinically important sustained benefits.

OBJECTIVE

To compare the radiographic and clinical outcomes of patients undergoing up to 3-level ACDF with PEEK vs structural allograft implants.

METHODS

In this cohort study, radiographic and symptomatic nonunion rates were compared in consecutive patients who underwent 1 to 3 level ACDF with allograft or PEEK implant. Prospectively collected clinical data and patient-reported outcome (PRO) scores were compared between the allograft and PEEK groups. Regression analysis was performed to determine the predictors of nonunion.

RESULTS

In total, 194 of 404 patients met the inclusion criteria (79% allograft vs 21% PEEK). Preoperative demographic variables were comparable between the 2 groups except for age. The rate of radiographic nonunion was higher with PEEK implants (39% vs 27%, P = .0035). However, a higher proportion of nonunion in the allograft cohort required posterior instrumentation (14% vs 3%, P = .039). Patients with multilevel procedures and PEEK implants had up to 5.8 times the risk of radiographic nonunion, whereas younger patients, active smokers, and multilevel procedures were at higher risk of symptomatic nonunion.

CONCLUSION

Along with implant material, factors such as younger age, active smoking status, and the number of operated levels were independent predictors of fusion failure. Given the impact of nonunion on PRO, perioperative optimization of modifiable factors and surgical planning are essential to ensure a successful outcome.

Additive-manufactured Ti-6Al-4 V/Polyetheretherketone composite porous cage for Interbody fusion: bone growth and biocompatibility evaluation in a porcine model

Background

We developed a porous Ti alloy/PEEK composite interbody cage by utilizing the advantages of polyetheretherketone (PEEK) and titanium alloy (Ti alloy) in combination with additive manufacturing technology.

Methods

Porous Ti alloy/PEEK composite cages were manufactured using various controlled porosities. Anterior intervertebral lumbar fusion and posterior augmentation were performed at three vertebral levels on 20 female pigs. Each level was randomly implanted with one of the five cages that were tested: a commercialized pure PEEK cage, a Ti alloy/PEEK composite cage with nonporous Ti alloy endplates, and three composite cages with porosities of 40, 60, and 80%, respectively. Micro-computed tomography (CT), backscattered-electron SEM (BSE-SEM), and histological analyses were performed.

Results

Micro-CT and histological analyses revealed improved bone growth in high-porosity groups. Micro-CT and BSE-SEM demonstrated that structures with high porosities, especially 60 and 80%, facilitated more bone formation inside the implant but not outside the implant. Histological analysis also showed that bone formation was higher in Ti alloy groups than in the PEEK group.

Conclusion

The composite cage presents the biological advantages of Ti alloy porous endplates and the mechanical and radiographic advantages of the PEEK central core, which makes it suitable for use as a single implant for intervertebral fusion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04022-0.

The biomechanical effects of Ti versus PEEK used in the PLIF surgery on lumbar spine: a finite element analysis

Titanium (Ti) and polyetheretherketone (PEEK) are commonly used in posterior lumbar interbody fusion (PLIF). The study investigated biomechanical effects of Ti versus PEEK used as materials of cage and rods on the lumbar spine. Four different configurations of PLIF were constituted. Stiff Ti rods provided satisfactory initial stability but increased the stress on rods significantly under simulated physiological load conditions. Ti cage increased the stress on bone endplates significantly. Materials of cage and rods had insignificant effects on the nucleus pressure and facet joint force of non-instrumented segments. Further clinical studies and follow-up observations are essential for corroborating these findings.

Anterior Cervical Arthrodesis With Polyetheretherketone Spacers: What is the Role of the Grafting Material?

STUDY DESIGN

This was a retrospective study of 2 surgeons' use of a single polyetheretherketone (PEEK) device.

OBJECTIVE

Our objective was to investigate the fusion adjunct placed within PEEK devices to examine the likelihood of an arthrodesis, regardless of the PEEK interbody device itself.

SUMMARY OF BACKGROUND DATA

The effectiveness of PEEK interbody devices in anterior cervical arthrodesis has been questioned.

METHODS

The authors retrospectively reviewed the results of 121 patients with demineralized bone matrix (DBM) and 96 with local autograft bone placed within identical PEEK devices for anterior cervical arthrodesis (from 2011 to 2018); 1 surgeon used DBM and another local autograft bone. Arthrodesis was determined independently by a surgeon and 2 blinded neuroradiologists.

RESULTS

For DBM versus autograft; mean age was 60 versus 61 years, smoking status 42.1% versus 31%, diabetes mellitus 18.2% versus 28%, mean body mass index 31 versus 30, and follow up averaged 17 months in both groups. For DBM versus autograft; a radiographic arthrodesis was observed in 22.3% versus 76% of patients. Refusion at the index level was required in 5.8% of the DBM and 0% of the autograft patients.

CONCLUSIONS

A PEEK interbody device filled with local autograft resulted in a higher radiographic fusion rate and a lower need for reoperation at the index level than an identical device filled with DBM. Caution is warranted in assigning fusion failure to the PEEK device alone in anterior cervical discectomy and fusion surgery.

Two-year results of a double-blind multicenter randomized controlled non-inferiority trial of polyetheretherketone (PEEK) versus silicon nitride spinal fusion cages in patients with symptomatic degenerative lumbar disc disorders

Background

During lumbar spinal fusion, spacer cages are implanted to provide vertebral stability, restore sagittal alignment, and maintain disc and foraminal height. Polyetheretherketone (PEEK) is commonly used by most spine surgeons. Silicon nitride (Si₃N₄) is a less well-known alternative although it was first used as a spacer in lumbar fusion over 30 years ago. The present study was designed to see if Si₃N₄ cages would perform similarly to PEEK in a randomized controlled trial.

Methods

A non-inferiority multicenter 100-patient study was designed where both the observer and patient were blinded. Single- or double-level transforaminal lumbar interbody fusion with pedicle screw fixation using an oblique PEEK or Si₃N₄ cage was performed. The primary non-inferiority outcome was the Roland-Morris Disability Questionnaire (RMDQ). Secondary measures included the Oswestry Disability Questionnaire, Visual Analogue Scales (VAS) for back and leg pain, SF-36 Physical and Mental Function indices, patient and surgeon Likert scores on perceived recovery, and X-ray and CT radiological evaluations for subsidence, segmental motion, and fusion. Follow-up evaluations occurred at 3, 6, 12, and 24 months.

Results

After exclusions for protocol violations and canceled surgeries, 92 patients were randomized (i.e., 48 for PEEK and 44 for Si₃N₄). There were no differences in baseline demographics, pre-operative disabilities, or pain scores between the groups. Both treatment arms showed significant improvements in disability, pain, and recovery scores. No significant differences were observed for subsidence, segmental motion, or fusion. For the primary outcome (i.e., RMDQ scores), the non-inferiority of Si₃N₄ compared to PEEK could not be established using the original protocol criteria. However, the comparison was undermined by larger than anticipated patient fallout coupled with higher than expected RMDQ score standard deviations. A post hoc analysis coupled with a more extensive review of the literature was conducted which resulted in the selection of a revised clinically justified non-inferiority margin; and using this method, the non-inferiority of Si₃N₄ was affirmed.

Conclusions

This study demonstrated that the use of either PEEK or Si₃N₄ cages is safe and effective for patients undergoing lumbar spine fusion for chronic degenerative disc disease.

Regulation of surface micro/nano structure and composition of polyetheretherketone and their influence on the behavior of MC3T3-E1 pre-osteoblasts

The bio-inertness and inferior osseointegration of polyetheretherketone (PEEK) affect its long-term lifetime in clinical applications, and appropriate surface modification is an effective way to enhance osseointegration of PEEK implants. In the present study, a strategy of combining sulfonation with alkali treatment was proposed to endow PEEK with rapid apatite deposition and thus enhanced bioactivity. After 3 min of sulfonation with 98% H2SO4, the sample (PEEK-S-3) showed an optimized surface microporous network and obviously improved hydrophilicity. Its contact angle reduced from the original 106 ± 2.3° to 88 ± 4.0°. After a further 24 h of NaOH treatment on PEEK-S-3, Na element was introduced into the obtained sample (PEEK-Na-24), which had a similar surface morphology and chemical structure with PEEK-S-3 and had a further reduced contact angle (77.9 ± 2.9°). The in vitro bioactivity tests showed that after only 3 days of immersion in simulated body fluid (SBF), PEEK-Na-24 was fully covered with a layer of uniform bone-like apatite. The apatite deposition sharply decreased the contact angle of the sample (PEEK-HA) to 16.6 ± 2.6° and increased its surface roughness to 1.05 ± 0.27 μm, leading to the enhanced adsorption of serum proteins on PEEK-HA. The in vitro cell culture indicated that all the three surface-modified samples (PEEK-S-3, PEEK-Na-24 and PEEK-HA) could promote the adhesion, spreading, proliferation and osteoblastic differentiation of MC3T3-E1 pre-osteoblasts, and PEEK-HA presented the best effect. Thus, the surface bioactive PEEK resulting from the optimized surface modification, i.e. combination of sulfonation, alkali treatment and biomimetic apatite deposition, could have good potential in clinical application.