The in vivo response to a novel Ti coating compared with polyether ether ketone: evaluation of the periphery and inner surfaces of an implant

Comparing the Immune Response to PEEK as an Implant Material with and without P-15 Peptide as Bone Graft Material in a Rabbit Long Bone Model

P-15 is a 15-amino-acid-long biomimetic peptide widely demonstrated to enhance osteogenesis in vivo. Despite the prevalence of polyether-ether-ketone (PEEK) in interbody device manufacturing, a growing body of evidence suggests it may produce an unfavorable immune response. The purpose of this preliminary study was to characterize the immune response and new bone growth surrounding PEEK implants with and without a P-15 peptide-based osteobiologic. A bilateral femoral defect model was conducted using New Zealand white rabbits. A total of 17 test subjects received one implant in each distal femur, either with or without bone graft material. Animals were allowed to survive to 4 or 8 weeks, at which time the femurs were collected and subjected to micro-computer tomography (microCT) or cytokine analysis. MicroCT analysis included the quantification of bone growth and density surrounding each implant. The cytokine analysis of periprosthetic tissue homogenates included the quantification of interleukins (ILs) and TNF-α expression via ELISA kits. Improvements in bone volume were observed in the P-15 cohort for the regions of interest, 500-136 and 136-0 µm from the implant surface, at 8 weeks post-op. Concentrations of IL-1β, IL-4, and IL-6 cytokines were significantly higher in the P-15 cohort compared to the PEEK cohort at the 4-week timepoint. Significant reductions in the concentrations of IL-4 and IL-6 cytokines from the 4- to 8-week cohort were observed in the P-15 cohort only. The P-15 peptide has the potential to modulate the immune response to implanted materials. We observed improvements in bone growth and a more active micro-environment in the P-15 cohort relative to the PEEK control. This may indicate an earlier transition from the inflammatory to remodeling phase of healing.

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

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

Reduced Subsidence With PEEK-Titanium Composite Versus 3D Titanium Cages in a Retrospective, Self-Controlled Study in Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Retrospective Study.

OBJECTIVES

To compare subsidence and radiographic fusion rates of titanium-surface polyetheretherketone (PEEK-Ti) and 3D-Titanium (3D-Ti) cages, implanted within the same patient concurrently, during multi-level transforaminal lumbar interbody fusions (TLIF).

METHODS

Forty-eight patients were treated with both PEEK-Ti and 3D-Ti cages during 2- or 3-level TLIF and instrumented posterolateral fusion (108 spinal levels in all). Equivalent bone graft material was implanted within each patient. Radiographic analysis of CT and/or X-ray imaging was performed retrospectively for each spinal level throughout 12-month follow-up period. Fusion was defined as bridging trabecular bone and subsidence was incursion into one/both vertebral bodies >20% cage height. Outcomes were analyzed with Fisher's exact test.

RESULTS

At 6-months post-operative follow-up, incidence of subsidence was significantly lower for PEEK-Ti cages, with 4.8% subsidence, compared to a 27.9% subsidence rate for 3D-Ti cages (P = .007). Fusion rates were comparable at 100% for PEEK-Ti and 95.5% for 3D-Ti. Results at 12-months showed similar but not statistically significant trends of less subsidence with PEEK-Ti than 3D-Ti cages (14.3% PEEK-Ti, 37.5% 3D-Ti), and similar fusion rates of 100% for PEEK-Ti and 91.7% for 3D-Ti. Thirty-nine out of 48 total patients were available for follow-up at 6 months and 20 patients at 12 months. CT availability at 6 and 12-months was 100% and 90%, respectively.

CONCLUSIONS

A significantly lower subsidence rate was associated with a PEEK-Ti cage, compared to 3D-Ti, 6 months after TLIF. Results may not be generalized across technologies due to differences in cage designs; additional research studies are warranted.

The Formation Process and Mechanism of the 3D Porous Network on the Sulfonated PEEK Surface

A three-dimensional (3D) porous network can be prepared on the PEEK surface by sulfonation with enhanced osseointegration and antibacterial properties. However, few studies have been conducted on the formation mechanism of a 3D porous network. In this work, the surface and cross-sectional morphologies, chemical compositions, functional groups, surface wettability, and crystalline states of sulfonated PEEK were investigated at different sulfonation times and coagulant concentrations. The results show that the number of nodular structures and broken fibers on the sulfonated PEEK surface as well as the size of macrovoids in the cross sections increase with increasing sulfonation times when water is used as a coagulant. In contrast, dilute sulfuric acid as a coagulant can inhibit the formation of surface porous structures and macrovoids in the cross sections. Moreover, all of the sulfonated PEEK samples have the same chemical compositions but exhibit better hydrophilicity as the number of microsized pores decreases. It is proposed that non-solvent-induced phase separation (NIPS) occurs during the sulfonation process, and the formation mechanism of surface and cross-sectional morphologies is discussed. Furthermore, it is assumed that the air is trapped in the microsized pores, leaving the surface of the 3D porous network in the Cassie-wetting state. All of these preliminary results throw light on the nature of the sulfonation process and may guide further modification of the structures of sulfonated PEEK.

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

Objectives

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

Methods

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

Results

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

Conclusions

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

Long-term outcomes of the nano-hydroxyapatite/polyamide-66 cage versus the titanium mesh cage for anterior reconstruction of thoracic and lumbar corpectomy: a retrospective study with at least 7 years of follow-up

BACKGROUND

The nano-hydroxyapatite/polyamide-66 (n-HA/PA66) cage is a biomimetic cage with a lower elastic modulus than the titanium mesh cage (TMC). This study aimed to compare the long-term outcomes of the n-HA/PA66 cage and TMC in the anterior reconstruction of thoracic and lumbar fractures.

METHODS

We retrospectively studied 113 patients with acute traumatic thoracic or lumbar burst fractures, comprising 60 patients treated with the TMC and 53 treated with the n-HA/PA66 cage for anterior reconstruction following single-level corpectomy. The radiographic data (cage subsidence, fusion status, segmental sagittal alignment) and clinical data (visual analogue scale (VAS) for pain and Oswestry Disability Index (ODI) for function) were evaluated preoperatively, postoperatively, and at final follow-up after a minimum 7-year period.

RESULTS

The n-HA/PA66 and TMC groups had similar final fusion rates (96.2% vs. 95.0%). The cage subsidence at final follow-up was 2.3 ± 1.6 mm with subsidence of more than 3 mm occurring in 24.5% in the n-HA/PA66 group, which was significantly lower than the respective values of 3.9 ± 2.5 mm and 58.3% in the TMC group. The n-HA/PA66 group also had better correction of the bisegmental kyphotic angle than the TMC group (7.1° ± 7.5° vs 1.9° ± 8.6°, p < 0.01), with lower loss of correction (2.9° ± 2.5° vs 5.2° ± 4.1°, p < 0.01). The mean ODI steadily decreased after surgery in both groups. At final follow-up, the ODI and VAS were similar in the TMC and n-HA/PA66 groups.

CONCLUSIONS

The n-HA/PA66 cage is associated with excellent radiographic fusion, better maintenance of the height of the fused segment, and better correction of kyphosis than the TMC during 7 years of follow-up after one-level anterior corpectomy. With the added benefit of radiolucency, the n-HA/PA66 cage may be superior to the TMC in anterior reconstruction of thoracic or lumbar fractures.

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).

Biological Characteristics of Polyurethane-Based Bone-Replacement Materials

A study is presented on four polymers of the polyurethane family, obtained using a two-stage process. The first composition is the basic polymer; the others differ from it by the presence of a variety of fillers, introduced to provide radiopacity. The fillers used were 15% bismuth oxide (Composition 2), 15% tantalum pentoxide (Composition 3), or 15% zirconium oxide (Composition 4). Using a test culture of human fibroblasts enabled the level of cytotoxicity of the compositions to be determined by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay, along with variations in the characteristics of the cells resulting from their culture directly on the specimens. The condition of cells on the surfaces of the specimens was assessed using fluorescence microscopy. It was shown that introducing 15% bismuth, tantalum, or zinc compounds as fillers produced a range of effects on the biological characteristics of the compositions. With the different fillers, the levels of toxicity differed and the cells' proliferative activity or adhesion was affected. However, in general, all the studied compositions may be considered cytocompatible in respect of their biological characteristics and are promising for further development as bases for bone-substituting materials. The results obtained also open up prospects for further investigations of polyurethane compounds.

A Novel Nanostructured Surface on Titanium Implants Increases Osseointegration in a Sheep Model

BACKGROUND

A nanostructured titanium surface that promotes antimicrobial activity and osseointegration would provide the opportunity to create medical implants that can prevent orthopaedic infection and improve bone integration. Although nanostructured surfaces can exhibit antimicrobial activity, it is not known whether these surfaces are safe and conducive to osseointegration.

QUESTIONS/PURPOSES

Using a sheep animal model, we sought to determine whether the bony integration of medical-grade, titanium, porous-coated implants with a unique nanostructured surface modification (alkaline heat treatment [AHT]) previously shown to kill bacteria was better than that for a clinically accepted control surface of porous-coated titanium covered with hydroxyapatite (PCHA) after 12 weeks in vivo. The null hypothesis was that there would be no difference between implants with respect to the primary outcomes: interfacial shear strength and percent intersection surface (the percentage of implant surface with bone contact, as defined by a micro-CT protocol), and the secondary outcomes: stiffness, peak load, energy to failure, and micro-CT (bone volume/total volume [BV/TV], trabecular thickness [Tb.Th], and trabecular number [Tb.N]) and histomorphometric (bone-implant contact [BIC]) parameters.

METHODS

Implants of each material (alkaline heat-treated and hydroxyapatite-coated titanium) were surgically inserted into femoral and tibial metaphyseal cancellous bone (16 per implant type; interference fit) and in tibial cortices at three diaphyseal locations (24 per implant type; line-to-line fit) in eight skeletally mature sheep. At 12 weeks postoperatively, bones were excised to assess osseointegration of AHT and PCHA implants via biomechanical push-through tests, micro-CT, and histomorphometry. Bone composition and remodeling patterns in adult sheep are similar to that of humans, and this model enables comparison of implants with ex vivo outcomes that are not permissible with humans. Comparisons of primary and secondary outcomes were undertaken with linear mixed-effects models that were developed for the cortical and cancellous groups separately and that included a random effect of animals, covariates to adjust for preoperative bodyweight, and implant location (left/right limb, femoral/tibial cancellous, cortical diaphyseal region, and medial/lateral cortex) as appropriate. Significance was set at an alpha of 0.05.

RESULTS

The estimated marginal mean interfacial shear strength for cancellous bone, adjusted for covariates, was 1.6 MPa greater for AHT implants (9.3 MPa) than for PCHA implants (7.7 MPa) (95% CI 0.5 to 2.8; p = 0.006). Similarly, the estimated marginal mean interfacial shear strength for cortical bone, adjusted for covariates, was 6.6 MPa greater for AHT implants (25.5 MPa) than for PCHA implants (18.9 MPa) (95% CI 5.0 to 8.1; p < 0.001). No difference in the implant-bone percent intersection surface was detected for cancellous sites (cancellous AHT 55.1% and PCHA 58.7%; adjusted difference of estimated marginal mean -3.6% [95% CI -8.1% to 0.9%]; p = 0.11). In cortical bone, the estimated marginal mean percent intersection surface at the medial site, adjusted for covariates, was 11.8% higher for AHT implants (58.1%) than for PCHA (46.2% [95% CI 7.1% to 16.6%]; p < 0.001) and was not different at the lateral site (AHT 75.8% and PCHA 74.9%; adjusted difference of estimated marginal mean 0.9% [95% CI -3.8% to 5.7%]; p = 0.70).

CONCLUSION

These data suggest there is stronger integration of bone on the AHT surface than on the PCHA surface at 12 weeks postimplantation in this sheep model.

CLINICAL RELEVANCE

Given that the AHT implants formed a more robust interface with cortical and cancellous bone than the PCHA implants, a clinical noninferiority study using hip stems with identical geometries can now be performed to compare the same surfaces used in this study. The results of this preclinical study provide an ethical baseline to proceed with such a clinical study given the potential of the alkaline heat-treated surface to reduce periprosthetic joint infection and enhance implant osseointegration.

Comparison of Short-Term Radiographical and Clinical Outcomes After Posterior Lumbar Interbody Fusion With a 3D Porous Titanium Alloy Cage and a Titanium-Coated PEEK Cage

STUDY DESIGN

Clinical case series.

OBJECTIVES

To compare the short-term (≤1 year) radiographical and clinical outcomes between posterior lumbar interbody fusion (PLIF) with a titanium-coated poly-ether-ether-ketone (TCP) cage and PLIF with a three-dimensional porous titanium alloy (PTA) cage.

METHODS

Overall, 63 patients who had undergone 1- or 2-level PLIF since March 2015 were enrolled (median age, 71 years). The first 34 patients underwent PLIF with TCP cages (until June 2017) and the next 29 patients with PTA cages. Fusion status, vertebral endplate cyst formation (cyst sign: grade 0, none; grade 1, focal; and grade 2, diffuse), cage subsidence (grade 0, <1 mm; grade 1, 1-3 mm; and grade 2, >3 mm), and patient-reported quality of life (QOL) outcomes based on the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) were compared at 6 months and 1 year postoperatively between the 2 cage groups.

RESULTS

Cyst sign and cage subsidence grades were significantly lower in the PTA cage group than in the TCP cage group at 6 months postoperatively (cyst sign, p = 0.044; cage subsidence, p = 0.043). In contrast, the fusion rate and surgery effectiveness based on JOABPEQ at both 6 months and 1 year postoperatively were not different between the 2 groups.

CONCLUSIONS

Patient-reported QOL outcomes were similar between the TCP and PTA cage groups until 1 year postoperatively. However, a higher incidence and severity of postoperative vertebral endplate cyst formation in patients with the TCP cage was a noteworthy radiographical finding.

Biomaterials for Interbody Fusion in Bone Tissue Engineering

In recent years, interbody fusion cages have played an important role in interbody fusion surgery for treating diseases like disc protrusion and spondylolisthesis. However, traditional cages cannot achieve satisfactory results due to their unreasonable design, poor material biocompatibility, and induced osteogenesis ability, limiting their application. There are currently 3 ways to improve the fusion effect, as follows. First, the interbody fusion cage is designed to facilitate bone ingrowth through the preliminary design. Second, choose interbody fusion cages made of different materials to meet the variable needs of interbody fusion. Finally, complete post-processing steps, such as coating the designed cage, to achieve a suitable osseointegration microstructure, and add other bioactive materials to achieve the most suitable biological microenvironment of bone tissue and improve the fusion effect. The focus of this review is on the design methods of interbody fusion cages, a comparison of the advantages and disadvantages of various materials, the influence of post-processing techniques and additional materials on interbody fusion, and the prospects for the future development of interbody fusion cages.

Metal failure and nonunion at L5-S1 after long instrumented fusion distal to pelvis for adult spinal deformity: Anterior versus transforaminal interbody fusion

PURPOSE

Pseudoarthrosis and metal failure at L5-S1 following long fusion surgery for adult spinal deformity (ASD) remain major issues. Few studies report on which anterior column support technique is better in terms of achieving fusion and avoiding metal failures. Our study aimed to evaluate the fusion status and metal failure rate at L5-S1 after anterior lumbar interbody fusion (ALIF) versus transforaminal lumbar interbody fusion (TLIF).

METHODS

The study population included patients aged >50 years who underwent surgery for ASD. Anterior column supports at L5-S1 using ALIF and TLIF were compared with ≥ 2-year follow-up. Fusion status on 2-year computed tomography (CT) scan, metal failure, visual analog scale (VAS), and Oswestry disability index (ODI) were evaluated.

RESULTS

98 patients were included in this study (53 ALIF group and 45 TLIF group). We achieved solid fusion on 2-year CT scans in 88.9% and 69.8% patients in the TLIF and ALIF group, respectively. Metal failure developed in nine (17.0%) and six (13.3%) patients in the ALIF and TLIF group, respectively. The most common failure type was unilateral L5-S1 rod fracture (7 and five patients in the ALIF and TLIF group, respectively). Only one patient with bilateral rod fractures in the ALIF group required revision surgery. There were no differences in the VAS and ODI scores at the last follow-up.

CONCLUSIONS

TLIF showed a better fusion rate than ALIF at L5-S1 after long instrumented fusion for ASD. However, the capacity to restore sagittal parameters was greater in the ALIF group. There were no differences between the groups regarding metal failure rate, revision surgery, or clinical outcomes.

High-strength, porous additively manufactured implants with optimized mechanical osseointegration

Optimization of porous titanium alloy scaffolds designed for orthopedic implants requires balancing mechanical properties and osseointegrative performance. The tradeoff between scaffold porosity and the stiffness/strength must be optimized towards the goal to improve long term load sharing while simultaneously promoting osseointegration. Osseointegration into porous titanium implants covering a wide range of porosity (0%-90%) and manufactured by laser powder bed fusion (LPBF) was evaluated with an established ovine cortical and cancellous defect model. Direct apposition and remodeling of woven bone was observed at the implant surface, as well as bone formation within the interstices of the pores. A linear relationship was observed between the porosity and benchtop mechanical properties of the scaffolds, while a non-linear relationship was observed between porosity and the ex vivo cortical bone-implant interfacial shear strength. Our study supports the hypothesis of porosity dependent performance tradeoffs, and establishes generalized relationships between porosity and performance for design of topological optimized implants for osseointegration. These results are widely applicable for orthopedic implant design for arthroplasty components, arthrodesis devices such as spinal interbody fusion implants, and patient matched implants for treatment of large bone defects.

The effect of a novel pillar surface morphology and material composition demonstrates uniform osseointegration

Long-term survival of orthopedic implants requires a strong and compliant interface between the implant and surrounding bone. This paper further explores the in-vivo response to a novel, macro-scale osseointegration surface morphology. In this study, we examine the effects of material composition on osseointegration in relation to the controlled surface geometry. The pillared surface is constructed of discontinuous surface geometry which creates an open space for unencumbered bone migration. In creating an open, macro-scale morphology we have demonstrated a bone migration and integration that is less dependent on the underlying implant material and is substantially driven thru surface geometry. In this in-vivo study an established ovine model was used to examine the effects of implant material composition on bone ingrowth and mechanical performance. Cortical and cancellous sites in the tibia and distal femur were examined at 6 and 12 weeks with μCT, histology, histomorphometry, and mechanical performance. Implant materials tested included PEEK (Evonik, VISTAKEEP®), PEEK HA (Invibio, PEEK-OPTIMA HA Enhanced), Titanium coated PEEK, Titanium (Ti-6Al-4V, Grade 5), and Ultra-High Molecular Weight Polyethylene (UHMWPE). Extensive bone ingrowth was noted in all implant materials at 12 weeks with maturation of the bone within the pillar structure from 6 weeks to 12 weeks. Histology demonstrated little fibrous deposition at the implant interface with no adverse cellular reactions. Histomorphometric review of cortical sites revealed greater than 60% bone ingrowth at 6 weeks increasing to nearly 80% by the 12 week timepoint. Cancellous sites yielded a mean of 30% ingrowth at 6 weeks increasing to 35% by 12 weeks. Pushout testing of cortical site samples demonstrated increase in pushout force between the 6 and 12 week timepoints. Increases were significant in all but the UHMWPE samples. Stiffness likewise increased in all samples between the two times. These results demonstrated the effectiveness of the pillar morphology with full integrating from the surrounding bony tissue regardless of the material.

Facile surface functional polyetheretherketone with antibacterial and immunoregulatory activities for enhanced regeneration toward bacterium-infected bone destruction

Existing biologically inert or unmodified implants to treat infectious bone defects or osteomyelitis still cannot effectively solve bacterial infection and osseointegration. In this work, a simple co-deposition strategy was developed to modify porous polyetheretherketone (PEEK) with improved antibacterial activity and controllable immunoregulatory ability. After PEEK was treated by H₂SO₄ to obtain porous PEEK (SPEEK), the self-polymerization of dopamine was operated on SPEEK in the solution of dopamine and gentamicin sulfate (GS) to prepare polydopamine (pDA) and GS layer-modified SPEEK (labeled as SPEEK–pDA–GS). The morphology, surface property, and molecular structure of SPEEK–pDA–GS were investigated. Besides the antibacterial property of SPEEK–pDA–GS ascribed to the successful immobilization of GS, SPEEK–pDA–GS exhibited promoted osseointegration through the results of mineralization, alkaline phosphatase (ALP) levels and osteogenic gene expression. Furthermore, the evaluation of the cell proliferation suggested that SPEEK–pDA–GS possessed the biocompatibility and the immunoregulatory ability that induced macrophages to anti-inflammatory M2 phenotype. Using rat as model, in vivo results containing X-ray, μ-CT, immunohistochemistry, and pathological analysis showed the excellent healing effect of SPEEK–pDA–GS on bone defect with infection with biological safety. This work illustrates a new insight into the simple and effective modification of PEEK and other implants with antibacterial, immunoregulatory, and osseointegration abilities for clinical requirement.

In-Vivo response to a novel pillared surface morphology for osseointegration in an ovine model

Primary stability and secondary fixation of orthopedic implants to bony tissues are important for healing and long-term functionality. Load sharing and stress transfer are key requirements of an effective implant/tissue interface. This paper presents a novel, macro-scale osseointegration surface morphology which addresses the implant/tissue interface from both the biologic as well as biomechanical perspective. The surface morphology is a controlled, engineered, open topography manifested as discrete pillars projecting from the implant enabling continuous bone ingrowth. The pillared surface is distinct from other porous surfaces and can be differentiated by the localization of the implant material into discrete pillars enabling a continuous mass of bone to freely and easily interdigitate into the pillared structure. Traditional porous structures distribute the implant material throughout the surface forcing the bone to grow in a discontinuous manner. Creating an open and continuous space or "open porosity" in and around the pillar structure allows the bone to easily interdigitate with the implant surface without encumberment from a continuous porous structure. An in-vivo study, using an established ovine model, was undertaken examining the effects of pillar morphology on bone ingrowth and mechanical performance. Cortical and cancellous sites were evaluated utilizing histology, histomophometry, and mechanical pushout, at 4 and 12 weeks. Robust bone ingrowth occurred for all morphologies as was noted in review of the study results. An increase in volume and maturity of bone was noted between the intermediated and final time points. Histomophometry demonstrated over 40% and 80% new bone occupied the available "ingrowth" area at 12 weeks for cancellous and cortical sites (respectively). Histologic review showed little fibrous tissue ingrowth at the interface with no adverse cellular reactions. Testing of cortical samples demonstrated a significant increase in pushout load between the 4 and 12 week timepoints and a 4-8 fold increase in pushout load as compared to the grit blast control. These results demonstrated the effectiveness of the novel interface for orthopedic applications in an in-vivo ovine model.

Impact of mechanical stability on the progress of bone ongrowth on the frame surfaces of a titanium-coated PEEK cage and a 3D porous titanium alloy cage: in vivo analysis using CT color mapping

PURPOSE

To determine the impact of mechanical stability on the progress of bone ongrowth on the frame surfaces of a titanium-coated polyether ether ketone (TCP) cage and a three-dimensional porous titanium alloy (PTA) cage following posterior lumbar interbody fusion (PLIF) until 1 year postoperatively.

METHODS

A total of 59 patients who underwent one- or two-level PLIF for degenerative lumbar disorders since March 2015 were enrolled. Bone ongrowth of all cage frame surfaces (four surfaces per cage: TCP, 288 surfaces and PTA, 284 surfaces) was graded by 6-month and 1-year postoperative computed tomography color mapping (grade 0, 0‒25% of bone ongrowth; grade 1, 26‒50%; grade 2, 51‒75%; and grade 3, 76‒100%).

RESULTS

Bone ongrowth (≥ grade 1) was observed on 58.0% and 69.0% of the surfaces of TCP and PTA cages 6 months postoperatively and on 63.5% and 75.0% of those 1 year postoperatively, respectively. In the TCP cages, bone ongrowth grade increased from 6 months to 1 year postoperatively only in the union segments (median, 1 [interquartile range, IQR, 0-2] to 1 [IQR, 0-3], p = 0.006). By contrast, in the PTA cages, it increased at 6 months postoperatively in the union (1 [IQR, 1-2] to 2 [IQR, 1-3], p = 0.003) and non-union (0.5 [IQR, 0-2] to 1 [IQR, 0-2.75], p = 0.002) segments.

CONCLUSION

Early postoperative mechanical stability has a positive impact on the progress of bone ongrowth on both the TCP and PTA cage frame surfaces after PLIF.

Undercut macrostructure topography on and within an interbody cage improves biomechanical stability and interbody fusion

BACKGROUND CONTEXT

The interface and interactions between an interbody cage, graft material, and host bone can all participate in the fusion. Shortcomings of Poly(aryl-ether-ether-ketone) interbody cages have been addressed with novel titanium surfaces. Titanium surfaces paired with macroscale topography features on the endplates and within the aperture may provide additional benefits.

PURPOSE

To evaluate the influence of cage design parameters on interbody fusion in a large animal preclinical model.

STUDY DESIGN/SETTING

A comparative preclinical large animal model was performed to evaluate how macroscale topography features of an interbody cage can facilitate early integration between the host bone, graft material, and interbody cage and these effects on biomechanical stability and fusion.

METHODS

Forty single level interbody fusions (L4-L5) using iliac crest autograft and bilateral pedicle screw fixation were performed in adult sheep to evaluate the effect of undercut macrostructure topography features of an interbody cage on the endplates and within the aperture. Fusions were evaluated at 6 and 12 weeks (n=10 per group) using radiography, microcomputed tomography, biomechanical integrity, and histology endpoints.

RESULTS

The presence of the undercut macrostructures present on the endplates and within the aperture statistically improved biomechanical integrity at 6 and 12 weeks compared with controls. Microcomputed tomography and histology demonstrated bony interdigitation within the endplate and aperture features contributing to the improvement in properties.

CONCLUSIONS

The present study demonstrates that Poly(aryl-ether-ether-ketone) implants with titanium surfaces can be augmented by undercut macrostructures present on the endplates and within the aperture to provide opportunities for a series of anchoring points that, with new bone formation and remodelling, result in earlier and improved biomechanical integrity of the treated level.

CLINICAL SIGNIFICANCE

This preclinical study showed that bone interdigitation with the undercut macrostructures present on the endplates and within the aperture resulted in improved fusion and biomechanical stability in a clinically relevant spinal fusion model. Future clinical study is warranted to evaluate such implants' performance in humans.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PURPOSE

To design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.

METHODS

According to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.

RESULTS

By measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.

CONCLUSIONS

By measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.

Gaseous sulfur trioxide induced controllable sulfonation promoting biomineralization and osseointegration of polyetheretherketone implants

Fabricating a desired porous structure on the surface of biomedical polyetheretherketone (PEEK) implants for enhancing biological functions is crucial and difficult due to its inherent chemical inertness. In this study, a porous surface of PEEK implants was fabricated by controllable sulfonation using gaseous sulfur trioxide (SO₃) for different time (5, 15, 30, 60 and 90 min). Micro-topological structure was generated on the surface of sulfonated PEEK implants preserving original mechanical properties. The protein absorption capacity and apatite forming ability was thus improved by the morphological and elemental change with higher degree of sulfonation. In combination of the appropriate micromorphology and bioactive sulfonate components, the cell adhesion, migration, proliferation and extracellular matrix secretion were obviously enhanced by the SPEEK-15 samples which were sulfonated for 15 min. Finding from this study revealed that controllable sulfonation by gaseous SO₃ would be an extraordinarily strategy for improving osseointegration of PEEK implants by adjusting the microstructure and chemical composition while maintaining excellent mechanical properties.

Comparison in the same intervertebral space between titanium-coated and uncoated PEEK cages in lumbar interbody fusion surgery

BACKGROUNDS

Disadvantages of polyetheretherketone (PEEK) cages are their smooth and hydrophobic surfaces and their lack of osteoconductivity. Titanium (Ti) coated PEEK cage has been innovated to overcome these potential concerns. However, few well-designed studies have investigated the efficacy of Ti-coated PEEK cage on interbody fusion in humans. This study aimed to evaluate the efficacy of Ti coating on bone ongrowth at bone-implant surface by simultaneously comparing Ti-coated and uncoated PEEK cages in the same intervertebral space.

METHODS

This study is a prospective comparative study for the two different cages. Twenty-six subjects who underwent one-level instrumented posterior lumbar interbody fusion (PLIF) were included. Two PEEK cages [a plasma-sprayed Ti-coated (PTC-PEEK) and an uncoated PEEK cage] were inserted in the same intervertebral space. Fusion rates, cage subsidence, and vertebral cancellous condensation (VCC) around the cage, which indicates bone growth on the surface of each cage, were assessed by thin-slice computed tomography (CT) immediately (within 1 week) and at 3 months postoperatively. A functional radiograph was obtained at 3 and 12 months postoperatively.

RESULTS

Twenty-three subjects showed solid fusion at 3 months postoperatively (fusion rate, 88%). Cage subsidence was not observed. VCC was often observed around the PTC-PEEK cage as evaluated by completely synchronized CT images between immediately and at 3 months postoperatively. Quantified VCC around the cage was significantly larger in the PTC-PEEK cage than in the uncoated PEEK cage (P = 0.01).

CONCLUSIONS

The Ti-coated PEEK cage exhibits radiographic signs, suggesting bone ongrowth, as represented by VCC around the cage compared with that around the uncoated PEEK cage. The Ti-coated PEEK cage has the potential to promote solid fusion and to improve clinical outcomes in lumbar interbody fusion surgery.

A comparative study of three biomaterials in an ovine bone defect model

BACKGROUND

Polyetheretherketone (PEEK), and more recently titanium-coated PEEK, have been given serious consideration as biomaterial design choices for spinal interbody implants. Shortcomings in these materials necessitate further innovation into materials research, for example, on PEKK. Common complications such as surface delamination (as with titanium coating) and lack of bone apposition (as with PEEK) indicate the need for a new material that inherently displays preferable bone growth characteristics without sacrificing structural integrity.

PURPOSE

To compare three biomaterials with respect to their osseointegrative capacity.

STUDY DESIGN

Evaluate the in vivo material characteristics of three separate biomaterials in an ovine bone defect model: PEEK, titanium-coated PEEK (Ti-coated PEEK), and 3D-printed PEKK. Biomechanical, histologic, and radiographic testing was the basis for evaluation and material characterization.

METHODS

Eight ovine specimens were implanted with one of each of the three types of biomaterials tested in both left and right epicondyles using a femoral bone defect model, and were sacrificed at 8 and 16 weeks. Implants were then analyzed using a push-out method, histologic staining, and various radiographic tests. Industry funding was provided for the completion of this research study, followed by an independent third party review of all relevant data for publication.

RESULTS

PEKK implants demonstrated bone ingrowth, no radiographic interference, no fibrotic tissue membrane formation, significant increase in bony apposition over time, and significantly higher push-out strength compared to standard PEEK. The PEKK implant displayed bone growth characteristics comparable to Ti-coated PEEK with significant improvements in implant integrity and radiographic properties.

CONCLUSION

This study found that PEKK displayed preferable characteristics when compared to PEEK and Ti-coated PEEK, and is therefore a potential alternative to their use.

Does implantation site influence bone ingrowth into 3D-printed porous implants?

BACKGROUND CONTEXT

The potential for osseointegration to provide biological fixation for implants may be related to anatomical site and loading conditions.

PURPOSE

To evaluate the influence of anatomical site on osseointegration of 3D-printed implants.

STUDY DESIGN

A comparative preclinical study was performed evaluating bone ingrowth in cortical and cancellous sites in long bones as well as lumbar interbody fusion with posterior pedicle screw stabilization using the same 3D-printed titanium alloy design.

METHODS

3D-printed dowels were implanted in cortical bone and cancellous bone in adult sheep and evaluated at 4 and 12 weeks for bone ingrowth using radiography, mechanical testing, and histology/histomorphometry. In addition, a single-level lumbar interbody fusion using cages based on the same 3D-printed design was performed. The aperture was filled with autograft or ovine allograft processed with supercritical carbon dioxide. Interbody fusions were assessed at 12 weeks via radiography, mechanical testing, and histology/histomorphometry.

RESULTS

Bone ingrowth in long bone cortical and cancellous sites did not translate directly to interbody fusion cages. While bone ingrowth was robust and improved with time in cortical sites with a line-to-line implantation condition, the same response was not found in cancellous sites even when the implants were placed in a press fit manner. Osseointegration into the porous walls with 3D porous interbody cages was similar to the cancellous implantation sites rather than the cortical sites. The porous domains of the 3D-printed device, in general, were filled with fibrovascular tissue while some bone integration into the porous cages was found at 12 weeks when fusion within the aperture was present.

CONCLUSION

Anatomical site, surgical preparation, biomechanical loading, and graft material play an important role in in vivo response. Bone ingrowth in long bone cortical and cancellous sites does not translate directly to interbody fusions.

Enhanced bioactivity of titanium-coated polyetheretherketone implants created by a high-temperature 3D printing process

Polyetheretherketone (PEEK), one of the potential alternatives to metallic materials for implants, necessarily involves high temperature process conditions to be three-dimensionally (3D) printed. We developed a 3D printing setup equipped with thermally stabilized modules of the printing nozzle and building chamber, by which the PEEK implants could be successfully manufactured. Under optimized printing conditions, the maximal mechanical strength of the 3D printed sample attained over 80% of the original bulk property of PEEK. To enhance the interfacial biocompatibility, the as-printed implants were postprocessed with titanium (Ti) sputtering. The Ti-coated surfaces were evaluated through characterization studies of x-ray diffraction spectra, microscopic topographies, and wetting properties. For the in vitro tests, preosteoblasts were cultured on the developed PEEK-Ti structures and evaluated in terms of cell adhesion, proliferation, and osteogenic differentiation. In addition, the bone regeneration capability of the PEEK-Ti implants was confirmed by animal experiments using a rabbit tibia defect model for a period of 12 weeks. In the overall in vitro and in vivo tests, we confirmed the superior bioactivities of the Ti-modified and 3D printed interface by comparisons between the samples of machined and printed samples with or without Ti coating. Taken together, the comprehensive manufacturing approaches that involve 3D printing and biocompatible postprocessing are expected to have universal applicability in a wide range of bone tissue engineering.

ZnO and Hydroxyapatite-Modified Magnesium Implant with a Broad Spectrum of Antibacterial Properties and a Unique Minimally Invasive Defined Degrading Capability

ZnO and hydroxyapatite-based membranes have been proposed to improve the antibacterial properties and anticorrosion capabilities of the magnesium implant, simultaneously. More importantly, the concept of minimally invasive surgery has been introduced to define the degradation timing of the as-modified magnesium implant. With the aid of a Kirschner wire, the as-prepared membrane could immediately change from the "protective layer" to the "degradation accelerator" of the implant material. The subsequent studies have implied that this membrane could be a promising avenue to create a biocompatible and lightweight implant material with a valuable personal customized degradable timing capability.

[Safety and efficacy of an electron beam melting technique-manufactured titanium mesh cage for lumbar interbody fusion]

BACKGROUND

Electron beam melting (EBM) technique enables cage design changes such as the integration of guide rails on the cage surface or a 3D matrix for osseointegration. A change in manufacturing technique or design can lead to a decreased fusion rate or impaired applicability.

OBJECTIVE

The aim of the present study was to evaluate cage handling, lordosis reconstruction capability, and fusion rate 1 year after surgery.

MATERIALS AND METHODS

In this study, 50 patients who had undergone minimally invasive transforaminal lumbar interbody fusion (TLIF) or open posterior lumbar interbody fusion (PLIF) using an EBM-manufactured cage were retrospectively included. Fusion evaluation was based on routinely performed CTs and flexion-extension radiographs 12 months postoperatively. Lumbar and segmental lordosis were compared between pre-, post, and 1‑year follow-up. Postoperative cage position was used for evaluation of cage handling.

RESULTS

The radiological fusion rate was 97% at the 1‑year follow-up. Two cages were placed into the endplates during surgery without an effect on fusion. In 31% of the cages, placement at the anterior third of the disk space was possible. Lumbar lordosis was improved by a mean of 5° and segmental lordosis by a mean of 4°. At final follow-up, 1° was lost in both parameters. No implant-associated complications were registered.

CONCLUSION

The implant is safe and leads to a very high fusion rate. A learning curve results from the fact that the cage follows a defined radius dictated by the guide rails. Addressing this, exact placement at the anterior endplate can be achieved.

3-dimensional printing for anterior cervical surgery: a review

Age-related degenerative changes and non-spondylotic pathologies of the cervical spine such as trauma and tumor can lead to compression of neurological structures and result in substantial alteration of the structural anatomy. The end-goal of surgical intervention is to decompress the neural structures which can be achieved via an anterior or a posterior approach, and stabilization of segments to restore stability and alignment. Three-dimensional printing (3DP or Additive Manufacturing) has been applied to the field of medicine, in particular orthopedics and neurosurgery. Coupled with advances of medical imaging such as computed tomography (CT) scans and magnetic resonance imaging (MRI), accurate 3D models of patient anatomy can be produced, and patient-specific implants (PSIs) for complex anatomical reconstruction have all been applied with positive outcomes. 3D printed implants have been applied in particular to the cervical spine predominantly due to the complex and relatively small osteological anatomy and the proximity of important neurovascular structures to the surgical sites. The purpose of this review is to evaluate the current application of 3DP for cervical spinal implants. This includes a review on the available literature on 3D printed PSIs and current available 3D printed "off-the-shelf" (OTS) implants (3D-OTS). Suitable materials for 3DP of spinal implants and the future prospect of cervical implants will be discussed. The review will be concluded with a suggested guide for carrying future studies to evaluate the efficacy and safety of 3DP for cervical spinal implants.