Biological response to wear debris generated in carbon based composites as potential bearing surfaces for artificial hip joints

Effect of carbon-fiber-reinforced polyetheretherketone on stress distribution in a redesigned tumor-type knee prosthesis: a finite element analysis

Background: Surgery for bone tumors around the knee often involves extensive resection, making the subsequent prosthetic reconstruction challenging. While carbon fiber-reinforced polyetheretherketone (CF-PEEK) has been widely used in orthopedic implants, its application in tumor-type prosthesis is limited. This study aims to evaluate the feasibility of using 30wt% and 60wt% carbon fiber-reinforced polyetheretherketone (CF30-PEEK and CF60-PEEK) as materials for a redesigned tumor-type knee prosthesis through numerical analysis. Methods: A knee joint model based on CT data was created, and the resection and prosthetic reconstruction were simulated. Three finite element models of the prostheses, representing the initial and updated designs with CoCrMo and CFR-PEEK components, were constructed. Loading conditions during standing and squatting were simulated with forces of 700 N and 2800 N, respectively. Finite element analysis was used to analyze the von Mises stress and stability of all components for each prosthesis type. Results: After improvements in both material and design, the new Type 3 prosthesis showed significantly lower overall stress with stress being evenly distributed. Compared with the initial design, the maximum von Mises stress in Type 3 was reduced by 53.9% during standing and 74.2% during squatting. In the standing position, the maximum stress in the CF30-PEEK femoral component decreased by 57.3% compared with the initial design which was composed of CoCrMo, while the stress in the CF60-PEEK cardan shaft remained consistent. In the squatting position, the maximum stress in the femoral component decreased by 81.9%, and the stress in the cardan shaft decreased by 46.5%. Conclusion: The incorporation of CF30-PEEK effectively transmits forces and reduces stress concentration on the femoral component, while CF60-PEEK in the redesigned cardan shaft significantly reduces stress while maintaining stiffness. The redesigned prosthesis effectively conducts loading force and demonstrates favorable biomechanical characteristics, indicating the promising potential of utilizing CF30-PEEK and CF60-PEEK materials for tumor-type knee prostheses. The findings of this study could provide novel insights for the design and development of tumor-type knee prostheses.

An overview of the tribological and mechanical properties of PEEK and CFR-PEEK for use in total joint replacements

Poly-ether-ether-ketone (PEEK) and PEEK composites are outstanding candidates for biomedical applications, such as orthopedic devices, where biocompatibility and modulus match with surrounding tissue are requisite for long-term success. The mechanical properties can be optimized by incorporating fillers such as continuous and chopped carbon fibers. While much is known about the mechanical and tribological behavior of PEEK composites, there are few articles that summarize the viability of using PEEK reinforced with carbon fibers in orthopedic implants. This paper reviews biocompatibility, tribological, and mechanical studies on PEEK and their composites with carbon fibers, notably PEEK reinforced with polyacrylonitrile (PAN)-based carbon fibers and PEEK reinforced with pitch-based carbon fibers, for application in orthopedics and total joint replacements (TJRs). The main objectives of this review are two-fold. Firstly, this paper aims to assist designers in making informed decisions on the suitability of using PEEK and PEEK composites in orthopedic applications; as it is not well understood how these materials perform on the whole in orthopedics and TJRs. Secondly, this paper aims to serve as a centralized paper in which researchers can gain information on the tribological and mechanical advancements of PEEK and PEEK composites.

Long Term Results of a Rotating Hinge Total Knee Prosthesis With Carbon-Fiber Reinforced Poly-Ether-Ether-Ketone (CFR-PEEK) as Bearing Material

Background: The use of rotating hinge (RH) prostheses for severe primary as well as revision arthroplasty is widely established. Due to the steadily increasing number of RH prostheses, we aimed to assess the complication frequencies, complication types and clinical outcomes of a modern RH hinge prosthesis using a new bearing material with a minimum follow-up of 7 years.

Methods: Fifty-six consecutive patients who received the EnduRo^® RH prosthesis using carbon-fiber reinforced poly-ether-ether-ketone (CFR-PEEK) as bearing material were included in this prospective study: 21 patients (37.5%) received the prosthesis as a primary total knee arthroplasty (TKA) and 35 patients (62.5%) underwent revision total knee arthroplasties (rTKA). Clinical and radiographic examinations were performed preoperatively, postoperatively after three and 12 months and annually thereafter. Clinical scores were documented for each patient. Competing risk analysis was assessed with respect to indication and failure mode.

Results: Knee Society Score (KSS), Western Ontario and McMaster Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS) and range of motion (ROM) improved significantly compared to preoperative values (p < 0.0001). The overall cumulative incidence for revision surgery was 23.6% at 7 years and the cumulative incidence for complications associated with failure of the prothesis was 5.6% at 7 years, respectively. Complications occurred more frequently in the revision group (p = 0.002).

Conclusion: The evaluated RH prosthesis provided reliable and durable results for a minimum follow-up of 7 years. Prosthesis survival was successful considering the complexity of the cases. The use of this RH system in primary patients showed high survival rates and long-term functional outcomes and clinical outcomes proved to be satisfying in both revision and primary cases. No adverse events were associated with the new bearing material CFR-PEEK.

Disappointing long-term outcome of THA with carbon-fiber-reinforced poly-ether-ether-ketone (CFR-PEEK) as acetabular insert liner: a prospective study with a mean follow-up of 14.3 years

INTRODUCTION

Insert liner wear of the acetabular component is one of the predictive values for survival of total hip arthroplasties (THAs). This prospective single-centre study was designed to evaluate the follow-up of carbon-fiber-reinforced poly-ether-ether-ketone (CFR-PEEK) insert liner used as bearing in cementless THAs.

METHODS

29 healthy patients with an indication for cementless THA were selected for a CFR-PEEK insert liner and followed over time. All patients received a cementless THA with a CFR-PEEK insert liner used as bearing. At different follow-up moments patients were routinely examined and were analysed using the Oxford Hip Score (OHS), the modified Merle d'Aubigne-Postel (MAP) score, and radiologically. At the follow up moments the plain radiographics where assessed for loosening, cyst formations and wear of the CFR-PEEK liners.

RESULTS

At a mean of 14.3 years follow-up 4 revisions of the acetabular component were performed, resulting in a survival rate of 86.5% (CI 95%, 72.4-96.6). A statistically significant difference in OHS and MAP scores between pre- and postoperative follow-up moments was observed. The acetabular components of the remaining patients showed no radiological abnormalities at 14.3 years follow-up. The overall CFR-PEEK wear was low, with a mean of 0.81 (0.2-1.4) mm wear at 14.3 years follow-up.

CONCLUSIONS

In this series we found an aseptic loosening with unclear reasons in 4 well-positioned acetabular components, hence we do not recommend routine use of CFR-PEEK insert liners as bearing in cementless THAs. All the remaining THAs and acetabular components were in situ without abnormalities at 14.3 years follow-up.

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.

Chromium Oxide Nanoparticle Impaired Osteogenesis and Cellular Response to Mechanical Stimulus

Background

Release of metallic wear particles from hip replacement implants is closely associated with aseptic loosening that affects the functionality and survivorship of the prostheses. Chromium oxide nanoparticles (CrNPs) are the dominant form of the wear particles found in the periprosthetic tissues. Whether CrNPs play a role in the clinically observed particle-induced osteolysis, tissue inflammatory reactions and functional activities of human mesenchymal stem cells (MSCs) remain unknown.

Methods

A tibia-defect rat model, cytotoxicity assays and flow cytometry were applied to study the effect of CrNPs on MSCs survival and macrophage inflammatory response. Also, oscillatory fluid flow stimulation was used to analyse the osteogenic differentiation of MSCs while treated by CrNPs. In addition, the influence of CrNPs on MSC biomechanical properties was determined via atomic force microscope (AFM) and fluorescence microscopy.

Results

It was found that implantation of CrNPs significantly decreased bone formation in vivo. CrNPs had no obvious effects on inflammatory cytokines release of U937 macrophages. Additionally, CrNPs did not interfere with MSCs osteogenic differentiation under static culture. However, the upregulated osteogenic differentiation of MSCs due to fluid flow stimulation was reduced by CrNPs in a dose-dependent manner. Moreover, osteogenic gene expression of OPN, Cox2 and Rnux2 after mechanical stimulation was also decreased by CrNPs treatments. Furthermore, cell elasticity and adhesion force of MSCs were affected by CrNPs over 3 days of exposure. We further verified that these effects of CrNPs could be associated with its interruption on cell mechanical properties.

Conclusion

The results demonstrated that CrNPs impaired cellular response to mechanical stimulus and osteogenesis without noticeable effects on the survival of the human MSCs.

Probing the Influence of γ-Sterilization on the Oxidation, Crystallization, Sliding Wear Resistance, and Cytocompatibility of Chemically Modified Graphene-Oxide-Reinforced HDPE/UHMWPE Nanocomposites and Wear Debris

Osteolysis and aseptic loosening due to wear at the articulating interfaces of prosthetic joints are considered to be the key concerns for implant failure in load-bearing orthopedic applications. In an effort to reduce the wear and processing difficulties of ultrahigh-molecular-weight polyethylene (UHMWPE), our research group recently developed high-density polyethylene (HDPE)/UHMWPE nanocomposites with chemically modified graphene oxide (mGO). Considering the importance of sterilization, this work explores the influence of γ-ray dosage of 25 kGy on the clinically relevant performance-limiting properties of these newly developed hybrid nanocomposites in vitro. Importantly, this work also probes into the cytotoxic effects of the wear debris of different compositions and sizes on MC3T3 murine osteoblasts and human mesenchymal stem cells (hMSCs). In particular, γ-ray-sterilized 1 wt % mGO-reinforced HDPE/UHMWPE nanocomposites exhibit an improvement in the oxidation index (16%), free energy of immersion (-12.1 mN/m), surface polarity (5.0%), and hardness (42%). Consequently, such enhancements result in better tribological properties, especially coefficient of friction (+13%) and wear resistance, when compared with UHMWPE. A spectrum of analyses using transmission electron microscopy (TEM) and in vitro cytocompatibility assessment demonstrate that phagocytosable (0.5-4.5 μm) sterilized 1 mGO wear particles, when present in culture media at 5 mg/mL concentration, induce neither significant reduction in MC3T3 murine osteoblast and hMSC growth nor cell morphology phenotype, during 24, 48, and 72 h of incubation. Taken together, this study suggests that γ-ray-sterilized HDPE/UHMWPE/mGO nanocomposites can be utilized as promising articulating surfaces for total joint replacements.

Carbon/PEEK nails: a case-control study of 22 cases

BACKGROUND

Interest around carbon/PEEK plates and nails has been raising. The elastic modulus close to the bone, the high load-carrying capacity and radiolucency make CFR/PEEK materials a potential breakthrough. In the literature, there are abundant data about CFR/PEEK plates in the treatment of proximal humerus, distal radius and distal fibula fractures. In patients affected by bone metastasis, CFR/PEEK nails were proved effective and safe with 12 months of follow-up. Very little is known about performances of CFR/PEEK nails in patients affected by other pathologies.

PURPOSES

The aim of the study was to evaluate safety and efficacy of CFR/PEEK nails in the treatment of various pathological conditions. It was also investigated whatever radiolucency of this nails could lead to a more objective evaluation of bone callus or disease site.

PATIENTS AND METHODS

In the study group were included 20 patients (22 bone segments) who underwent CFR/PEEK nail implantation (eight humerus, one tibia, nine femur and four knee arthrodesis). They were affected by pathological fractures, and in four cases, they required an arthrodesis of the knee. They were retrospectively evaluated considering nail failures and bone callus or disease progression (RUSH scores). Mean follow-up time was 11 months (min 6.8-max 20.3). In the control group were included patients treated with titanium nails in the same institution for the same pathologies. An interclass correlation coefficient (ICC) analysis was performed in both groups considering RUSH scores by two expert surgeon from two institution to assess whether radiolucency could lead to a more objective evaluation of disease or bone callus site.

RESULTS

The ICC of mean values between RUSH scores was 0.882 (IC 95%: 0.702-0.953) in the CFR/PEEK group, while it was 0.778 (IC 95%: 0.41-0.91) in the titanium group. Observers' evaluation showed a significantly higher obscuration by titanium nails than by CFR/PEEK nails. No osteosynthesis failures were reported in both groups.

CONCLUSIONS

Our results confirm the safety of CFR/PEEK nails in the short-medium term. The radiolucency of these materials led our observers to perform more objective evaluations of bone callus formation or disease progression compared to the titanium group given the higher ICC.

LEVEL OF EVIDENCE

III Case-control therapeutic study.

Effect of insert material on forces on quadriceps, collateral ligament, and patellar tendon after rotating platform mobile-bearing total knee arthroplasty

BACKGROUND

There is a gradual increase in the number of patients for total knee arthroplasty (TKA), and TKA demonstrates reliable clinical outcomes. The orthopaedic biomaterials community continuously attempted over the past decades to improve the longevity of UHMWPE in TKA by using various improved technologies. Polyetheretherketone (PEEK) and carbon fiber reinforced-PEEK(CFR-PEEK) are suggested as potential tibial insert materials to replace UHMWPE in some applications. The aim of this study involves evaluating the biomechanical effects of UHMWPE and CFR-PEEK tibial materials on mobile-bearing TKA.

METHODS

The finite element (FE) model was obtained by conducting computed tomography and magnetic resonance imaging. The FE investigation included three types of loading conditions corresponding to the loads used in the experiments for FE model validation and model predictions under deep-knee bend loading conditions. We investigated forces on quadriceps, collateral ligament and patellar tendon with UHMWPE and CCFR-PEEK tibial insert materials under the deep-knee-bend condition.

RESULTS

Quadriceps force decreased with flexion for CFR-PEEK when compared to that for UHMWPE. A similar trend was observed in terms of the patellar tendon force. An opposite trend was observed in the collateral ligament. Medial collateral ligament force in the CFR-PEEK exceeded that in the UHMWPE, and lateral collateral ligament force in the UHMWPE exceeded that in the CFR-PEEK.

CONCLUSION

The CFR-PEEK represents an alternative insert material given its superior biomechanical effect after mobile-bearing total knee arthroplasty. However, a balance between the medial and lateral ligaments is considered as an important factor in the CFR-PEEK tibial insert due to its opposite biomechanical effect.

Prediction of Wear on Tibial Inserts Made of UHMWPE, PEEK, and CFR-PEEK in Total Knee Arthroplasty Using Finite-Element Analysis

The wear of tibial inserts in total knee arthroplasty (TKA) remains a major limitation of longevity. However, wear tests are expensive and time-consuming. Computational wear prediction using a finite-element (FE) model followed by validation through comparison with experimental data is effective for assessing new prosthetic designs or materials prior to functional testing and surgical implementation. In this study, the kinematics, volumetric wear, and wear depth of tibial inserts made of different materials (ultrahigh-molecular weight polyethylene (UHMWPE), polyetheretherketone (PEEK), and carbon fiber-reinforced PEEK (CFR–PEEK)) in TKA were evaluated by employing FE models and analysis. The differences among the materials were evaluated using adaptive wear modeling to predict the wear depth, volumetric wear, and kinematics under a gait loading condition. The volumetric wear and wear depth of the CFR–PEEK decreased by 87.4% and 61.3%, respectively, compared with those of the UHMWPE, whereas the PEEK exhibited increased volumetric wear and wear depth. These results suggest that CFR–PEEK is a good alternative to UHMWPE as a promising and suitable material for tibial inserts used in TKA. However, orthopedic research should be performed to evaluate the threshold conditions and appropriate applications for the newly developed and introduced biomaterial.

Prediction of in vivo lower cervical spinal loading using musculoskeletal multi-body dynamics model during the head flexion/extension, lateral bending and axial rotation

Cervical spine diseases lead to a heavy economic burden to the individuals and societies. Moreover, frequent post-operative complications mean a higher risk of neck pain and revision. At present, controversy still exists for the etiology of spinal diseases and their associated complications. Knowledge of in vivo cervical spinal loading pattern is proposed to be the key to answer these questions. However, direct acquisition of in vivo cervical spinal loading remains challenging. In this study, a previously developed cervical spine musculoskeletal multi-body dynamics model was utilized for spinal loading prediction. The in vivo dynamic segmental contributions to head motion and the out-of-plane coupled motion were both taken into account. First, model validation and sensitivity analysis of different segmental contributions to head motion were performed. For model validation, the predicted intervertebral disk compressive forces were converted into the intradiskal pressures and compared with the published experimental measurements. Significant correlations were found between the predicted values and the experimental results. Thus, the reliability and capability of the cervical spine model was ensured. Meanwhile, the sensitivity analysis indicated that cervical spinal loading is sensitive to different segmental contributions to head motion. Second, the compressive, shear and facet joint forces at C3–C6 disk levels were predicted, during the head flexion/extension, lateral bending and axial rotation. Under the head flexion/extension movement, asymmetric loading patterns of the intervertebral disk were obtained. In comparison, symmetrical typed loading patterns were found for the head lateral bending and axial rotation movements. However, the shear forces were dramatically increased during the head excessive extension and lateral bending. Besides, a nonlinear correlation was seen between the facet joint force and the angular displacement. In conclusion, dynamic cervical spinal loading was both intervertebral disk angle-dependent and level-dependent. Cervical spine musculoskeletal multi-body dynamics model provides an attempt to comprehend the in vivo biomechanical surrounding of the human head-neck system.

Wear and Friction of UHMWPE-on-PEEK OPTIMA™

PEEK-OPTIMA™ is being considered as an alternative bearing material to cobalt chrome in the femoral component of total knee replacement to provide a metal-free implant. The aim of this study was to investigate the influence of lubricant temperature (standard rig running and elevated temperature (~36 °C)) on the wear of a UHMWPE-on-PEEK OPTIMA™ bearing couple using different lubricant protein concentrations (0%, 2%, 5%, 25% and 90% bovine serum) in a simple geometry pin-on-plate configuration. Friction was also investigated under a single temperature condition for different lubricant protein concentrations. The studies were repeated for UHMWPE-on-cobalt chrome in order to compare relationships with temperature (wear only) and lubricant protein concentration (wear and friction). In low lubricant protein concentrations (≤ 5%) there was no influence of temperature on the wear factors of UHMWPE-on-PEEK. With 25% bovine serum, the wear factor of UHMWPE-on-PEEK reduced by half at elevated temperature. When tested in high protein concentration (90% serum), there was no influence of temperature on the wear factor of UHMWPE-on-PEEK. These temperature dependencies were not the same for UHMWPE-on-cobalt chrome. For both material combinations, there was a trend of decreasing friction with increasing protein concentration once protein was present in the lubricant. This study has shown the importance of the selection of appropriate test conditions when investigating the wear and friction of different materials, in order to minimise test artefacts such as polymer transfer, and protein precipitation and deposition.

Cobalt and Titanium nanoparticles influence on human osteoblast mitochondrial activity and biophysical properties of their cytoskeleton

We investigated the biophysical effects (cell elasticity and spring constant) caused on Saos-2 human osteoblast-like cells by nanosized metal (Co and Ti) wear debris, as well as the adhesive characteristics of cells after exposure to the metal nanoparticles. Cell mitochondrial activity was investigated using the MTT assays; along with LDH assay, metal uptake, cell apoptosis and mineralisation output (alizarin red assay) of the cells. Osteoblasts mitochondrial activity was not affected by Ti nanoparticles at concentrations up to 1 mg/ml and by Cobalt nanoparticles at concentrations < 0.5 mg/ml; however elasticity and spring constant were significantly modified by the exposure to nanoparticles of these metals in agreement with the alteration of cell conformation (shape), as result of the exposure to simulated wear debris, demonstrated by fluorescence images after actin staining.

Midterm Results of a New Rotating Hinge Knee Implant: A 5-Year Follow-Up

Background

In the current study, we investigated midterm results of a new rotating hinge total knee arthroplasty (EnduRo prosthesis), which uses a new bearing material (CFR PEEK).

Methods

We prospectively analysed data of 50 patients with a minimum follow-up of 5 years. In 24 (48%) patients, a primary implantation was performed and 26 (52%) were revision cases. Clinical and radiographic examinations were performed preoperatively as well as postoperatively after 3 and 12 months and annually thereafter. The Knee Society Score (KSS), WOMAC, Oxford Knee Score (OKS), and range of motion (ROM) were used for clinical assessment.

Results

KSS, WOMAC, OKS, and ROM significantly improved between the preoperative and the follow-up investigations. The overall survival rate with revision for any reason as an endpoint was 77.9% after five years. The number of complications was significantly higher in the revision group (p = 0.003).

Conclusion

The EnduRo prosthesis provides highly satisfying clinical and functional results in severe primary as well as in revision cases. Implant-associated complications were rare. However, in cases of revision surgery, the risk for complications was considerably high, mostly related to previous joint infections and poor soft tissue quality.

The Biologic Response to Polyetheretherketone (PEEK) Wear Particles in Total Joint Replacement: A Systematic Review

BACKGROUND

Polyetheretherketone (PEEK) and its composites are polymers resistant to fatigue strain, radiologically transparent, and have mechanical properties suitable for a range of orthopaedic applications. In bulk form, PEEK composites are generally accepted as biocompatible. In particulate form, however, the biologic response relevant to joint replacement devices remains unclear. The biologic response to wear particles affects the longevity of total joint arthroplasties. Particles in the phagocytozable size range of 0.1 µm to 10 µm are considered the most biologically reactive, particularly particles with a mean size of < 1 µm. This systematic review aimed to identify the current evidence for the biologic response to PEEK-based wear debris from total joint arthroplasties.

QUESTIONS/PURPOSES

(1) What are the quantitative characteristics of PEEK-based wear particles produced by total joint arthroplasties? (2) Do PEEK wear particles cause an adverse biologic response when compared with UHMWPE or a similar negative control biomaterial? (3) Is the biologic response affected by particle characteristics?

METHODS

Embase and Ovid Medline databases were searched for studies that quantified PEEK-based particle characteristics and/or investigated the biologic response to PEEK-based particles relevant to total joint arthroplasties. The keyword search included brands of PEEK (eg, MITCH, MOTIS) or variations of PEEK types and nomenclature (eg, PAEK, CFR-PEEK) in combination with types of joint (eg, hip, knee) and synonyms for wear debris or immunologic response (eg, particles, cytotoxicity). Peer-reviewed studies, published in English, investigating total joint arthroplasty devices and cytotoxic effects of PEEK particulates were included. Studies investigating devices without articulating bearings (eg, spinal instrumentation devices) and bulk material or contact cytotoxicity were excluded. Of 129 studies, 15 were selected for analysis and interpretation. No studies were found that isolated and characterized PEEK wear particles from retrieved periprosthetic human tissue samples.

RESULTS

In the four studies that quantified PEEK-based particles produced using hip, knee, and spinal joint replacement simulators, the mean particle size was 0.23 µm to 2.0 µm. The absolute range reported was approximately 0.01 µm to 50 µm. Rod-like carbon particulates and granular-shaped PEEK particles were identified in human tissue by histologic analysis. Ten studies, including six animal models (rat, mouse, and rabbit), three cell line experiments, and two human tissue retreival studies, investigated the biologic response to PEEK-based particles. Qualitative histologic assessments showed immunologic cell infiltration to be similar for PEEK particles when compared with UHMWPE particles in all six of the animal studies identified. However, increased inflammatory cytokine release (such as tumor necrosis factor-α) was identified in only one in vitro study, but without substantial suppression in macrophage viability. Only one study tested the effects of particle size on cytotoxicity and found the largest unfilled PEEK particles (approximately 13 µm) to have a toxic effect; UHMWPE particles in the same size range showed a similar cytotoxic effect.

CONCLUSIONS

Wear particles produced by PEEK-based bearings were, in almost all cases, in the phagocytozable size range (0.1-10 µm). The studies that evaluated the biologic response to PEEK-based particles generally found cytotoxicity to be within acceptable limits relative to the UHMWPE control, but inconsistent when inflammatory cytokine release was considered.

CLINICAL RELEVANCE

To translate new and advanced materials into clinical use more quickly, the clinical relevance and validity of preclinical tests need to be improved. To achieve this for PEEK-based devices, human tissue retrieval studies including subsequent particle isolation and characterization analyses are required. In vitro cell studies using isolated wear particles from tissue or validated joint replacement simulators, instead of manufactured particles, are also required.

PEEK-OPTIMA™ as an alternative to cobalt chrome in the femoral component of total knee replacement: A preliminary study

PEEK-OPTIMA^™ (Invibio Ltd, UK) has been considered as an alternative joint arthroplasty bearing material due to its favourable mechanical properties and the biocompatibility of its wear debris. In this study, the potential to use injection moulded PEEK-OPTIMA^™ as an alternative to cobalt chrome in the femoral component of a total knee replacement was investigated in terms of its wear performance. Experimental wear simulation of three cobalt chrome and three PEEK-OPTIMA^™ femoral components articulating against all-polyethylene tibial components was carried out under two kinematic conditions: 3 million cycles under intermediate kinematics (maximum anterior-posterior displacement of 5 mm) followed by 3 million cycles under high kinematic conditions (anterior-posterior displacement 10 mm). The wear of the GUR1020 ultra-high-molecular-weight polyethylene tibial components was assessed by gravimetric analysis; for both material combinations under each kinematic condition, the mean wear rates were low, that is, below 5 mm³/million cycles. Specifically, under intermediate kinematic conditions, the wear rate of the ultra-high-molecular-weight polyethylene tibial components was 0.96 ± 2.26 mm³/million cycles and 2.44 ± 0.78 mm³/million cycle against cobalt chrome and PEEK-OPTIMA^™ implants, respectively (p = 0.06); under high kinematic conditions, the wear rates were 2.23 ± 1.85 mm³/million cycles and 4.44 ± 2.35 mm³/million cycles, respectively (p = 0.03). Following wear simulation, scratches were apparent on the surface of the PEEK-OPTIMA^™ femoral components. The surface topography of the femoral components was assessed using contacting profilometry and showed a statistically significant increase in measured surface roughness of the PEEK-OPTIMA^™ femoral components compared to the cobalt chrome implants. However, this did not appear to influence the wear rate, which remained linear over the duration of the study. These preliminary findings showed that PEEK-OPTIMA^™ gives promise as an alternative bearing material to cobalt chrome alloy in the femoral component of a total knee replacement with respect to wear performance.

Histopathological Analysis of PEEK Wear Particle Effects on the Synovial Tissue of Patients

Introduction. Increasing interest developed in the use of carbon-fiber-reinforced-poly-ether-ether-ketones (CFR-PEEK) as an alternative bearing material in knee arthroplasty. The effects of CFR-PEEK wear in in vitro and animal studies are controversially discussed, as there are no data available concerning human tissue. The aim of this study was to analyze human tissue containing CFR-PEEK as well as UHMWPE wear debris. The authors hypothesized no difference between the used biomaterials. Methods and Materials. In 10 patients during knee revision surgery of a rotating-hinge-knee-implant-design, synovial tissue samples were achieved (tibial inserts: UHMWPE; bushings and flanges: CFR-PEEK). One additional patient received revision surgery without any PEEK components as a control. The tissue was paraffin-embedded, sliced into 2 μm thick sections, and stained with hematoxylin and eosin in a standard process. A modified panoptical staining was also done. Results. A “wear-type” reaction was seen in the testing and the control group. In all samples, the UHMWPE particles were scattered in the tissue or incorporated in giant cells. CFR-PEEK particles were seen as conglomerates and only could be found next to vessels. CFR-PEEK particles showed no giant-cell reactions. In conclusion, the hypothesis has to be rejected. UHMWPE and PEEK showed a different scatter-behavior in human synovial tissue.

A matched-pair comparison of two different locking plates for valgus-producing medial open-wedge high tibial osteotomy: peek-carbon composite plate versus titanium plate

PURPOSE

The first purpose of this study was to compare the clinical and radiographic outcome of two different locking plates used for valgus-producing medial open-wedge high tibial osteotomy (HTO). The second purpose was to histologically evaluate peek-carbon wear for biocompatibility.

METHODS

Twenty-six consecutive patients undergoing open-wedge HTO using the first-generation PEEKPower HTO-Plate® (Group I) were matched with 26 patients after open-wedge HTO with the TomoFix™ plate (Group II). Clinical scores (visual analogue scale for pain, WOMAC, Lysholm score) were obtained preoperatively and at a minimum follow-up of 24 months postoperatively. Fixation stability was evaluated radiographically by comparing the medial proximal tibial angle (MPTA) and tibial slope 2 days after open-wedge HTO and after implant removal. Tissue samples of Group I were collected at the time of implant removal for histologic evaluation.

RESULTS

Implant-related complications occurred in 15 % (n = 4) of Group I and 0 % of Group II. Out of them, 3 implant replacements were excluded from statistical analyses. After a final median follow-up of 25 months (range 24-31), the clinical scores in both groups showed significant improvements compared to preoperatively (visual analogue scale, WOMAC, Lysholm score; p < 0.001), without significant group differences (visual analogue scale, n.s.; WOMAC, n.s.; Lysholm score, n.s.). No significant differences between baseline and follow-up measurements for MPTA and tibial slope were observed within each group (MPTA: Gr. I, n.s.; Gr. II, n.s.; tibial slope: Gr. I, n.s.; Gr. II, n.s.) or between the two groups (MPTA, n.s.; tibial slope, n.s.). In histologic samples, CF PEEK abrasion did not induce inflammation or tissue necrosis.

CONCLUSION

The first-generation PEEKPower HTO-Plate® provided a higher rate of implant-related complications compared to the TomoFix™ plate at a minimum follow-up of 24 months after valgus-producing open-wedge HTO. Therefore, it is not recommended to use the first-generation PEEKPower HTO-Plate® in the clinical practice.

LEVEL OF EVIDENCE

III.

The Use of Carbon-Fiber-Reinforced (CFR) PEEK Material in Orthopedic Implants: A Systematic Review

Carbon-fiber-reinforced polyetheretherketone (CFR-PEEK) has been successfully used in orthopedic implants. The aim of this systematic review is to investigate the properties, technical data, and safety of CFR-PEEK biomaterial and to evaluate its potential for new innovation in the design of articulating medical devices. A comprehensive search in PubMed and EMBASE was conducted to identify articles relevant to the outcomes of CFR-PEEK orthopedic implants. The search was also expanded by reviewing the reference sections of selected papers and references and benchmark reports provided by content experts. A total of 23 articles were included in this review. There is limited literature available assessing the performance of CFR-PEEK, specifically as an implant material for arthroplasty systems. Nevertheless, available studies strongly support CFR-PEEK as a promising and suitable material for orthopedic implants because of its biocompatibility, material characteristics, and mechanical durability. Future studies should continue to investigate CFR-PEEK’s potential benefits.

Effects of CoCr metal wear debris generated from metal-on-metal hip implants and Co ions on human monocyte-like U937 cells

Hip resurfacing with cobalt-chromium (CoCr) alloy was developed as a surgical alternative to total hip replacement. However, the biological effects of nanoparticles generated by wear at the metal-on-metal articulating surfaces has limited the success of such implants. The aim of this study was to investigate the effects of the combined exposure to CoCr nanoparticles and cobalt ions released from a resurfacing implant on monocytes (U937 cells) and whether these resulted in morphology changes, proliferation alterations, toxicity and cytokine release. The interaction between prior exposure to Co ions and the cellular response to nanoparticulate debris was determined to simulate the situation in patients with metal-on-metal implants receiving a second implant. Effects on U937 cells were mainly seen after 120h of treatment. Prior exposure to Co ions increased the toxic effects induced by the debris, and by Co ions themselves, suggesting the potential for interaction in vivo. Increased TNF-α secretion by resting cells exposed to nanoparticles could contribute to osteolysis processes in vivo, while increased IFN-γ production by activated cells could represent cellular protection against tissue damage. Data suggest that interactions between Co ions and CoCr nanoparticles would occur in vivo, and could threaten the survival of a CoCr metal implant.

Interactions between mammalian cells and nano- or micro-sized wear particles: physico-chemical views against biological approaches

Total joint arthroplasty (TJA) is a more and more frequent approach for the treatment of end-stage osteoarthritis in young and active adults; it successfully relieves joint pain and improves function significantly enhancing the health-related quality of life. Aseptic loosening and other wear-related complications are some of the most recurrent reasons for revision of TJA. This review focuses on current understanding of the biological reactions to prosthetic wear debris comparing in vivo and in vitro results. Mechanisms of interactions of various types of cells with metal, polymeric and ceramic wear particles are summarised. Alternative views based on multidisciplinary approaches are proposed to consider physico-chemical, surface parameters of wear particles (such as: particle size, geometry and charge) and material (particle chemical composition and its nature) with biological effects (cellular responses).

Early results of a new rotating hinge knee implant

Background. Indication for rotating hinge (RH) total knee arthroplasty (TKA) includes primary and revision cases, with contradictory results. The aim of this study was to report prospective early results of a new modular rotating hinge TKA (EnduRo). For this implant several new design features and a new bearing material (carbon-fiber reinforced poly-ether-ether-ketone) have been developed. Furthermore, we tried to establish a new classification of failure modes for revision TKA. Methods. 152 EnduRo rotating-hinge prostheses were implanted in two centers. In 90 patients a primary implantation has been performed and 62 patients were revision cases. Knee Society Score (KSS), Western Ontario and McMaster Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS), and Range of motion (ROM) were assessed before surgery, 3 months postoperatively, 12 months postoperatively, and annually thereafter. We defined 3 types of complications: Type 1, infection; type 2, periprosthetic complications; type 3, implant failures. Results. KSS, WOMAC, OKS, and ROM revealed significant improvements between the preoperative and the follow-up investigations. There were 14 complications (9.2%) leading to revision surgery, predominantly type 2. Conclusion. Our study shows excellent clinical results of the EnduRo TKA. Furthermore, no premature material failure or unusual biological response to the new bearing material could be detected.

Future bearing surfaces in total hip arthroplasty

One of the most important issues in the modern total hip arthroplasty (THA) is the bearing surface. Extensive research on bearing surfaces is being conducted to seek an ideal bearing surface for THA. The ideal bearing surface for THA should have superior wear characteristics and should be durable, bio-inert, cost-effective, and easy to implant. However, bearing surfaces that are currently being implemented do not completely fulfill these requirements, especially for young individuals for whom implant longevity is paramount. Even though various new bearing surfaces have been investigated, research is still ongoing, and only short-term results have been reported from clinical trials. Future bearing surfaces can be developed in the following ways: (1) change in design, (2) further improvement of polyethylene, (3) surface modification of the metal, (4) improvement in the ceramic, and (5) use of alternative, new materials. One way to reduce wear and impingement in THA is to make changes in its design by using a large femoral head, a monobloc metal shell with preassembled ceramic liner, dual mobility cups, a combination of different bearing surfaces, etc. Polyethylene has improved over time with the development of highly crosslinked polyethylene. Further improvements can be made by reinforcing it with vitamin E or multiwalled carbon nanotubes and by performing a surface modification with a biomembrane. Surface modifications with titanium nitride or titanium niobium nitride are implemented to try to improve the metal bearings. The advance to the fourth generation ceramics has shown relatively promising results, even in young patients. Nevertheless, further improvement is required to reduce fragility and squeaking. Alternative materials like diamond coatings on surfaces, carbon based composite materials, oxidized zirconium, silicon nitride, and sapphire are being sought. However, long-term studies are necessary to confirm the efficacy of these surfaces after enhancements have been made with regard to fixation technique and implant quality.

The current state of bearing surfaces in total hip replacement

We reviewed the literature on the currently available choices of bearing surface in total hip replacement (THR). We present a detailed description of the properties of articulating surfaces review the understanding of the advantages and disadvantages of existing bearing couples. Recent technological developments in the field of polyethylene and ceramics have altered the risk of fracture and the rate of wear, although the use of metal-on-metal bearings has largely fallen out of favour, owing to concerns about reactions to metal debris. As expected, all bearing surface combinations have advantages and disadvantages. A patient-based approach is recommended, balancing the risks of different options against an individual’s functional demands.

Cite this article: Bone Joint J 2014;96-B:147–56.

Elevated cytokine expression of different PEEK wear particles compared to UHMWPE in vivo

Due to their mechanical properties, there has been growing interest in poly-ether-ether-ketone (PEEK) and its composites as bearing material in total and unicompartmental knee arthroplasty. The aim of this study was to analyze the biological activity of wear particles of two different (pitch and PAN) carbon-fiber-reinforced- (CFR-) PEEK varieties in comparison to ultra-high-molecular-weight-polyethylene (UHMWPE) in vivo. The authors hypothesized no difference between the used biomaterials. Wear particle suspensions of the particulate biomaterials were injected into knee joints of Balb/c mice, which were sacrificed after seven days. The cytokine expression (IL-1β, IL-6, TNF-α) was analyzed immunohistochemically in the synovial layer, the adjacent bone marrow and the articular cartilage. Especially in the bone marrow of the two CFR-PEEK varieties there were increased cytokine expressions compared to the control and UHMWPE group. Furthermore, in the articular cartilage the CFR-PEEK pitch group showed an enhanced cytokine expression, which could be a negative predictor for the use in unicondylar knee systems. As these data suggest an increased proinflammatory potential of CFR-PEEK and its composites in vivo, the initial hypothesis had to be refuted. Summarizing these results, CFR-PEEK seems not to be an attractive alternative to UHMWPE as a bearing material, especially in unicompartmental knee arthroplasty.

Biotribology of a new bearing material combination in a rotating hinge knee articulation

The objective of the present study was to evaluate the biotribological behaviour, in terms of wear and particle release, of bushings and flanges made of carbon fibre reinforced poly-ether-ether-ketone (CFR-PEEK) in articulation with a zirconium nitride (ZrN) multilayer surface coating in a rotating hinge knee system. For the bushings of the rotational and flexion axles and the medial and lateral flanges, a CFR-PEEK with 30% polyacrylonitrile fibre content was used in a new bearing combination with ZrN. In vitro wear simulation was performed for patients with metal ion hypersensitivity, using a new rotating hinge knee design with a ZrN surface articulation in comparison with the clinically established cobalt-chromium version. For the bushings and flanges made of CFR-PEEK subjected to wear simulation, the volumetric wear rates were 2.3±0.48mm(3)million(-1) cycles in articulation to cobalt-chromium as reference and 0.21±0.02mm(3)million(-1) cycles in the coupling with ZrN, a 10.9-fold decrease. The released CFR-PEEK particles were comparable in size and shape for the coupling to cobalt-chromium and ZrN with most of the particles in a size range between 0.1 and 2μm. The study reveals comparable low wear and no macroscopic surface fatigue in a new rotating hinge knee design with highly congruent flanges and axles bushings made of CFR-PEEK articulating to a ZrN multilayer surface coating. Favourable wear behaviour of the newly introduced CFR-PEEK/ZrN coupling in comparison with the clinically established CFR-PEEK/cobalt-chromium articulation was found.

Mechanical properties and cytotoxicity of a resorbable bioactive implant prepared by rapid prototyping technique

Bioceramic processing using rapid prototyping technique (RPT) results in a fragile device that requires thermal treatment to improve the mechanical properties. This investigation evaluates the effect of thermal treatment on the mechanical, porosity, and bioactivity properties as well as the cytotoxicity of a porous silica-calcium phosphate nanocomposite (SCPC) implant prepared by RPT. Porous SCPC implant was subject to 3-h treatment at 800°C, 850°C, or 900°C. The compressive strength (s) and modulus of elasticity (E) were doubled when the sintering temperature is raised from 850 to 900°C measuring (s = 15.326 ± 2.95 MPa and E = 1095 ± 164 MPa) after the later treatment. The significant increase in mechanical properties takes place with minimal changes in the surface area and the percentage of pores in the range 1-356 μm. The SCPC implant prepared at 900°C was loaded with rh-BMP-2 and grafted into a segmental defect in the rabbit ulna. Histology analyses showed highly vascularized bone formation inside the defect. Histopathological analyses of the liver, spleen, kidney, heart, and the lung of rabbits grafted with and without SCPC demonstrated healthy tissues with no signs of toxicity or morphology alterations. Results of the study suggest that it is possible to engineering the mechanical properties of the SCPC implant without compromising its bioactivity. The enhanced bone formation inside the porous SCPC facilitated cell-mediated graft resorption and prohibited any accumulation of the material in the body organs.

A new volar plate DiPhos-RM for fixation of distal radius fracture: preliminary report

We analyzed the efficiency of a new plate DiPhos-RM in CFR-PEEK [carbon-fiber-reinforced poly (etheretherketone)] for the volar fixation of distal radius fractures. The new plate's composition has the advantage of x-ray absolute transparency, therefore allowing to monitor the healing of the fracture. The desired combination of high strength and low rigidity is obtained through the use of the polymer composites CFR-PEEK. In this preliminary study (from March 2012 to June 2012), 10 cases of intra-articular distal radius fractures were treated with DiPhos-RM produced by Lima Corporate (Italy). The fractures were classified according to the AO classification, 4 fractures were type C1, 3 type C2, and 3 were A2. A preoperative computed tomography scan was carried out in all patients. One patient also underwent a postoperative computed tomography scan. Grip strength, range of motion, and DASH score were evaluated at follow-up. There were no cases of hardware failure. Specifically, no loss of position or alignment of fixed-angle locking screws or breakage of the plate were observed. Radiographic union was present at an average of 6 weeks (range, 5 to 8 wk). The overall preliminary experience with this new plate is favorable. The new plate is easy to apply and provides the surgeon dual options of fixed-angle or variable-angle screws. It was rigid enough to maintain the reduction also in AO type C articular fractures.

Significance of nano- and microtopography for cell-surface interactions in orthopaedic implants

Cell-surface interactions play a crucial role for biomaterial application in orthopaedics. It is evident that not only the chemical composition of solid substances influence cellular adherence, migration, proliferation and differentiation but also the surface topography of a biomaterial. The progressive application of nanostructured surfaces in medicine has gained increasing interest to improve the cytocompatibility and osteointegration of orthopaedic implants. Therefore, the understanding of cell-surface interactions is of major interest for these substances. In this review, we elucidate the principle mechanisms of nano- and microscale cell-surface interactions in vitro for different cell types onto typical orthopaedic biomaterials such as titanium (Ti), cobalt-chrome-molybdenum (CoCrMo) alloys, stainless steel (SS), as well as synthetic polymers (UHMWPE, XLPE, PEEK, PLLA). In addition, effects of nano- and microscaled particles and their significance in orthopaedics were reviewed. The significance for the cytocompatibility of nanobiomaterials is discussed critically.

PEEK (Polyether-ether-ketone) Based Cervical Total Disc Arthroplasty: Contact Stress and Lubrication Analysis

This paper presents a theoretical analysis of the maximum contact stress and the lubrication regimes for PEEK (Polyether-ether-ketone) based self-mating cervical total disc arthroplasty. The NuNec® cervical disc arthroplasty system was chosen as the study object, which was then analytically modelled as a ball on socket joint. A non-adhesion Hertzian contact model and elastohydrodynamic lubrication theory were used to predict the maximum contact stress and the minimum film thickness, respectively. The peak contact stress and the minimum film thickness between the bearing surfaces were then determined, as the radial clearance or lubricant was varied. The obtained results show that under 150 N loading, the peak contact stress was in the range 5.9 – 32.1 MPa, well below the yield and fatigue strength of PEEK; the calculated minimum film thickness ranged from 0 to 0.042 µm and the corresponding lambda ratio range was from 0 to 0.052. This indicates that the PEEK based cervical disc arthroplasty will operate under a boundary lubrication regime, within the natural angular velocity range of the cervical spine.

PEEK (Polyether-ether-ketone) Based Cervical Total Disc Arthroplasty: Contact Stress and Lubrication Analysis

This paper presents a theoretical analysis of the maximum contact stress and the lubrication regimes for PEEK (Polyether-ether-ketone) based self-mating cervical total disc arthroplasty. The NuNec^® cervical disc arthroplasty system was chosen as the study object, which was then analytically modelled as a ball on socket joint. A non-adhesion Hertzian contact model and elastohydrodynamic lubrication theory were used to predict the maximum contact stress and the minimum film thickness, respectively. The peak contact stress and the minimum film thickness between the bearing surfaces were then determined, as the radial clearance or lubricant was varied. The obtained results show that under 150 N loading, the peak contact stress was in the range 5.9 – 32.1 MPa, well below the yield and fatigue strength of PEEK; the calculated minimum film thickness ranged from 0 to 0.042 µm and the corresponding lambda ratio range was from 0 to 0.052. This indicates that the PEEK based cervical disc arthroplasty will operate under a boundary lubrication regime, within the natural angular velocity range of the cervical spine.

The effect of betacyclodextrin and hydroxypropyl betacyclodextrin incorporation into plasticized poly(vinyl chloride) on its compatibility with human U937 cells

Di (2-ethyl hexyl) phthalate (DEHP) is one of the main plasticizers used in poly(vinyl chloride) (PVC) medical devices and is currently the only one listed for use in the European Pharmacopoeia Monograph. It leaches out of PVC when the material is in contact with lipophilic media, for example, blood and certain nutritional feeds. Consequently, concerns have been expressed since in certain animal species, DEHP has been shown to exhibit both carcinogenic and reproductive toxic effects. Incorporation of beta cyclodextrin (BCD) and hydroxypropyl betacyclodectrin (HPBCD) into plasticized materials has been reported to decrease the leaching of DEHP. We have investigated whether this results in improved in vitro biocompatibility by measuring the responses of U937 cells to plasticized PVC in the presence and absence of added BCD or HPBCD. Growth and viability of the U937 cells, as well as tumor necrosis factor-α (TNF-α) production in contact with these materials revealed no significant difference between unmodified plasticized PVC materials and those containing BCD or HPBCD. Lipopolysaccharide (LPS) was used to elicit TNF-α production, and the response of cells to LPS in the presence of the PVC materials was evaluated. When PVC was modified by addition of HPBCD there was a significant reduction in the TNF-α production in response to LPS. Modification of plasticized PVC biomaterials by adding cyclodextrins did not significantly improve their biocompatibility. However, the HPBCD modified plasticized PVC materials caused a reduction in the production in TNF-α induced by LPS which may have implications for the inflammatory potential of these biomaterials.

Biotribology of alternative bearing materials for unicompartmental knee arthroplasty

The objective of our wear simulator study was to evaluate the suitability of two different carbon fibre-reinforced poly-ether-ether-ketone (CFR-PEEK) materials for fixed bearing unicompartmental knee articulations with low congruency. In vitro wear simulation was performed according to ISO 14243-1:2002 (E) with the clinically introduced Univation F fixed bearing unicompartmental knee design (Aesculap AG, Tuttlingen, Germany) made of UHMWPE/CoCr29Mo6 in a direct comparison to experimental gliding surfaces made of CFR-PEEK pitch and CFR-PEEK PAN. Gliding surfaces of each bearing material (n=6+2) were gamma-irradiated, artificially aged and tested for 5 million cycles with a customized four-station knee wear simulator (EndoLab, Thansau, Germany). Volumetric wear assessment, optical surface characterization and an estimation of particle size and morphology were performed. The volumetric wear rate of the reference PE1-6 was 8.6 +/- 2.17 mm(3) per million cycles, compared to 5.1+/-2.29 mm(3) per million cycles for PITCH1-6 and 5.2 +/- 6.92 mm(3) per million cycles for PAN1-6; these differences were not statistically significant. From our observations, we conclude that CFR-PEEK PAN is obviously unsuitable as a bearing material for fixed bearing knee articulations with low congruency, and CFR-PEEK pitch also cannot be recommended as it remains doubtful wether it reduces wear compared to polyethylene. In the fixed bearing unicompartmental knee arthroplasty examined, application threshold conditions for the biotribiological behaviour of CFR-PEEK bearing materials have been established. Further in vitro wear simulations are necessary to establish knee design criteria in order to take advantage of the biotribiological properties of CFR-PEEK pitch for its beneficial use to patients.

Wear studies on the likely performance of CFR-PEEK/CoCrMo for use as artificial joint bearing materials

It is well known that a reduction in the volume of wear produced by articulating surfaces in artificial joints is likely to result in a lower incidence of failure due to wear particle induced osteolysis. Therefore, new materials have been introduced in an effort to produce bearing surfaces with lower, more biologically acceptable wear. Polyetheretherketone (PEEK-OPTIMA) has been successfully used in a number of implant applications due to its combination of mechanical strength and biocompatibility. Pin-on-plate wear tests were performed on various combinations of PEEK-OPTIMA and carbon fibre reinforced PEEK-OPTIMA (CFR-PEEK) against various CoCrMo alloys to assess the potential of this material combination for use in orthopaedic implants. The PEEK/low carbon CoCrMo produced the highest wear. CFR-PEEK against high carbon or low carbon CoCrMo provided low wear factors. Pin-on-plate tests performed on ultra-high molecular weight polyethylene (UHMWPE) against CoCrMo (using comparable test conditions) have shown similar or higher wear than that found for CFR-PEEK/CoCrMo. This study gives confidence in the likelihood of this material combination performing well in orthopaedic applications.

Pitch-based carbon-fibre-reinforced poly (ether—ether—ketone) OPTIMA® assessed as a bearing material in a mobile bearing unicondylar knee joint

The introduction of unicondylar knee prostheses has allowed the preservation of the non-diseased compartment of the knee while replacing the diseased or damaged compartment. In an attempt to reduce the likelihood of aseptic loosening, new material combinations have been investigated within the laboratory. Tribological tests (friction, lubrication, and wear) were performed on metal-on-carbon-fibre-reinforced (CFR) poly (ether—ether—ketone) (PEEK) (pitch-based) mobile unicondylar knee prostheses up to 5×106 cycles. Both a loaded soak control and an unloaded soak control (both medial and lateral components) were used to compensate for weight change due to lubricant absorption. For this material combination the loaded soak control gave slightly lower wear for both the medial and the lateral components than did the unloaded soak control. The medial components gave higher steady state wear than the lateral components (1.70 mm3 per 106 cycles compared with 1.02 mm3 per 106 cycles with the loaded soak control). The results show that the CFR PEEK unicondylar knee joints performed well in these wear tests. They gave lower volumetric wear rates than conventional metal-on-ultra-high-molecular-weight polyethylene prostheses have given in the past when tested under similar conditions. The friction tests showed that, at physiological viscosities, these joints operated in the boundary—mixed-lubrication regime. The low wear produced by these joints seems to be a function of the material combination and not of the lubrication regime.

Tribological assessment of a flexible carbon-fibre-reinforced poly(ether—ether—ketone) acetabular cup articulating against an alumina femoral head

New material combinations have been introduced as the bearing surfaces of hip prostheses in an attempt to prolong their life by overcoming the problems of failure due to wear-particle-induced osteolysis. This will hopefully reduce the need for revision surgery. The study detailed here used a hip simulator to assess the volumetric wear rates of large-diameter carbon-fibre-reinforced pitch-based poly(ether—ether—ketone) (CFR-PEEK) acetabular cups articulating against alumina femoral heads. The joints were tested for 25×106 cycles. Friction tests were also performed on these joints to determine the lubrication regime under which they operate. The average volumetric wear rate of the CFR-PEEK acetabular component of 54 mm diameter was 1.16 mm3/106 cycles, compared with 38.6 mm3/106 cycles for an ultra-high-molecular-weight polyethylene acetabular component of 28 mm diameter worn against a ceramic head. This extremely low wear rate was sustained over 25×106 cycles (the equivalent of up to approximately 25 years in vivo). The frictional studies showed that the joints worked under the mixed—boundary lubrication regime. The low wear produced by these joints showed that this novel joint couple offers low wear rates and therefore may be an alternative material choice for the reduction of osteolysis.

Technical and histologic analysis of a retrieved carbon fiber-reinforced poly-ether-ether-ketone composite alumina-bearing liner 28 months after implantation

A new innovative low-wear bearing for use in total hip arthroplasty, a wear couple consisting of carbon fiber-reinforced poly-ether-ether-ketone (CF-PEEK), has been shown to be highly biocompatible and to have excellent tribological performance in the laboratory. We report the results of our technical and histologic analysis of a CF-PEEK composite acetabular cup component articulating against an alumina-head total hip arthroplasty prosthesis retrieved because of posttrauma infection from a patient in whom the components had been in place for 28 months. Histologic findings showed only a small amount of particles from the composite insert in the patient's periprosthetic tissue. Additional clinical study is necessary to estimate the relevant in vivo wear performance of CF-PEEK liners.

PEEK biomaterials in trauma, orthopedic, and spinal implants

Since the 1980s, polyaryletherketones (PAEKs) have been increasingly employed as biomaterials for trauma, orthopedic, and spinal implants. We have synthesized the extensive polymer science literature as it relates to structure, mechanical properties, and chemical resistance of PAEK biomaterials. With this foundation, one can more readily appreciate why this family of polymers will be inherently strong, inert, and biocompatible. Due to its relative inertness, PEEK biomaterials are an attractive platform upon which to develop novel bioactive materials, and some steps have already been taken in that direction, with the blending of HA and TCP into sintered PEEK. However, to date, blended HA-PEEK composites have involved a trade-off in mechanical properties in exchange for their increased bioactivity. PEEK has had the greatest clinical impact in the field of spine implant design, and PEEK is now broadly accepted as a radiolucent alternative to metallic biomaterials in the spine community. For mature fields, such as total joint replacements and fracture fixation implants, radiolucency is an attractive but not necessarily critical material feature.

The wear properties of CFR-PEEK-OPTIMA articulating against ceramic assessed on a multidirectional pin-on-plate machine

In an attempt to prolong the lives of rubbing implantable devices, several 'new' materials have been examined to determine their suitability as joint couplings. Tests were performed on a multidirectional pin-on-plate machine to determine the wear of both pitch and PAN (polyacrylonitrile)-based carbon fibre reinforced-polyetheretherketone (CFR-PEEK-OPTIMA) pins articulating against both BioLox Delta and BioLox Forte plates (ceramic materials). Both reciprocation and rotational motion were applied to the samples. The tests were conducted using 24.5 per cent bovine serum as the lubricant (protein concentration 15 g/l). Although all four material combinations gave similar low wear with no statistically significant difference (p > 0.25), the lowest average total wear of these pin-on-plate tests was provided by CFR-PEEK-OPTIMA pitch pins versus BioLox Forte plates. This was much lower than the wear produced by conventional joint materials (metal-on-polyethylene) and metal-on-metal combinations when tested on the pin-on-plate machine. This therefore indicates optimism that these PEEK-OPTIMA-based material combinations may perform well in joint applications.