Biological reactions to wear debris in total joint replacement

Ceramic Wear Particles: Can They Be Retrieved In Vivo and Duplicated In Vitro?

BACKGROUND

Little is known about retrieved zirconia platelet toughened alumina (ZPTA) wear particles from ceramic-on-ceramic (COC) total hip arthroplasty. Our objectives were to evaluate clinically retrieved wear particles from explanted periprosthetic hip tissues and to analyze the characteristics of in vitro-generated ZPTA wear particles.

METHODS

Periprosthetic tissue and explants were received for 3 patients who underwent a total hip replacement of ZPTA COC head and liner. Wear particles were isolated and characterized via scanning electron microscopy and energy dispersive spectroscopy. The ZPTA and control (highly cross-linked polyethylene and cobalt chromium alloy) were then generated in vitro using a hip simulator and pin-on-disc testing, respectively. Particles were assessed in accordance with American Society for Testing and Materials F1877.

RESULTS

Minimal ceramic particles were identified in the retrieved tissue, consistent with the retrieved components demonstrating minimal abrasive wear with material transfer. Average particle diameter from in vitro studies was 292 nm for ZPTA, 190 nm for highly cross-linked polyethylene, and 201 nm for cobalt chromium alloy.

CONCLUSION

The minimal number of in vivo ZPTA wear particles observed is consistent with the successful tribological history of COC total hip arthroplasties. Due to the relatively few ceramic particles located in the retrieved tissue, in part due to implantation times of 3 to 6 years, a statistical comparison was unable to be made between the in vivo particles and the in vitro-generated ZPTA particles. However, the study provided further insight into the size and morphological characteristics of ZPTA particles generated from clinically relevant in vitro test setups.

An automated system for polymer wear debris analysis in total disc arthroplasty using convolution neural network

Introduction: Polymer wear debris is one of the major concerns in total joint replacements due to wear-induced biological reactions which can lead to osteolysis and joint failure. The wear-induced biological reactions depend on the wear volume, shape and size of the wear debris and their volumetric concentration. The study of wear particles is crucial in analysing the failure modes of the total joint replacements to ensure improved designs and materials are introduced for the next generation of devices. Existing methods of wear debris analysis follow a traditional approach of computer-aided manual identification and segmentation of wear debris which encounters problems such as significant manual effort, time consumption, low accuracy due to user errors and biases, and overall lack of insight into the wear regime. Methods: This study proposes an automatic particle segmentation algorithm using adaptive thresholding followed by classification using Convolution Neural Network (CNN) to classify ultra-high molecular weight polyethylene polymer wear debris generated from total disc replacements tested in a spine simulator. A CNN takes object pixels as numeric input and uses convolution operations to create feature maps which are used to classify objects. Results: Classification accuracies of up to 96.49% were achieved for the identification of wear particles. Particle characteristics such as shape, size and area were estimated to generate size and volumetric distribution graphs. Discussion: The use of computer algorithms and CNN facilitates the analysis of a wider range of wear debris with complex characteristics with significantly fewer resources which results in robust size and volume distribution graphs for the estimation of the osteolytic potential of devices using functional biological activity estimates.

Glycolytic reprogramming underlies immune cell activation by polyethylene wear particles

Primary total joint arthroplasties (TJAs) are widely and successfully applied reconstructive procedures to treat end-stage arthritis. Nearly 50 % of TJAs are now performed in young patients, posing a new challenge: performing TJAs which last a lifetime. The urgency is justified because subsequent TJAs are costlier and fraught with higher complication rates, not to mention the toll taken on patients and their families. Polyethylene particles, generated by wear at joint articulations, drive aseptic loosening by inciting insidious inflammation associated with surrounding bone loss. Down modulating polyethylene particle-induced inflammation enhances integration of implants to bone (osseointegration), preventing loosening. A promising immunomodulation strategy could leverage immune cell metabolism, however, the role of immunometabolism in polyethylene particle-induced inflammation is unknown. Our findings reveal that immune cells exposed to sterile or contaminated polyethylene particles show fundamentally altered metabolism, resulting in glycolytic reprogramming. Inhibiting glycolysis controlled inflammation, inducing a pro-regenerative phenotype that could enhance osseointegration.

Increased UHMWPE Particle-Induced Osteolysis in Fetuin-A-Deficient Mice

Particle-induced osteolysis is a major cause of aseptic prosthetic loosening. Implant wear particles stimulate tissue macrophages inducing an aseptic inflammatory reaction, which ultimately results in bone loss. Fetuin-A is a key regulator of calcified matrix metabolism and an acute phase protein. We studied the influence of fetuin-A on particle-induced osteolysis in an established mouse model using fetuin-A-deficient mice. Ten fetuin-A-deficient (Ahsg−/−) mice and ten wild-type animals (Ahsg+/+) were assigned to test group receiving ultra-high molecular weight polyethylene (UHMWPE) particle implantation or to control group (sham surgery). After 14 days, bone metabolism parameters RANKL, osteoprotegerin (OPG), osteocalcin (OC), alkaline phosphatase (ALP), calcium, phosphate, and desoxypyridinoline (DPD) were examined. Bone volume was determined by microcomputed tomography (μCT); osteolytic regions and osteoclasts were histomorphometrically analyzed. After particle treatment, bone resorption was significantly increased in Ahsg−/− mice compared with corresponding Ahsg+/+ wild-type mice (p = 0.007). Eroded surface areas in Ahsg−/− mice were significantly increased (p = 0.002) compared with Ahsg+/+ mice, as well as the number of osteoclasts compared with control (p = 0.039). Fetuin-A deficiency revealed increased OPG (p = 0.002), and decreased levels of DPD (p = 0.038), OC (p = 0.036), ALP (p < 0.001), and Ca (p = 0.001) compared with wild-type animals. Under osteolytic conditions in Ahsg−/− mice, OPG was increased (p = 0.013), ALP (p = 0.015) and DPD (p = 0.012) were decreased compared with the Ahsg+/+ group. Osteolytic conditions lead to greater bone loss in fetuin-A-deficient mice compared with wild-type mice. Reduced fetuin-A serum levels may be a risk factor for particle-induced osteolysis while the protective effect of fetuin-A might be a future pathway for prophylaxis and treatment.

The impact of free-radical stabilization techniques on in vivo subsurface mechanical properties in highly cross-linked polyethylene acetabular liners

Highly cross-linked polyethylene (HXLPE) for total hip arthroplasty was developed to improve wear resistance in vivo and associated complications in comparison to ultrahigh molecular weight polyethylene. This material typically goes through various free-radical stabilization techniques by remelting, single-annealing, or sequentially annealing the polyethylene to improve in vivo oxidation and wear properties. The purpose of this study is to determine if there is evidence of subsurface microhardness changes in retrieved HXLPE liner at the rim and articular subsurface after extended in vivo time that could be associated with oxidation and its effects on mechanical properties and implant integrity. Retrieved HXLPE liners were chosen based on peak subsurface Fourier transform infrared spectroscopy oxidation values. Each was mechanically tested for subsurface microhardness at both the rim and articular surface using a validated microindentation technique. Rim testing demonstrated a decrease in mechanical integrity that corresponded to higher subsurface oxidation values regardless of the free-radical stabilization technique. At the articular surface, a decrease in mechanical integrity was observed near the surface corresponding to peak oxidation and Vicker's hardness, which decreased with increasing depths. This was found in all groups, with the exception of the single-annealed liners, which demonstrated decreased mechanical integrity trends at greater depths between 1.0 and 2.0 mm. Our results suggest that subsurface mechanical properties do change in vivo for certain implants. Though it is likely that the mechanical failures are multifactorial, we have shown that mechanical property degradation of HXLPE liners does occur with long-term in vivo exposure and should be considered a possible risk factor.

Strategies to improve bioactive and antibacterial properties of polyetheretherketone (PEEK) for use as orthopedic implants

Polyetheretherketone (PEEK) has gradually become the mainstream material for preparing orthopedic implants due to its similar elastic modulus to human bone, high strength, excellent wear resistance, radiolucency, and biocompatibility. Since the 1990s, PEEK has increasingly been used in orthopedics. Yet, the widespread application of PEEK is limited by its bio-inertness, hydrophobicity, and susceptibility to microbial infections. Further enhancing the osteogenic properties of PEEK-based implants remains a difficult task. This article reviews some modification methods of PEEK in the last five years, including surface modification of PEEK or incorporating materials into the PEEK matrix. For surface modification, PEEK can be modified by chemical treatment, physical treatment, or surface coating with bioactive substances. For PEEK composite material, adding bioactive filler into PEEK through the melting blending method or 3D printing technology can increase the biological activity of PEEK. In addition, some modification methods such as sulfonation treatment of PEEK or grafting antibacterial substances on PEEK can enhance the antibacterial performance of PEEK. These strategies aim to improve the bioactive and antibacterial properties of the modified PEEK. The researchers believe that these modifications could provide valuable guidance on the future design of PEEK orthopedic implants.

Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices

This review summarizes recent research on the design of polymer material systems based on biomimetic concepts and reports on the medical devices that implement these systems. Biomolecules such as proteins, nucleic acids, and phospholipids, present in living organisms, play important roles in biological activities. These molecules are characterized by heterogenic nature with hydrophilicity and hydrophobicity, and a balance of positive and negative charges, which provide unique reaction fields, interfaces, and functionality. Incorporating these molecules into artificial systems is expected to advance material science considerably. This approach to material design is exceptionally practical for medical devices that are in contact with living organisms. Here, it is focused on zwitterionic polymers with intramolecularly balanced charges and introduce examples of their applications in medical devices. Their unique properties make these polymers potential surface modification materials to enhance the performance and safety of conventional medical devices. This review discusses these devices; moreover, new surface technologies have been summarized for developing human-friendly medical devices using zwitterionic polymers in the cardiovascular, cerebrovascular, orthopedic, and ophthalmology fields.

Metal-on-metal total hip arthroplasty: does increasing modularity affect clinical outcome?

BACKGROUND

Modularity of metal-on-metal (MoM) implants has come under scrutiny due to concerns regarding additional sources of metal debris. This study is a retrieval analysis of implants from the same manufacturer with the same MoM bearing surface. The difference between the implants was presence or absence of modular junctions.

METHODS

This is a retrospective study of 31 retrieved implants from 31 patients who received a Conserve Wright Medical MoM hip prosthesis. The 31 implants consisted of 16 resurfacings and 15 implants with modular junctions; 4 conventional THAs and 11 modular-neck THAs.

RESULTS

43% of pre-revision MRI scans performed on resurfacing implants and 91% performed on the modular implants illustrated evidence of an adverse local tissue reaction. There was no difference in pre-revision blood metal ion levels or bearing surface wear between the resurfacings and modular implants. The neck-head tapers of the modular group showed low levels of material loss. However, the neck-stem tapers showed increased severity of corrosion and material loss.

CONCLUSIONS

The modular implants had an increased incidence of adverse local tissue reaction. This could be related to the presence of modular junctions, particular the neck-stem junction which showed increased susceptibly to corrosion.

Bionate Biocompatibility: In Vivo Study in Rabbits

Response to foreign materials includes local tissue reaction, osteolysis, implant loosening, and migration to lymph nodes and organs. Bionate 80A human explants show minor wear and slight local tissue reaction, but we do not know the response at the spinal cord, nerve roots, lymph nodes, or distant organs. This study aims to figure out reactions against Bionate 80A when implanted at the spinal epidural space of 24 20-week-old New Zealand white rabbits. In one group of 12 rabbits, we implanted Bionate 80A on the spinal epidural space, and another group of 12 rabbits was used as the control group. We studied tissues, organs, and tissue damage markers on blood biochemistry, urine tests, and necropsy. The animals' clinical parameters and weight showed no statistically significant differences. At 3 months, the basophils increased slightly in the implant group, platelets decreased in all, and at 6 months, implanted animals showed slight eosinophilia, but none of these changes was statistically significant. External, organ, and spinal tissue examination showed neither toxic reaction, inflammatory changes, or noticeable differences between groups or survival periods. Under microscopic examination, the Bionate 80A particles induced a chronic granulomatous response always outside the dura mater, with giant multinucleated cells holding phagocytized particles and no particle migration to lymph nodes or organs. Thus, it was concluded that Bionate particles, when implanted in the rabbit lumbar epidural space, do not generate a significant reaction limited to the surrounding soft tissues with giant multinucleated cells. In addition, the particles did not cross the dura mater or migrate to lymph nodes or organs.

Nanoplastics affect the inflammatory cytokine release by primary human monocytes and dendritic cells

So far, the human health impacts of nano- and microplastics are poorly understood. Thus, we investigated whether nanoplastics exposure induces inflammatory processes in primary human monocytes and monocyte-derived dendritic cells. We exposed these cells in vitro to nanoplastics of different shapes (irregular vs. spherical), sizes (50-310 nm and polydisperse mixtures) and polymer types (polystyrene; polymethyl methacrylate; polyvinyl chloride, PVC) using concentrations of 30-300 particles cell^-1. Our results show that irregular PVC particles induce the strongest cytokine release of these nanoplastics. Irregular polystyrene triggered a significantly higher pro-inflammatory response compared to spherical nanoplastics. The contribution of chemicals leaching from the particles was minor. The effects were concentration-dependent but varied markedly between cell donors. We conclude that nanoplastics exposure can provoke human immune cells to secrete cytokines as key initiators of inflammation. This response is specific to certain polymers (PVC) and particle shapes (fragments). Accordingly, nanoplastics cannot be considered one homogenous entity when assessing their health implications and the use of spherical polystyrene nanoplastics may underestimate their inflammatory effects.

Insights into tribofilm formation on Ti-6V-4Al in a bioactive environment: Correlation between surface modification and micro-mechanical properties

Ti-6Al-4V has been used as a surgical implant material for a long time because of its combination of strength, corrosion resistance and biocompatibility. However, there remains much that is not understood about how the surface reacts with the environment under tribocorrosion conditions. In particular, the conditions under which tribofilms form and their role on friction and wear are not clear. To evaluate the complicated nature of the dynamic surface microstructural changes on the wear track, high resolution transmission electron microscopy (TEM), scanning transmission electron microscope (STEM) and electron energy loss spectroscopy (EELS) have been used to characterise the structure and chemical composition of the tribofilm. Detailed analysis of the formation and structure of the tribofilm and the metal surface deformation behaviour were studied as a function of applied potential and the role of proteins in the lubricant. For the first time, graphitic and onion-like carbon structures from wear debris were found in the testing solution. The presence of carbon nanostructures in the tribocorrosion process and the formation of the tribofilm leads to an improved tribocorrosion behaviour of the system, in particular a reduction in wear and friction. A detailed, quantitative, analysis of surface deformation was undertaken, in particular, the geometrically necessary dislocation (GND) density was quantified using precession electron diffraction (PET). A clear correlation between applied potential, tribofilm formation and the surface strain was established. STATEMENT OF SIGNIFICANCE: The formation of tribofilm and microstructure modification of the Ti-6Al-4V surface during tribocorrosion in a physiological environment is not fully understood. In particular, the correlation between microstructural changes and electrochemical conditions is not clear. This study presents a detailed investigation of the structure and chemical composition of tribofilms at the nanoscale during tribocorrosion tests in simulated body fluid and gives a detailed and quantitative description of the evolved surface structure. A clear correlation between applied potential, tribofilm formation and the surface strain was established. Moreover, particular attention is paid to the wear debris particles captured from the lubricating solution, including nanocarbon onion structures. The implications for tribocorrosion of the alloy in its performance as an implant are discussed.

Global Trends and Current Status in Osteonecrosis of the Femoral Head: A Bibliometric Analysis of Publications in the Last 30 Years

INTRODUCTION

Osteonecrosis of the femoral head (ONFH) is a progressive and disabling disease with severe socioeconomic burdens. In the last 30 years, a growing number of publications have reported significant advances in understanding ONFH. However, only a few studies have clarified its global trends and current status. Thus, the purpose of our study was to summarize the global trends and current status in ONFH through bibliometrics.

MATERIALS AND METHODS

Publications related to ONFH from 1991 to 2020 were searched from the Web of Science (WOS) core collection database. The data were analyzed with bibliometric methods. Microsoft Excel was used for statistical analysis and to draw bar charts. SPSS was applied to perform linear regression analysis. VOSviewer was used to conduct bibliographic coupling analysis, co-authorship analysis, co-citation analysis and co-occurrence analysis.

RESULTS

A total of 5,523 publications were covered. The United States consistently ranked first in total publications, sum of times cited, average citations per item and H-index. Kyushu University was the main contributor to ONFH. Clinical Orthopaedics and Related Research was the major publishing channels for ONFH-related articles. Takuaki Yamamoto published the most ONFH-related articles. Studies regarding ONFH could be divided into five clusters: 1) mechanism study, 2) treatment study, 3) complication study, 4) radiological study and 5) etiological study. Mechanism study might become a hot spot in the future.

CONCLUSIONS

The total number of publications in ONFH has generally increased over the last three decades. The United States was the leading country in ONFH research. Transplantation, engineering, cell and molecular biology, pharmacology and endocrinology have gradually increased and become hot topics in ONFH research. Mechanism study in ONFH including mesenchymal stem cells, apoptosis, oxidative stress, adipogenesis, osteogenic differentiation and endothelial progenitor cells, have attracted more attention and will become a hot spot in the future.

Quantitative analysis and degradation mechanisms of different protein degradation methods

The abrasive debris produced by wear test of artificial joints in vitro is encapsulated by proteins in serum lubricants, which hinder the characterization of debris analysis. One of the key issues of isolating wear debris from serum is degrading the proteins wrapping the wear debris. In this article, the proteins in calf serum were degraded by a strong alkali, a strong acid, and an enzyme. The residual concentration of proteins in calf serum was detected by UV absorption. Quantitative analysis of protein degradation and the protein degradation rate was proposed, following treatment with different degradation reagents and different incubation times. The results showed that when 10 mL of 25% volume calf serum was added with 40 mL of NaOH and incubated at 65°C for 24 h, the protein degradation rate reached a maximum of 95.52%. The protein degradation rate in the solution ranged from 31.86% to 71.64% when a different volume of 37% HCl was added and incubated at 60°C. The highest protein degradation rate was 94.98% in the protease degradation solution. When the protein degradation rate is less than 70%, the particles were coated by protein. When the protein degradation rate was more than 95%, there was no protein coating around the particles. The three protein degradation methods have different processes and protein degradation rates. A suitable method for protein degradation can be selected according to these practical applications.

Impact of scandium on mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of a β-type Ti-24Nb-38Zr-2Mo alloy for orthopedic applications

β-type titanium (Ti) alloys have been extensively investigated as orthopedic implant materials due to their unique combination of low elastic modulus, high specific strength, corrosion resistance, and biocompatibility. In this study the mechanical properties, corrosion behavior, friction and wear performance, and cytotoxicity of β-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) have been comparatively investigated for orthopedic applications. Cold-rolling (CR) and cold-rolling plus solution-treatment (CR+ST) were performed on the as-cast (AC) alloys and their microstructures and material properties were characterized. The impact of Sc addition on the mechanical and corrosion properties, friction and wear behavior, and in vitro cytocompatibility of the TNZMS alloy was assessed. The CR+ST TNZMS alloy exhibited the best combination of properties among all the alloy samples, with a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and hardness of 265 HV. Electrochemical testing in Hanks' Solution indicated that the CR+ST TNZMS sample also showed the highest corrosion resistance with a corrosion potential of -0.234 V, corrosion current density of 0.07 µA/cm², and corrosion rate of 1.2 µm/y. Friction and wear testing revealed that the TNZMS alloy showed higher wear resistance compared to the TNZM alloy and the wear resistance of the different samples was ranked CR > CR+ST > AC. Finally, both the CR+ST TNZM and TNZMS showed no-cytotoxicity towards MG-63 cells and the TNZMS exhibited slightly higher cytocompatibility than the TNZM alloy. STATEMENT OF SIGNIFICANCE: This work reports the β-type Ti-24Nb-38Zr-2Mo (TNZM) and Ti-24Nb-38Zr-2Mo-0.1Sc (TNZMS) alloys fabricated by as-cast (AC), cold-rolling (CR), and cold-rolling plus solution-treatment (CR+ST) for potential orthopedic applications. The experimental results showed that the TNZMS alloy exhibited significantly enhanced mechanical, wear, and corrosion properties than those of TNZM alloy; and the CR+ST TNZMS possess a unique combination of the best mechanical and corrosion properties including a yield strength of 780 MPa, ultimate strength of 809 MPa, elongation of 19%, Young's modulus of 65.4 GPa, and corrosion rate of 1.2 µm/y in Hanks' Solution. Both the CR+ST TNZM and TNZMS alloys exhibited non-cytotoxicity towards MG-63 cells and TNZMS showed a higher cytocompatibility than that of TNZM.

Titanium Wear Particles Exacerbate S. epidermidis-Induced Implant-Related Osteolysis and Decrease Efficacy of Antibiotic Therapy

Total joint arthroplasty (TJA) surgeries are common orthopedic procedures, but bacterial infection remains a concern. The aim of this study was to assess interactions between wear particles (WPs) and immune cells in vitro and to investigate if WPs affect the severity, or response to antibiotic therapy, of a Staphylococcus epidermidis orthopedic device-related infection (ODRI) in a rodent model. Biofilms grown on WPs were challenged with rifampin and cefazolin (100 µg/mL) to determine antibiotic efficacy. Neutrophils or peripheral blood mononuclear cells (PBMCs) were incubated with or without S. epidermidis and WPs, and myeloperoxidase (MPO) and cytokine release were analyzed, respectively. In the ODRI rodent model, rats (n = 36) had a sterile or S. epidermidis-inoculated screw implanted in the presence or absence of WPs, and a subgroup was treated with antibiotics. Bone changes were monitored using microCT scanning. The presence of WPs decreased antibiotic efficacy against biofilm-resident bacteria and promoted MPO and pro-inflammatory cytokine production in vitro. WPs exacerbated osteolytic responses to S. epidermidis infection and markedly reduced antibiotic efficacy in vivo. Overall, this work shows that the presence of titanium WPs reduces antibiotic efficacy in vitro and in vivo, induces proinflammatory cytokine release, and exacerbates S. epidermidis-induced osteolysis.

Third body damage and wear in arthroplasty bearing materials: A review of laboratory methods

Third body wear of arthroplasty bearing materials can occur when hard particles such as bone, bone cement or metal particles become trapped between the articulating surfaces. This can accelerate overall implant wear, potentially leading to early failure. With the development of novel bearing materials and coatings, there is a need to develop and standardise test methods which reflect third body damage seen on retrieved implants. Many different protocols and approaches have been developed to replicate third body wear in the laboratory but there is currently no consensus as to the optimal method for simulating this wear mode, hence the need to better understand existing methods. The aim of this study was to review published methods for experimental simulation of third body wear of arthroplasty bearing materials, to discuss the advantages and limitations of different approaches, the variables to be considered when designing a method and to highlight gaps in the current literature. The methods were divided into those which introduced abrasive particles into the articulating surfaces of the joint and those whereby third body damage is created directly to the articulating surfaces. However, it was found that there are a number of parameters, for example the influence of particle size on wear, which are not yet fully understood. The study concluded that the chosen method or combination of methods used should primarily be informed by the research question to be answered and risk analysis of the device.

Effect of Oxidative Stress on Bone Remodeling in Periprosthetic Osteolysis

The success of implant performance and arthroplasty is based on several factors, including oxidative stress-induced osteolysis. Oxidative stress is a key factor of the inflammatory response. Implant biomaterials can release wear particles which may elicit adverse reactions in patients, such as local inflammatory response leading to tissue damage, which eventually results in loosening of the implant. Wear debris undergo phagocytosis by macrophages, inducing a low-grade chronic inflammation and reactive oxygen species (ROS) production. In addition, ROS can also be directly produced by prosthetic biomaterial oxidation. Overall, ROS amplify the inflammatory response and stimulate both RANKL-induced osteoclastogenesis and osteoblast apoptosis, resulting in bone resorption, leading to periprosthetic osteolysis. Therefore, a growing understanding of the mechanism of oxidative stress-induced periprosthetic osteolysis and anti-oxidant strategies of implant design as well as the addition of anti-oxidant agents will help to improve implants’ performances and therapeutic approaches.

Proximal femoral reconstruction with modular megaprostheses in non-oncological patients

Introduction

Multiple revision hip arthroplasties and critical trauma might cause severe bone loss that requires proximal femoral replacement (PFR). The aim of this retrospective study was to analyse complication- and revision-free survivals of patients who received modular megaprostheses in an attempt to reconstruct massive non-neoplastic bone defects of the proximal femur.

Questions/purposes

(1) What were general complication rates and revision-free survivals following PFR? (2) What is the incidence of complication specific survivals? (3) What were risk factors leading to a diminished PFR survival?

Materials and methods

Twenty-eight patients with sufficient follow-up after receiving a modular proximal femoral megaprosthesis were identified. The indications for PFR included prosthetic joint infection (PJI), periprosthetic fracture, aseptic loosening, non-union and critical femoral fracture. Complications were grouped according to the ISOLS-classification of segmental endoprosthetic failure by Henderson et al.

Results

Overall, the complication-free survival was 64.3% at one year, 43.2% at five years and 38.4% at ten years, with 16 patients (57%) suffering at least one complication. Complications were dislocation in eight patients (29%), PJI in 6 patients (21%), periprosthetic fracture in five patients (18%), and aseptic loosening in six patients (21%). Prosthesis stem cementation showed a lower risk for revision in a cox proportional hazard model (95% CI 0.04–0.93, HR 0.2, p = 0.04).

Conclusion

PFR with modular megaprostheses represents a viable last resort treatment with high complication rates for patients with severe proximal femoral bone loss due to failed arthroplasty or critical fractures. In revision arthroplasty settings, PFR cementation should be advocated in cases of impaired bone quality.

Does Maximum Voluntary Clenching Force Pose a Risk to Overloading Alloplastic Temporomandibular Joint Replacement?-A Prospective Cohort Study

PURPOSE

The amount of maximum voluntary clenching (MVC) force may influence functional loading at the polyethylene/metal bearing surfaces in alloplastic total temporomandibular joint replacement (TMJR). The aim of this study was to measure ipsilateral MVC and estimate the risk for revision due to overloading of the TMJR.

METHODS

A prospective cohort study design was used to study patients who underwent alloplastic TMJR. The primary predictor was time after TMJR, the secondary predictors were age at TMJR placement, coronoidectomy, prior ipsilateral TMJ surgeries, TMJR design (custom, stock), and bite location. The primary outcome variable was MVC, the secondary outcome was need for TMJR revision. Data were collected preoperatively (T0), and 1 year (T1), 2 to 3 years (T2) and ≥4 years postoperatively (T3). Analysis of variance (ANOVA) with post hoc Tukey-HSD and regression analysis was used for statistical analysis. P < .05 was considered significant.

RESULTS

Thirty-seven patients (58 TMJR) with unilateral (n = 16) and bilateral (n = 21) TMJR were enrolled; 8 males (12 TMJR) and 29 females (46 TMJR). Average age was 46.4 ± 14.9 years. MVC increased significantly over the observation period (P = .000). At all observation time points, age at TMJR placement and bite location significantly influenced MVC (P = .000). Coronoidectomy and prior ipsilateral TMJ surgeries did not demonstrate a significant influence on MVC. TMJR design influenced MVC significantly at T3 (P = .006). Regression analysis identified age as a significant factor for higher MVC. No TMJR required revision or replacement.

CONCLUSIONS

Based on this study, ipsilateral MVC increases significantly after TMJR. However, since MVC is significantly lower than in healthy test-patients, a considerably lower functional loading at the polyethylene/metal bearing surfaces can be assumed. Lower loading at the TMJR bearing surfaces and at the cortical screw fixation sites suggest a potential longer lifespan compared to other artificial joints like hip and knee prostheses.

A bicentric approach evaluating the combination of a hemispheric cup with a novel ceramic head in total hip arthroplasty

Medical ceramics are frequently used biomaterials as a liner in total hip arthroplasty. Strong efforts have been made to improve material properties over the last decades. Alumina toughened zirconia ceramics seem to be promising alternatives to further reduce fracture rates and squeaking phenomena. To answer the question if alumina toughened zirconia ceramic liners in combination with a cementless, hemispheric cup are able to reduce squeaking phenomena and fracture rates, we initiated a bicentric, mid-term trial. Noise phenomena will be recorded using MONA Score (Melbourne Orthopaedic Noise Assessment). Functional outcome (Harris Hip Score, University of California-Los Angeles, Forgotten Joint Score, EQ-5D Score, Visual Analogue Scale) and radiographic parameters will serve as secondary parameters. The study has been set up for 5 years, with follow-ups after 6-14 weeks, 12, 24 and 60 months.

Effect of deep rolling on subsurface conditions of CoCr28Mo6 wrought alloy to improve the wear resistance of endoprostheses

Wear of orthopaedic endoprostheses is associated with adverse local and systemic reactions and can lead to early implant failure. Manufacturing determines the initial subsurface microstructure of an alloy that influences the implant's wear behaviour. Therefore, this study aims at generating enhanced wear resistances by a modification of the surface and subsurface microstructure of a CoCr28Mo6 wrought alloy by applying deep rolling. The state of the art was investigated by means of eleven retrieved CoCr28Mo6 hip implant components from different manufacturers with respect to their subsurface microstructure and micro hardness profiles. CoCr28Mo6 wrought alloy samples (DIN EN ISO 5832-12) were aged at 750 °C for 24 h and/or plastically deformed by deep rolling with varying axial forces (170 N, 230 N and 250 N). The samples were metallographically prepared and investigated using optical and scanning electron microscopy with EDS and EBSD, micro hardness testing, XRD and tribological testing. The retrieved implant components revealed that, independent of the manufacturer, neither the head nor the stem trunnion exhibited a defined subsurface condition. The dominant phase within the implants was face-centered cubic (fcc). Some implants exhibited single hexagonal close-packed (hcp) grains due to a stress-induced phase transformation. The initial CoCr28Mo6 wrought alloy had a fcc crystal structure. After isothermal aging, the matrix entirely transformed to a hcp structure. In the initial fcc-condition, deep rolling generated a plastically deformed surface layer within the first 100 μm and stress-induced phase transformation to hcp was observed. Micro hardness gradients were present in the subsurface of up to 600 μm depth and exhibited a maximum increase of 34% by deep rolling in comparison to the initial fcc-matrix. This trend was confirmed by a correlated increase in residual compressive stresses. In tribological tests under serum lubrication, the modified samples generated lower wear in comparison to the contemporarily used fcc-matrix samples. This study demonstrates that deep rolling is an effective processing to modify the subsurface of a biomedical CoCr28Mo6 wrought alloy in order to increase the wear resistance. The intentional transformation from the fcc to the hcp phase induced by deformation offers great potential for implant application.

Plastics in Total Knee Replacement: Processing to Performance

Polyethylene (PE) is the key component of total knee replacement (TKR). The wear of polyethylene, a common cause of revision surgeries, depends on multiple factors. The mechanical properties, wear characteristics, and oxidative resistance of PE can be manipulated by the techniques of processing, sterilization, and packaging methods. This article describes the making of conventional and cross-linked poly, packaging, sterilization, processing techniques, and a summary of commercially available plastics and their rationale in TKR including the latest advances.

Bioactive, Ion-Releasing PMMA Bone Cement Filled with Functional Graphenic Materials

Graphene oxide and functionalized graphenic materials (FGMs) have promise as platforms for imparting programmable bioactivity to poly(methyl methacrylate) (PMMA)-based bone cement. To date, however, graphenic fillers have only been feasible in PMMA cements at extremely low loadings, limiting the bioactive effects. At higher loadings, graphenic fillers decrease cement strength by aggregating and interfering with curing process. Here, these challenges are addressed by combining bioactive FGM fillers with a custom cement formulation. These cements contain an order of magnitude more graphenic filler than previous reports. Even at 1 wt% FGM, these cements have compressive strengths of 78- 88 MPa, flexural strengths of 74-81 MPa, and flexural stiffnesses of 1.8-1.9 GPa, surpassing the ASTM requirements for bone cement and competing with traditional PMMA cement. Further, by utilizing designer FGMs with programmed bioactivity, these cements demonstrate controlled release of osteogenic calcium ions (releasing a total of 5 ± 2 µmol of Ca2+ per gram of cement over 28 d) and stimulate a 290% increase in expression of alkaline phosphatase in human mesenchymal stem cells in vitro. Also, design criteria are described to guide creation of future generations of bone cements that utilize FGMs as platforms to achieve dynamic biological activity.

Quantitative ultrahigh-molecular-weight polyethylene wear in total elbow retrievals

BACKGROUND

The purpose of this study was to evaluate ultrahigh-molecular-weight polyethylene (UHMWPE) wear and damage from retrieved total elbow arthroplasty components and compare in vivo wear with wear produced in vitro.

METHODS

Explanted total elbow components were collected at revision surgery. UHMWPE damage was characterized visually, whereas penetration and wear were quantified using micro-computed tomography and gas pycnometry. Volumetric wear rates were compared with historical hip data, and wear data were compared with reported in vitro wear test data.

RESULTS

Humeral bushing damage primarily occurred in the form of burnishing, scratching, and pitting at the articular face in the region of contact with the ulnar component. Wear of the ulnar bushings was concentrated on the edge of the component at the point of contact with the axis pin. Pitting and embedded debris were dominant damage modes, in addition to burnishing and delamination. Backside wear was negligible. The median linear penetration rates of the lateral, medial, and ulnar bushings were 0.14 mm/yr (range, 0.01-0.78 mm/yr), 0.12 mm/yr (range, 0.03-0.55 mm/yr), and 0.11 mm/yr (range, 0.01-0.69 mm/yr), respectively. The volumetric wear rates of the lateral, medial, and ulnar bushings were 5.5 mm³/yr (range, 0.7-37.2 mm³/yr), 5.9 mm³/yr (range, 0.6-25.5 mm³/yr), and 5.5 mm³/yr (range, 1.2-51.2 mm³/yr), respectively.

CONCLUSIONS

The observed wear rates were similar to those reported in well-functioning total hip replacement patients with conventional UHMWPE bearings. We found limitations in reported in vitro testing resulting in wear that was not consistent with our retrieval data. We recommend further investigation to clinically validate in vitro simulation to provide appropriate loading protocols for elbow wear simulation.

Comparative meta-analysis of pyrocarbon and silicone for joint replacement surgery

OBJECTIVE

To investigate the efficacy and complications that might be associated with pyrocarbon compared with silicone in patients undergoing joint replacement surgery.

METHODS

The full-text papers about the clinical efficacy of pyrocarbon and silicone were retrieved from multiple databases. Review Manager version 5.0 was adopted for meta-analysis and analyses of sensitivity and bias.

RESULTS

Ultimately, we studied 232 patients across eight studies that met the eligibility criteria. The meta-analysis suggested a significant difference between the pyrocarbon and silicone groups in terms of the Disabilities of the Arm, Shoulder, and Hand (DASH) score (standard mean difference (SMD) = 1.48; 95% CI [0.97, 1.99]; P = .009; P for Heterogeneity <0.00001; I = 63%); Visual Analogue Score (VAS) (SMD = 1.68; 95% CI [1.36, 1.99]; P < .00001; P for heterogeneity = 0.01; I = 61%), and the abnormal radiolucent line (RR = 6.66; 95% CI [3.19, 13.89]; P < .00001; P for heterogeneity = 0.87, I = 0%); and ossification development (RR = 0.90; 95% CI [0.56, 1.44], P = .66; P for heterogeneity = 0.94, I = 0%).

CONCLUSION

This study showed that pyrocarbon might be an efficient material compared with silicone for joint replacement surgery, but resulted in poorer functional and pain outcomes compared with silicone.

Genotoxic properties of materials used for endoprostheses: Experimental and human data

Approximately 2 million endoprostheses are implanted annually and metal ions as well as particles are released into the body from the materials which are used. This review describes the results of studies concerning genotoxic damage caused by artificial joints. DNA damage leads to various adverse long-term health effects in humans including cancer. Experiments with mammalian cells showed that metal ions and particles from orthopedic materials cause DNA damage. Induction of chromosomal aberrations (CA) was found in several in vitro experiments and in studies with rodents with metals from orthopedic materials. Human studies focused mainly on induction of CA (7 studies). Only few investigations (4) concerned sister chromatid exchanges, oxidative DNA damage (2) and micronucleus formation (1). CA are a reliable biomarker for increased cancer risks in humans) and were increased in all studies in patients with artificial joints. No firm conclusion can be drawn at present if the effects in humans are due to oxidative stress and if dissolved metal ions or release particles play a role. Our findings indicate that patients with artificial joints may have increased cancer risks due to damage of the genetic material. Future studies should be performed to identify safe materials and to study the molecular mechanisms in detail.

Morphology and Plastic Yielding of Ultrahigh Molecular Weight Polyethylene

The structure, morphology, and mechanical properties of two compression-molded grades of ultrahigh-molecular-weight polyethylene (UHMWPE) and, for comparison, one conventional linear polyethylene (HDPE) were studied. Compression molding resulted in some preferred orientation of lamellae in the compression direction in UHMWPE samples, while no preferred orientation in HDPE. The mean crystal thickness estimated from the size distribution agrees better with those obtained from small-angle X-ray scattering (SAXS) and mechanical yield data than the thickness determined from the melting peak temperature. Microscopic examination of microtomed and etched UHMWPE samples showed that the lamellae are in the form of platelets with the width and length in the range of 300–700 nm. The lamellae radiate from primary nuclei forming small embryonal spherulites; their radial growth ends at 0.3–0.7 μm from the center. There is no evidence of branching and secondary nucleation from those primary lamellae. Because the lamellae are radially ordered, there is no parallel stacking of lamellae. Samples were subjected to deformation by plane-strain compression at a constant true strain rate. In axial UHMWPE samples, where lamellae were preferentially oriented along the loading direction, the second yield was clearly observed. The second yield was found to be related to the deformation instability leading to kinking of lamellae oriented initially along the loading direction. Kinking was clearly shown by SAXS and microscopic observation of microtomed and etched samples. No cooperativity of kinking was observed because the lamellae are arranged in small spherulites and not parallel in stacks. The stress–strain curves were fitted with model curves assuming crystal plasticity and network elasticity in the amorphous component. The effective density of the molecular network within the amorphous phase depended on the molecular weight of UHMWPE.

Biocompatible implant mimicking cartilage: A new horizon for reconstructive facial field

Cartilage is avascular with limited to no regenerative capacity, so its loss could be a challenge for reconstructive surgery. Current treatment options for damaged cartilage are also limited. In this aspect there is a tremendous need to develop an ideal cartilage-mimicking biomaterial that could repair maxillofacial defects. Considering this fact in this study we have prepared twelve silicone-based materials (using Silicone 40, 60, and 80) reinforced with hydroxyapatite, tri-calcium phosphate, and titanium dioxide which itself has proven their efficacy in several studies and able to complement the shortcomings of using silicones. Among the mechanical properties (Young's modulus, tensile strength, percent elongation, and hardness), hardness of Silicone-40 showed similarities with goat ear (P > .05). Silicone peaks have been detected in FTIR. Both AFM morphology and SEM images of the samples confirmed more roughed surfaces. All the materials were nonhemolytic in hemocompatibility tests, but among the twelve materials S2, S3, S5, and S6 showed the least hemolysis. For all tested bacterial strains, adherence was lower on each material than that grown on the plain industrial silicone material which was used as a positive control. S2, S3, S5, and S6 samples were selected as the best based on mechanical characterizations, surface characterizations, in vitro hemocompatibility tests and bacterial adherence activity. So, outcomes of this present study would be promising when developing ideal cartilage-mimicking biocomposites and their emerging applications to treat maxillofacial defects due to cartilage damage.

Spectroscopic characterization of tissue and liquids during arthroscopic radio-frequency ablation

PURPOSE

Radio-frequency ablation devices generating a local plasma are widely used as a safe and precise tool for tissue removal in arthroscopic surgeries. During this process, specific light emissions are generated. The aim of this study was to investigate the diagnostic potential of optical emission spectrum analysis for liquid and tissue characterization.

METHODS

The emissions in different saline solutions and during porcine tendon, muscle, and bone tissue ablation were recorded and analyzed in the range of 200-1000 nm.

RESULTS

Specific atomic lines (Na, K, Ca, H, O, W) and molecular bands (OH, CN, C2) were identified, originating from compounds in the liquids and tissues in contact with the probe. A linear correlation between the concentration of both Na and K in solution with the intensities of their spectral lines was observed (Na: R²  = 0.986, P < 0.001; K: R²  = 0.963, P < 0.001). According to the Wilcoxon rank-sum test, the Ca- and K-peak intensities between all three tissue samples and the CN-peak intensities between muscle and bone and tendon and bone differed significantly (P < 0.05).

CONCLUSIONS

These findings prove the general feasibility of spectroscopic analysis as a tool for characterization of liquids and tissues ablated during radio-frequency ablation. This method can potentially be further developed into an intraoperative, real-time diagnostic feature aiding the surgical team in further optimizing the procedure.

Structural and tribological characteristics of ultra-low-wear polyethylene as artificial joint materials

Ultra-low-wear polyethylene (ULWPE) is a new metallocene catalyzed high density polyethylene (HDPE)material. Previous studies have demonstrated that it has excellent biocompatibility and wear resistance, whereupon indicating great potential in the applications to artificial joints. However, as a newly developed material, its tribological behavior and wear resistance mechanism has not been well understood. In the current study, we experimentally evaluated the tribological behavior of ULWPE, and investigated its high wear resistance mechanism in terms of microstructure, crystallization properties, mechanical, physical, and chemical properties. ULWPE manifested the best tribological performance on pin-on-disc (POD) wear tests compared with the most widely used artificial joints materials, with a wear volume of 0.720 ± 0.032 mm³/million cycles (Mc) and 0.600 ± 0.027 mm³/Mc against cobalt-chromium (CoCr) alloy disc and zirconia toughened alumina (ZTA) ceramic disc, respectively. The results of the wear morphology analysis showed that the surface of ULWPE was the slightest, with no obvious surface damage, debris shedding and wear pits. We reveal that three major factors mainly contributed to its high wear resistance. First, ULWPE demonstrated a high crystallinity and a compact crystalline morphology comprised of long linear molecular chains, which contributed to its good mechanical performance. As confirmed by the mechanical test, ULWPE had a very high density, hardness, and tensile elongation at break. The high hardness and strength laid a solid foundation to a low wear volume, and its high ductility and hardness helped to endure abrasive and adhesive wear, resulting in excellent wear resistance. Second, the results of wettability analysis showed that the contact angle formed on the surface of ULWPE was the lowest and the surface energy was the highest. The hydrophilicity of ULWPE provided good lubrication conditions in body fluid. Third, it also had a lower oxidation index. The high hardness, high strength, high ductility and good wetting of ULWPE materials reduced the damage of the material to adhesion and abrasive wear, resulting in excellent wear resistance.

Control of Microstructure for Co-Cr-Mo Fibers Fabricated by Unidirectional Solidification

Co-Cr-Mo alloy fibers of 2 mm in diameter were fabricated from the melt at 1, 2, and 5 mm/min growth rates by unidirectional solidification using an alloy-micro-pulling-down (A-µ-PD) method to control the microstructure. All elements, Co, Cr, and Mo, were distributed in stripes elongated along the growth direction due to constitutional undercooling. Both Co-Cr-Mo fibers fabricated at 2 and 5 mm/min growth rates were composed of the γ phase with a face-centered cubic structure (fcc-γ phase) and ε-phase with a hexagonal close-packed structure (hcp-ε phase), and the ratio of the fcc-γ phase in the fiber fabricated at 5 mm/min growth rate was higher than that in the fiber fabricated at 2 mm/min. The results suggest that a faster growth rate increases the ratio of the fcc-γ phase in the Co-Cr-Mo fiber fabricated by unidirectional solidification.

A Comparative Study of Friction and Wear Processes of Model Metallic Biomaterials Including Registration of Friction-Induced Temperature Response of a Tribological Pair

Nowadays, metallic alloys are extensively used in wear-related biomedical applications. However, it was shown that one of the factors which may contribute to the premature implant failure is the temperature effect caused by the sliding action between the bearing surfaces. Nevertheless, there are not many papers where the wear-related temperature phenomena of biomedical alloys are discussed. Thus, in our paper, we present findings from the tribological tests of the model metallic biomaterials-316L steel, CoCrMo alloy and Ti gr. 2. In our study, the temperature alterations induced by the wear action of the examined materials were analyzed. According to the findings, the temperature response of the biomedical alloys is tribological pair dependent. While the mass loss of the tribological pair 316L-316L steel was the slightest, at the same time the temperature increase was the greatest. Based on the presented findings, further analyses in friction-induced temperature response of biomedical alloys is recommended.

Surface area- and mass-based comparison of fine and ultrafine nickel oxide lung toxicity and augmentation of allergic response in an ovalbumin asthma model

Background: The correlation of physico-chemical properties with mechanisms of toxicity has been proposed as an approach to predict the toxic potential of the vast number of emerging nanomaterials. Although relationships have been established between properties and the acute pulmonary inflammation induced by nanomaterials, properties' effects on other responses, such as exacerbation of respiratory allergy, have been less frequently explored.Methods: In this study, the role of nickel oxide (NiO) physico-chemical properties in the modulation of ovalbumin (OVA) allergy was examined in a murine model. Results: 181 nm fine (NiO-F) and 42 nm ultrafine (NiO-UF) particles were characterized and incorporated into a time course study where measured markers of pulmonary injury and inflammation were associated with NiO particle surface area. In the OVA model, exposure to NiO, irrespective of any metric was associated with elevated circulating total IgE levels. Serum and lung cytokine levels were similar with respect to NiO surface area. The lower surface area was associated with an enhanced Th2 profile, whereas the higher surface area was associated with a Th1-dominant profile. Surface area-normalized groups also exhibited similar alterations in OVA-specific IgE levels and lung neutrophil number. However, lung eosinophil number and allergen challenge-induced alterations in lung function related more to particle size, wherein NiO-F was associated with an increased enhanced pause response and NiO-UF was associated with increased lung eosinophil burden.Conclusions: Collectively, these findings suggest that although NiO surface area correlates best with acute pulmonary injury and inflammation following respiratory exposure, other physico-chemical properties may contribute to the modulation of immune responses in the lung.

Finite element analysis of polyethylene wear in total hip replacement: A literature review

Evaluation and prediction of wear play a key role in product design and material selection of total hip replacements, because wear debris is one of the main causes of loosening and failure. Multifactorial clinical or laboratory studies are high cost and require unfeasible timeframes for implant development. Simulation using finite element methods is an efficient and inexpensive alternative to predict wear and pre-screen various parameters. This article presents a comprehensive literature review of the state-of-the-art finite element modelling techniques that have been applied to evaluate wear in polyethylene hip replacement components. A number of knowledge gaps are identified including the need to develop appropriate wear coefficients and the analysis of daily living activities.

Evaluation of Aerosol Electrospray Analysis of Metal-on-Metal Wear Particles from Simulated Total Joint Replacement

Wear is a common cause for aseptic loosening in artificial joints. The purpose of this study was to develop an automated diagnostical method for identification of the number and size distribution of wear debris. For this purpose, metal debris samples were extracted from a hip simulator and then analyzed by the electrospray method combined with a differential mobility analyzer, allowing particle detection ranging from several nanometers up to 1 µm. Wear particles were identified with a characteristic peak at 15 nm. The electrospray setup was successfully used and validated for the first time to characterize wear debris from simulated total joint replacement. The advantages of this diagnostic method are its time- and financial efficiency and its suitability for testing of different materials.

Intervertebral Disc Nucleus Repair: Hype or Hope?

Chronic back pain is a common disability, which is often accredited to intervertebral disc degeneration. Gold standard interventions such as spinal fusion, which are mainly designed to mechanically seal the defect, frequently fail to restore the native biomechanics. Moreover, artificial implants have limited success as a repair strategy, as they do not alter the underlying disease and fail to promote tissue integration and subsequent native biomechanics. The reported high rates of spinal fusion and artificial disc implant failure have pushed intervertebral disc degeneration research in recent years towards repair strategies. Intervertebral disc repair utilizing principles of tissue engineering should theoretically be successful, overcoming the inadequacies of artificial implants. For instance, advances in the development of scaffolds aided with cells and growth factors have opened up new possibilities for repair strategies. However, none has reached the stage of clinical trials in humans. In this review, we describe the hitches encountered in the musculoskeletal field and summarize recent advances in designing tissue-engineered constructs for promoting nucleus pulposus repair. Additionally, the review focuses on the effect of biomaterial aided with cells and growth factors on achieving effective functional reparative potency, highlighting the ways to enhance the efficacy of these treatments.

Hip simulator testing of the taper-trunnion junction and bearing surfaces of contemporary metal-on-cross-linked-polyethylene hip prostheses

Adverse reaction to metal debris released from the taper-trunnion junction of modular metal-on-polyethylene (MoP) total hip replacements (THRs) is an issue of contemporary concern. Therefore, a hip simulator was used to investigate material loss, if any, at both the articulating and taper-trunnion surfaces of five 32-mm metal-on-cross-linked-polyethylene THRs for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum femoral heads articulating against cross-linked polyethylene (XLPE) acetabular liners were mounted on 12/14 titanium (Ti6Al4V) trunnions. Weight loss (mg) was measured gravimetrically and converted into volume loss (mm³ ) for heads, liners, and trunnions at regular intervals. Additionally, posttest volumetric wear measurements of the femoral tapers were obtained using a coordinate measuring machine (CMM). The surface roughness (Sa) of femoral tapers was measured posttest. After 5 Mc, the mean volumetric wear rate for XLPE liners was 2.74 ± 0.74 mm³ /Mc. The CMM measurements confirmed material loss from the femoral taper with the mean volumetric wear rate of 0.045 ± 0.024 mm³ /Mc. The Sa on the worn area of the femoral taper showed a significant increase (p < 0.001) compared with the unworn area. No other long-term hip simulator tests have investigated wear from the taper-trunnion junction of contemporary MoP THRs. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:156-166, 2020.

In vitro and in vivo investigations of a-C/a-C:Ti nanomultilayer coated Ti6Al4V alloy as artificial femoral head

Hydrogen-free a-C/a-C:Ti nanomultilayer (a-C NM) films were deposited on medical Ti6Al4V by the magnetron sputtering technique under bias-graded voltage. Cell tests and implantations were performed for the a-C NM films coated Ti6Al4V with the uncoated Ti6Al4V as the control. The canine total hip arthroplasty (THA) surgeries were conducted for 12 dogs using the coated femoral heads, with the CoCr heads as the control. Results of cell tests showed that the coated Ti6Al4V had no cytotoxicity, and there was no statistical difference of the cell attachment rates between the coated and uncoated sample (P = 0.091). No significant difference of the tissue response around the coated and uncoated implants were observed after the intramuscular (P = 0.679) and intraosseous implantations (P = 0.122). After two years of successful canine THA, the polyethylene wear particles isolated from periprosthetic soft tissue showed similar sizes, shapes and counts in the two groups (all of the P values >0.05). The retrieved femoral heads showed slightly change of the surface roughness, but no statistical differences between groups (P = 0.696). However, the systemic metal ion analysis indicated that the content of Co and Cr ions released in the coated group (Co: 0.71 ± 0.06 μg/L, Cr: 0.52 ± 0.05 μg/L) were significant lower than that in the control (Co: 1.98 ± 0.16 μg/L, Cr: 1.17 ± 0.19 μg/L) (both P < 0.005). Histological analysis of the periprosthetic tissue in CoCr group showed a severer histiocyte response than that in the coated group (P = 0.029). The head-taper interfaces showed galvanic corrosion attack in the CoCr group, but not in the coated Ti6Al4V group. Therefore, the a-C NM films coated Ti6Al4V exhibited good biocompatibility as an implant material. Compared with the CoCr, the coated Ti6Al4V femoral head could provide comparable in vivo wear properties, release less harmful metal ions and reduce the inflammatory response in periprosthetic tissue, which may help to prolong the longevity of prostheses.

Structural, chemical and mechanical study of TiAlV film on UHMWPE produced by DC magnetron sputtering

Ultra High Molecular Weight Polyethylene (UHMWPE), with a semi-trapezoidal topography, and glass samples were coated with a TiAlV film using magnetron sputtering in order to study its structure, chemical composition and the adhesion film properties on the polymer surfaces. The magnetron sputtering is a PVD technique that depending on the deposited parameter produces a coating with structural, chemical and specific topographic characteristics that increase the electrical, mechanical, optical and biological surface properties of the organic compounds. The quantities of Vanadium (V) and Aluminum (Al) were similar to that of Ti64 alloy. The metallic film obtained presents α-Ti phase structure with a (200) preferential orientation. The TiAlV film on polymeric surfaces with semi-trapezoidal topography exhibit irregularities and uncoated zones but on the glass, the metallic coating was smooth and continuous. The scratch tests were carried out using an incremental load configuration with a Tribotechnic scratch tester equipment. The metallic film decreased the viscoelastic recovering of the polymeric surface but increased the load capacity. The metallic film did not present complete delamination but fractures and small zones of coating detachment were observed on all the scratch tracks.

Histopathological Evaluation of Orthopedic Medical Devices: The State-of-the-art in Animal Models, Imaging, and Histomorphometry Techniques

Orthopedic medical devices are continuously evolving for the latest clinical indications in craniomaxillofacial, spine, trauma, joint arthroplasty, sports medicine, and soft tissue regeneration fields, with a variety of materials from new metallic alloys and ceramics to composite polymers, bioresorbables, or surface-treated implants. There is great need for qualified medical device pathologists to evaluate these next generation biomaterials, with improved biocompatibility and bioactivity for orthopedic applications, and a broad range of knowledge is required to stay abreast of this ever-changing field. Orthopedic implants require specialized imaging and processing techniques to fully evaluate the bone-implant interface, and the pathologist plays an important role in determining the proper combination of histologic processing and staining for quality slide production based on research and development trials and validation. Additionally, histomorphometry is an essential part of the analysis to quantify tissue integration and residual biomaterials. In this article, an overview of orthopedic implants and animal models, as well as pertinent insights for tissue collection, imaging, processing, and slide generation will be provided with a special focus on histopathology and histomorphometry evaluation.

An antioxidant stabilized, chemically cross-linked UHMWPE with superior toughness

Chemical cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) using an organic peroxide followed by high temperature melting results in a large increase in toughness accompanied by a decrease in cross-link density, which, surprisingly does not compromise the wear resistance. We compared the mechanical properties and wear behavior of a vitamin E blended, chemically cross-linked and high temperature melted UHMWPE produced by ram extrusion (PRX HTM) to those measured with the clinically available 100-kGy irradiated and melted UHMWPE (CISM 100). We also assessed the local biocompatibility of PRX-HTM in rabbit subcutaneous pouch and osteochondral defect models. The ultimate tensile strength and pin-on-disc wear rate were similar to CISM 100; whereas the elongation-at-break and impact toughness were much higher with PRX-HTM. The stress intensity factor range at crack inception was also higher with PRX-HTM. Accelerated aging did not result in any measurable oxidation or changes in mechanical properties. Hip simulator wear rate of acetabular liners made with PRX-HTM was 0.3 ± 0.4 mg/million-cycle, similar to that reported for CISM 100 liners. The wear particles were largely spherical with a number-averaged particle size of 0.95 μm with ~75% of particles below 1 μm. The subcutaneous and osteochondral rabbit implantations showed no histological differences between PRX-HTM and the control CISM 100. Pre-clinical wear, mechanical, and biocompatibility testing of PRX HTM showed feasibility for the use of this material as a total joint arthroplasty implant bearing surface. This process has the potential of eliminating the additional step of radiation cross-linking by combining consolidation and cross-linking while improving toughness. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1945-1952, 2019.