Characterization and comparison of wear debris from failed total hip implants of different types

Long-term survival of hybrid total hip replacement for prior failed proximal femoral nail antirotation: a retrospective study with a median 10-year follow-up

Background

Hybrid total hip replacement (THR) is commonly used in the management of proximal femur fractures in elderly individuals. However, in the context of the revision, the literature on hybrid THR is limited, and differences in the long-term survival outcomes reported in the literature are obvious. This retrospective study aimed to evaluate the long-term survival of hybrid THR for failed proximal femoral nail antirotation (PFNA) in elderly individuals aged ≥ 75 years.

Methods

An observational cohort of 227 consecutive individuals aged ≥ 75 years who experienced hybrid THRs following prior primary PFNAs was retrospectively identified from the Joint Surgery Centre, the First Affiliated Hospital, Sun Yat-sen University. Implant survival was estimated using the Kaplan–Meier method. The primary end point was the implant survivorship calculated using the Kaplan–Meier method with revision for any reason as the end point; secondary end points were the function score measured using the modified Harris Hip Score (mHHS) and the incidence of main orthopaedic complications.

Results

In total, 118 individuals (118 THRs) were assessed as available. The median follow-up was 10 (3–11) years. The 10-year survivorship with revision for any reason as the endpoint was 0.914 (95% confidence interval [CI], 0.843–0.960). The most common indication for revision was aseptic loosening (70.0%), followed by periprosthetic fracture (30.0%). At the final follow-up, the median functional score was 83.6 (79.0–94.0). Among the 118 patients included in this study, 16 experienced 26 implant-related complications. The overall incidence of key orthopaedic complications was 13.5% (16/118).

Conclusion

For patients aged ≥ 75 years old with prior failed PFNAs, hybrid THR may yield satisfactory long-term survival, with good functional outcomes and a low rate of key orthopaedic complications.

Analytical Problems with Preparation of Paraspinal Tissues from Patients with Spinal Fusion for Analysis of Titanium

Preparation of paraspinal tissue of patients with implants for elemental analysis is a challenge because it contains titanium in the ionic form, as well as metallic debris. Most literature reports focus on dissolving the tissue, but the impact of digestion conditions on metallic debris of Ti has not been investigated. In our work, various digestion conditions, including systems, compositions of oxidising mixture, and time, were tested aiming (i) to digest the tissue without digestion of metallic titanium to quantify soluble Ti and (ii) to digest metallic titanium debris to asses total Ti content in tissue. The experiments were performed in a closed mode using a microwave-assisted system and a carbon heating block. Our study revealed that total digestion of titanium was impossible in the tested conditions and the maximal level of digested titanium was below 70%. The mineralisation with the use of concentrated nitric acid was optimal to prepare paraspinal samples to analyse the soluble titanium form because metallic titanium passivated and did not migrate to the solution. The elaborated conditions were applied to determine titanium ion in the periimplant tissue of patients with three different titanium-based surgical systems, including traditional growing rod (TGR), guided growth systems (GGS), and vertical expandable prosthesis titanium rib (VEPTR).

Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) as a Promising Polymer Material for Biomedical Applications: A Concise Review

Ultra-High Molecular Weight Polyethylene (UHMWPE) is used in biomedical applications due to its high wear-resistance, ductility, and biocompatibility. A great deal of research in recent decades has focused on further improving its mechanical and tribological performances in order to provide durable implants in patients. Several methods, including irradiation, surface modifications, and reinforcements have been employed to improve the tribological and mechanical performance of UHMWPE. The effect of these modifications on tribological and mechanical performance was discussed in this review.

Multilayers of poly(ethyleneimine)/poly(acrylic acid) coatings on Ti6Al4V acting as lubricated polymer-bearing interface

To achieve an efficient lubricated interface on titanium alloy (Ti6Al4V) alloy, polyelectrolyte multilayer (PEM) polymer coatings, based on poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA), were fabricated on the surface of Ti6Al4V alloy substrates using the layer-by-layer (LbL) assembly technique. Their composition and morphology were confirmed by Fourier-transform infrared/attenuated total reflectance (FTIR/ATR) spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The tribological properties were investigated by a ball-on-disk rotating tribometer using deionized water, saline, and calf serum. The results exhibit that (PEI/PAA)*n coatings have the internal cross-linked network and porous structure on the surface. The surface of PEI/PAA coatings-modified Ti6Al4V shows the sufficient wettability. The polymer-bearing interface of (PEI/PAA)*10 exhibits a low friction coefficient, 0.059, for 2 hr, and represents an 88% decline compared with bare Ti6Al4V. Moreover, the wear track on the polymer-bearing interface is superlow. There is no obvious wear volume, which indicates effective wear resistance. The hydrated layer, the cross-linked network structure, and the porous structure of PEM coatings are the main factors for efficient tribological properties. The multilayer PEI/PAA coating shows the potential uses of developing the lubricated-bearing interface on Ti6Al4V alloy.

Acetabular revision arthroplasty using press-fitted jumbo cups: an average 10-year follow-up study

INTRODUCTION

Acetabular revision arthroplasty using jumbo cups for moderate-to-severe acetabular defects has varied outcomes. We evaluated the clinical and radiological outcomes of acetabular revision arthroplasty using a press-fitted jumbo cup and sought to identify factors that influence outcomes during intermediate follow-up.

MATERIALS AND METHODS

Eighty patients (47 men, 33 women; 80 hips) who underwent acetabular revision arthroplasty using press-fitted jumbo cups were included. The mean follow-up period was 10.4 years. Harris hip score (HHS), presence of groin pain, radiographic results, and Kaplan-Meier survival curves were evaluated. Implant design and surgery-related and patient-related factors were assessed to identify influential factors for cup loosening. Migration and wear analyses were performed using Einzel-Bild-Röntgen-Analyse software.

RESULTS

The mean preoperative HHS of 53 had improved to 77 at the final follow-up (p = 0.005). Nine patients experienced groin pain. Acetabular cup loosening was observed in seven cups (8.7%), and one jumbo cup was replaced with a reinforcement cage. The survival rate of the acetabular cup was 91% at 16 years according to the Kaplan-Meier analysis. Osteolysis was identified around the cup in six cases (7.5%). Acetabular cup loosening occurred more frequently in patients with conventional polyethylene liners than in those with highly cross-linked polyethylene liners (p = 0.045). The mean total migration was 1.52 mm, and the mean total wear was 0.98 mm. There was a positive correlation between total migration and total wear (p = 0.023; Spearman's rho = 0.388). The mean wear rate of the patients with the cup inclination angle < 50° was significantly lower than those with the cup inclination angle > 50° (p = 0.001). There were four cases of complications (three dislocations and one infection) that did not require revision surgery.

CONCLUSION

Press-fitted jumbo cups for acetabular revision arthroplasty exhibited encouraging results during follow-up for an average of 10 years. Use of highly cross-linked polyethylene liners and proper placement of the acetabular component with an inclination angle < 50° may contribute to better clinical outcomes after acetabular revision arthroplasty with jumbo cups.

Recovery of low volumes of wear debris from rat stifle joint tissues using a novel particle isolation method

Less than optimal particle isolation techniques have impeded analysis of orthopaedic wear debris in vivo. The purpose of this research was to develop and test an improved method for particle isolation from tissue. A volume of 0.018 mm³ of clinically relevant CoCrMo, Ti-6Al-4V or Si₃N₄ particles was injected into rat stifle joints for seven days of in vivo exposure. Following sacrifice, particles were located within tissues using histology. The particles were recovered by enzymatic digestion of periarticular tissue with papain and proteinase K, followed by ultracentrifugation using a sodium polytungstate density gradient. Particles were recovered from all samples, observed using SEM and the particle composition was verified using EDX, which demonstrated that all isolated particles were free from contamination. Particle size, aspect ratio and circularity were measured using image analysis software. There were no significant changes to the measured parameters of CoCrMo or Si₃N₄ particles before and after the recovery process (KS tests, p > 0.05). Titanium particles were too few before and after isolation to analyse statistically, though size and morphologies were similar. Overall the method demonstrated a significant improvement to current particle isolation methods from tissue in terms of sensitivity and efficacy at removal of protein, and has the potential to be used for the isolation of ultra-low wearing total joint replacement materials from periprosthetic tissues.

STATEMENT OF SIGNIFICANCE

This research presents a novel method for the isolation of wear particles from tissue. Methodology outlined in this work would be a valuable resource for future researchers wishing to isolate particles from tissues, either as part of preclinical testing, or from explants from patients for diagnostic purposes. It is increasingly recognised that analysis of wear particles is critical to evaluating the safety of an orthopaedic device.

The implication of the osteolysis threshold and interfacial gaps on periprosthetic osteolysis in cementless total hip replacement

Osteolysis around joint replacements may develop due to migration of wear particles from the joint space into gaps between the interface bone and the implant where they can accumulate in high concentrations to cause tissue damage. Osteolysis may appear in various postoperative times and morphological shapes which can be generalized into linear and focal. However, there are no clear explanations on the causes of such variations. Patients' degree of sensitivity to polyethylene particles (osteolysis thresholds), the local particle concentration and the access route provided by the interface gaps have been described as determining factors. To study their effects, a 2D computational fluid dynamics model of the hip joint capsule in communication with an interfacial gap and the surrounding bone was employed. Particles were presented using a discrete phase model (DPM). High capsular fluid pressure was considered as the driving force for particle migration. Simulations were run for different osteolysis thresholds ranging from 5×10⁸ to 1×10¹² particle number per gram of tissue and fibrous tissue generation in osteolytic lesion due to particles was simulated for the equivalent of ten postoperative years. In patients less sensitive to polyethylene particles (higher threshold), osteolysis may be linear and occur along an interfacial gap in less than 5% of the interfacial tissue. Focal osteolysis is more likely to develop in patients with higher sensitivity to polyethylene particles at distal regions to an interfacial gaps where up to 80% of the interfacial tissue may be replaced by fibrous tissue. In these patients, signs of osteolysis may also develop earlier (third postoperative year) than those with less sensitivity who may show very minor signs even after ten years. This study shows the importance of patient sensitivity to wear particles, the role of interfacial gaps in relation to morphology and the onset of osteolysis. Consequently, it may explain the clinically observed variation in osteolysis development.

How has the introduction of new bearing surfaces altered the biological reactions to byproducts of wear and modularity?

BACKGROUND

Biological responses to wear debris were largely elucidated in studies focused on conventional ultrahigh-molecular-weight polyethylene (UHMWPE) and some investigations of polymethymethacrylate cement and orthopaedic metals. However, newer bearing couples, in particular metal-on-metal but also ceramic-on-ceramic bearings, may induce different biological reactions.

QUESTIONS/PURPOSES

Does wear debris from the newer bearing surfaces result in different biological responses compared with the known responses observed with conventional metal-on-UHMWPE bearings?

METHODS

A Medline search of articles published after 1996 supplemented by a hand search of reference lists of included studies and relevant conference proceedings was conducted to identify the biological responses to orthopaedic wear debris with a focus on biological responses to wear generated from metal-on-highly crosslinked polyethylene, metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings. Articles were selected using criteria designed to identify reports of wear debris particles and biological responses contributing to prosthesis failure. Case reports and articles focused on either clinical outcomes or tribology were excluded. A total of 83 papers met the criteria and were reviewed in detail.

RESULTS

Biological response to conventional UHMWPE is regulated by the innate immune response. It is clear that the physical properties of debris (size, shape, surface topography) influence biological responses in addition to the chemical composition of the biomaterials. Highly crosslinked UHMWPE particles have the potential to alter, rather than eliminate, the biological response to conventional UHMWPE. Metal wear debris can generate elevated plasma levels of cobalt and chromium ions. These entities can provoke responses that extend to the elicitation of an acquired immune response. Wear generated from ceramic devices is significantly reduced in volume and may provide the impression of an "inert" response, but clinically relevant biological reactions do occur, including granulomatous responses in periprosthetic tissues.

CONCLUSIONS

The material composition of the device, the physical form of the debris, and disease pathophysiology contribute to complex interactions that determine the outcome to all wear debris. Metal debris does appear to increase the complexity of the biological response with the addition of immunological responses (and possibly direct cellular cytotoxicity) to the inflammatory reaction provoked by wear debris in some patients. However, the introduction of highly crosslinked polyethylene and ceramic bearing surfaces shows promising signs of reducing key biological mechanisms in osteolysis.

Metal debris concentrations in soft tissues adjacent to loosened femoral stems is higher in uncemented than cemented implants

Background

There are still many questions related to aseptic femoral stem loosening. Systemic and local immune responses to the implanted “foreign body” is one of the reasons for loosening. The purpose of the study was to measure metal ion concentration (Ti, Co, Cr, Mo, Ni, Al) around loosened femoral stems and compare their levels around uncemented and cemented implants.

Methods

This paper reports 50 hips operated for isolated stem loosening, in 50 patients at the mean age of 57 years (from 21 to 87). There were 25 cemented (Co,Cr_29,Mo,Ni) and 25 uncemented (Ti, Al) stems. The mean follow-up from primary hip replacement to revision was 10.1 years (from 0.5 to 17). During the procedure, scar tissue around the stem was taken for analysis of metal ions.

Results

The concentrations of titanium and aluminium in soft tissues around uncemented loosened stems were higher than cemented ones (p < 0.001, p < 0.001 respectively). However, no statistically significant differences were observed between both types of stems in terms of ions of the metal of which cemented implants had been made of (Co, Cr, Mo, Ni).

Conclusions

In soft tissue around a loosened stem, the concentrations of metal ions from implants are much higher in case of uncemented stems than of cemented ones. Metal ions from vitalium femoral heads were found around uncemented stems in similar values to cemented streams.

Macrophages-Key cells in the response to wear debris from joint replacements

The generation of wear debris is an inevitable result of normal usage of joint replacements. Wear debris particles stimulate local and systemic biological reactions resulting in chronic inflammation, periprosthetic bone destruction, and eventually, implant loosening, and revision surgery. The latter may be indicated in up to 15% patients in the decade following the arthroplasty using conventional polyethylene. Macrophages play multiple roles in both inflammation and in maintaining tissue homeostasis. As sentinels of the innate immune system, they are central to the initiation of this inflammatory cascade, characterized by the release of proinflammatory and pro-osteoclastic factors. Similar to the response to pathogens, wear particles elicit a macrophage response, based on the unique properties of the cells belonging to this lineage, including sensing, chemotaxis, phagocytosis, and adaptive stimulation. The biological processes involved are complex, redundant, both local and systemic, and highly adaptive. Cells of the monocyte/macrophage lineage are implicated in this phenomenon, ultimately resulting in differentiation and activation of bone resorbing osteoclasts. Simultaneously, other distinct macrophage populations inhibit inflammation and protect the bone-implant interface from osteolysis. Here, the current knowledge about the physiology of monocyte/macrophage lineage cells is reviewed. In addition, the pattern and consequences of their interaction with wear debris and the recent developments in this field are presented.

Cell viability, collagen synthesis and cytokine expression in human osteoblasts following incubation with generated wear particles using different bone cements

In total hip arthroplasty, wear particles generated at articulating surfaces and interfaces between bone, cement and implants have a negative impact on osteoblasts, leading to osteolysis and implant loosening. The aim of this experimental study was to determine the effects of particulate wear debris generated at the interface between straight stainless steel hip stems (Exeter(®)) and three different bone cements (Palacos(®) R, Simplex™ P and Cemex(®) Genta) on cell viability, collagen synthesis and cytokine expression in human osteoblasts. Primary osteoblasts were treated with various concentrations of wear particles. The synthesis of procollagen type I and different cytokines was analysed, and markers for apoptosis and necrosis were also detected. The cytokine synthesis rates in the osteoblasts were initially increased and varied, depending on incubation time and particle concentration. Specific differences in the synthesis rates of interleukin (IL)‑6, IL-8, vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) were observed with the different bone cements examined. The negative effect of the particles on the synthesis of procollagen type I and increased rates of cell apoptosis and necrosis were observed with all three cements analysed. Our present data suggest that wear particles from the interface between the total hip stem and bone cement have a significant effect on viability, cytokine expression and collagen synthesis in human osteoblasts, depending on the bone cement used.

Toll-like receptor 4 signaling pathway mediates proinflammatory immune response to cobalt-alloy particles

Metal orthopedic implant debris-induced osteolysis of hip bone is a major problem in patients with prosthetic-hips. Although macrophages are the principal targets for implant-wear debris, the receptor(s) and mechanisms underlying these responses are not fully elucidated. We examined whether the TLR4 pathway mediates immune response to metal-on-metal (MoM) implant-generated wear particles. Human monocytes (THP-1) were exposed to Co-alloy particles at increasing particle:cell ratio for 24 h. Challenge with particles caused up-regulation of IL-1β, TNF-α and IL-8, and mediated degradation of cytosolic I-κB and nuclear translocation of NF-κB. Blocking antibodies against TLR4 or gene silencing of MyD88 and IRAK-1 prevented particle-induced I-κB/NF-κB activation response and markedly inhibited IL-8 release. Particle-mediated IL-8 response was not observed in TLR4-negative HEK293T cells; whereas transfection-based TLR4-overexpression in HEK293T enabled particle-sensitivity, as observed by I-κB degradation and IL-8 expression in response to particles. Results demonstrate that Co-alloy particles trigger immune response via the TLR4-MyD88-dependent signaling pathway.

The influence of bone cement type on production of fretting wear on the femoral stem surface: a preliminary study

BACKGROUND

It has been reported that bone cement correlates with survivorship of cemented total hip replacement. However, little research has been published to investigate the influence of bone cement type on production of fretting wear on the femoral stem.

METHODS

In the present study, we performed six in vitro wear simulations using the same type of femoral stem (polished Exeter V40™) and three different bone cements (Simplex P, Palacos R, and CMW 3).

FINDINGS

Fretting wear was consistently reproduced on the stem surface and the wear locations compared well with the results of retrieval studies. Selected 3D surface parameters were utilised to quantitatively evaluate fretting wear and no significant difference was identified in terms of fretting wear severity between these simulations. The bone cements were all badly damaged in those sites contacting the fretting wear areas on the femoral stem. Additionally, there were plenty of wear debris present on the cement surface, and the energy dispersive X-ray analysis confirmed that it was just cement particles for Simplex P bone cement, whilst it included metallic particles for Palacos R and CMW 3 bone cements.

INTERPRETATION

This preliminary study shed some light on the influence of bone cement type on production of fretting wear on the femoral stem surface but further research is needed to gain a better understanding on this issue.

The John Charnley Award: an accurate and extremely sensitive method to separate, display, and characterize wear debris: part 2: metal and ceramic particles

BACKGROUND

Metal-on-metal and ceramic-on-ceramic bearings were introduced as alternatives to conventional polyethylene in hip arthroplasties to reduce wear. Characterization of wear particles has been particularly challenging due to the low amount and small size of wear particles. Current methods of analysis of such particles have shortcomings, including particle loss, clumping, and inaccurate morphologic and chemical characterization.

QUESTIONS/PURPOSES

We describe a method to recover and characterize metal and ceramic particles that (1) improves particle purification, separation, and display; (2) allows for precise particle shape characterization; (3) allows accurate chemical identification; and (4) minimizes particle loss.

METHODS

After enzymatic digestion, a single pass of ultracentrifugation cleaned and deposited particles onto silicon wafers or grids for imaging analysis. During centrifugation, particles were passed through multiple layers of denaturants and a metal-selective high-density layer that minimized protein and nucleic acid contamination. The protocol prevented aggregation, providing well-dispersed particles for chemical and morphologic analysis. We evaluated the efficacy and accuracy of this protocol by recovering gold nanobeads and metal and ceramic particles from joint simulator wear tests.

RESULTS

The new protocol recovered particles ranging in size from nanometers to micrometers and enabled accurate morphologic and chemical characterization of individual particles.

CONCLUSION

Both polyethylene and metal wear debris can be simultaneously analyzed from the same sample by combining a silicon wafer display protocol for polyethylene and the metal and ceramics silicon wafer display protocol.

CLINICAL RELEVANCE

Accurate analysis of wear debris is essential in understanding the processes that produce debris and a key step in development of more durable and biocompatible implants.

Are periprosthetic tissue reactions observed after revision of total disc replacement comparable to the reactions observed after total hip or knee revision surgery?

STUDY DESIGN

Comparative study.

OBJECTIVE

To compare periprosthetic tissue reactions observed after total disc replacement (TDR), total hip arthroplasty (THA), and total knee arthroplasty (TKA) revision surgery.

SUMMARY OF BACKGROUND DATA

Prosthetic wear debris leading to particle disease, followed by osteolysis, is often observed after THA and TKA. Although the presence of polyethylene (PE) particles and periprosthetic inflammation after TDR has been proven recently, osteolysis is rarely observed. The clinical relevance of PE wear debris in the spine remains poorly understood.

METHODS

The number, size, and shape of PE particles, as well as quantity and type of inflammatory cells in periprosthetic tissue retrieved during CHARITÉ TDR (n = 22), THA (n = 10), and TKA (n = 4) revision surgery were compared. Tissue samples were stained with hematoxylin/eosin and examined by using light microscopy with bright field and polarized light.

RESULTS

After THA, large numbers of PE particles of size less than 6 μm were observed, which were mainly phagocytosed by macrophages. The TKA group had a broad size range with many larger PE particles and more giant cells. In TDR, the size range was similar to that observed in TKA. However, the smallest particles were the most prevalent with 75% of the particles being less than 6 μm, as seen in revision THA. In TDR, both macrophages and giant cells were present with a higher number of macrophages.

CONCLUSION

Both small and large PE particles are present after TDR revision surgery compatible with both THA and TKA wear patterns. The similarities between periprosthetic tissue reactions in the different groups may give more insight into the clinical relevance of PE particles and inflammatory cells in the lumbar spine. The current findings may help to improve TDR design as applied from technologies previously developed in THA and TKA with the goal of a longer survival of TDR.

Polyethylene and metal wear particles: characteristics and biological effects

This paper first presents a brief overview about the mechanism of wear particle formation as well as wear particle characteristics in metal-on-polyethylene and metal-on-metal artificial hip joints. The biological effects of such particles are then described, focusing on the inflammatory response induced by each type of particles as well as on how metal wear products may be the source of a T lymphocyte-mediated specific immune response, early adverse tissue responses, and genotoxicity. Finally, some of the current in vivo models used for the analysis of tissue response to various wear particles are presented.

Abrasion resistance of oxidized zirconium in comparison with CoCrMo and titanium nitride coatings for artificial knee joints

Most total knee replacement joints consist of a metal femoral component made from a cobalt-chromium- molybdenum (CoCrMo)-alloy and a tibial component with an ultrahigh molecular weight polyethylene (UHMWPE) bearing surface. Wear of the UHMWPE remains the primary disadvantage of these implants. The allergic potential ascribed to CoCrMo-alloys is a further concern. Other metallic alloys with and without ceramic coatings are clinically used to avoid these problems. This study compared the mechanical surface properties of an oxidized zirconium alloy with those of cast and wrought CoCrMo and TiAlV6-4. Additionally, the influence of a titanium nitride (TiN)-plasma coating on the surface properties was investigated. The composition of the oxidized zirconium layer was analyzed. Micro- and macrohardness tests as well as adhesion tests were used to reveal material differences in terms of their abrasive wear potential in artificial joints.

Comparison of periprosthetic tissue digestion methods for ultra-high molecular weight polyethylene wear debris extraction

There is considerable interest in characterization of wear debris from polyethylene (UHMWPE) bearing components used in total joint replacement. To isolate UHMWPE wear debris, tissue samples must be excised from regions adjacent to revised UHMWPE implant components, followed by exposure to one of many available tissue digestion methods. Numerous studies demonstrate successful digestion, but the relative efficiency of each method is not clear. The purpose of this study was to evaluate a variety of conditions for tissue digestion to provide a quantitative comparison of methods. Porcine and human hip tissues were exposed for 24 h to basic, acidic or enzymatic agents, filtered and digestion efficiency calculated based on the percentage of initial to final tissue weight. Of the conditions tested, 5 M NaOH, 5 M KOH, 15 M KOH or 15.8 M HNO(3) yielded the most complete porcine hip tissue digestion (<1% residual tissue weight; p < 0.05). Proteinase K and Liberase Blendzyme 3 did not effectively digest tissue in a 24 h period. Similar to results from the porcine dataset, human tissues digestion was most efficient using 5 M NaOH, 5 M KOH or 15.8 M HNO(3) (<1% residual tissue weight; p < 0.05). To verify that particle surface modifications did not occur after prolonged reagent exposure, GUR415 and Ceridust 3715 particles were immersed in each solution for 24 h. Overall, this study provides a framework for thorough and efficient digestive methods for UHMWPE wear debris extraction.

Metal wear particles: What we know, what we do not know, and why

The importance of wear particle characterization for orthopaedic implants has long been established in the hip and knee arthroplasty literature. With the increasing use of motion preservation implants in the spine, the characterization of wear debris, particularly metallic nature, is gaining importance. An accurate morphological analysis of wear particles provides for both a complete characterization of the biocompatibility of the implant material and its wear products, and an in-depth understanding of the wear mechanisms, ion release, and associated corrosive activity related to the wear particles. In this paper, we present an overview of the most commonly-used published protocols for the isolation and characterization of metal wear particles, and highlight the limitations and uncertainties inherent to metal particle analysis.

PGE2 signaling through the EP4 receptor on fibroblasts upregulates RANKL and stimulates osteolysis

Periprosthetic osteolysis is the most common cause of aseptic loosening in total joint arthroplasty. The role of inflammatory mediators such as prostaglandin E2 (PGE2) and osteoclast promoting factors including RANKL in the pathogenesis of osteolysis has been well characterized. However, the PGE2 receptor (EP1, EP2, or EP4), and cell type in which it is expressed, which is responsible for PGE2 induction of RANKL during wear debris-induced osteolysis, has yet to be elucidated. To address this, we used mice genetically deficient in these EP receptors to assess PGE2 and wear debris responses in vitro and in vivo. Wear debris-induced osteolysis and RANKL expression were observed at similar levels in WT, EP1(-/-), and EP2(-/-) mice, indicating that these receptors do not mediate PGE2 signals in this process. A conditional knockout approach was used to eliminate EP4 expression in FSP1(+) fibroblasts that are the predominant source of RANKL. In the absence of EP4, fibroblasts do not express RANKL after stimulation with particles or PGE2, nor do they exhibit high levels of osteoclasts and osteolysis. These results show that periprosthetic fibroblasts are important mediators of osteolysis through the expression of RANKL, which is induced after PGE2 signaling through the EP4 receptor.

Total hip replacement in younger patientsSurvival rate after avascular necrosis of the femoral head

BACKGROUND

A high risk of loosening has been reported in replacements performed because of avascular necrosis.

PATIENTS AND METHODS

To study cementless total hip replacement (THR) in younger patients with avascular necrosis (AVN), we analyzed retrospectively the outcome in 129 cases: 46 Mittelmeier monobloc ceramic hips (22 cases with AVN), and 83 Zweymüller total hip systems (35 cases with AVN) clinically and radiographically.

RESULTS

At follow-up, 17 Mittelmeier prostheses (10 AVN) and 4 Zweymüller prostheses (none with AVN) had been revised. The diagnosis did not affect the implant survival, but the Zweymüller THR fared better than the Mittelmeier system. The main reason for revision of Mittelmeier implants was aseptic loosening, 3 of 4 Zweymüller revisions were necessary due to polyethylene wear. This difference was confirmed by the radiographic evaluation of the still intact implants: Zweymüller THR showed better values for signs of osseointegration, radiolucent lines around the implants and migration, but more acetabular wear. None of these differences was affected by the AVN diagnosis.

INTERPRETATION

We could not confirm that AVN is a risk factor in total hip replacement.

Titanium particles stimulate COX-2 expression in synovial fibroblasts through an oxidative stress-induced, calpain-dependent, NF-kappaB pathway

In prosthetic loosening, bone resorption is induced by wear debris particles generated from the artificial joint articulation. Our prior work showed that synovial-like fibroblasts respond to titanium particles by producing receptor activator of NF-kappaB ligand (RANKL), a critical activator of osteoclastogenesis. While this effect occurs through a cyclooxygenase-2 (COX-2)-dependent pathway, the mechanism of COX-2 stimulation by titanium particles is not clear. Here we show that titanium particles induce COX-2 gene expression by activating NF-kappaB signaling. Inhibitor of NF-kappaB (IkappaBalpha) is degraded following particle treatment, permitting active NF-kappaB to translocate to the nucleus where it interacts with the COX-2 promoter and drives transcription. NF-kappaB activation is dependent on reactive oxygen species since antioxidants block the NF-kappaB signaling induced by particles. Surprisingly, IkappaBalpha degradation is independent of IKK (IkappaB kinase) and the 26S proteasome. Instead, calpain inhibitor can block the IkappaBalpha degradation induced by particles. Furthermore, the calpain-targeted COOH-terminal PEST sequence of IkappaBalpha is necessary for phosphorylation and degradation, consistent with a proteasome-independent mechanism of catabolism. Altogether, the data demonstrate a signaling pathway by which titanium particles induce oxidative stress, stimulate calpain-mediated NF-kappaB activation, and activate target gene expression, including COX-2. These findings define important targets for osteolysis but may also have importance in other diseases where fibroblasts respond to environmental particles, including pulmonary diseases.

The role of the surface chemistry of CoCr alloy particles in the phagocytosis and DNA damage of fibroblast cells

Surface chemistry of CoCr particles is demonstrated to be fundamental to the process of phagocytosis by fibroblast cells in vitro. Particles preincubated in serum for 5 days and washed in water before addition to cell cultures were phagocytosed less readily than were particles preincubated in minimal essential medium (MEM) for 1 h and washed in water. This was explained by the coating of calcium phosphate and protein on the serum-immersed particles investigated by time-of-flight secondary ion mass spectroscopy. The cells incubated with the serum-immersed particles had a reduced mitotic index when compared with the MEM-immersed particles, indicating that the phagocytosed particles were causing cell cycle arrest. The release of soluble ions measured by electrothermal atomic absorption spectroscopy within the first hour of particle immersion in MEM was identified as the most likely cause for the DNA damage measured by single cell gel electrophoresis ("Comet" assay). Cryofocused ion beam SEM with a spatial resolution of 8 nm was used to cross section cells, to investigate the location of the phagocytosed particles, some of which were found within the nuclear membrane. This paper demonstrated that consideration of the surface chemistry is essential to understand the processes of the effects of orthopedic wear debris.

Synergistic effects of mixed TiAlV and polyethylene wear particles on TNFα response in THP-1 macrophages / Synergistische Effekte gemischter TiAlV- und Polyethylen-Abriebpartikel auf die TNFα-Antwort in THP-1 Makrophagen

TNFalpha is a potent osteoclastogenic cytokine that has a fundamental role in the pathogenesis of wear particle-induced osteolysis. Wear particles of one composition and their biological effects are well characterised. In contrast, little is known about the effects of mixed particles with respect to mix ratio and particle concentration. We evaluated the effects of different mix ratios of polyethylene and TiAlV particles on TNFalpha response. We used a human monocytic cell line (THP-1) in this in vitro study. THP-1 monocytes were differentiated to macrophage-like cells and exposed to different mixtures of lipopolysaccharide-detoxified polyethylene and TiAlV particles. TNFalpha was analysed in culture supernatants using ELISAs. Both polyethylene and TiAlV particles induced a dose- and time-related release of TNFalpha, with maximum levels after 6 h. A PE/TiAlV mix ratio of 36:1 at 10(8) particles/ml induced significantly higher TNFalpha concentrations compared to equal particle concentrations of isolated TiAlV (p=0.047) or PE (p=0.044), indicating the synergistic effect of mixed particles. These results provide evidence that TiAlV and polyethylene particles have significant synergistic effects, depending on the mix ratio and particle concentrations. This supra-additive effect can contribute substantially to the pathogenesis of implant particle-induced osteolysis.

The entrapment of corrosion products from CoCr implant alloys in the deposits of calcium phosphate: a comparison of serum, synovial fluid, albumin, EDTA, and water

Physical wear of orthopedic implants is inevitable. CoCr alloy samples, typically used in joint reconstruction, corrode rapidly after removal of the protective oxide layer. The behavior of CoCr pellets immersed in human serum, foetal bovine serum (FBS), synovial fluid, albumin in phosphate-buffered saline (PBS), EDTA in PBS, and water were studied using X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS). The difference in the corrosive nature of human serum, water, albumin in PBS and synovial fluid after 5 days of immersion was highlighted by the oxide layer, which was respectively 15, 3.5, 1.5, and 1.5 nm thick. The thickness of an additional calcium phosphate deposit from human serum and synovial fluid was 40 and 2 nm, respectively. Co and Cr ions migrated from the bulk metal surface and were trapped in this deposit by the phosphate anion. This may account for the composition of wear debris from CoCr orthopedic implants, which is known to consist predominantly of hydroxy-phosphate compounds. Known components of synovial fluid including proteoglycans, pyrophosphates, phospholipids, lubricin, and superficial zone protein (SZP), have been identified as possible causes for the lack of significant calcium phosphate deposition in this environment. Circulation of these compounds around the whole implant may inhibit calcium phosphate deposition.

Periprosthetic osteolysis: an immunologist's update

PURPOSE OF REVIEW

Inflammation-induced osteolysis is a problem in both inflammatory arthritis and total joint arthroplasty. New drug therapies have been shown to slow, halt, or even reverse the osteolysis associated with inflammatory arthritis. Unfortunately, similar advances in the medical treatment of periprosthetic osteolysis have not occurred. This review will update the state of periprosthetic osteolysis.

RECENT FINDINGS

Preliminary results with phase I and II clinical trials with AMG-162, a human IgG2 that binds receptor activator of nuclear factor kappaB (RANK) ligand, have been reported. Based on these results AMG-162 appears to be safe and to have a potent effect on osteoclast function. Based on animal studies, it is expected that regents such as AMG-162 that block RANK-ligand/RANK interaction will have activity in inflammation-induced osteolysis. Volumetric three-dimensional and magnetic resonance imaging scans for detecting and quantifying periprosthetic osteolysis have been validated in cadaver studies. Lymphocytic infiltrates and positive skin tests to cobalt have been found in patients with periprosthetic osteolysis after second generation metal-on-metal prostheses. These findings again raise the question of whether metal allergy may contribute to implant failure in these patients. A new subset of T helper cells that are neither Th1 nor Th2, but secrete a unique pattern of cytokines including IL-17, has recently been discovered. The importance of these cells in modifying particle-induced osteolysis remains to be determined.

SUMMARY

There have been significant advances in our understanding of periprosthetic osteolysis, imaging technology to quantify osteolysis, and drug development. The time now seems ripe to translate these advances in clinical trials.

Particulate endocytosis mediates biological responses of human mesenchymal stem cells to titanium wear debris

Continual loading and articulation cycles undergone by metallic (e.g., titanium) alloy arthroplasty prostheses lead to liberation of a large number of metallic debris particulates, which have long been implicated as a primary cause of periprosthetic osteolysis and postarthroplasty aseptic implant loosening. Long-term stability of total joint replacement prostheses relies on proper integration between implant biomaterial and osseous tissue, and factors that interfere with this integration are likely to cause osteolysis. Because multipotent mesenchymal stem cells (MSCs) located adjacent to the implant have an osteoprogenitor function and are critical contributors to osseous tissue integrity, when their functions or activities are compromised, osteolysis will most likely occur. To date, it is not certain or sufficiently confirmed whether MSCs endocytose titanium particles, and if so, whether particulate endocytosis has any effect on cellular responses to wear debris. This study seeks to clarify the phenomenon of titanium endocytosis by human MSCs (hMSCs), and investigates the influence of endocytosis on their activities. hMSCs incubated with commercially pure titanium particles exhibited internalized particles, as observed by scanning electron microscopy and confocal laser scanning microscopy, with time-dependent reduction in the number of extracellular particles. Particulate endocytosis was associated with reduced rates of cellular proliferation and cell-substrate adhesion, suppressed osteogenic differentiation, and increased rate of apoptosis. These cellular effects of exposure to titanium particles were reduced when endocytosis was inhibited by treatment with cytochalasin D, and no significant effect was seen when hMSCs were treated only with conditioned medium obtained from particulate-treated cells. These findings strongly suggest that the biological responses of hMSCs to wear debris are triggered primarily by the direct endocytosis of titanium particulates, and not mediated by secreted soluble factors. In this manner, therapeutical approaches that suppress particle endocytosis could reduce the bioreactivity of hMSCs to particulates, and enhance long-term orthopedic implant prognosis by minimizing wear-debris periprosthethic osteolysis.

Isolation and characterization of wear debris generated in patients wearing polyethylene Hylamer inserts, gamma irradiated in air

Hylamer polyethylene was used in the early 1990s to make hip-joint components. Clinical experience has shown that these components, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which then leads to osteolysis. The authors analyzed polyethylene wear particles in seven patients who had received Hylamer polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening. The results were compared to those of six controls, who had received traditional polyethylene implants, sterilized by the same method. The frequency distribution of globular and fibrillar particles was similar in both groups (38.5% in Hylamer, 45.2% in controls). The globular particles in the Hylamer samples had a mean area of 0.12 microm2, which was significantly lesser than that of the controls (0.30 microm2). The width of fibrillar particles in the Hylamer samples was significantly lesser than that of the controls. Therefore, the two materials, despite undergoing the same type of sterilization, produced different types of wear, due to their different properties. In conclusion, the difference in the morphology of Hylamer polyethylene wear particles in comparison with PCA might have caused a more intensive biological response, early and massive osteolysis, and therefore, early loosening.

Activation of NF-kappaB signalling and TNFalpha-expression in THP-1 macrophages by TiAlV- and polyethylene-wear particles

Wear particles are believed to induce periprosthetic inflammation which contributes to periprosthetic osteolysis. TNFalpha plays a pivotal role in the pathogenesis of this process. The molecular mechanisms leading to the development of periprosthetic inflammation with upregulated TNFalpha expression in monocytic cells in response to different wear particles have yet to be defined. In this study we evaluated the effects of polyethylene- and TiAlV-particles on activation of NF-kappaB signalling pathways and TNFalpha biosynthesis and release in monocytic cells with respect to periprosthetic osteoclastogenesis. THP-1 monocytic cells were differentiated to macrophage-like cells and exposed to LPS-detoxified polyethylene and prosthesis-derived TiAlV-particles. TNFalpha release was analyzed in culture supernatant by ELISA. NF-kappaB activation was examined by electrophoretic mobility shift assay (EMSA), and NF-kappaB target promoter activities including transactivation of the TNFalpha promoter were determined by luciferase reporter gene assays. Differentiated THP-1 macrophages were exposed to increasing numbers of particles for 0, 60, 180 and 360 min. Both, polyethylene- and TiAlV-particles induced a significant activation of both NF-kappaB and TNFalpha promoters at 180 min. A significant TNFalpha release was detected after 360 min exposure to polyethylene- and TiAlV-particles in a dose dependent manner. In comparison, LPS induced a much greater activation of NF-kappaB and TNFalpha promoters, and TNFalpha secretion into the supernatant was strongly induced. These results provide evidence that induction of the NF-kappaB signal transduction pathway in macrophages plays a major role in initiating and mediating the inflammatory response leading to periprosthetic osteolysis.

Fibroblasts express RANKL and support osteoclastogenesis in a COX-2-dependent manner after stimulation with titanium particles

Synovial fibroblasts are possible mediators of osteolysis. Fibroblasts respond directly to titanium particles and increase RANKL expression through a COX-2/PGE2/EP4/PKA signaling pathway. Fibroblasts pretreated with titanium or PGE2 stimulated osteoclast formation, showing the functional importance of RANKL induction. Synovial fibroblasts and their activation pathways are potential targets to prevent osteolysis.

INTRODUCTION

Bone loss adjacent to the implant is a major cause of joint arthroplasty failure. Although the cellular and molecular response to microscopic wear debris particles is recognized as causative, little is known concerning role of synovial fibroblasts in these events.

MATERIALS AND METHODS

Murine embryonic fibroblasts and knee synovial fibroblasts in culture stimulated with titanium particles were examined by FACS, real time RT-PCR, Northern blot, and Western blot for expressions of vascular cell adhesion molecule (VCAM)1, RANKL, cyclooxygenase (COX)-1, and COX-2, and the four prostaglandin E2 (PGE2) receptor isoforms. Experiments were performed in the presence and absence of COX inhibitors, protein kinase A (PKA) and protein kinase C (PKC) inhibitors, and various EP receptor agonists. Osteoclast formation was examined in co-cultures of pretreated glutaraldehyde-fixed fibroblasts and primary murine spleen cells treated with macrophage-colony stimulating factor (M-CSF) for 7-days.

RESULTS

TNF-alpha stimulated VCAM1 expression, consistent with a synovial fibroblast phenotype. Titanium particles stimulated RANKL gene and protein expressions in fibroblasts in a dose-dependent manner. Gene expression was increased 5-fold by 4 h, and protein levels reached a maximum after 48 h. Within 1 h, titanium particles also induced COX-2 mRNA and protein levels, whereas both indomethacin and celecoxib blocked the stimulation of RANKL, suggesting a COX-2-mediated event. Furthermore, PGE2 induced RANKL gene and protein expression and rescued RANKL expression in titanium-treated cultures containing COX-2 inhibitors. Fibroblast cultures pretreated with either PGE2 or titanium particles enhanced osteoclast formation, indicating the functional importance of RANKL induction. EP4 was the most abundant PGE2 receptor isoform, EP1 and EP2 were expressed at low levels, and EP3 was absent. The EP1 selective agonist iloprost and the EP2 selective agonist butaprost minimally stimulated RANKL. In contrast, the EP2 and EP4 agonist misoprostol induced RANKL to a magnitude similar to PGE2. Finally, PKA antagonism strongly repressed RANKL stimulation by PGE2.

CONCLUSION

Fibroblasts respond directly to titanium particles and increase RANKL expression through a COX-2/PGE2/EP4/PKA signaling pathway. Thus, the synovial fibroblast is important mediator of osteolysis and target for therapeutic strategies.

The effects of calcium phosphate deposition upon corrosion of CoCr alloys and the potential for implant failure

Physical wear of orthopedic implants is inevitable. CoCr metal samples, typically used in joint reconstruction, corrode rapidly after removal of the protective oxide layer. The behavior of CoCr pellets immersed in human serum, fetal bovine serum (FBS), synovial fluid, and water were studied using time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The differences in the corrosive nature of human serum, FBS, synovial fluid, and water after 5 days immersion were highlighted by the oxide/hydroxide layer, which was, respectively, 25, 10, 1.5, and 3-3.5 nm thick. The thickness of calcium phosphate deposit from human serum, FBS, and synovial fluid was, respectively, 30, 20, and 2 nm. Co and Cr ions migrated from the bulk metal surface and were trapped in the serum deposits, where chromium existed as oxides, hydroxides, and phosphates, whereas the cobalt chemistry was dominated only by phosphates and hydroxides. This may account for the composition of wear debris from CoCr orthopedic implants, which are predominantly hydroxyphosphate compounds. From the literature, proteoglycans, pyrophosphates, phospholipids, lubricin, and superficial zone protein (SZP) have been identified as possible causes for the insignificant deposit of calcium phosphate from synovial fluid. Circulation of these compounds around the whole implant may inhibit calcium phosphate deposition and therefore contribute to osteolysis.

Dosages sanguins de métaux chez 48 patients porteurs d’une prothèse totale de hanche en chrome-cobalt à couple métal-polyéthylène

PURPOSE OF THE STUDY

Component wear and dissemination of wear debris, particularly with metal-on-metal combinations, is the predominant long-term complication of total hip arthroplasty. The purpose of our work was to search for metal pArticles released when using the metal-on-polyethylene combination by analyzing serum levels of chromium (Cr), cobalt (Co), nickel (Ni), and molybdium (Mo) in patients with a metal-on-polyethylene chromium-cobalt total hip arthroplasty. We compared the observed levels with those observed in a control population and studied changes as a function of signs of loosening.

MATERIAL AND METHODS

During a thirty-Month period, 53 patients with degenerative hip disease underwent total hip arthroplasty. The same implant, PVL, being used for all hips. Forty-eight patients were available for analysis at a minimum follow-up of 32 Months. Results of the clinical and radiological examination of the operated hip were recorded. Serum metal levels were assayed by mass spectrometry on total blood samples. Patient activity was determined with the Devane classification and hip function with the Postel-Merle-d'Aubligné score; walking distance was recorded in kilometers. Signs of prosthetic loosening were identified on plain radiograms (AP and lateral views) searching for femoral and/or acetabular lucent lines, cement fracture, granuloma. The control group included 56 patients scheduled for total hip arthroplasty. Non-parametric statistical analysis was used to search for correlations between the clinical, radiological, and biological parameters.

RESULTS

At mean 44 Months follow-up, 17% of the patients had a fair or mediocre function score and 37% had radiological signs of femoral component loosening. Serum cobalt increased significantly in the implanted group (serum cobalt >or=0.60 microg/L in 50% of patients) compared with the control group (serum cobalt >or=0.60 microg/L in 9%) (P<0.001, Mann-Whittney test). Increased serum cobalt was highest in patients with radiographic signs of loosening. This significant difference was not found for other metals. Patient activity, hip function, and follow-up were not correlated with serum levels.

DISCUSSION

Serum cobalt appears to be a good biological marker of prosthetic function although intra- and inter-individual variations are influenced by assay technique, metal ion solubility, and metal dissemination in the organism. The metal-on-metal combination does not appear to be the only friction couple which increases the serum level of metal ions. Our results do not allow defining a time of latency between onset of radiographic signs and increased serum levels.

Mechanisms of failure of total hip replacements: lessons learned from retrieval studies

The value of implant retrieval analysis in orthopaedic surgery has been well recognized. Prosthetic devices retrieved for cause at revision surgery (for implant failure) or devices retrieved postmortem from patients with clinically successful reconstructions provide a unique set of specimens that can be studied to evaluate the effect of the implant on the host environment and the effect of the host environment on the implant. A systematic analysis of retrieved components, in combination with histologic, radiographic, and clinical data can provide valuable insights into the mechanisms of failure of the biomaterials used in joint replacement applications. From the hip implant retrieval studies reported to date, it has been established that the local reaction to particulate wear debris initiates the formation of a granulomatous tissue that ultimately invades the bone-implant interface and results in aseptic loosening. Cement mantle defects, noncircumferential porous coatings, and screw holes can serve as preferential access pathways for the progression of this granulomatous process yielding distinctive patterns of implant loosening and osteolysis. Continued surveillance of retrieved devices is strongly recommended to deepen our understanding of implant failure mechanisms and to evaluate the impact of newer designs and materials on the performance of joint replacement devices.

New insight into the mechanism of hip prosthesis loosening: effect of titanium debris size on osteoblast function

The incidence of rheumatoid arthritis and osteoarthritis is on the rise due to our expanding elderly population. Total joint arthroplasty is the most successful, prevalent treatment modality for these and other degenerative hip conditions. Despite the wide array of prosthetic devices commercially available, hip prostheses share a common problem with a gradual and then accelerating loss of bone tissue and bone-implant interface integrity, followed by implant instability and loosening. Implant failure is largely the result of inevitable wear of the device and generation of wear debris. To provide information for the development of improved prosthetic wear characteristics, we examined the effects of size-separated titanium particles on bone forming cell populations. We demonstrate unequivocally that particle size is a critical factor in the function, proliferation, and viability of bone-forming osteoblasts in vitro. In addition, we have elucidated the time-dependent distribution of the phagocytosed particles within the osteoblast, indicating an accumulation of particles in the perinuclear area of the affected cells. The report finds that particle size is a critical factor in changes in the bone formation-related functions of osteoblasts exposed to simulate wear debris, and that 1.5-4 microm titanium particles have the greatest effect on osteoblast proliferation and viability in vitro. The size of titanium particles generated through wear of a prosthetic device may be an important consideration in the development of superior implant technology.

PGE2 and IL-6 production by fibroblasts in response to titanium wear debris particles is mediated through a Cox-2 dependent pathway

Aseptic loosening of orthopaedic implants is precipitated by wear debris-induced osteolysis. Central to this process are the pro-inflammatory mediators that are produced in response to wear by the fibroblastic cells, which comprise the majority of periprosthetic membranes. Since this pro-inflammatory cascade is mediated by a plethora of factors with redundant functions, it is imperative to establish a hierarchy. Two well-known fibroblast derived pro-inflammatory factors that stimulate wear debris-induced osteoclastic resorption are prostaglandin E2 (PGE2) and IL-6. However, their relationship to each other in this process is poorly defined. Here we show immunohistochemistry of retrieval membranes indicating that COX-2 is the principal cyclooxygenase responsible for PGE2 production in fibroblasts around failed implants. We also performed in vitro experiments with fibroblasts derived from wild-type (WT), COX-1 (-/-) and COX-2 (-/-) mice, which demonstrated that COX-2 is required for Ti wear debris-induced PGE2 production. Interestingly, COX-2 was also required for IL-6 production in these assays, which could be rescued by the addition of exogenous PGE2 (10(-6) M). Pharmacology studies that utilized the COX-1 selective inhibitor SC 560, the COX-2 selective inhibitor celecoxib, and the nonselective COX inhibitor indomethacin confirmed these results. Taken together, these results indicate that selective inhibition of prostaglandin signaling could favorably impact aseptic loosening beyond its direct effects on PGE2 synthesis, in that it inhibits downstream pro-inflammatory/pro-osteoclastic cytokine production.

Biological reaction to alumina, zirconia, titanium and polyethylene particles implanted onto murine calvaria

Periprosthetic osteolysis is a serious problem that limits long-term survival of total hip arthroplasty. Ceramics have been introduced as a joint surface material to reduce osteolysis due to wear particles. The aim of this study is to investigate the biological reaction of ceramic particles on murine calvarial bone, in comparison with polyethylene and titanium particles. Sixty CL/BL6 mice were divided into five groups according to the materials implanted onto the murine calvariae: control, Al(2)O(3), ZrO(2), high-density polyethylene (HDP) and Ti6Al4V. One week after the implantation, each calvarial tissue was dissected and the release of proinflammatory mediators (IL-1beta, IL-6, TNF-alpha) and bone resorption were assessed. The particles of HDP and Ti6Al4V induced three and two times larger osteolytic lesions than the control, respectively. The levels of IL-1beta and IL-6 were significantly elevated in the medium subcultured with the calvariae of HDP and Ti6Al4V groups. Any particle type did not increase the levels of TNF-alpha. There were no significant differences observed in the levels of proinflammatory mediators or osteolytic area among Al(2)O(3), ZrO(2) and control groups. The inflammatory response and bone resorption induced by ceramic particles were much smaller than those induced by HDP and Ti6Al4V. These biological features suggest the biocompatibility of ceramics as a joint surface material for artificial joints.

The nature and dissemination of UHMWPE wear debris retrieved from periprosthetic tissue of THR

The role of wear debris in provoking joint replacement failure through bone resorption is now supported by much research. This study presents the analysis of 104 tissue samples using laser diffraction wear particle analysis in conjunction with standard histologic methods. The number and volume distributions were correlated to a range of joint and patient parameters. The median particle diameter by number was 0.69 microm. No particles smaller than 0.113 microm were resolved. No variation in terms of particle distribution was found among joint types. The ability of particles to migrate away from their point of origin was found to be inversely proportional to their size. The numbers of particles per gram of tissue found in various regions around the prosthesis varied little. Further, the numbers of particles in tissue samples shown to have a chronic foreign-body reaction was > 1 x 10(9) particles/gram.

Morphological characteristics of total joint arthroplasty-derived ultra-high molecular weight polyethylene (UHMWPE) wear debris that provoke inflammation in a murine model of inflammation

It is recognized that the chronic inflammation in peri-prosthetic tissue that contributes to implant failure frequently is provoked by the presence of wear debris. Some wear debris is inevitable because of the nature of the prosthesis, but not all patients develop severe inflammatory responses. The precise factors that mediate the severity of tissue inflammation to wear debris has yet to be fully defined. Because wear debris retrieved from peri-prosthetic tissue consists of a heterogeneous mixture of materials with various sizes and shapes, this study evaluated the influence of two major physical aspects of ultra-high molecular weight polyethylene (UHMWPE) wear debris (shape and surface texture) using a model of tissue inflammation. UHMWPE debris particulates recovered from 50 peri-prosthetic tissue samples were examined by scanning electron microscopy and categorized into four groups based upon aspect ratio and surface texture of the material. The four groups were defined as: 1) smooth and globular, 2) smooth and fibular, 3) rough and globular, and 4) rough and fibular. Histological analysis and ELISA assays were conducted to evaluate variations in cellular responses and cytokine production between the groups. The strongest expression of tumor necrosis factor alpha and interleukin-1 beta was found in tissues exposed to UHMWPE debris with both a rough surface texture and fibular shape, and this response was significantly elevated over debris particles with a smooth surface texture and globular shape. The data suggest that both shape and texture influence the severity of specific inflammatory responses and that rough debris surface texture exerts a marked effect on adverse tissue responses when combined with particles that have a sharp, elongated shape.

Particles and periimplant bone resorption

There is compelling evidence that the most important factor in late periprosthetic bone resorption is an inflammatory reaction to debris. Based on results from several laboratories, it seems likely that opsonized particles activate the macrophage nuclear factor-kappa B signal transduction system via membrane receptors, leading to release of tumor necrosis factor-alpha and other cytokines and growth factors. Tumor necrosis factor stimulates osteoblasts to release cytokines that recruit inflammatory cells and osteoclast precursors to the site and promote the differentiation of early osteoclasts. Tumor necrosis factor influences fibroblasts to release tissue metalloproteinases, and induces c-src in osteoclast precursors, the expression of which is necessary for additional bone resorption. Phagocytosis of debris by osteoblasts may reduce collagen synthesis, whereas phagocytosis by fibroblasts may induce chemokines that amplify inflammation. Bone has been partially protected from particle-induced resorption in animals with defective or inhibited tumor necrosis factor or nuclear factor-kappa B signaling. Many aspects of this inflammatory reaction require clarification, including identifying the factors that influence variability among patients, and testing the importance of costimulatory molecules such as bacterial endotoxin, but the fundamental importance of particles in most cases of aseptic loosening seems certain.

Analysis of retrieved uncemented porous-coated acetabular components in patients with and without pelvic osteolysis

Retrieved polyethylene liners and femoral heads from a consecutive series of revision components of one design were examined. All patients had Long-Term Stable Fixation (OsteoTechnology International, Timonium, Md) total hip arthroplasties (THAs) implanted between 1987 and 1992. The retrieved femoral heads and liners from patients with osteolysis were compared to those without osteolysis. Patients with osteolysis had significantly thinner polyethylene (5.1 mm versus 7.4 mm, P<.01 ) and a higher linear wear rate (0.5 mm/y versus 0.3 mm/y, P=.05). The average femoral head surface roughness also was significantly greater in patients with osteolysis (67 nm versus 35 nm, P<.05). Patients with osteolysis had more total volumetric wear, total linear wear, and volumetric wear rate compared to patients without osteolysis. Age, obesity index, time in situ, and cup inclination were not different between the two groups. Excessive polyethylene wear, probably accelerated by surface roughness of the femoral heads, was associated with pelvic osteolysis in these patients.

The effect of particle wear debris on NFkappaB activation and pro-inflammatory cytokine release in differentiated THP-1 cells

Orthopedic wear debris has been thought to be an important factor associated with osteolysis and loosening of total joint arthroplasties. Previous in vitro studies have reported that particles of wear debris induce the release of pro-inflammatory cytokines and other inflammatory mediators from macrophages and other cells. Several recent investigations, however, have suggested that the wear particles themselves may not be primarily responsible for the inflammatory cellular responses, but that the observed cytokine release in vitro may be caused by endotoxin adsorbed to commercially available particle preparations. The intracellular pathways involved in macrophage signal transduction also are poorly understood. The purposes of this study are to use isolated orthopedic wear debris particles to evaluate pro-inflammatory cytokine release and nuclear factor kappa B (NFkappaB) activation from macrophages. Cells from human monocyte/macrophage cell line (THP-1) were differentiated and incubated with particles of debris that had been isolated from a failed human total hip arthroplasty. The titanium-alloy particles did not evoke release of TNF-alpha or IL-1beta whereas lipopolysaccharide (LPS) or LPS-treated debris particles induced both TNF-alpha and IL-1beta. LPS-treated particles, but not particles alone, stimulated NFkappaB activation. Our results suggest that at the concentrations tested in this study, endotoxin-free wear debris particles may not themselves initiate inflammatory cellular responses in differentiated THP-1 cells. It is unclear whether adsorbed endotoxin is clinically associated with osteolysis and/or loosening in total joint arthroplasties, but several factors, including adsorbed endotoxin, need to be investigated to explore the cellular responses responsible for osteolysis and/or loosening.

Bone graft incorporation in radiographically successful human intervertebral body fusion cages

STUDY DESIGN

Biopsies were obtained from within radiographically successful human intervertebral body fusion cages to document the histology of remodeling bone graft.

OBJECTIVES

The purpose of this study is to describe the tissue within successful human interbody cages with special reference to the viability of bone and the presence or absence of debris particles.

SUMMARY OF BACKGROUND DATA

The use of interbody fusion cages is gaining rapid acceptance, but there is little histologic documentation of the nature of tissue within successful human interbody fusion cages.

METHODS

Needle biopsies were obtained of tissue within radiographically successful intervertebral body fusion cages at the time of pedicle screw removal for back pain or fusion of adjacent spinal level in nine spinal levels of eight patients. Preoperative diagnoses of these eight adult patients included disease conditions in the sagittal plane: spondylosis (5), degenerative disc disease (6), failed laminectomy and discectomy (2), radiculopathy (1), and spondylolisthesis (1). In all cases the cages had been packed with autograft (iliac crest 7, local 1) at the time of insertion. Cage implantation was performed with anterior (anterior lumbar interbody fusion 4, corpectomy and plate fixation 1), and posterior (posterior lumbar interbody fusion 4), segmental instrumentation (plate 1, or pedicle screws 8). All cases except one cervical case had posterolateral fusion or bilateral facet fusion. The cages were composed of carbon fiber-reinforced polymer (Brantigan cage; DePuy AcroMed, Raynham, MA, n = 5) or titanium mesh (Harms Cage; DePuy AcroMed, Raynham, MA, n = 4). Cages had been in situ from 8 to 72 months (mean 28 months). All nine biopsies from eight patients were obtained from within the center of the cages. Specimens were decalcified, routinely embedded in paraffin, stained with hematoxylin and eosin, and viewed qualitatively with transmitted and polarized light.

RESULTS

All needle biopsies were obtained from within the center of the cages, and no patient developed spinal instability after the biopsy. All nine biopsies showed small fragments of necrotic bone associated with viable bone and restoration of hematopoietic bone marrow. Numerous cement lines demarcated the edges of previous cycles of remodeling. The ratio of necrotic to viable bone varied greatly among cases. Small particles of debris were associated with four of the five carbon-fiber cages and one of the four specimens from titanium cages, but there was no visible bone resorption or inflammation.

CONCLUSIONS

Autogenous bone graft was incorporated in these radiographically successful human intervertebral body fusion cages. A few debris particles were observed, but there was no histologic evidence of particle-induced bone resorption or inflammation.

Development and characteristics of a synovial-like interface membrane around cemented tibial hemiarthroplasties in a novel rat model of aseptic prosthesis loosening

OBJECTIVE

Aseptic prosthesis loosening (APL) is related to the formation and aggressive growth of a synovial-like interface membrane (SLIM) between prosthesis and bone. However, investigation of the early phases of SLIM development in humans presents major difficulties. This study was undertaken to develop and characterize the usefulness of a novel animal model of APL that is based on an established model of defined exercise in a running wheel by Wistar rats that have been subjected to intracranial self-stimulation (ICSS).

METHODS

Cemented tibial hemiarthroplasties were implanted into the left knees of 7 male Wistar rats. After 2 weeks, exercise in a running wheel was started in all rats, with a running-load of 2 hours/day for 5 days/week. Six months postoperatively, the knee joints were removed, decalcified, and embedded in paraffin. Histologic evaluation on hematoxylin and eosin-stained sections was performed to investigate the development of a SLIM and the presence of cement debris particles. To characterize the SLIM on a molecular level and investigate growth-regulating factors, the expression of transforming growth factor beta (TGFbeta) and the anti-apoptotic molecule Bcl-2 was analyzed by immunohistochemistry.

RESULTS

Although the prostheses appeared mechanically stable after 6 months, the development of SLIM with areas of bone resorption was seen in all samples. Resembling human SLIM, these membranes consisted of loose fibrous tissue, with cement debris particles located particularly at sites originally attached to the prostheses. Immunohistochemistry studies revealed the expression of TGFbeta and Bcl-2 in all specimens. Interestingly, staining for TGFbeta and Bcl-2 was restricted to areas where the SLIM were attached to bone. In contrast, there was only negligible expression of both proteins at sites adjacent to the prostheses.

CONCLUSION

Our findings demonstrate that the ICSS Wistar rat model constitutes a feasible tool for studying early stages of APL, and specifically the effect of defined running exercise on SLIM formation. The results further suggest that both cellular proliferation, as stimulated by TGFbeta, and altered apoptosis contribute to early stages of SLIM formation. The expression patterns of TGFbeta and Bcl-2 indicate that the growth of the SLIM is initiated and promoted from the bone rather than from the prosthesis.

Paratibial cyst associated with wear debris after total knee arthroplasty

We present a case in which a synovial cyst arose from the proximal tibia and expanded in the calf of a patient after total knee arthroplasty. A cystogram showed a direct communication between the joint cavity and the cyst, apparently associated with a screw that penetrated the tibial cortex. Histologic examination of the cyst showed an inflammatory reaction, including macrophages, foreign body giant cells, and metal and polyethylene particles. To our knowledge, this is the first case report illustrating a paraosseous cyst that developed after total knee arthroplasty. Wear debris from the total knee prosthesis may have been responsible for this unusual cyst.

Combined effect of titanium particles and TNF-alpha on the production of IL-6 by osteoblast-like cells

To clarify the role of tumor necrosis factor (TNF)-alpha on osteoblast functions in the presence of metal particles, two human osteoblast-like cell lines (MG-63 and SaOS-2) were cultured with TNF-alpha in the presence or absence of titanium particles in vitro. A combination of TNF-alpha and titanium particles showed additive effects on inhibition of cell proliferation and alkaline phosphatase production. On the other hand, production of interleukin-6, which is well known to induce osteoclastogenesis and to directly stimulate bone resorption, was additively stimulated by the combination of TNF-alpha and titanium particles. These results suggest that the association of TNF-alpha and titanium particles may play an important role in the pathogenesis of periprosthetic osteolysis through two different pathways: a reduced periprosthetic bone formation due to inhibition of osteoblast proliferation and alkaline phosphatase production, and osteoblast-mediated activation of osteoclastic bone resorption as suggested by the enhancement of interleukin-6 production.

Influence of stability and mechanical properties of a spinal fixation device on production of wear debris particles in vivo

A prospective and quantitative animal study was performed to evaluate the production of wear particles from a spinal fixation device, and to test the hypothesis that the concentration of wear debris particles adjacent to spinal fixation hardware is correlated with the stiffness of the spinal fusion construct and local bone formation at the fusion site. An established canine segmental spinal fusion model with three interfacet fusions was used in this study. Several bone substitute materials were grafted to the area of the interfacet fusion. Internal fixation was performed on both sides of the spinous processes at each site using a stainless steel plate system in 19 dogs. After 12 weeks, spinal segments were excised, then 3-dimensional computerized tomography was used to measure bone volume and bone area of the individual fusion sites. The stiffness of each segment was tested using a servohydraulic materials testing machine. Biopsies were obtained from the soft tissues immediately around the plate system, and wear particles were collected and characterized using an electrical resistance particle analyzer, light and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX). Biopsies from para-spinal tissue from adjacent, unoperated spinal levels served as negative controls. Histologically, 24 of 57 specimens (42.1%) showed only fibrous tissue with no recognizable macrophages, inflammation, or debris. Fourteen of 57 specimens (24.6%), however, contained many particles that were composed of Fe, Cr, and Ni, corresponding to elements found in the fixation hardware. Another 19 specimens showed only occasional particles. The mean concentration of particles from the tissue around the plate system was 2.8 x 10(9) per gram dry tissue weight, compared to 0.5 x 10(9) particles per gram for controls (p < 0.05). Statistical analyses showed significant inverse correlation between the log particle number and stiffness (r = -0.41, p < 0.01), bone volume (r = -0.28, p < 0.05), and bone area (r = -0.34, p < 0. 05) of the corresponding segments. The concentration of particles in the tissue showed a significant inverse correlation with stiffness, bone volume, and bone area of the fusion constructs.