Analysis of polyethylene particles isolated from periprosthetic tissue of loosened hip arthroplasty and comparison with radiographic appearance

In vitro immunomodulatory effects of novel strontium and zinc-containing GPCs

BACKGROUND

Glass polyalkenoate cements (GPCs) are bio-adhesives which consist of ionomeric glass particles embedded in a poly-salt matrix. These materials have been used in dentistry and orthodontics extensively but are presently being optimized as bone putties for orthopedic applications.

OBJECTIVE

This study utilized a patented ionomeric glass (mole fraction: SiO2:0.48, ZnO:0.36, CaO:0.12, SrO:0.04) to formulate two GPCs: GPC A (<45 μm particle size glass) and GPC B (45 μm-63 μm). These formulations were previously assessed for their effect on osteoblast viability and osteogenic function. However, the immunomodulatory effects of GPC A and B have not previously been investigated.

METHOD

Non-toxic concentrations of (a) GPC dissolution products and (b) fragmented GPC particles were tested for their ability to affect the secretion of cytokines (TNF-α, IL-1β, IL-6 and IL-10) by rat peripheral blood mononuclear cells (PBMCs), in the presence or absence of the stimulant liposaccharide (LPS). Additionally, the ionic concentrations of Sr, Zn, Ca, and Si were measured in GPC ionic extracts, and the size, shape and concentration of fragmented GPC particles in deionized water were characterized using an optical microscope-based particle analyzer.

RESULTS

The results showed that GPC A ionic products reduced the concentration of TNF-α secreted by stimulated cells compared with cells stimulated in the absence of GPC products. Interestingly, the particles released from GPC A significantly increased the secretion of both TNF-α and IL-6 from unstimulated cells, compared to control cells.

CONCLUSION

Neither GPC B ionic products nor released particles were found to be biologically active with respect to PBMC cytokine secretion.

Effect of particle size on in vivo performances of long-acting injectable drug suspension

Herein, entecavir-3-palmitate (EV-P), an ester prodrug of entecavir (EV), was employed as a model drug, and the effect of drug particle size on in vivo pharmacokinetic profiles and local inflammatory responses, and those associations were evaluated following intramuscular (IM) injection. EV-P crystals with different median diameters (0.8, 2.3, 6.3, 15.3 and 22.6 μm) were prepared using the anti-solvent crystallization method, with analogous surface charges (-10.7 ~ -4.7 mV), and crystallinity (melting point, 160-170 °C). EV-P particles showed size-dependent in vitro dissolution profiles under sink conditions, exhibiting a high correlation between the median diameter and Hixon-Crowell's release rate constant (r² = 0.94). Following IM injection in rats (1.44 mg/kg as EV), the pharmacokinetic profile of EV exhibited marked size-dependency; 0.8 μm-sized EV-P particles about 1.6-, 3.6-, and 5.6-folds higher systemic exposure, compared to 6.3, 15.3, and 22.6 μm-sized particles, respectively. This pharmacokinetic pattern, depending on particle size, was also highly associated with histopathological responses in the injected tissue. The smaller EV-P particles (0.8 or 2.3 μm) imparted the larger inflammatory lesion after 3 days, lower infiltration of inflammatory cells, and thinner fibroblastic bands around depots after 4 weeks. Conversely, severe fibrous isolation with increasing particle size augmented the drug remaining at injection site over 4 weeks, impeding the dissolution and systemic exposure. These findings regarding the effects of formulation variable on the in vivo behaviors of long-acting injectable suspension, provide constructive knowledge toward the improved design in poorly water-soluble compounds.

Nano/micro implant debris affect osteogenesis by chondrocytes: Comparison between ceramic and UHMWPE from hip walking simulator

A new generation of ceramic on ceramic (BIOLOX ®delta) bearings has emerged more than 10 years ago proving a high resistance to wear and good clinical results. However, biological reactions to wear debris, particularly the nanoparticles, need to be evaluated. The first originality of this study is to start from real wear particles obtained by the hip walking simulator (CERsim). These particles were compared with particles obtained by usual methods to assess the biocompatibility of materials: press machine (CERpress). Two ranges of ceramic particles were thus observed: ceramic particles with micron (intergranular fractures) and nano sizes (intragranular fractures), and characterized compared to ultra-high molecular weight polyethylene (UHMWPE). The second originality of this work is to assess the cellular reaction using the primary joint chondrocyte cultures simulating the osteogenesis process and not the cell lines, which are used to simulate the biological reaction of osteolysis. The first results showed a significant difference in cell viability between the cells in contact with particles from the walking simulator and those obtained with the press machine. On the other hand, it was found that the way of extraction of the particles from the lubricant could significantly affect the biological reaction. More interestingly, nano-sized ceramic particles showed a significant impact on the secretion of functional inflammatory mediators, agreeing with recent results in vivo. These novel methods of characterizing the osteogenic impact of UHMWPE and ceramic wear debris can complement the conventional expertise method focusing previously on the osteolysis aspect.

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.

Wear Debris Characterization and Corresponding Biological Response: Artificial Hip and Knee Joints

Wear debris, of deferent sizes, shapes and quantities, generated in artificial hip and knees is largely confined to the bone and joint interface. This debris interacts with periprosthetic tissue and may cause aseptic loosening. The purpose of this review is to summarize and collate findings of the recent demonstrations on debris characterization and their biological response that influences the occurrence in implant migration. A systematic review of peer-reviewed literature is performed, based on inclusion and exclusion criteria addressing mainly debris isolation, characterization, and biologic responses. Results show that debris characterization largely depends on their appropriate and accurate isolation protocol. The particles are found to be non-uniform in size and non-homogeneously distributed into the periprosthetic tissues. In addition, the sizes, shapes, and volumes of the particles are influenced by the types of joints, bearing geometry, material combination, and lubricant. Phagocytosis of wear debris is size dependent; high doses of submicron-sized particles induce significant level of secretion of bone resorbing factors. However, articles on wear debris from engineered surfaces (patterned and coated) are lacking. The findings suggest considering debris morphology as an important parameter to evaluate joint simulator and newly developed implant materials.

Characterization of polyethylene wear particle: The impact of methodology

Due to the prevalence of problems caused by wear particles, the reduced durability of total joint replacements is well documented. The characterization of wear debris enables the size and morphology of these wear particles to be measured and provides an assessment of the biological response in vivo. However, the impact of different methodologies of particle analysis is not yet clear. Hence, the aim of this investigation was to analyze the influence of different particle characterization methods performed by three research centers within the scope of a "round robin test". To obtain knowledge about possible pitfalls, single steps of the particle characterization process (storage, pore size of the filter, coating durations by gold sputtering and scanning electron microscopy (SEM) magnification) were analyzed. The round robin test showed significant differences between the research groups, especially for the morphology of the particles. The SEM magnification was identified as having the greatest influence on the size and shape of the particles, followed by the storage conditions of the wear particle containing lubricant. Gold sputter coating and filter pore size also exhibit significant effects. However, even though they are statistically significant, it should be emphasized that the differences are small. In conclusion, particle characterization is a complex analytical method with a multiplicity of influencing factors. It becomes apparent that a comparison of wear particle results between different research groups is challenging.

[Experimental studies of microcirculatory changes in the bone]

INTRODUCTION/AIMS

Our aim was to characterize the periosteal microvascular reaction induced by the destruction of endosteal vasculature by reaming, and to monitor the time sequence of the events. We have also compared the microcirculatory effects of different implant materials that are most frequently employed in human endoprosthetics.

MATERIALS AND METHODS

The right tibia of male Wistar rats was reamed by microsurgical means and implanted with titanium, steel-alloy or polyethylene nails. Intravital videomicroscopic examinations of the anteromedial and anterolateral surfaces of the tibial periosteum were performed to evaluate the changes in the overall vascular and capillary densities. Microscopic mechanical tests were used to assess the stability of the implants. In control groups, reaming without nailing was performed and the microvascular changes were examined 6 and 12 weeks after surgery.

RESULTS

Reaming alone caused a significant increase in the vascular density of the anteromedial periosteum and a bilateral increase in capillary density. Vascular density at the anteromedial side was increased after all of the implant materials applied, while only polyethylene induced remarkable increases in the capillary and vascular densities at the anterolateral side. Furthermore, polyethylene did not bring about osseointegration.

CONCLUSIONS

Enhanced periosteal angiogenesis could be demonstrated after 12 weeks following tibial reaming. The compensatory microvascular reactions evoked by destruction of endosteal microcirculation of long bones are not influenced by osseo-integrative implant materials, but materials of poor osseointegration properties induce considerable compensatory increases in the microvascular density of the periosteum.

Periosteal microvascular reorganization after tibial reaming and intramedullary nailing in rats

BACKGROUND

Intramedullary reaming and nailing of long bones impairs the endosteal circulation, often causing necrosis of the inner region of the bone cortex. We hypothesized that compensatory hypertrophy of the periosteal microcirculation may develop in response to mechanical destruction of the endosteum, and that this may affect bone survival in these circumstances. In these studies, nailing was performed with materials that affect regeneration of the endosteum differently, and the effects on the tibial periosteal microvasculatory organization were examined.

METHODS

In male Wistar rats, the right tibia was reamed and implanted with an inert titanium nail or a less osseointegrative polyethylene nail; the contralateral tibial endosteum was destroyed by reaming. Reaming without nailing or sham operation was performed on both extremities in two other groups of rats. Twelve weeks later, the anteromedial and anterolateral surfaces of the tibias were exposed by a microsurgical technique. The structural characteristics of the periosteal microcirculation (vessel density and distribution of vessel diameters) were determined by intravital videomicroscopy and computer-assisted analysis. The stability of the implants was assessed on the basis of grades 0-2 on a qualitative scale.

RESULTS

Tibial reaming alone caused significant increases in overall blood vessel and capillary densities in the periosteum compared with those of the intact tibias. Implantation with a titanium nail resulted in firm embedding of the nail and caused changes in the periosteal vasculature similar to those after reaming alone. In contrast, implantation of a polyethylene nail was followed by the development of marked instability of the endomedullary implant and significant increases in the percentage of capillaries and the vessel density in the periosteum.

CONCLUSIONS

Destruction of the endosteal microcirculation per se brings about an increase in periosteal vascular density, which is further augmented if implantation is performed with a material which delays regeneration of the endosteal circulation.

Nano-osteoimmunology as an important consideration in the design of future implants

The size of wear particles emanating from a prosthesis at interfaces is critical to the interfacial properties of the joint replacement and responses from the biological environment. Nanoscale particles in particular require investigation. This project aimed to evaluate the osteoimmunological response to nanoscale ultrahigh molecular weight polyethylene (UHMWPE) wear particles in vitro, including dendritic cells (DCs), macrophages, osteoclasts (OCs), cytokine secretion, and co-cultured OCs and osteoblasts (OBs). The wear particles generated from a constant-load knee prosthesis actuator were profiled using atomic force microscopy and fractionated into sizes of 0.05-0.2, 0.2-0.8, 0.8-1, 1-5 and 5-10 μm. The fractions were exposed to DCs isolated from mice spleen, human OCs, and co-cultured human OBs and OCs, and the effects of the particles on the cells were determined. Results revealed that exposure to nanoscale UHMWPE wear particles induced significant DC activation (p<0.05) and consequently increased cytokine interleukin (IL)-6 and IL-1β secretion (p<0.05). Exposure to nanoscale particles promoted OC maturation, resulting in the suppression of OB proliferation in OB and OC co-cultures. Therefore, the results of this study could contribute to a more mechanistic understanding of wear-debris-associated prosthesis failure. Furthermore, nanoscale UHMWPE wear particles should be considered as mediators of periprosthetic inflammation in the future development of biomaterials for joint replacement bearing surfaces.

Large acetabular defects can be managed with cementless revision components

BACKGROUND

Optimal techniques for acetabular revision in the setting of major pelvic osteolysis have not been established. Bilobed components, structural grafts, and reinforcement cages have demonstrated 10-24% midterm failure rates. While cementless hemispherical components have been utilized to treat large acetabular defects, most reports have not focused specifically on patients with extensive deficiencies.

QUESTIONS/PURPOSES

We report midterm clinical scores, component revisions, and complications following focal bone grafting and cementless acetabular revision in cases with major periacetabular osteolysis.

METHODS

We identified 30 patients (32 hips) who underwent cementless acetabular revision to treat massive acetabular bone loss at an average followup of 53 months. We excluded three patients lost to followup and two patients who died prior to minimum 24 month followup. Harris Hip Scores were assessed before and after surgery. Postoperative radiographs were evaluated for graft incorporation and component migration. Component revision and component migration are reported as failures.

RESULTS

Mean Harris Hip Score improved from 52.5 (range, 17.7-90.7) to 87.3 (range, 25.3-100) points. Three hips (9%) were revised for aseptic loosening. Three components (10.7%) demonstrated radiographic migration, but were not revised. Complete graft incorporation was seen in 17 cases (68%). There were five major complications (14%).

CONCLUSIONS

Cementless acetabular fixation and bone grafting result in clinical scores and survivorship comparable to other options at midterm followup, with potential for biological fixation.

LEVEL OF EVIDENCE

Level IV, clinical research study. See the Guidelines for Authors for a complete description of levels of evidence.

Distribution of polyethylene wear particles and bone fragments in periprosthetic tissue around total hip joint replacements

Ultra-high molecular weight polyethylene (UHMWPE) wear particles play a significant role in failures of total joint replacements (TJRs). In this work, we investigated the distribution of these wear particles in periprosthetic tissues obtained from nine revisions of hip TJR. In the first step, all periprosthetic tissues were combined and mechanically separated into granuloma tissue (containing hard granules visible to the naked eye) and surrounding tissue (without visible granules). In the second step, the tissues were hydrolyzed by protease from Streptomyces griseus and granules were separated by filtration; this divided the sample into four groups: (i) lyzate and (ii) non-degraded large granules from the granuloma tissue plus (iii) lyzate and (iv) non-degraded small granules from the surrounding tissue. In the third step, the large as well as small granules were hydrolyzed by collagenase from Clostridium histolyticum. In the last step, the UHMWPE wear particles from all four groups were purified by HNO3 digestion and weighed. The purity of the isolated particles was verified by scanning electron microscopy, infrared spectroscopy and energy-dispersive X-ray analysis. Of the total amount of polyethylene particles in the whole granuloma tissue, 72% of particles in the size range 0.1-10 microm and 68% of those larger than 10 microm were found in granules. Therefore, the formation of granules significantly lowers the effective amount of wear particles available for interaction with reactive cells and seems to be a natural defense mechanism.

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.

Endosomal damage and TLR2 mediated inflammasome activation by alkane particles in the generation of aseptic osteolysis

Ultra-high molecular weight polyethylene is widely used as a bearing surface in prosthetic arthroplasty. Over time the generation of implant-derived wear particles can initiate an inflammatory reaction characterized by periprosthetic inflammation and ultimately bone resorption at the prosthetic bone interface. Herein we present evidence that the different sized particles as well as the different length alkane polymers generated by implant wear leads to a two component inflammatory response. Polymeric alkane structures, with side chain oxidations, directly bind and activate the TLR-1/2 signaling pathway. Whereas micron- and nanometer-sized particulate debris are extensively phagocyted and induce enlargement, fusion and disruption of endosomal compartments. The resulting lysosomal damage and subsequent enzymatic leakage induces the NALP3 inflammasome activation as determined by cathepsins S and B cytosolic release, Caspase 1 activation and processing of pro-IL-1beta, and pro-IL-18. These two processes synergistically results in the initiation of a strong inflammatory response with consequent cellular necrosis and extracellular matrix degradation.

Alteration of the amount and morphology of wear particles by the addition of loading profile transitions during artificial hip wear testing

Current validation tests of total hip arthroplasty endo-prostheses capture only a single activity performed by patients: continuous walking. A more representative test that includes transitions from a static loaded position to dynamic motion would simulate common motions by patients in which they change from standing to walking. The introduction of such transitions into a traditional test protocol could provide insight into actual wear behaviours and more realistic wear particle properties such as size and shape. First, the introduction of transitions will increase the measured wear rate. Second, the amount of wear will be positively correlated to the number of transitions per day. Finally, the size and shape of polyethylene particle produced via testing with transitions will differ from those of a conventional continuous walking test. Three identical sets of four cobalt chromium femoral heads and sterilized acetabular cups sterilized in ethylene oxide were tested in 30 per cent bovine serum under three conditions: continuous walking (0 transitions/day), 10 transitions/day, and 100 transitions/day. A day was defined as 2500 steps. The static and peak dynamic loads were 260 N and 1.9 kN respectively. A testing duration of 106 cycles was completed for each of the three tests. The wear rate was found to be inversely related to the number of transitions. Particle analysis showed that the particle size decreased as the number of transitions increased. Particles from the 100 transitions/day test were more fibular and produced more particles of the size known to promote an immune reactive response. Contrary to our hypothesis, as the number of transitions performed by patients increased, the wear rate and accumulated wear decreased. In addition, as the number of transitions increased, a larger percentage of wear particles were in the submicron size range. Consequently, despite a decrease in wear due to the presence of loading profile transitions, there is a potentially greater risk of osteolysis owing to the increased production of immunoreactive particles.

Immunogenecity of modified alkane polymers is mediated through TLR1/2 activation

BACKGROUND

With the advancement of biomedical technology, artificial materials have been developed to replace diseased, damaged or nonfunctional body parts. Among such materials, ultra high molecular weight alkane or modified alkyl polymers have been extensively used in heart valves, stents, pacemakers, ear implants, as well as total joint replacement devices. Although much research has been undertaken to design the most non-reactive biologically inert polyethylene derivatives, strong inflammatory responses followed by rejection and failure of the implant have been noted.

METHODOLOGY/PRINCIPAL FINDINGS

Purification of the alkane polymers from the site of inflammation revealed extensive "in vivo" oxidation as detected by fourier transformed infra-red spectroscopy. Herein, we report the novel observation that oxidized alkane polymers induced activation of TLR1/2 pathway as determined by ligand dependent changes in intrinsic tyrosine fluorescence intensity and NF-kappaB luciferase gene assays. Oxidized polymers were very effective in activating dendritic cells and inducing secretion of pro-inflammatory cytokines. Molecular docking of the oxidized alkanes designated ligand specificity and polymeric conformations fitting into the TLR1/2 binding grooves.

CONCLUSION/SIGNIFICANCE

This is the first report of a synthetic polymer activating immune responses through TLR binding.

13-Jahres-Ergebnisse der CLS-Spreizpfanne in der primären Hüftendoprothetik

BACKGROUND

Clinical studies of the CLS expansion cup in hybrid hip arthroplasty generally show good results. However, follow-up times are limited to between 5 and 10 years. The aim of our study was to assess the clinical and radiological outcome of the CLS cup after more than 10 years.

MATERIAL AND METHOD

After a follow-up of 13 years (10-15 years), 41 of 186 patients with a total of 41 CLS cups were available for clinical and radiological evaluation. In addition, a digital analysis of all radiographs was done. This included measurement of the migration, inclination, polyethylene wear, shaft subsidence, and osteolytic lesions.

RESULTS

The average preoperative Harris hip score was 48, which increased to 81 at final follow-up. No acetabular loosening was found. Two cups (5%) showed osteolytic lesions not exceeding 50% of the specific zone according to DeLee and Charnley and were considered stable. There was no migration or inclination of the cups. The average polyethylene wear corresponded to 0.1 mm/year. Sixteen patients (39%) showed osteolyses around the stem and were considered loose.

CONCLUSION

The CLS expansion cup provides excellent clinical results after 13 years in hybrid total hip arthroplasty. Time-correlative polyethylene wear and the extremely high rate of stem loosening have no consequences for the cup stability in our patient group. Acetabular osteolysis is rare.