Analysis of particles in acetabular components from patients with osteolysis

Similar polyethylene wear between cemented and cementless Oxford medial UKA: a 5-year follow-up randomized controlled trial on 79 patients using radiostereometry

Background and purpose - Hydroxyapatite (HA)-coated implants have been associated with high polyethylene wear in hip arthroplasties. HA coating as a promoter of wear in knee arthroplasties has not been investigated. We compared the wear-rate of the polyethylene bearing for cemented and cementless HA-coated Oxford medial unicondylar knee arthroplasties (UKA). Secondarily, we investigated whether wear-rates were influenced by overhang or impingement of the bearing. Patients and methods - 80 patients (mean age 64 years), treatment-blinded, were randomized to 1 of 3 Oxford medial UKA versions: cemented with double-pegged or single-pegged femoral component or cementless HA-coated with double-pegged femoral component (ratios 1:1:1). We compared wear between the cemented (n = 55) and cementless group (n = 25) (ratio 2:1). Wear, impingement, and overhang were quantified between surgery and 5-year follow-up using radiostereometry. Clinical outcome was evaluated with the Oxford Knee Score. Results - The mean wear-rate for patients without bearing overhang was 0.04 mm/year (95% CI 0.02-0.07) for the cemented group and 0.05 mm/year (CI 0.02-0.08) for the cementless group. The mean difference in wear was 0.008 mm/year (CI -0.04 to 0.03). No impingement was identified. Half of the patients had medial bearing overhang, mean 2.5 mm (1-5). Wear increased by 0.014 mm/year for each mm increment in overhang. The mean Oxford Knee Score was 39 for the cementless group and 38 for the cemented group at the 5-year follow-up. Interpretation - The wear-rates were similar for the 2 fixation methods, which supports further use of the cementless Oxford medial UKA. However, a caveat is a relatively large 95% CI of the mean difference in wear-rate. Component size and position is important as half of the patients presented with an additional increase in wear-rate due to medial bearing overhang.

Is there any difference between tapered titanium stems with similar geometry and hydroxyapatite coating?

PURPOSE

Several tapered stems with similar geometry and extensive hydroxyapatite coating have recently been introduced. It is not clear, however, whether they share the same design or whether they exhibit any difference that might affect their clinical performances. In this study, we analysed five tapered stems fully coated with hydroxyapatite to establish whether they exhibit similar geometric features and may therefore be used indifferently when a cementless stem is indicated.

METHODS

The length of the stem, the coronal and sagittal diameters, the length of the stem shoulder and the metadiaphyseal angle were measured. The ratio between the proximal and distal coronal diameters of the stem and that between the proximal and distal cross-sectional areas were calculated as a flare index and tapered index, respectively.

RESULTS

The proximal coronal diameter ranged between 24.9 and 28 mm in the smaller size and between 34 and 38.4 mm in the largest sizes. The proximal sagittal diameter ranged between 10.2 and 11.8 in the smallest size and between 14.4 and 17.2 in the largest. A significant difference was found between stems of different brands in the flare index, tapered index, length of stem shoulder and metadiaphyseal angle.

CONCLUSIONS

Lookalike tapered stems with extensive HA coating actually exhibit significant differences in several geometric features potentially affecting their clinical performances. As a result, these stems should not be used indifferently, but rather they should be selected on the basis of the femoral morphology of the operated patient.

Defect-related luminescent bur-like hydroxyapatite microspheres induced apoptosis of MC3T3-E1 cells by lysosomal and mitochondrial pathways

When orthopedic joints coated by hydroxyapatite (HA) were implanted in the human body, they release wear debris into the surrounding tissues. The generation and accumulation of wear particles will induce aseptic loosening. However, the potential bioeffect and mechanism of HA-coated orthopedic implants on bone cells are poorly understood. In this study, defect-related luminescent bur-like hydroxyapatite (BHA) microspheres with the average diameter of 7-9 μm which are comparable to that of the wear-debris particles from aseptically loosened HA implants or HA debris have been synthesized by hydrothermal synthesis and the MC3T3-E1 cells were set as a cells model to study the potential bioeffect and mechanism of BHA microspheres. The studies demonstrated that BHA microspheres could be taken into MC3T3-E1 cells via endocytosis involved in micropinocytosis- and clathrin-mediated endocytosis process, and exert cytotoxicity effect. BHA microspheres could induce the cell apoptosis by intracellular production of reactive oxygen species (ROS), which led to not only an increase in the permeability of lysosome and release of cathepsins B, but also mitochondrial dysfunction and DNA damage. Our results provide novel evidence to elucidate their toxicity mechanisms and might be helpful for more reasonable applications of HA-based orthopaedic implants in the future.

The Influence of Hydroxyapatite Nanoparticle Morphology on Embryonic Development in a Zebrafish Exposure Model

Nanomaterials are used in many different industries such as cosmetics, food, clothing, and electronics. There is increasing concern that exposure to nanoparticles (NPs) during pregnancy can adversely affect fetal development. It is well known that the size, charge, and chemistry of a nanoparticle can modulate embryological development. The role that particle morphology plays on early development, however, is still widely unknown. The present study aims to investigate the effect of hydroxyapatite nanoparticle (HANP) morphology on embryological development in a zebrafish exposure model. Four distinct HANP morphologies (dots, long rods, sheets, and fibers) were fabricated and characterized. Zebrafish embryos were exposed to HANPs (0–100 mg/L), and viability and developmental deformities were evaluated for up to 5 days post-fertilization (dpf). Malformations such as pericardial edema and axial curvature were apparent in embryos as early as 1 dpf, following exposure to the dot and fiber particles, and developed in embryos by 3 dpf in the sheet and long rod particle groups. Minimal death was observed in response to dot, long rod, and sheet particles (≤25%), while fiber particles induced overwhelming toxicity (≤60%) after 1 dpf, and complete toxicity during all subsequent time points. Collectively, these results suggest that nanoparticle morphology can significantly impact embryological development and should be a required consideration when designing nanomaterials for commercial use.

Strontium-Substituted Bioceramics Particles: A New Way to Modulate MCP-1 and Gro-α Production by Human Primary Osteoblastic Cells

Background: To avoid morbidity and limited availability associated with autografts, synthetic calcium phosphate (CaP) ceramics were extensively developed and used as bone filling materials. Controlling their induced-inflammatory response nevertheless remained a major concern. Strontium-containing CaP ceramics were recently demonstrated for impacting cytokines’ secretion pattern of human primary monocytes. The present study focuses on the ability of strontium-containing CaP to control the human primary bone cell production of two major inflammatory and pro-osteoclastogenic mediators, namely MCP-1 and Gro-α, in response to ceramics particles. Methods: This in vitro study was performed using human primary osteoblasts in which their response to ceramics was evaluated by PCR arrays, antibody arrays were used for screening and real-time PCR and ELISA for more focused analyses. Results: Study of mRNA and protein expression highlights that human primary bone cells are able to produce these inflammatory mediators and reveal that the adjunction of CaP in the culture medium leads to their enhanced production. Importantly, the current work determines the down-regulating effect of strontium-substituted CaP on MCP-1 and Gro-α production. Conclusion: Our findings point out a new capability of strontium to modulate human primary bone cells’ communication with the immune system.

A 3D finite element model to investigate prosthetic interface stresses of different posterior tibial slope

PURPOSE

Posterior tibial slope that is created during proximal tibial resection in total knee arthroplasty has emerged as an important factor in the mechanics of the knee joint and the surgical outcome. But the ideal degree of posterior tibial slope for recovery of the knee joint function and preventions of complications remains controversial and should vary in different racial groups. The objective of this paper is to investigate the effects of posterior tibial slope on contact stresses in the tibial polyethylene component of total knee prostheses.

METHODS

Three-dimensional finite element analysis was used to calculate contact stresses in tibial polyethylene component of total knee prostheses subjected to a compressive load. The 3D finite element model of total knee prosthesis was constructed from the images produced by 3D scanning technology. Stresses in tibial polyethylene component were calculated with four different posterior tibial slopes (0°, 3°, 6° and 9°).

RESULTS

The 3D finite element model of total knee prosthesis we presented was well validated. We found that the stress distribution in the polythene as evaluated by the distributions of the von Mises stress, the maximum principle stress, the minimum principle stress and the Cpress were more uniform with 3° and 6° posterior tibial slopes than with 0° and 9° posterior tibial slopes. Moreover, the peaks of the above stresses and trends of changes with increasing degree of knee flexion were more ideal with 3° and 6° posterior slopes.

CONCLUSIONS

The results suggested that the tibial component inclination might be favourable to 7°-10° so far as the stress distribution is concerned. The range of the tibial component inclination also can decrease the wear of polyethylene. Chinese posterior tibial slope is bigger than in the West, and the current domestic use of prostheses is imported from the West, so their demands to tilt back bone cutting can lead to shorten the service life of prostheses; this experiment result is of important clinical significance, guiding orthopaedic surgeon after the best angle to cut bone.

Uncemented fully hydroxyapatite-coated hip stem for intracapsular femoral neck fractures in osteoporotic elderly patients: a multicenter study

There is still debate over the limits of age and bone stock quality of patients on whom to use an un-cemented straight stem coated with hydroxyapatite (HA). We studied a group of 244 patients with a displaced intracapsular fracture of the femoral neck who underwent cementless hemiarthroplasty or total hip arthroplasty. 143 patients were reviewed at the two-year follow up. A fully HA-coated stem for intracapsular hip fracture results in a satisfactory return to pre-injury mobility and a low complications rate. The advantage reported in the literature of a low mortality rate with use of an un-cemented implant in elderly patients was shown to be greater still on finding an immediate primary stability and rapid osteointegration of the implant.

[Primary cancellous bone formation around micro-chambered beads]

OBJECTIVES

The question has been raised whether benign bone defects in patients can be treated with bone forming osteoconductive ceramics achieving primarily a cancellous bone scaffold, which is under load from the beginning.

MATERIAL AND METHODS

Ten reconstructions were performed in 9patients (6women and 3male), with a mean age of 49 (25-65)years, suffering a high variety of epi- and metaphyseal defects, four tibial fractures, two calcaneal fractures, one pathological phalangeal fracture, one chondroma of the distal femur and two open-wedge osteotomies were filled with micro-chambered ceramic beads of 4 and 6mm in diameter. The mean follow up was 22 (7- 8)months. X-rays and CT-scans formed the basis for the evaluation of the reconstruction of the cancellous bone scaffolds.

RESULTS

All cancellous structures were rebuilt, if completely filled with bone-forming elements. If the filling was incomplete, no physiological cancellous bone scaffold resulted. The β-TCP micro-chambered beads were completely reabsorbed or sandwich-like incorporated at the time of evaluation. The HA micro-chambered beads revealed a contrast enhancement and were integrated in the osseous construction of the bone scaffold.

CONCLUSION

Primary cancellous bone formation can be achieved with osteoconductive ceramic micro-chambered beads and can be combined with any osteosynthesis for stable fixation.

Inflammatory cell response to calcium phosphate biomaterial particles: an overview

Bone is a metabolically active and highly organized tissue consisting of a mineral phase of hydroxyapatite (HA) and amorphous calcium phosphate (CaP) crystals deposited in an organic matrix. One objective of bone tissue engineering is to mimic the chemical and structural properties of this complex tissue. CaP ceramics, such as sintered HA and beta-tricalcium phosphate, are widely used as bone substitutes or prosthesis coatings because of their osteoconductive properties. These ceramic interactions with tissues induce a cell response that can be different according to the composition of the material. In this review, we discuss inflammatory cell responses to CaP materials to provide a comprehensive overview of mechanisms governing the integration or loosening of implants, which remains a major concern in tissue engineering. A focus on the effects of the functionalization of CaP biomaterials highlights potential ways to increase tissue integration and limit rejection processes.

Primary cancellous bone formation with BMP and micro-chambered beads: experimental study on sheep

PROBLEM

The physiological reconstruction of cancellous bone defects in surgery of the locomotor system is an unsatisfactorily solved problem.

AIMS

The aims of this study are to examine whether micro-chambered ß-tricalcium-phosphate (ß-TCP) beads provide a certain capillary force suctioning in blood and bone marrow thus forming a stable "negative"-replica of the bone marrow spaces. If so, a new approach for osteoconduction would yield primarily a scaffold of lamellar cancellous bone under load without a long-lasting remodeling process. Recombinant human bone morphogenetic protein (rhBMP) might even enhance all processes of defect healing, remodeling and ß-TCP resorption; gentamicin-loaded ε-caprolactone might protect the implant.

MATERIAL AND METHODS

Ten sheep were operated on; the patella-groove model and the tibial head were used. A defect of 9.4 × 20 mm was created using wet-grinding-diamond instruments. Micro-chambered ß-TCP-beads of 4-6 mm with 0.35 mg rhBMP-7 + 0.1 g collagen per animal, or 1.5 g demineralized bone matrix (DBM) paste on the contra-lateral side were implanted. Both osteoinduction groups were compared with the defect in the tibial heads where plain micro-chambered ceramic beads were inserted. Added to the beads was 12.5 mg gentamicin sulphate in 12.5 mg ε-caprolactone-carrier. Outward diffusion was prevented using a 1-mm-thick press-fit inserted ceramic lid. The bone healing, remodeling and resorption of the ceramic in a right-left comparison of the patella groove and the tibial head was examined at 6 weeks, 2 and 3 months; one animal in reserve was followed for 14 months. The animals were perfusion-fixed, the vasculature micro-casted with an acrylate and nondemineralized processed, and with μ-CT and microscopically documented.

RESULTS

A primary load-bearing spongiosa had developed around the beads, which shortened the remodeling process. The strong micro-chambered, resorbable ß-TCP-beads demonstrate high capillary strength, resorb blood and bone marrow, and represent a stable formative material which, as a carrier for the controlled local release of BMP, that accelerates bone healing, shortens resorption and remodeling compared with plain and DBM loaded implants.

CONCLUSION

Micro-chambered beads represent the bone-forming element, BMP yields a fast defect healing and enhanced remodeling of bone and resorption of ß-TCP compared to delayed and incomplete reconstruction and resorption of ß-TCP on the DBM-side, the plain implants reached nearly the same reconstruction, but far later compared with the BMP loaded implants.

Effect of strontium-substituted biphasic calcium phosphate on inflammatory mediators production by human monocytes

Calcium phosphate materials are widely used as bone substitutes because of their properties close to those of the mineral phase of bones. Nevertheless, after several months, calcium phosphate-based materials release particles that may be phagocytosed by monocytes, leading to an inflammatory reaction. Strontium is well known to counteract the osteoporosis process, but little is known about its effect on inflammatory processes. The purpose of this work was to study the effect of biphasic calcium phosphate (BCP) particles substituted with strontium on the inflammatory reaction. Human primary monocytes stimulated or not by lipopolysaccharide (LPS) were exposed to BCP particles containing strontium for 6 and 24 h. Inflammatory mediators (cytokines and matrix metalloproteinases (MMPs)) production was then quantified by ELISA and zymography. We observed that the presence of strontium had few effects on unstimulated cells, but it decreased the production of pro-inflammatory cytokines and the chemokine interleukin 8 in LPS-stimulated cell-conditioned medium. This work suggests for the first time that strontium may be involved in the control of inflammatory processes following BCP phagocytosis by human monocytes.

Scratching vulnerability of conventional vs highly cross-linked polyethylene liners because of large embedded third-body particles

The hypothesis of this study was that acetabular liner vulnerability to scratching from femoral heads, roughened by third bodies embedded in the liner, is not significantly lower for highly cross-linked polyethylene (HXPE) than for conventional polyethylene (CPE). Six CPE and 6 HXPE acetabular liners were each reproducibly embedded with 5 cobalt-chromium-molybdenum (CoCrMo) beads then run for 10,000 cycles in a joint simulator. By visual rank ordering, there was low association between liner scratch severity and polyethylene type. The CPE and HXPE liner scratches were not significantly different in scratch peak-valley height or width or in liner roughness in the vicinity of the embedded beads. This model indicated that high cross-linking of polyethylene does not offer appreciable protection against severe scratching induced by large embedded third-body particles.

A new insight into the dissociating effect of strontium on bone resorption and formation

Calcium phosphates are widely used as biomaterials and strontium (Sr) is known to have the ability to modify the bone balance towards osteosynthesis. In the present study we investigated the capacity of Sr-substituted sol-gel calcium phosphate to modify the expression of genes and proteins involved in extracellular matrix synthesis by primary bone cells. We first determined the most effective concentration of strontium using human primary bone cells. Sol-gel biphasic calcium phosphate (BCP) powders were then synthesised to obtain release of the optimal concentration of strontium. Finally, human osteoblasts obtained from explant cultures were cultured in the presence of sol-gel BCP, Sr-substituted BCP (5% Sr-substituted BCP, corresponding to a release of 5×10(-5)M [Sr(2+)] under the culture conditions (BCP(5%))) and medium containing strontium chloride (SrCl(2)). Viability, proliferation, cell morphology, protein production and protein activity were studied. We demonstrated that 5×10(-5)M SrCl(2) and BCP(5%) increased the expression of type I collagen and SERPINH1 mRNA and reduced the production of matrix metalloproteinases (MMP-1 and MMP-2) without modifying the levels of the tissue inhibitors of MMPs (TIMPs). Thus strontium has a positive effect on bone formation.

Size dependent induction of proinflammatory cytokines and cytotoxicity of particulate beta-tricalciumphosphate in vitro

Cellular responses to particulate calcium phosphate ceramics can lead to inflammatory reactions under certain conditions that depend on particle composition, size and morphology. In this context, the potential influence of varying sizes of particulate beta-tricalciumphosphate (beta-TCP) on the induction of inflammation and cytotoxicity remains to be determined. The present work investigates the effects of beta-TCP particles of five different sizes (1, 3, 13, 32 and 40 μm) on human peripheral blood mononuclear cells (PBMC) in vitro concerning the release of TNF-alpha, IL-1beta and IL-8 after six and 18 h of incubation (ELISA) as well as intracellular TNF-alpha, IFN-gamma, IL-1alpha, IL-1beta and IL-8 levels within distinct PBMC subpopulations after 12 h (FACS). Potential cytotoxic effects were determined by assaying lactate dehydrogenase (LDH) and morphological analyses (electron microscopy). Beta-TCP 1 μm did not induce any cytokine after 6 h but slightly increases TNF-alpha, IL-1beta and IL-8 release after 18 h. Larger particles (32 and 40 μm) consistently caused higher levels of cytokine release by increasing the fraction of cytokine producing monocytes. They also caused higher levels of LDH release as did smaller, phagocytosable particles. These data suggest a less inflammatory and cytotoxic profile of beta-TCP devices with a smaller primary particle size when compared to larger particles.

Cementless femoral fixation in total hip arthroplasty

A number of cementless femoral stems are associated with excellent long-term survivorship. Cementless designs differ from one another in terms of geometry and the means of obtaining initial fixation. Strict classification of stem designs is important in order to compare results among series. Loosening and thigh pain are less prevalent with modern stem designs. Stress-shielding is present in most cases, even with newer stem designs.

Twenty-year results of the cementless Corail stem

The concept of an extensive hydroxyapatite (HA) coating for the fixation of a tapered femoral stem (Corail®) was introduced 25 years ago in the hope that we could achieve durable biological fixation while preserving normal periprosthetic bone activity. The value of uncemented fixation using HA-coated implants is now widely admitted. However, the characteristics of implant coating and more specifically its extent still remain a subject of debate or even controversy. This prospective study conducted over a 20-year period has greatly contributed to demonstrating the reliability of the Corail® prosthesis, in terms of functional abilities, radiographic evidence and global survivorship. A full HA coating applied on a straight and proximally flared stem induces substantial short-, mid- and long-term benefits without any deleterious effects reported. Modifications of the bone pattern have been strictly limited: slight resorption at the calcar level, absence of cortical hypertrophy and alleged stress shielding. The radiological "silence" is one of the paramount facts clearly demonstrated.

Inferior survival of hydroxyapatite versus titanium-coated cups at 15 years

Hydroxyapatite (HA) particles have long been suspected to disintegrate from implant surfaces, become entrapped in joint spaces of orthopaedic bearing couples, and start a cascade leading to progressive polyethylene (PE) wear, increased osteolysis, and aseptic loosening. We compared cup revision at 15 years' followup in a randomized group of patients with 26 cementless THA components with titanium (Ti) versus first-generation HA coating. We also assessed radiographic PE wear and osteolysis to the 12-year followup or end point revision at a minimum of 5 years (mean, 10.9 years; range, 5-12.6 years). Two Ti-coated cups (17%) and eight HA-coated cups (57%) were revised at 15 years' followup. Femoral head penetration rate was 0.46 mm/year (standard deviation, 0.26) with the HA-coated cups (n = 12) and 0.38 mm/year (standard deviation, 0.14) with the Ti-coated cups (n = 10); we observed a wide variance of linear wear with the HA-coated cups. We also observed a positive association between high wear rate and revision, and between a high volume of osteolysis and revision. Our findings suggest inferior survival of medium-thickness spray-dried HA-coated cups with individual cases of excessive PE wear and premature cup failure. These findings apply to first-generation modular cups and may not apply to other cup designs and new HA-coating technologies.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Proinflammatory and osteoclastogenic effects of beta-tricalciumphosphate and hydroxyapatite particles on human mononuclear cells in vitro

Particulate wear debris can activate defence cells and osteoclasts at the bone-implant interface possibly leading to bone resorption and implant failure. Cellular responses and inflammatory effects have been reported for particulate hydroxyapatite (HA). However, the immunological effects of particulate beta-tricalciumphosphate (beta-TCP) have not been studied and the question of whether beta-TCP is more biocompatible in this regard as is HA remains to be determined. Therefore the present work investigates effects of endotoxin-free HA and beta-TCP particles of the same size (d(50)=1 microm) and dose (SAR 10:1) on human peripheral blood mononuclear cells in vitro. The production of proinflammatory cytokines (TNF-alpha, IL-1beta, IL-8) and cytokines connected to osteoclast and dendritic cell differentiation (OPG, RANKL, M-CSF, GM-CSF) was determined by ELISA. After 6 and 18 h of incubation HA and beta-TCP caused a quite similar induction of TNF-alpha, IL-1beta and IL-8. Effects of particles on the production of M-CSF and OPG were not detectable. However, in sharp contrast to HA, beta-TCP caused less induction of GM-CSF and not any of RANKL, both known for promoting dendritic cells and osteoclastogenesis respectively. Therefore these in vitro data suggest that wear debris of beta-TCP poses lesser risk of the detrimental effects of osteoclast induction known from HA.

Polymorphonuclear neutrophil response to hydroxyapatite particles, implication in acute inflammatory reaction

Hydroxyapatite (HA) is widely used as a bone substitute or coating biomaterial in bone diseases or prosthesis metal parts. The release of HA particles induces an inflammatory response and, if uncontrolled, could result in implant loss. Among the hallmarks of such inflammatory response is early recruitment of the polymorphonuclear cells (PMNs). The purpose of this work is to investigate the response of PMNs following exposure to HA in terms of secreted mediators. Our study shows that HA particles increase the release of pro-inflammatory mediators such as interleukin-1alpha, as well as chemotactic factors such as interleukin-8, macrophage inflammatory protein-1alpha and macrophage inflammatory protein-1beta. HA also induces an increase in matrix metalloproteinase 9 expression. Taken together, our data demonstrate for the first time that HA is capable of activating PMNs, a phenomenon that could potentially contribute to the onset of implant-associated inflammation.

Calcium phosphate-based particles influence osteogenic maturation of human mesenchymal stem cells

Biphasic calcium phosphates (BCPs) consist of a mixture of hydroxyapatite and beta-tricalcium phosphate and are recommended as alternatives or additives to autogenous bone for orthopaedic and dental applications. There is clinical evidence showing particle release from bioceramics, which might impair the ability of human mesenchymal stem cells (hMSC) from bone marrow to proliferate or mature into a functional osteoblast phenotype. This study analyses the influence of BCP particles and their precursors, calcium-deficient apatite (CDA) particles, on in vitro hMSC behaviour. Both types of particles were efficiently internalized by hMSC. Cell viability, morphology and actin cytoskeleton reorganization were unaffected by exposure of hMSC to BCP or CDA particles. Direct exposure to BCP particles impaired hMSC osteogenic differentiation and bone matrix mineralization to a lesser extent than CDA, as assayed by evaluation of alkaline phosphatase activity, osteopontin secretion and mineralized nodule formation. The ability of bioceramic particles to affect osteogenic maturation through modification of soluble factors in media was assayed in an in vitro system that avoids direct cell-particle contact. Indirect exposure to CDA particles severely impaired hMSC osteogenic maturation owing to the uptake of Ca2+ from the culture media. Lower textural properties of BCP and the lack of calcium deficiency in its composition prevented Ca2+ uptake, allowing the development of a functional osteoblast phenotype.

Uncemented stems in hip replacement--hydroxyapatite or plain porous: does it matter? Based on a prospective study of HA Omnifit stems at 15-years minimum follow-up

For many years, acrylic cement has been regarded as the unique available means for a long term and secure fixation of components in hip arthroplasty. A new generation of uncemented implants coated in hydroxyapatite (HA) has arisen since the mid-1980s, aiming to provide a 'biological interface' between metal and surrounding bone, and thus the hydroxyapatite interface was defined some years ago as a distinct entity from both cemented and 'plain porous' fixation. Based upon our 20-year experience with the HA Omnifit stem, this paper aims to discuss the efficiency of hydroxyapatite as a means of fixation for femoral components in hip arthroplasty, then examine whether the addition of a calcium phosphate layer induces any adverse effects, and finally make comparisons between HA-coated versus porous hip stems reported in the literature. With respect to fixation of femoral components in hip arthroplasty we report excellent results from the partially coated HA Omnifit stem in our series, with 99.20% of survival rate at 17-year follow-up, these results being consistent and similar to other HA series in the literature. HA 'uncemented' fixation can therefore be considered reliable and efficient. Furthermore, two decades of hydroxyapatite coatings have resulted in the identification of no major adverse effects. In fact calcium phosphate ions participate in the physiological turn-over of bone remodelling, and the HA coating is replaced by new bone formation without any fibrous tissue layer. Since HA particles are biodegradable and do not produce any inflammatory reaction in the surrounding bone, fears of osteolysis or third body wear due to HA debris have not been confirmed. Finally, comparison between HA versus plain porous femoral components through the literature has demonstrated better results with HA than porous alone both in terms of the quantity and quality of bone remodelling, and the potential migration and subsidence of the stem.

Effects of episodic subluxation events on third body ingress and embedment in the THA bearing surface

In total joint arthroplasty, third body particle access to the articulating surfaces results in accelerated wear. Hip joint subluxation is an under-recognized means by which third body particles could potentially enter the otherwise closely conforming articular bearing space. The present study was designed to test the hypothesis that, other factors being equal, even occasional events of femoral head subluxation greatly increase the number of third body particles that enter the bearing space and become embedded in the acetabular liner, as compared to level-walking cycles alone. Ten metal-on-polyethylene hip joint head-liner pairs were tested in a multi-axis joint motion simulator, with CoCrMo third body particles added to the synovial fluid analog. All component pairs were tested for 2h of level walking; half were also subjected to 20 intermittent subluxation events. The number and location of embedded particles on the acetabular liners were then determined. Subluxation dramatically increased the number of third body particles embedded in the acetabular liners, and it considerably increased the amount of scratch damage on the femoral heads. Since both third body particles and subluxation frequently occur in contemporary total hip arthroplasty, their potent synergy needs to be factored prominently into strategies to minimize wear.

Effect of Different Hydroxyapatite Particles on Malignant Melanoma Cell Behavior

The effect of different hydroxyapatite particles on malignant melanoma cell was evaluated in vitro. Two kinds of short-rode hydroxyapatite particles, which range from 0.4 to 1 um and 0.5 to 1.5 um, were co-cultured with human’s malignant melanoma (MM) cell line A375 for 24, 48, and 72 h. Both of these HA particles showed the same cell proliferation rate as blank control, and there was no statistically significant correlation of matrix metalloproteinases-2 (MMP-2) expression to the HA particle size. SEM images showed that the membrane of tumor cell, which co-cultured with HA particles, was shrunk. The cell superficial sentus was reduced and small size particle’ effect was more obvious. Since immunohistochemistry and SEM data are qualitative technique, further precise methods might bring more information about the effect of HA particles on tumor behaviors. But this study can provide the bio-security test of micrometer HA particles in transplantation after tumor excision.

Influence of Different Hydroxyapatite Particles on the Behavior of Highly Malignant Melanoma Cells

The aim of this study is to reveal the response of highly malignant tumor cell to different hydroxyapatite particles. Human’s highly malignant melanoma (MM) cell line A875 is exposed to two kinds of short-rod hydroxyapatite particles. After incubated with hydroxyapatite particles at different time points, the effects of MM cell morphology, proliferation and invasion are evaluated by SEM, MTT, and MMP2 protein immunohistochemistry respectively. SEM figures show that superficial sentus of MM cells reduce; more secretion is found; and smaller HA particles have more obvious effect. At the same time, no statistic difference can be found in MTT assay and MMP2 expression measurement. This study also provides useful information about biosecurity of hydroxyapatite ceramic in transplantation after highly malignant tumor excision.

Three-dimensional laser micrometry characterization of surface wear in total hip arthroplasty

Even after decades of clinical use, our ability to quantify wear across total hip replacement implant surfaces is largely limited to single value measurements. The influence of patient factors on wear remains enigmatic. This pilot study for the development of three-dimensional laser micrometry (3DLM) introduces an easy, accurate means of 'mapping' and quantifying material removal. A three-dimensional laser micrometer was constructed using a laser micrometer having an accuracy of 0.5 microm. A 3D surface map is triangulated from a point cloud consisting of approximately 140,000 individual points. Comparison to a reference sphere determines radial wear over the entire surface. 3DLM was able to map and quantify fine scale surface features. Even for zirconia on relatively soft ultra-high molecular weight polyethylene, this technique maps the contributions of localized wear at the macroscopic level. The 0.5 microm (or greater) accuracy of these lasers allows us to image surfaces with a high degree of confidence. This analysis lends itself well to automation, and we anticipate that this advance will prove valuable in establishing that each head and cup combination emerging from a given clinical environment has unique wear patterns as observed in this trial data set.

Involvement of toll-like receptor 4 in the inflammatory reaction induced by hydroxyapatite particles

Hydroxyapatite (HA) is widely used to coat metal parts in order to improve their biocompatibility. Analysis of retrieved tissues associated with failed implants, suggest that phagocytosis of HA wear debris by monocytes/macrophages might provide a potent stimulus for the release of a variety of cytokines. Phagocytosis involved a large variety of cellular receptors like toll-like receptors that results in activation of the transcriptional nuclear factor-kappaB (NF-kappaB) via a cell-signalling pathway. In the present paper, we aimed to evaluate the role of the toll-like receptor 4 (TLR4) in the production of inflammatory cytokines induced by HA particles using TLR4(+) and TLR4(-) peritoneal macrophages. We investigated the production of TNF-alpha and the activation of the nuclear transcription factor NF-kappaB. Our data clearly show for the first time that the production of TNF-alpha by macrophages exposed to HA particles was TLR4 dependent but not the activation of NF-kappaB. All these results open future therapies to reduce the inflammatory response induced by HA biomaterials.

Early failure of hemispheric hydroxyapatite-coated acetabular cups

Total hip arthroplasties with hydroxyapatite coatings have shown encouraging results after early-term followup. We presumed hydroxyapatite-coating on a smooth hemispheric press-fit acetabular cup would enhance bone osseointegration and maintain stability of cup after midterm (minimum 5-year) followup. Sixty-three patients had 70 consecutive total hip arthroplasties. Five patients (eight hips) died from problems unrelated to surgery. The remaining patients (62 hips) were followed up for an average of 7 years (range, 6-9 years). The mean age of the patients was 49 years (range, 23-61 years). The average Harris hip score improved from 59 points (range, 32-82 points to 82 points (range, 37-100 points) at final followup. There were seven acetabular component revisions. Of the 55 unrevised cups, 47 hips (85%) were stable by bony ingrowth, five hips (9%) were fibrous stable, and three hips (5%) were unstable with cup migration. Osteolysis around the cup was observed in 18 hips (33%). The average polyethylene wear rate was 0.15 mm/year. Survival rates of the cups at 6 and 8 years were 94.3% and 60.5%, respectively. Total hip arthroplasties using an hydroxyapatite-coated smooth hemispheric acetabular cup showed an unexpected high failure rate in terms of fixation, occurrence of osteolysis, and revision after midterm followup.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

[Long term bone behavior in total primary hip arthroplasty with a fully hydroxyapatite-coated femoral stem: a continuous series of 120 cases with twelve years follow-up]

PURPOSE OF THE STUDY

Cementless hydroxyapatite-coated total prostheses have proven their reliability for more than twenty years. The intimate contact between the receiver bone and the implant allows "union" between the inert and living material. Osteointegration is maintained over time. The purpose of this work was to study the long-term reaction of femoral bone to wear debris after insertion of cementless hydroxyapatite implants.

MATERIAL AND METHODS

One hundred twenty implants constituted a continuous series of total hip arthroplasties performed since 1989 for primary joint degeneration in patients followed for at least twelve years. The same femoral implant totally coated with hydroxyapatite was used for all patients in combination with a metal cup and a polyethylene insert. Twelve years later, twenty-seven patients had died, five were contacted by telephone, and three were lost to follow-up, giving a study population of 85 total hip arthroplasties with complete review and radiographic data. Clinical and radiological findings are reported with a measure of polyethylene wear and femoral bone behavior in contact with femoral implants.

RESULTS

At twelve year follow-up, there were no cases of implant loosening. Clinical outcome was satisfactory, 90% of the hips were pain free. Radiologically, mean polyethylene wear was 0.1 mm per year with calcar changes (zone VII) in 27% and trochanter changes (zone I) in 14%. There was no evidence of osteolysis extension or granuloma formation in the shaft zone. Implant survival at twelve years was 99.1% (97.2-100%).

DISCUSSION

Hydroxyapatite-coated cementless implants resist well to polyethylene wear debris. At twelve years, osteolysis caused by macrophage activation remained limited to zones I and VII. There appeared to be an intimate plug between the implant and the living bone preventing wear debris migration along the implant as was visualized along the entire length of the implant. Polyethylene wear was however real and the risk of osteolysis remains a threat to implant stability. Improved survival of hydroxyapatite-coated total hip implants will thus depend on improvements in the weight-bearing couple.

Importance of the surface area ratio on cytokines production by human monocytes in vitro induced by various hydroxyapatite particles

A possible complication associated with the implantation of hydroxyapatite (HA)-based prosthesis is the release of particles. Those particles can be phagocyted by monocytes that are among the first cells to colonize the inflammatory site. The activated monocytes produce inflammatory mediators, such as cytokines, which cause osteoclasts activation. It has previously been demonstrated using a surface area ratio (ratio of the total surface of the given particles to the surface area of cells) of 1 to 1 that there was a correlation between the expression and production of cytokines induced by HA. The present work studies the effect of physical characteristics of HA particles on the production of various inflammatory cytokines (tumour necrosis factor-alpha, interleukin (IL)-6, and IL-8) and anti-inflammatory cytokine (IL-10). However, the experiments were performed using a surface area ratio of 10 to 1. Our data demonstrate that all the particles, whatever their characteristics, induced a high expression of cytokines but the production was different, meaning that there was a post-transcriptional regulation. The size and sintering temperature seemed to be a characteristics that were less important compared to the shape; the needle particles appeared to induce the most important production of all the cytokines studied.

Biologic fixation and bone ingrowth

Total hip arthroplasty has provided thousands of patients with pain relief and has improved their quality of life. Advances in orthopaedic surgical techniques and implant biomaterials now allow predictable surgical results in most patients. Despite the overwhelming success of this surgical procedure, the debate continues surrounding the optimal choice of implants. Femoral and acetabular implants with varying geometries and fixation methods are currently available. Acrylic bone cement has been used extensively in the past for acetabular and femoral fixation. This mode of component fixation currently remains the technique used most frequently throughout Europe and has shown excellent long-term results. Problems inherent with acrylic bone cement, however, have encouraged other surgeons to use alternative surfaces to allow biologic fixation.

No effect of hydroxyapatite particles in phagocytosable sizes on implant fixation: An experimental study in dogs

The influence of wear debris on bone healing around orthopedic implants is debated. Hydroxyapatite (HA) particles and polyethylene (PE) particles have been shown to have a negative effect on osteoblast cultures in vitro. The present study investigated the in vivo effects of HA and PE particles on the mechanical fixation and gap healing around experimental HA implants. Nonloaded implants (n = 30) were inserted bilaterally into the proximal tibia of 15 dogs with a 2-mm gap to the bone. The peri-implant gap was either (1) empty (n = 6) or filled with (2) hyaluronic acid (n = 8), (3) hyaluronic acid and HA particles (n = 8), or (4) hyaluronic acid and PE particles (n = 8). After 4 weeks, the animals were killed. The implant interface was evaluated by pushout testing until failure and by histomorphometry. Both HA and PE particles were found to be phagocytosed by macrophage-like cells in the interfacial tissue. HA particles were also integrated in newly formed bone. We found no negative effect of the particulate material on mechanical fixation of the implants or on bone formation around the implants.

In vivo evaluation of a biomimetic apatite coating grown on titanium surfaces

Osteoconductive mineral coatings represent an established technology for enhancing the integration of orthopedic implants with living bone. However, current coatings have limitations related to fabrication methods, attachment strength to metal substrates, and in vivo performance. Low temperature biomimetic growth is a coating technique wherein the device to be coated is immersed in a meta-stable saturated solution of the coating constituents and growth of the coating is then allowed to proceed on the surface of the device. This study focused on the in vivo evaluation of a biomimetic apatite coating fabricated under these conditions. The experiment was designed to specifically test the amount of bone ingrowth into the coated channels versus the uncoated channels of an established bone chamber system, with emphasis placed on the amount of bone present on the coupon surface. Three types of measurements were taken on each channel: linear ingrowth %, area ingrowth %, and continuous bone apposition %. The experiments demonstrated that under controlled conditions, the apatite coating appears to resorb in 8 weeks and did stimulate early osseointegration with the metal surface with a reduction in fibrous tissue encapsulation. This coating may, therefore, be useful in facilitating early bone ingrowth into porous surfaces without the potential for coating debris, macrophage infiltration, fibrous tissue encapsulation, and eventual coating failure as may occur with current plasma-sprayed hydroxapatite coating techniques.

Quantifying the effect of resin type and sterilization method on the degradation of ultrahigh molecular weight polyethylene after 4 years of real-time shelf aging

Alternative sterilization methods including ethylene oxide, gas plasma, and gamma-radiation in an inert environment were implemented in the late 1990s, to limit oxidative degradation of ultrahigh molecular weight polyethylene (PE). There was also a simultaneous transition to PE resins that did not contain calcium stearate. Shelf storage duration of PE inserts following gamma-irradiation in air has been correlated to poor clinical performance and increased wear. This study aimed to determine how sterilization method and resin type influenced degradation of PE after 4 years of real-time shelf aging. It was hypothesized that gamma-irradiation and stearate containing resins would incur significantly more degradation than nonradiated, stearate-free resins. Gamma-irradiated PE samples in air and nitrogen had a significantly increased density and oxidation index, compared to nonirradiated PE after 4 years of shelf aging. Alternative sterilization methods such as ethylene oxide and gas plasma appeared to have significantly less oxidation regardless of PE resin type. A partial correlation demonstrated that density and oxidation index were not correlated (r(2) = 0.079) when examining the influence of sterilization method. The data supported that after 4 years of real-time shelf aging, the type of sterilization method had a larger influence on PE degradation than resin type.

Importance of hydroxyapatite particles characteristics on cytokines production by human monocytes in vitro

Calcium phosphate bioceramics have been applied as bone substitutes for several decades. Aseptic loosening after total joint arthroplasty is a major problem in orthopaedic surgery. Hydroxyapatite particles from materials wear have been reported as the main cause of implant failure. For this reason, an investigation into possible wear particles from materials used in the implant may lead to longevity after arthroplasty. Monocytes are among the first cells to colonize the inflammatory site. In the present study, we have evaluated the inflammatory response after exposition to particles with different characteristics (size, sintering temperature and shape). Our data demonstrate that the most important characteristic was the shape and the size of the particles. The needle shaped particles induced the larger production of TNF-alpha, IL-6 and IL-10 by cells. To a less manner, the smallest particles induced an increase of the expression and production of the cytokines studied (TNF-alpha, IL-6 and IL-10). The sintering temperature appeared to be a less important characteristic even though it was involved in the dissolution/precipitation process.

Osteoconductive coatings for total joint arthroplasty

Osteoconductive calcium phosphate coatings for total joint arthroplasty have been in clinical use since the mid1980s. The basic principles involved and basic science evidence for the efficacy of osteoconductive coatings were examined. Hydroxyapatite coatings provide consistent and better filling with bone of the gaps and spaces around cementless joint components after surgery as compared with porous-coated implant surfaces, resulting in better implant stability. Of all the calcium phosphate coatings, hydroxyapatite coatings have had the most widespread application in hip arthroplasty. Their clinical advantages over more conventional implant surfaces are evident in primary and revision hip arthroplasties. A clinical survival rate in the author's series of 97% at a minimum of 11 years followup for the femoral component in a young active patient population (average age, 53 years) was obtained with no mechanical failures. The average polyethylene wear rate in this group was 0.129 mm/year. In a similar group of young patients with revision arthroplasty using hydroxyapatite-coated femoral components, an 11-year survival rate of 93% was obtained. Histologic analysis of specimens retrieved at autopsy confirmed the excellent bony fixation of components. Advantages of the more recent biomimetic hydroxyapatite coatings were examined.

Possible explanation for the white band artifact seen in clinically retrieved polyethylene tibial components

Studies have focused attention on the appearance of a subsurface white band in clinically retrieved polyethylene components and the possible contribution of this phenomenon to early polyethylene delamination. Unconsolidated polyethylene particles and oxidation have been suggested as possible reasons for the appearance of the white band. Calcium stearate and other additives used in processing ultra-high molecular weight polyethylene may also contribute to formation of the white band. A quantitative investigation was conducted on 11 retrieved tibial components that exhibited a subsurface white band to determine whether the amount of calcium stearate particles and additives were greater in the white band region when compared with the mid-portion of the same section of polyethylene. Calcium stearate particles and other additives were quantified using backscattered electron imaging with correlated elemental analysis. The particles were identified based on morphology and elemental patterns similar to reference calcium stearate particles and known additives. Significantly more (p < 0. 0001) calcium stearate particles and additives were present in the white band region (4578 +/- 418 particles/mm(2); mean +/- standard error) than the mid-portion region (1250 +/- 147 particles/mm(2)) of the sectioned tibial inserts. The percent area occupied by calcium stearate particles and additives was five times higher (p < 0.0001) within the white band region (0.81 +/- 0.10%) than the mid-portion region (0.16 +/- 0.03%). The increased presence of calcium stearate and other additives in the white band region suggests that they may play a role in the formation of the white band. In future investigations it may be important to consider how calcium stearate and other additives in polyethylene resins affect white band formation and the possible contribution to crazing, early delamination, and osteolysis in total joint replacement.