Cellular immune responses to orthopaedic implant materials following cemented total joint replacement

Vitamin E-added Highly Cross-Linked Polyethylene Decreases the Risk of Osteolysis in an In Vivo Arthroplasty Model

Introduction Aseptic loosening is one of the most important complications of arthroplasty surgery. It is known that immune response against particles plays role in the pathogenesis of aseptic loosening. Polyethylene (PE) has an important place in these particles. There are limited in vivo studies examining aseptic loosening caused by PE residues. Objective The aim of the present study is to evaluate the aseptic loosening created by highly cross-linked PE (HXLPE) and vitamin E-added PE particles in an in vivo knee prosthesis model. Materials and methods Thirty-nine male Sprague-Dawley rats, which were randomized into three groups, were included in the study. After surgical exposure of knee joints of rats, femoral intramedullary canals were drilled and instilled with isolated saline solution and saline solution that contained standard PE or vitamin E-added PE particles according to their groups. Afterwards, a titanium implant was placed on the femoral articular surface of each animal. Rats received intraarticular injections weekly of the same solution, which was initially instilled into their femoral canal. The rats were sacrificed at the end of the third week and then underwent radiological and histopathological evaluations. Result In histopathological evaluation, periprosthetic membrane formation, inflammatory cell change, and cellular damage of cartilage and bone tissue around the implant were assessed. There was a statistically lesser amount of cellular damage and periprosthetic membrane formation in the vitamin-E/HXLPE group compared to the HXLPE group (p=0.04, p=0.001). No significant difference was found between the PE groups with respect to inflammatory cells (p=0.715). Conclusions HXLPE caused more significant osteolysis compared to VE-HXLPE. Antioxidants in PE could provide a reduction in osteolysis and aseptic loosening.

Allergies in orthopaedic and trauma surgery

Hypersensitivity reactions to implants in orthopaedic and trauma surgery are a rare but devastating complication. They are considered as a delayed-type of hypersensitivity reaction (type IV), characterized by an antigen activation of sensitized T-lymphocytes releasing various cytokines and may result in osteoclast activation and bone resorption. Potential haptens are originated from metal alloys or bone-cement. A meta-analysis has confirmed a higher probability of developing a metal hypersensitivity postoperatively and noted a greater risk of failed replacements compared to stable implants. Hypersensitivity to implants may present with a variety of symptoms such as pain, joint effusion, delayed wound/bone healing, persistent secretion, allergic dermatitis (localized or systemic), clicking noises, loss of joint function, instability and failure of the implant. Various diagnostic options have been offered, including patch testing, metal alloy patch testing, histology, lymphocyte transformation test (LTT), memory lymphocyte immunostimulation assay (MELISA), leukocyte migration inhibition test (LIF) and lymphocyte activation test (LAT). No significant differences between in vivo and in vitro methods have been found. Due to unconvincing evidence for screening methods, predictive tests are not recommended for routine performance. Infectious aetiology always needs to be excluded. As there is a lack of evidence on large-scale studies with regards to the optimal treatment option, management currently relies on individual case-by-case decisions. Several options for patients with (suspected) metal-related hypersensitivity exist and may include materials based on ceramic, titanium or oxinium or modified surfaces. Promising results have been reported, but long-term experience is lacking. More large-scaled studies are needed in this context. In patients with bone-cement hypersensitivity, the component suspected for hypersensitivity should be avoided. The development of (predictive) biomarkers is considered as a major contribution for the future.

Local gene transfer of OPG prevents joint damage and disease progression in collagen-induced arthritis

This study examined the influence of osteoprotegerin (OPG) gene transfer on a murine collagen-induced arthritis model. A single periarticular injection of AAV-OPG or AAV-LacZ on the arthritic paw successfully incorporated the exogenous gene to the local tissue and resulted in marked transgene expression in the joint homogenate for at least three weeks. Clinical disease scores were significantly improved in OPG treated mice starting at 28-day post-treatment (P < 0.05). Histological assessment demonstrated that OPG gene transfer dramatically protected mice from erosive joint changes compared with LacZ controls (P < 0.05), although treatment appeared less effective on the local inflammatory progress. MicroCT data suggested significant protection against subchondral bone mineral density changes in OPG treated CIA mice. Interestingly, mRNA expressions of IFN-g and MMP3 were noticeably diminished following OPG gene transfer. Overall, gene transfer of OPG effectively inhibited the arthritis-associated periarticular bone erosion and preserved the architecture of arthritic joints, and the study provides evidence that the cartilage protection of the OPG gene therapy may be associated with the down-regulation of MMP3 expression.

Titanium particle-challenged osteoblasts promote osteoclastogenesis and osteolysis in a murine model of periprosthestic osteolysis

The current study investigates the interactive behavior of titanium alloy particle-challenged osteoblastic bone marrow stromal cells (BMSCs) and macrophage lineage cells in a murine knee-prosthesis failure model. BMSCs were isolated from male BALB/c mice femurs and induced in osteogenic medium. At 24h after isolation, BMSCs in complete induction medium were challenged with 1, 3 or 5mgml(-1) titanium particles for 7days. Culture media were collected at 2, 4 and 6days and cells were harvested at 7days for alkaline phosphatase (ALP) assay/stains. Cell proliferation in the presence of Ti particles was periodically evaluated by MTT assay. Mice implanted with titanium-pin tibial implants were given an intra-articular injection of 50μl medium containing 5×10(5) Ti particles-challenged bone-marrow-derived osteoblastic cells, followed by a repeat injection at 2weeks post-operation. Control mice with titanium-pin implants received a naïve osteoblastic cell transfusion. After sacrifice at 4weeks, the implanted knee joint of each group was collected for biomechanical pin-pullout testing, histological evaluation and reverse transcriptase polymerase chain reaction analysis of mRNA extracted from the joint tissues. Ti particles significantly stimulated the proliferation of BMSC-derived osteoblastic cells at both high and low particle concentrations (p<0.05), with no marked differences between the particle doses. ALP expression was diminished following Ti particle interactions, especially in the high-dose particle group (p<0.05). In addition, the culture media collected from short-term challenged (48h) osteoblasts significantly increased the numbers of TRAP+ cells when added to mouse peripheral blood monocytes cultures, in comparison with the monocytes cells receiving naïve osteoblasts media (p<0.05). Intra-articular introduction of the osteoblastic cells to the mouse pin-implant failure model resulted in reduced implant interfacial shear strength and thicker peri-implant soft-tissue formation, suggesting that titanium particles-challenged osteoblasts contributed to periprosthetic osteolysis. Comparison of the gene expression profiles among the peri-implant tissue samples following osteoblast injection did not find significant difference in RunX2 or Osterix/Sp7 between the groups. However, MMP-2, IL-1, TNF-α, RANKL, and TRAP gene expressions were elevated in the challenged-osteoblast group (p<0.05). In conclusion, titanium alloy particles were shown to interfere with the growth, maturation, and functions of the bone marrow osteoblast progenitor cells. Particle-challenged osteoblasts appear to express mediators that regulate osteoclastogenesis and peri-prosthetic osteolysis.

Metal sensitivity in patients with orthopaedic implants: a prospective study

BACKGROUND

Sensitization to orthopaedic implant materials is an unpredictable event that might affect implant performance.

OBJECTIVES

In candidates for hip or knee joint prosthesis implantation, to evaluate preoperative assessments for identifying patients with metal sensitivity, to determine the percentage of patients who developed metal sensitivity at 1 year after prosthesis implantation, and to examine the clinical relevance of patch tests and lymphocyte transformation tests (LTT-MELISA®) for the evaluation of metal sensitization.

PATIENTS AND METHODS

A total of 100 patients referred for total hip or total knee arthroplasty were assessed preoperatively and then at 1 year post-implantation by means of patch tests with the metals present in the implant alloys. In a pilot study, 20 patients also underwent both patch testing and a lymphocyte transformation test (LTT-MELISA®) for the same metals.

RESULTS

Only 72 of 100 patients were patch tested both before and after surgery, and 12 of 20 also underwent LTT-MELISA® before and after surgery. Of 31/100 patients with an apparent history of nickel sensitivity determined during preoperative assessment of subjects, 12 tested negative on both tests, and 4 with a negative history of nickel sensitivity tested positive. One year post-implantation (72 patients), 5 patients who had initially tested negative for a metal allergy became positive for at least one or more metal constituents of the prosthesis on at least one or the other test.

CONCLUSIONS

Given the discrepancies between the information obtained while taking patient histories and test results, preoperative history-taking alone appears to be insufficient for identifying patients with metal sensitivity. Moreover, the increase in the percentage of patients who tested positive for metal sensitivity 1 year post-implantation suggests the possibility of prosthesis-induced sensitization. Therefore, objective determination of metal sensitivity at preoperative assessment should be considered in planning arthroplasty intervention, as it would help the surgeon in selecting the most appropriate prosthesis for the patient and could benefit implant performance.

New insights into wear and biological effects of metal-on-metal bearings

BACKGROUND

Despite the renewed interest in metal-on-metal implants in the past two decades, the underlying wear mechanisms and biological effects are still not fully understood.

METHODS

This paper first reviews the tribology of metal-on-metal bearings, bringing new insights into the interaction of wear and corrosion, and putting the characteristics and the potential origin of wear particles in perspective with the proposed wear mechanisms. It then summarizes the current knowledge on the biological effects of particles and metal ions in relation to these wear mechanisms.

RESULTS

Tribochemical reactions play an important role in the wear of metal-on-metal joints. The generated tribomaterial, which progressively forms by mechanical mixing of the uppermost nanocrystalline zone of the metal surface with proteins from the synovial fluid, governs the wear rate and influences the corrosive behavior of the bearing. Nanometer-sized wear particles may initially originate from the passivation layer covering the implant surface and then detach from this tribolayer. The inflammatory response observed surrounding metal-on-metal implants appears to be lower than that around metal-on-polyethylene implants. However, metallic byproducts, which can complex with proteins, may lead to a T lymphocyte-mediated hypersensitivity response.

CONCLUSIONS

The tribolayer appears to have beneficial effects on the wear rate. Much information has been gained on wear particle characteristics, but the exact mechanisms of particle detachment remain to be further elucidated. Excessive wear along with a hypersensitivity response may be at the origin of the early adverse tissue reactions that have been recently reported in some patients with metal-on-metal implants.

Polymethylmethacrylate and titanium alloy particles activate peripheral monocytes during periprosthetic inflammation and osteolysis

We investigated the interactions of particulate PMMA or titanium alloy, patient blood monocytes, and periprosthetic tissues using a SCID-hu model of aseptic loosening. Periprosthetic tissues and bone chips obtained at revision surgery for loosening were transplanted into muscles of SCID mice. Peripheral blood monocytes (PBMCs) isolated from the same donors were fluorescently labeled and co-cultured with PMMA or Ti-6Al-4V particles before intraperitoneal injection. Control mice with periprosthetic tissue or non-inflammatory ligament xenografts received naive PBMCs transfusion. Mice were euthanized 2 weeks after PBMC transfusion. The human tissues were well accepted in SCID mice. Transfused fluorescent-labeled PBMCs were markedly accumulated in transplanted periprosthetic tissues. Multinucleated osteoclast-like cells were commonly seen within retrieved xenograft tissue, and focal bone erosions were ubiquitous. Total cell densities and CD68+ cells within the xenograft were significantly increased in mice transfused with PMMA and Ti-provoked PBMCs compared to the naïve PBMC animals (p < 0.05). Immunohistochemical staining identified much stronger positive IL-1 and TNF stains in xenografts from either PMMA or Ti-stimulated monocytes transfusion groups (p < 0.05). TRAP+ cells were found around bone chips in both activated-PBMCs groups, although markedly more aggregated TRAP+ cells in the PMMA-challenged group than in the titanium group (p < 0.05). MicroCT assessment confirmed the significant decrease of bone mineral density in chips interacted with activated-monocytes/osteoclasts. In conclusion, PMMA or titanium particles readily activate peripheral monocytes and promote the cell trafficking to the debris-containing prosthetic tissues. Particles-provoked PBMCs participated in and promoted the local inflammatory process, osteoclastogenesis, and bone resorption.

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.

In vivo imaging of particle-induced inflammation and osteolysis in the calvariae of NFκB/luciferase transgenic mice

Wear debris causes biological response which can result in periprosthetic osteolysis after total joint replacement surgery. Nuclear factor-kappa B (NFκB), a representative transcription factor involved in inflammation, is believed to play an important role in this event by regulating the production of proinflammatory mediators and osteoclastogenesis. In this study, we sought to determine whether activation of NFκB in response to stimulation by particles could be visualized by in vivo imaging. We loaded polyethylene (PE) particles onto the calvaria of NFκB/luciferase transgenic mouse, and detected luminescence generated by activation of NFκB. On day 7 after loading, the level of luminescence was maximal. Levels of luminescence were significantly correlated with the levels of luciferase activity, proinflammatory mediator mRNAs, and bone resorption parameters. This system, which enabled us to evaluate particle-induced inflammation and osteolysis without sacrificing mice, constitutes a useful tool for evaluating the efficacy of prophylaxis or treatments for particle-induced osteolysis.

Cell-based osteoprotegerin therapy for debris-induced aseptic prosthetic loosening on a murine model

Exogenous OPG gene modification appears a therapeutic strategy for osteolytic aseptic loosening. The feasibility and efficacy of a cell-based OPG gene delivery approach were investigated using a murine model of knee prosthesis failure. A titanium pin was implanted into mouse proximal tibia to mimic a weight-bearing knee arthroplasty, followed by titanium-particles challenge to induce periprosthetic osteolysis. Mouse fibroblast-like synoviocytes were transduced in vitro with either AAV-OPG or AAV-LacZ before transfused into the osteolytic prosthetic joint 3 weeks post surgery. Successful transgene expression at the local site was confirmed 4 weeks later after sacrifice. Biomechanical pull-out test indicated a significant restoration of implant stability following the cell-based OPG gene therapy. Histology revealed that inflammatory pseudo-membranes existed ubiquitously at bone-implant interface in control groups, while only observed sporadically in OPG gene-modified groups. TRAP+ osteoclasts and TNFα, IL-1β, CD68+ expressing cells were significantly reduced in periprosthetic tissues of OPG gene-modified mice. No transgene dissemination or tumorigenesis was detected in remote organs and tissues. Data suggest that cell based ex vivo OPG gene therapy was comparable in efficacy with in vivo local gene transfer technique to deliver functional therapeutic OPG activities, effectively halted the debris-induced osteolysis and regained the implant stability in this model.

Effect of oral erythromycin therapy in patients with aseptic loosening of joint prostheses

There is currently no cure for aseptic loosening (AL) of total joint replacement (TJR) except surgical revision. The purpose of this study was to determine whether oral EM could improve the periprosthetic tissue profiles and reduce serum cytokine production in AL patients who are candidates for surgical revision. We recruited 32 AL patients. AL patients were treated with either EM (600 mg/day, n=18) or placebo (n=14) daily, started one month before surgery and ending on the day of surgery. Blood samples were obtained before EM treatment and during surgery. Periprosthetic tissues and joint fluids were collected during surgery. Our results demonstrate that oral EM reduces the inflammation of periprosthetic tissues, as manifested by the reduction of the numbers of infiltrating cells, CD68+ macrophages, RANKL+ cells, and TRAP+ cells. Remarkable decreases of TNFalpha (9.6-fold), IL-1beta (21.2-fold), and RANKL (76-fold) gene transcripts were observed in periprosthetic tissues of patients treated with oral EM. Serum levels of both TNFalpha and (to a lesser extent) IL-1beta were significantly reduced following EM treatment (p<0.05). Our results suggest that EM represents a biological cure or prevention for those patients who might need repeated revision surgeries and/or show the early signs of progressive osteolysis after TJR.

Expansion of CD14+CD16+ peripheral monocytes among patients with aseptic loosening

OBJECTIVE AND DESIGN

In this study, we have investigated the relevance of peripheral blood inflammatory CD14(+)CD16(+) monocytes phenotype to patients with aseptic loosening (AL).

MATERIAL AND TREATMENT

Immunophenotypes of monocytes were examined among patients with AL (n = 43), patients with mechanical loosening (ML, n = 30), patients with stable implant (SI, n = 16), and patients with osteoarthritis (OA, n = 17) using flow cytometry.

METHODS

Immunological assay was used to measure TNF-alpha and IL-1 beta levels in both sera and culture media of implant wear stimulated CD14(+)CD16(+) and CD14(++)CD16(-) monocytes. Periprosthetic tissues were collected during surgery for histological assessment.

RESULTS

The frequency of CD14(+)CD16(+) monocytes showed significant increase in AL patients than in ML, SI, and OA patients. A positive association was found between the subpopulation of CD14(+)CD16(+) monocytes and plasma TNF-alpha and IL-1 beta level in AL patients. Furthermore, a positive correlation existed between the subpopulation of CD14(+)CD16(+) monocytes and the total histopathology score.

CONCLUSION

The results indicate that CD14(+)CD16(+) monocytes represent a sensitive marker for the disease activity of AL, and may serve as an effective prognostic index to identify total joint replacement recipients who are at increased risk for osteolysis and progression of AL.

Dynamic Cellular Adhesion Mediated by Copolymeric Nanofilm Substrates

Amphiphilic block copolymers are finding increased potential in biological and medical research due to their innate alternating hydrophilic and hydrophilic blocks/segments which can be used to package therapeutics, or coat a broad array of biological interfaces. Some studies are already directed towards utilizing these copolymers' ability to form micelles or vesicles to develop novel methods of drug delivery to prevent inflammation or pro-cancer activity. Our study, however, aims to investigate the more fundamental cell-block copolymer interaction for use in protective nanofilms to prevent bio-fouling of non-tissue based implantable devices. Block copolymers could potentially fill the demand for biologically inert, highly functionalizable biomaterials desirable for this type of application. Two such polymers used in our study include PMOXA-PDMS-PMOXA triblock copolymer and PEO/PMMA diblock copolymer. Each block copolymer possesses hydrophilic and hydrophobic blocks that enable it to mimic the cell lipid membrane. So far we have shown that triblock copolymer is capable of inhibiting the accumulation of murine macrophages onto glass substrates. Preliminary evidence has suggested that the triblock copolymer has anti-adsorptive as well as non-inflammatory capabilities during short incubation periods (7 days) in vitro. While the diblock copolymer displays minimal anti-adsorptive activities, nanofilms comprised of a mixture of the two copolymers were able to significantly reduce macrophage accumulation onto glass substrates. The disparate behavior seen by macrophages on the different materials may be due to specific inherent properties such as preference for hydrophobic vs. hydrophilic surfaces and/or rough vs. smooth nano-textures. Furthermore, the specific end groups of the two polymers may exhibit varying capacities to resisting non-specific protein adsorption. Continued investigation outlining the physical and chemical properties desirable for an anti-adsorptive nano-film coating will serve as a basis upon which to design durable implant-tissue interfaces that can react to various external stimuli.

Wear particles, periprosthetic osteolysis and the immune system

The immune system modulates many key biological processes in humans. However, the exact role of the immune system in particle-associated periprosthetic osteolysis is controversial. Human tissue retrieval studies, in vivo and in vitro experiments suggest that the immune response to polymer particles is non-specific and macrophage-mediated. Lymphocytes may modulate this response. However direct lymphocyte activation by polymer particle-protein complexes seems unlikely. However, metallic byproducts may complex with serum proteins and lead to a Type IV, lymphocyte-mediated immune reaction. In predisposed individuals, this reaction may rarely lead to persistent painful joint effusions, necessitating debridement and excision of the bearing surfaces of the prosthesis. In these patients, retrieved periprosthetic tissues exhibit histological evidence of perivascular lymphocytic cuffing. These findings are worrisome, given the fact that increasing numbers of metal-on-metal joint implants are being implanted in younger more active individuals worldwide.

Murine model of prosthesis failure for the long-term study of aseptic loosening

We examined a novel mouse model of wear debris-induced prosthesis instability and osteolysis, and its application for the evaluation of therapy. A stainless steel or titanium-alloy pin was implanted into the proximal tibia to form a contiguous surface with the articular cartilage. In some mice, titanium particles were injected into the tibial canal during the surgery, followed by monthly intraarticular injection. MicroCT scans revealed that the implants without particle challenge were stable without bone mineral density changes for 6 months. Histological analysis showed new bone formation around the implant at 6 weeks postsurgery. Periprosthetic soft tissue with inflammatory cells was a ubiquitous finding at the interface between the implant and surrounding bone in samples exposed to titanium particles, and expression of IL-1beta, TNFalpha, and CD68 was common in these joints. Pullout tests indicated that an average 5N load was required to pull out stable implants from surrounding bone. However, particle stimulation dramatically reduced the pullout force to less than 0.4 N. The feasibility of in vivo gene transfer on this model was confirmed by X-gal staining of synovial membrane and periprosthetic tissue after injection of AAV-LacZ in the prosthetic joint. This murine model of weight-bearing knee prosthesis provides an economical, reproducible, and easily obtained means to study joint arthroplasty failure. The ability to evaluate the biomechanical properties of the prosthetic joint, in addition to histological and biochemical examination, results in a useful model to investigate many of the properties of prosthetic joint components during the response to debris-associated osteolysis.

Preparation of Graded Zirconia—Hydroxyapatite Composite Bioceramic and Its Immunocompatibility in vitro

To obtain immunocompatibility, graded zirconia—hydroxyapatite (ZrO 2-HA) composite bioceramic and simplex ZrO2-HA composite bioceramic are prepared. Peripheral blood mononuclear cells (PBMCs) harvested from healthy individuals are cultured with the two ceramic extracts to assess their effect on the transformation of lymphocytes, apoptotic ratio, CD69 expression, and expression of cytokine of TNFα and IL-6, with or without phytohemoagglutinin (PHA)-stimulated cells. Ceramic extracts did not activate the resting lymphocytes, whereas the response of the PHA-stimulated cells was significantly modified. The PBMCs activated by graded ZrO2-HA composite bioceramic is noticeably smaller than that by simplex ZrO2-HA composite bioceramic; these results, however can only be seen under the amplified effect of PHA-stimulation.

Erythromycin inhibits wear debris-induced inflammatory osteolysis in a murine model

Up to 20% of patients with total joint arthroplasty will develop radiographic evidence of aseptic loosening (AL), which most likely results from an inflammatory response to billions of wear debris shed from the implant. Our previous work has demonstrated that erythromycin (EM), a macrolide antibiotic, inhibits wear debris-induced inflammatory osteoclastogenesis through the reduction of cytokine production and osteoclast differentiation, both of which involve the NF-kappaB pathway. The aim of the current study was to determine whether EM inhibits wear debris-induced inflammatory osteolysis in a murine osteolysis model. Ultrahigh molecular-weight polyethylene (UHMWPE) debris was introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. EM (2 mg/kg/day) was given to mice intraperitoneally 2 days before UHMWPE introduction and maintained until the sacrifice of the mice. Mice with and without EM treatment, as well as control mice injected with saline alone were included in this study. Pouch tissues were collected 14 days after UHMWPE inoculation for molecular and histology analysis. Our findings indicate that: (1) EM reduced UHMWPE-induced tissue inflammation, including the diminished pouch membrane thickness, reduced inflammatory cellular infiltration, and lowered IL-1beta and TNF-alpha expression (mRNA and protein); (2) EM inhibited UHMWPE-induced osteoclastogenesis, with reduced gene activation of RANK, RANKL, and CPK, and diminished RANKL expression in UHMWPE stimulated pouches, and (3) EM markedly reduced the number of TRAP(+) cells in pouch tissues, and protected against bone collagen depletion. In conclusion, this study provides the evidence that EM inhibits the UHMWPE particles-induced inflammatory osteolysis in a murine model, and represents a promising therapeutic candidate for the prevention and treatment of AL.

Lymphocyte responses in patients with total hip arthroplasty

How lymphocyte-mediated metal sensitivity affects orthopaedic implant performance remains poorly understood. Do patients with implants exhibit elevated lymphocyte reactivity to metals and is this reactivity more generalized or more implant-alloy specific? We investigated these questions by measuring lymphocyte responses to implant metals (Cr(+3), Co(+2), Ni(+2) at 0.1mM, and Ti(+4) at 0.001 mM) in six subject groups: Group 1a=young controls, Group 1b=age matched controls, Group 2a=subjects with osteoarthritis (OA) and no history of metal sensitivity, Group 2b=OA subjects with history of metal sensitivity, Group 3a=total hip arthroplasty (THA) subjects with no to mild radiographic osteolysis, and Group 3b=THA subjects with moderate osteolysis. Lymphocyte proliferation, using Lymphocyte Transformation Testing (LTT), and cytokine release provided quantitative reactivity measurement, where a stimulation index of >2 indicated metal sensitivity. OA subjects with a history of metal sensitivity (Group 2b) were more metal reactive to Ni than any other group, as expected (66% incidence and Stimulation Index >20). However, THA subjects (Groups 3a and b) were >3 fold more reactive to Cr (p<0.04), than were controls (Groups 1a & b) or OA subjects (Groups 2a & b). THA subjects with moderate vs mild osteolysis (Group 3b vs 3a) were more reactive to Co (43% vs 0% incidence). Only osteolytic THA subjects demonstrated increased cytokine responses with >two-fold (p<0.05) increases in soluble interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) levels in response to Cr challenge. This elevated incidence and averaged level of lymphocyte reactivity supports a metal-specific adaptive immune response and suggests involvement in the pathogenesis of poor implant performance, e.g. aseptic osteolysis.

Immune responses correlate with serum-metal in metal-on-metal hip arthroplasty

Cell-mediated hypersensitivity associated with metal components may be related to levels of implant debris. We tested this hypothesis by comparing lymphocyte reactivity to soluble Co, Cr, Ni, and Ti of patients with metal-on-polyethylene and metal-on-metal arthroplasties with healthy controls, and patients with osteoarthritis. The metal-on-metal group (n=9) demonstrated significantly elevated serum Co and Cr concentrations (13- and 58-fold, P<.05, respectively) and significantly elevated lymphocyte reactivity to Co (SI>5, P<.004) and Ni (SI>2.5, P<.01) when compared to controls (n=12) and subjects with metal-on-poly implants (n=7). These elevated in vivo metal levels demonstrated positive linear correlation with lymphocyte reactivity supporting our hypothesis that lymphocyte metal-induced reactivity increases with increased metal exposure. These results represent the first direct link between in vivo metal exposure and lymphocyte reactivity. Whether this lymphocyte reactivity to metal debris is etiologically linked to poor implant performance remains uncertain.

Protective effects of IL-1Ra or vIL-10 gene transfer on a murine model of wear debris-induced osteolysis

The current study evaluated the protective effects of anti-inflammatory cytokine gene transfer on osteolysis provoked by orthopedic biomaterial particles using a murine model of inflammatory bone loss. A section of bone was surgically implanted into an air pouch established on a syngeneic recipient mouse. Inflammation was provoked by introduction of ultra-high-molecular-weight polyethylene (UHMWPE) particles into the pouch, and retroviruses encoding for interleukin-1 receptor antagonist (hIL-1Ra), viral interleukin-10 (vIL-10), or LacZ genes were injected. Pouch fluid and tissue were harvested 7 days later for histological and molecular analyses. The results indicated that IL-1Ra or vIL-10 gene transfer significantly inhibited IL-1beta and tumor necrosis factor (TNF) expression at both mRNA and protein levels. There were significantly lower mRNA expressions of calcitonin receptor and cathepsin K in RNA isolated from hIL-1Ra- or vIL-10-transduced pouches than LacZ-transduced and virus-free controls. Both anti-inflammatory cytokine gene transfers significantly reduced the mRNA expression of M-CSF (70-90%) and RANK (>65%) in comparison with LacZ- and virus-free controls. Histological examination showed that hIL-1Ra or vIL-10 gene transfer dramatically abolished UHMWPE-induced inflammatory cellular infiltration and bone pit erosion compared to LacZ-transduced and virus-free controls. Histochemical staining revealed significantly fewer osteoclast-like cells in samples treated with IL-1Ra or vIL-10 gene transfer. In addition, bone collagen content was markedly preserved in the groups with anti-inflammatory cytokine gene transfers compared with the other two groups. Overall, retrovirus-mediated hIL-1Ra or vIL-10 gene transfer effectively protected against UHMWPE-particle-induced bone resorption, probably due to the inhibition of IL-1/TNF-induced M-CSF production and the consequent osteoclast recruitment and maturation.

Adeno-associated virus-mediated osteoprotegerin gene transfer protects against particulate polyethylene-induced osteolysis in a murine model

OBJECTIVE

Osteoprotegerin (OPG), a natural negative regulator of osteoclastogenesis and bone resorption, may be a potential therapeutic agent for treatment of osteolysis-associated prosthetic joint loosening. Using an in vivo adeno-associated virus (AAV)-mediated gene transfer technique, this study was designed to evaluate the protective effects of OPG transgene against orthopedic wear debris-induced bone loss in a murine model of osteolysis.

METHODS

Bone tissue was implanted into established pouches on BALB/c mice, followed by the introduction of ultra-high-molecular-weight polyethylene (UHMWPE) particles to provoke inflammation and osteolysis. The viruses encoding human OPG gene (rAAV-hOPG) or beta-galactosidase marker gene (rAAV-LacZ) were injected into the air pouches, and the tissue was harvested 7 days after viral infection for histologic and molecular analyses.

RESULTS

Successful transgene expression was confirmed by the detection of OPG by enzyme-linked immunosorbent assay and positive X-Gal staining of pouch tissue (LacZ). Real-time polymerase chain reaction indicated significant diminishment of messenger RNA expression of osteoclast markers in OPG-transduced pouches compared with rAAV-LacZ-transduced pouches. The transduction and expression of OPG also markedly decreased the gene copies of the biologic receptor activator of nuclear factor kappaB. The expression of OPG in the bone-implanted pouch reduced bone calcium release by a mean of 39% compared with the calcium release in the other 2 groups. Computerized image analysis revealed that expression of OPG significantly protected against bone collagen loss.

CONCLUSION

OPG gene transfer mediated by rAAV effectively protects against particulate polyethylene-induced bone resorption in this experimental model. Data suggest that gene transfer using rAAV-OPG may be a feasible and effective therapeutic candidate to treat or prevent wear debris-associated osteolysis and aseptic loosening.

Effects of bone cement extracts on the cell-mediated immune response

The aim of the study was to evaluate some aspects of the immunocompatibility of 10 acrylic bone cements. Mononuclear cells harvested from healthy individuals were cultured with cement extracts which were tested to assess their effect on the viability of lymphocytes, unstimulated and phytohaemoagglutinin (PHA)-stimulated, activating resting lymphocytes, and changing the reactivity of PHA-stimulated lymphocytes. After 24 h the extracts did not increase the percentage of dead cells in unstimulated or PHA-stimulated lymphocytes. The early apoptotic events of culture were evaluated after 4 and 24 h in PHA-stimulated lymphocytes: at 4 h three cements, namely Zimmer-dough type, Palacos R and CMW-1, increased significantly the percentage of apoptotic cells, while at 24 h no differences were found. Cement extracts did not activate the resting lymphocytes, whereas the response of the PHA-stimulated cells was significantly modified. All cements decreased the expression of the interleukin 2 receptor (CD25) and the lymphocyte proliferation, whereas only two materials (Zimmer-dough type, CMW 1) affected the expression of early activation antigen (CD69). These findings show that the products released from bone cement are not able, by themselves, to elicit a specific immune response; on the contrary they hamper the function of lymphocytes activated by an exogenous stimulus.

Osteolysis: basic science

Since the recognition of aseptic loosening by Charnley in the early 1960s, much information has been gained on the basic science of periprosthetic bone loss. Initially termed cement disease, it now generally is accepted that, in most instances, osteolysis is a manifestation of an adverse cellular response to phagocytosable particulate wear and corrosion debris, possibly facilitated by local hydrodynamic effects. Tissue explant, animal, and cell culture studies have allowed us to compile an appreciation of the complexity of cellular interactions and chemical mediators involved in osteolysis. Cellular participants have been shown to include the macrophage, osteoblast, fibroblast, and osteoclast. The plethora of chemical mediators that are responsible for the cellular responses and effects on bone include prostaglandin E2, tumor necrosis factor-alpha, interleukin-1, and interleukin 6. However, an increasing number of other proinflammatory and antiinflammatory cytokines, prostenoids, and enzymes have been shown to play important roles in this process. The ultimate goal of basic research is to develop novel strategies for evaluation and treatment of patients with osteolysis. Although initial animal studies are promising for possible pharmacologic treatment and prevention of osteolysis, well-controlled human trials are required before agents such as bisphosphonates can be recommended for general clinical use.

Fluorine-18 fluorodeoxyglucose-position emission tomography: a highly accurate imaging modality for the diagnosis of chronic musculoskeletal infections

BACKGROUND

The noninvasive diagnosis of chronic musculoskeletal infections remains a challenge. Recent studies have indicated that fluorine-18 fluorodeoxyglucose-positron emission tomography is a highly accurate imaging technique and is significantly more accurate than the combination of a bone scan and a white blood-cell scan for the diagnosis of chronic infection in the central skeleton (p < 0.05). However, patients who had had surgery within the previous two years were excluded from study. It was our aim to evaluate the technique in an unselected, clinically representative population.

METHODS

Sixty patients with a suspected chronic musculoskeletal infection involving the central skeleton (thirty-three patients) or the peripheral skeleton (twenty-seven patients) were studied with fluorine-18 fluorodeoxyglucose-positron emission tomography. Thirty-five patients had had surgery within the previous two years. The fluorine-18 fluorodeoxyglucose-positron emission tomography studies were read in a blinded, independent manner by two experienced readers. The final diagnosis was based on histopathological studies or microbiological culture (eighteen patients) or on clinical findings after at least six months of follow-up (forty-two patients).

RESULTS

On the final composite assessment, twenty-five patients had infection and thirty-five did not. All twenty-five infections were correctly identified by both readers. There were four false-positive findings; in two of these cases, surgery had been performed less than six months prior to the study. The sensitivity, specificity, and accuracy were 100%, 88%, and 93% for the whole group; 100%, 90%, and 94% for the subgroup of patients with a suspected infection of the central skeleton; and 100%, 86%, and 93% for the subgroup of patients with a suspected infection of the peripheral skeleton. Interobserver agreement was excellent (kappa = 0.97).

CONCLUSIONS

Fluorine-18 fluorodeoxyglucose-positron emission tomography is highly accurate as a single technique for the evaluation of chronic musculoskeletal infections. It is especially valuable in the evaluation of the central skeleton, where white blood-cell scans are less useful. Because of its simplicity and high degree of accuracy, it has the potential to become a standard technique for the diagnosis of chronic musculoskeletal infections. Further studies are needed to assess its ability to identify infections at the sites of total joint replacements and to distinguish infection from aseptic loosening of these prostheses.

Metal sensitivity in patients with orthopaedic implants

All metals in contact with biological systems undergo corrosion. This electrochemical process leads to the formation of metal ions, which may activate the immune system by forming complexes with endogenous proteins. Implant degradation products have been shown to be associated with dermatitis, urticaria, and vasculitis. If cutaneous signs of an allergic response appear after implantation of a metal device, metal sensitivity should be considered. Currently, there is no generally accepted test for the clinical determination of metal hypersensitivity to implanted devices. The prevalence of dermal sensitivity in patients with a joint replacement device, particularly those with a failed implant, is substantially higher than that in the general population. Until the roles of delayed hypersensitivity and humoral immune responses to metallic orthopaedic implants are more clearly defined, the risk to patients may be considered minimal. It is currently unclear whether metal sensitivity is a contributing factor to implant failure.

Modulation of pro- and anti-apoptotic genes in lymphocytes exposed to bone cements

The ability of bone cements to modify the apoptotic program in activated immune cells and the mechanisms by which they act were evaluated. Mononuclear cells were collected from healthy individuals, cultured for 4 and 24 h with phytohemoagglutinina-P and cement extracts and then tested to assess: (a) cell viability; (b) early apoptotic events, by Annexin V/propidium iodide staining; and (c) the expression of pro- (p53, c-myc, ICE) and anti-apoptotic (bcl-2) genes. After 4 h three cements were able to increase significantly the percentage of apoptotic cells, while after 24 h no differences were found. The proportion of dead cells was not significantly changed at either culture time. The simultaneous expression of both pro-apoptotic (ICE, c-myc, p53) and antiapoptotic genes (bcl-2) was investigated only with regard to the materials which induced significant changes in apoptosis: two cements induced the p53 expression, while the third down-regulated bcl-2. As apoptosis regulates the balance of immune response, the authors recommend that the interaction between materials and immune cells should be assessed, so that the use of pro-apoptotic materials may be avoided in patients with immune defects.

Expression of the CD69 activation antigen on lymphocytes of patients with hip prosthesis

The aim of the study was to evaluate the sensitization to metals in patients with Co-Cr hip prosthesis. Peripheral blood mononuclear cells (PBMC) were collected from 14 healthy donors and three groups of patients: 10 candidates for primary total joint replacements, 11 patients with well-fixed implant and 13 patients with aseptic loosening of the hip prosthesis. PBMCs were cultured with the metal ions employed for implant manufacturing and the expression of CD69 activation antigen on CD3/T lymphocytes was detected by flow cytometry. Chromium extract increased significantly the expression of CD3/CD69 phenotype in patients with loosening of hip prosthesis. The chromium-induced 'activation index' was higher in patients with loosening of hip prosthesis than in healthy donors and in pre-implant patients. The cobalt-stimulated PBMC of patients with either well-fixed or loosened prosthesis had an 'activation index' significantly higher than healthy donors. The activation index values were used to graduate the PBMC-response as 'normal' (> or = 0.9 and < 2), 'low' (< 0.9) and 'high' (> or = 2): an high-activation index was observed only in chromium-exposed PBMC of patients with prosthesis. Our data show that chromium released from orthopedic implants could be responsible for the lymphocyte sensitization and flow cytometry is an easy and reliable method for monitoring the hypersensitivity state in patients with metal prostheses. Activated lymphocytes in the peri-implant tissue are likely to elicit a localized immune response and contribute to maintain the inflammatory process evolving in the implant failure.

Alternate bearing surfaces in total joint arthroplasty: biologic considerations

The problem of periprosthetic osteolysis is currently the major limiting factor in joint arthroplasty longevity. Because this process has been shown to be primarily a biologic response to wear particles, corrosion products, or both, efforts to reduce particle generation are being undertaken. These efforts include the development of modified polyethylene and alternative articulating surfaces. These alternate bearing surfaces currently include ceramic-on-polyethylene, ceramic-on-ceramic, and metal-on-metal. Although these alternate bearings diminish or eliminate the generation of polyethylene particles, ceramic and metal particles are produced. The purpose of the current review is to discuss the literature that addresses the biologic response to these particles, locally and systemically.

In vitro cytokine production by mononuclear cells exposed to bone cement extracts

The authors evaluated the ability of bone cement to modify the profile of pro-inflammatory cytokines secreted by the immune cells. Peripheral blood mononuclear cells (PBMC) collected from healthy individuals were cultured with cement extracts and tested to assess the release of IL-1beta, TNFalpha, GM-CSF and IL-6 in both unstimulated and PHA-stimulated PBMC. The cytokine release of unstimulated PBMC was very poor, and in particular the IL-1beta was undetectable: the addition of cement extract increased both TNFalpha and GM-CSF release and decreased IL-6, sometimes significantly. The most recurrent observation in PHA-stimulated PBMCs exposed to bone cement extract was the increase in both IL-1beta and IL-6 release, while both the mean concentration and the index of release of TNFalpha and GM-CSF were changeable. In conclusion our results showed that leachable components of some bone cements can induce in vitro the release of pro-inflammatory cytokines which are known to be involved in the bone resorption associated with aseptic loosening of hip prostheses. These findings allowed us to identify materials endowed with the highest inflammatory power.

Effects of metal ions on white blood cells of patients with failed total joint arthroplasties

In this study twenty-two patients who had revision surgery for aseptic loosening of joint prostheses were examined. The concentration in serum of soluble products of corrosion from the implant, that is, chromium (Cr), cobalt (Co), and nickel (Ni) ions, and the number of white blood cells (leucocytes, myeloid cells, lymphocyte subpopulations) were measured. Twenty patients with no implants were used as controls. The patients who had revision surgery showed normal Ni concentration whereas by statistical analysis that same patient group was shown to have serum Cr and Co levels significantly higher than those of the control. By flow cytometry, a significant decrease of leucocytes, myeloid cells, lymphocytes, and CD16 populations as found in patients versus controls whereas CD3, CD4, CD8, and CD20 positive cells were decreased, but not significantly. In the arthroplasty patients the Cr concentrations were inversely correlated with some of the immunologic parameters while no significant correlation was found between Co levels and decreased lymphocyte subpopulations. Only in revision surgery patients with high Cr concentrations did we find a significant decrease of lymphocytes, namely of CD4 and CD16 positive cells; revision surgery patients with normal Cr concentrations did not show a significant decrease of lymphocyte subpopulations. These data suggest that the presence of metal ions, especially chromium, released from prosthesis components could be associated with changes of lymphocyte subpopulations in patients with loosening of joint prostheses.