Suppression of polyethylene particle-induced osteolysis by exogenous osteoprotegerin

The wettability of electron spun membranes by synovial fluid

Aseptic loosening due to periprosthetic osteolysis has been accepted as one of the leading causes of revision procedures in patients with previous joint arthroplasty. Recently, several strategies for suppression of osteolysis were proposed, mostly based on biological treatment such as mitigation of chronic inflammatory reactions. However, these biological treatments do not stop the debris migration but only reduce the inflammatory reaction. To address this shortcoming, we propose the concept of ultrahigh molecular weighted polyethylene particles filtration storage by electrospun membranes. Firstly, the surface tension of synovial fluid (SF) is obtained by use of a pendant droplet. Secondly, the contact angle of the electrospun membranes wetted by two different liquids is measured to obtain the free surface energy using of the Owens-Wendt model. Additionally, the wettability of electrospun membranes by SF as a function of technology parameters is studied.

The Effects of Biomaterial Implant Wear Debris on Osteoblasts

Aseptic loosening subsequent to periprosthetic osteolysis is the leading cause for the revision of arthroplasty failure. The biological response of macrophages to wear debris has been well established, however, the equilibrium of bone remodeling is not only dictated by osteoclastic bone resorption but also by osteoblast-mediated bone formation. Increasing evidence shows that wear debris significantly impair osteoblastic physiology and subsequent bone formation. In the present review, we update the current state of knowledge regarding the effect of biomaterial implant wear debris on osteoblasts. The interaction of osteoblasts with osteoclasts and macrophages under wear debris challenge, and potential treatment options targeting osteoblasts are also presented.

Leptin Increases Particle-Induced Osteolysis in Female ob/ob Mice

Particles generated from wear of prosthesis joint bearing surfaces induce inflammation-mediated periprosthetic bone resorption (osteolysis). Morbidly obese leptin-deficient ob/ob mice are resistant to polyethylene particle-induced bone loss, suggesting that leptin, a hormone produced by adipocytes that circulates in concentrations proportional to total body adiposity, increases osteolysis. To confirm that particles induce less osteolysis in leptin-deficient mice after controlling for cold stress (room temperature)-induced bone loss, ob/ob mice on a C57BL/6 (B6) background and colony B6 wildtype (WT) mice housed at thermoneutral temperature were randomized to control or particle treatment groups (N = 5/group). Polyethylene particles were implanted over calvaria and mice sacrificed 2 weeks later. Compared to particle-treated WT mice, particle-treated ob/ob mice had lower osteolysis score, less infiltration of immune cells, and less woven bone formation. To determine the role of leptin in particle-induced osteolysis, ob/ob mice were randomized into one of 4 groups (n = 6-8/group): (1) control, (2) particles, (3) particles + continuous leptin (osmotic pump, 6 μg/d), or (4) particles + intermittent leptin (daily injection, 40 μg/d). Leptin treatment increased particle-induced osteolysis in ob/ob mice, providing evidence that the adpiokine may play a role in inflammation-driven bone loss. Additional research is required to determine whether altering leptin levels within the physiological range results in corresponding changes in polyethylene-particle-induced osteolysis.

Polyethylene particles inserted over calvarium induce cancellous bone loss in femur in female mice

Focal bone resorption (osteolysis) induced by wear particles contributes to long-term orthopedic joint failure. However, the impact of focal osteolysis on remote skeletal sites has received less attention. The goal of this study was to determine the effects of polyethylene particles placed over calvaria on representative axial and appendicular skeletal sites in female mice. Because recent work has identified housing temperature as an important biological variable in mice, response to particle treatment was measured in animals housed at room (22 °C) and thermoneutral (32 °C) temperature. Osteolysis was evident in skeletal tissue adjacent to particle insertion. In addition, cancellous bone loss was observed in distal femur metaphysis. The bone loss was associated with lower osteoblast-lined perimeter and lower mineralizing perimeter in distal femur, lower osteocalcin gene expression in tibia, and lower serum osteocalcin, suggesting the response was due, at least in part, to reduced bone formation. Mild cold stress induced by sub-thermoneutral housing resulted in cancellous bone loss in distal femur and lumbar vertebra but did not influence skeletal response to particles. In summary, the results indicate that focal inflammation induced by polyethylene particles has the potential to result in systemic bone loss. This is significant because bone loss is a risk factor for fracture.

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Wear particles contribute to orthopedic joint failure by promoting focal inflammation- mediated osteolysis.

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Here we investigated effects of polyethylene particles placed over calvaria on remote skeletal sites in female mice.

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Particles placed over calvaria resulted in focal inflammation and cancellous bone loss in distal femur metaphysis.

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Lower osteoblast-lined perimeter suggests reduced bone formation contributed to bone loss in distal femur.

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Our results suggest focal inflammation induced by polyethylene particles has the potential to result in systemic bone loss.

Comparison of Biocompatibility of Cemented vs. Cementless Hip Joint Endoprostheses Based on Postoperative Evaluation of Proinflammatory Cytokine Levels

BACKGROUND The yearly increase in the number of procedures involving implantation of hip joint endoprostheses forces prosthetics manufacturers to search for biologically neutral implants. The goal of this study was to assess the concentration of Interleukin-6 (IL-6) and its correlation with C-reactive protein (CRP), depending on the type of hip joint endoprosthesis (cemented or cementless endoprosthesis) in order to determine implant biotolerance during the early postoperative period. MATERIAL AND METHODS The sample comprised 200 patients [mean age=64 (31-81) years] with coxarthrosis. All patients underwent hip joint arthroplasty using a cemented or cementless endoprosthesis. Blood samples were collected 3 times: before the procedure, on the first day after the procedure, and after 6 weeks. IL-6 and CRP levels were assayed using immunoenzymatic methods. The results were subjected to statistical analysis using the Shapiro-Wilk test. RESULTS On the 1st day after the procedure, CRP and IL-6 concentration increased rapidly after implantation of both cemented and cementless endoprostheses. At 6 weeks postoperatively, the CRP value remained at a similar level in patients after cemented arthroplasty and was almost 2-fold lower in patients who underwent cementless arthroplasty. The IL-6 value returned to the baseline level in patients after cementless arthroplasty and showed an ongoing increasing tendency in patients after cemented arthroplasty. CONCLUSIONS 1. The measurement of C-reactive protein and Interleukin-6 is a high-sensitivity test, assessing implant biotolerance. 2. The implantation of a cemented endoprosthesis induces a higher increase in the level of proinflammatory cytokines as compared with a cementless endoprosthesis. 3. For a complete assessment of both early and later body responses to implantation and the related surgical procedure, further studies using available approaches and tools are recommended.

Intermittent Administration of Parathyroid Hormone [1-34] Prevents Particle-Induced Periprosthetic Osteolysis in a Rat Model

We examined whether intermittent administration of parathyroid hormone [1-34] (PTH[1-34]; 60 μg/kg/day) can prevent the negative effects of titanium (Ti) particles on implant fixation and periprosthetic osteolysis in a rat model. Eighteen adult male rats (12 weeks old, bones still growing) received intramedullary Ti implants in their bilateral femurs; 6 rats from the blank group received vehicle injections, and 12 rats from the control group and PTH treatment group received Ti particle injections at the time of operation and intra-articular injections 2 and 4 weeks postoperatively. Six of the rats that received Ti particles from the PTH group also received PTH[1-34] treatment. Six weeks postoperatively, all specimens were collected for assessment by X-ray, micro-CT, biomechanical, scanning electron microscopy (SEM), and dynamic histomorphometry. A lower BMD, BV/TV, Tb.N, maximal fixation strength, and mineral apposition rate were observed in the control group compared to the blank group, demonstrating that a periprosthetic osteolysis model had been successfully established. Administration of PTH[1-34] significantly increased the bone mineral density of the distal femur, BV/TV, Tb.N, Tb.Th, Tb.Sp, Con.D, SMI, and maximal fixation strength in the PTH group compared to that in the control group. SEM revealed higher bone-implant contact, thicker lamellar bone, and larger trabecular bone area in the PTH group than in the control group. A higher mineral apposition rate was observed in the PTH group compared to both the blank and control groups. These findings imply that intermittent administration of PTH[1-34] prevents periprosthetic osteolysis by promoting bone formation. The effects of PTH[1-34] were evaluated at a suprapharmacological dosage to the human equivalent in rats; therefore, additional studies are required to demonstrate its therapeutic potential in periprosthetic osteolysis.

Pharmaceutical inhibition of glycogen synthetase kinase 3 beta suppresses wear debris-induced osteolysis

Aseptic loosening is associated with the development of wear debris-induced peri-implant osteolytic bone disease caused by an increased osteoclastic bone resorption and decreased osteoblastic bone formation. However, no effective measures for the prevention and treatment of peri-implant osteolysis currently exist. The aim of this study was to determine whether lithium chloride (LiCl), a selective inhibitor of glycogen synthetase kinase 3 beta (GSK-3β), mitigates wear debris-induced osteolysis in a murine calvarial model of osteolysis. GSK-3β is activated by titanium (Ti) particles, and implantation of Ti particles on the calvarial surface in C57BL/6 mice resulted in osteolysis caused by an increase in the number of osteoclasts and a decrease in the number of osteoblasts. Mice implanted with Ti particles were gavage-fed LiCl (50 or 200 mg kg(-1)d(-1)), 6 days per week for 2 weeks. The LiCl treatment significantly inhibited GSK-3β activity and increased β-catenin and axin-2 expression in a dose-dependent manner, dramatically mitigating the Ti particle-induced suppression of osteoblast numbers and the expression of bone formation markers. Finally, we demonstrated that inhibition of GSK-3β suppresses osteoclast differentiation and reduces the severity of Ti particle-induced osteolysis. The results of this study indicate that Ti particle-induced osteolysis is partly dependent on GSK-3β and, therefore, the canonical Wnt signaling pathway. This suggests that selective inhibitors of GSK-3β such as LiCl may help prevent and treat wear debris-induced osteolysis.

Orthopaedic implant failure: aseptic implant loosening–the contribution and future challenges of mouse models in translational research

Aseptic loosening as a result of wear debris is considered to be the main cause of long-term implant failure in orthopaedic surgery and improved biomaterials for bearing surfaces decreases significantly the release of micrometric wear particles. Increasingly, in-depth knowledge of osteoimmunology highlights the role of nanoparticles and ions released from some of these new bearing couples, opening up a new era in the comprehension of aseptic loosening. Mouse models have been essential in the progress made in the early comprehension of pathophysiology and in testing new therapeutic agents for particle-induced osteolysis. However, despite this encouraging progress, there is still no valid clinical alternative to revision surgery. The present review provides an update of the most commonly used bearing couples, the current concepts regarding particle–cell interactions and the approaches used to study the biology of periprosthetic osteolysis. It also discusses the contribution and future challenges of mouse models for successful translation of the preclinical progress into clinical applications.

Pharmacologic augmentation of implant fixation in osteopenic bone

Osteoporosis presents a challenge for successful implant fixation due to an impaired healing response. Preclinical studies have consistently reported reduced osseointegration capability in trabecular bone. Although clinical studies of implant success in dentistry have not found a negative effect due to osteoporosis, low bone mass is a significant risk factor for implant migration in orthopedics. Pharmacologic treatment options that limit bone resorption or upregulate formation have been studied preclinically. While, both treatment options improve implant fixation, direct comparisons to-date have found anti-catabolic more effective than anabolic treatments for establishing implant fixation, but combination approaches are better than either treatment alone. Clinically, anti-catabolic treatments, particularly bisphosphonates have been shown to increase the longevity of implants, while limited clinical evidence on the effects of anabolic treatment exists. Preclinical experiments are needed to determine the effects of osteoporosis and subsequent treatment on the long-term maintenance of fixation and recovery after bone loss.

Direct subcutaneous injection of polyethylene particles over the murine calvaria results in dramatic osteolysis

PURPOSE

The murine calvarial model has been widely employed for the in vivo study of particle-induced osteolysis, the most frequent cause of aseptic loosening of total joint replacements. Classically, this model uses an open surgical technique in which polyethylene (PE) particles are directly spread over the calvarium for the induction of osteolysis. We evaluated a minimally invasive modification of the calvarial model by using a direct subcutaneous injection of PE particles.

METHODS

Polyethylene (PE) particles were injected subcutaneously over the calvaria of C57BL6J ten-week-old mice ("injection" group) or were implanted after surgical exposure of the calvaria ("open" group) (n = 5/group). For each group, five additional mice received no particles and served as controls. Particle-induced osteolysis was evaluated two weeks after the procedure using high-definition microCT imaging.

RESULTS

Polyethylene particle injection over the calvaria resulted in a 40% ± 1.8% decrease in the bone volume fraction (BVF), compared to controls. Using the "open surgical technique", the BVF decreased by 16% ± 3.8% as compared to controls (p < 0.0001).

CONCLUSIONS

Direct subcutaneous injection of PE particles over the murine calvaria produced more profound resorption of bone. Polyethylene particle implantation by injection is less invasive and reliably induces osteolysis to a greater degree than the open technique. This subcutaneous injection method will prove useful for repetitive injections of particles, and the assessment of potential local or systemic therapies.

Local effect of IL-4 delivery on polyethylene particle induced osteolysis in the murine calvarium

Wear particles generated with use of total joint replacements incite a chronic macrophage-mediated inflammatory reaction, which leads to implant failure. Macrophage activation may be polarized into two states, with an M1 proinflammatory state dominating an alternatively activated M2 anti-inflammatory state. We hypothesized that IL-4, an activator of M2 macrophages, could modulate polyethylene (PE) particle-induced osteolysis in an experimental murine model. Four animal groups included (a) calvarial saline injection with harvest at 14 days (b) single calvarial injection of PE particles subcutaneously (SC) without IL-4 (c) PE particles placed as in (b), then IL-4 given SC for 14 consecutive days and (d) PE particles as in (b) then IL-4 beginning 7 days after particle injection for 7 days. The calvarial bone volume to total tissue volume was measured using microCT and histomorphometry. Calvaria were cultured for 24 h to assess release of RANKL, OPG, TNF-α, and IL-1ra and isolation and identification of M1 and M2 specific proteins. MicroCT and histomorphometric analysis showed that bone loss was significantly decreased following IL-4 administration to PE treated calvaria for both 7 and 14 days. Western blot analysis showed an increased M1/M2 ratio in the PE treated calvaria, which decreased with addition of IL-4. Cytokine analysis showed that the RANKL/OPG ratio and TNF-α/IL-1ra ratio decreased in PE-treated calvaria following IL-4 addition for 14 days. IL-4 delivery mitigated PE particle-induced osteolysis through macrophage polarization. Modulation of macrophage polarization is a potential treatment strategy for wear particle induced periprosthetic osteolysis.

Low-intensity pulsed ultrasound (LIPUS) may prevent polyethylene induced periprosthetic osteolysis in vivo

We investigated the effect of local low-intensity pulsed ultrasound (LIPUS) on polyethylene debris induced periprosthetic osteolysis. The periprosthetic osteolysis model was made by injecting endotoxin-free pure polyethylene particles into the distal part of the femur canal and inserting a stainless steel plug into this femur. The effects of polyethylene and LIPUS were assessed histologically and by the shear strength test and periprosthetic bone mineral density (BMD) test. Sixteen rabbits received a stainless steel plug on one side and both polyethylene and a stainless steel plug on the other side. Three months later, the side that received polyethylene showed periprosthetic osteolysis. Subsequently, another 16 rabbits received polyethylene plus local LIPUS (200 mW/cm(2) for 20 min daily) on one side and polyethylene alone on the other side. Three months later, LIPUS effectively prevented the periprosthetic osteolysis caused by polyethylene in this rabbit model.

Inhibitory effect of (-)-epigallocatechin gallate on titanium particle-induced TNF-α release and in vivo osteolysis

Tumor necrosis factor-α (TNF-α) and inflammatory cytokines released from activated macrophages in response to particulate debris greatly impact periprosthetic bone loss and consequent implant failure. In the present study, we found that a major polyphenolic component of green tea, (-)-epigallocatechin gallate (EGCG), inhibited Ti particle-induced TNF-α release in macrophages in vitro and calvarial osteolysis in vivo. The Ti stimulation of macrophages released TNF-α in a dose- and time-dependent manner, and EGCG substantially suppressed Ti particle-induced TNF-α release. Analysis of signaling pathway showed that EGCG inhibited the Ti-induced c-Jun N-terminus kinase (JNK) activation and inhibitory κB (IκB) degradation, and consequently the Ti-induced transcriptional activation of AP-1 and NF-κB. In a mouse calvarial osteolysis model, EGCG inhibited Ti particle-induced osteolysis in vivo by suppressing TNF-a expression and osteoclast formation. Therefore, EGCG may be a potential candidate compound for osteolysis prevention and treatment as well as aseptic loosening after total replacement arthroplasty.

Role of polyethylene particles in peri-prosthetic osteolysis: A review

There is convincing evidence that particles produced by the wear of joint prostheses are causal in the peri-prosthetic loss of bone, or osteolysis, which, if it progresses, leads to the phenomenon of aseptic loosening. It is important to fully understand the biology of this bone loss because it threatens prosthesis survival, and loosened implants can result in peri-prosthetic fracture, which is disastrous for the patient and presents a difficult surgical scenario. The focus of this review is the bioactivity of polyethylene (PE) particles, since there is evidence that these are major players in the development and progression of osteolysis around prostheses which use PE as the bearing surface. The review describes the biological consequences of interaction of PE particles with macrophages, osteoclasts and cells of the osteoblast lineage, including osteocytes. It explores the possible cellular mechanisms of action of PE and seeks to use the findings to date to propose potential non-surgical treatments for osteolysis. In particular, a non-surgical approach is likely to be applicable to implants containing newer, highly cross-linked PEs (HXLPEs), for which osteolysis seems to occur with much reduced PE wear compared with conventional PEs. The caveat here is that we know little as yet about the bioactivity of HXLPE particles and addressing this constitutes our next challenge.

Index radial collateral ligament repair with titanium mini-suture anchor: osteolysis complication of an underreported injury

We are reporting on a case of an index radial collateral ligament tear repaired with a titanium Mitek bone suture anchor. The development of cystic radiographic changes and increased pain and weakness led to suture anchor removal at 10 months post-repair. Periprosthetic osteolysis due to titanium-induced osteoclastogenesis and micromotion was suspected to be the cause. This case report provides a dual focus by stressing the importance of the diagnosis and treatment of this underreported ligament tear and highlighting our osteolysis complication via the mechanism of titanium-induced osteoclastogenesis for future therapeutic preventive measures.

Cellular chemotaxis induced by wear particles from joint replacements

The destruction of bone around joint replacements (periprosthetic osteolysis) is an adverse biological response associated with the generation of excessive wear particles. Wear debris from the materials used for joint replacements stimulate a chronic inflammatory and foreign body reaction that leads to increased osteoclast differentiation and maturation, and decreased bone formation. Wear debris induces both local and systemic trafficking of inflammatory cells to the site of particle generation. Recent studies have shown that this effect is mediated primarily by chemotactic cytokines (chemokines) including macrophage chemotactic protein-1 (MCP-1, also known as CCL2), macrophage inhibitory protein-1 (MIP-1), Interleukin-8 (IL-8 or CXCL8) and others. These ligands migrate along a concentration gradient to interact with G-protein-linked transmembrane receptors on the cell surface. Chemokines are involved in the innate and adaptive immune responses, angiogenesis, wound healing and tissue repair. In vitro, in vivo and tissue retrieval studies have shown that chemokine-directed systemic trafficking of polymorphonuclear leukocytes and cells of the monocyte/macrophage lineage to wear particles result in the release of pro-inflammatory factors and subsequent bone loss. Modulation of the chemokine ligand-receptor axis is a potential strategy to mitigate the adverse effects of wear particles from joint replacements.

Immobilized-OPG-Fc on a titanium surface inhibits RANKL-dependent osteoclast differentiation in vitro

The purpose of the present study was to examine the effect of osteoprotegerin (OPG)-Fc fusion protein immobilized on a titanium surface on the initial differentiation of osteoclast precursor RAW264.7 cells. These cells were cultured on titanium specimens over which OPG-Fc was immobilized. The enhancement of tartrate-resistant acid phosphatase (TRAP) and cathepsin K mRNA expression in RAW264.7 cells exposed to receptor activator of NF-kappaB ligand (RANKL) stimulation on OPG-Fc-coated titanium was significantly lower than that in RAW264.7 cells exposed to RANKL on titanium specimens without immobilized OPG-Fc (ANOVA, P < 0.01). Preincubation of OPG-Fc-coated titanium, in a medium supplemented with 10% fetal bovine serum at 37 degrees C for two days before the cells were seeded, had no significant effect on the decrease in mRNA expression (ANOVA, P < 0.01). Taken together, these results indicate that OPG-Fc immobilized on a titanium surface blocks the differentiation of RAW264.7 cells induced by RANKL stimulation.

Alumina ceramic particles, in comparison with titanium particles, hardly affect the expression of RANK-, TNF-alpha-, and OPG-mRNA in the THP-1 human monocytic cell line

Particle-induced osteolysis is the most frequent cause of aseptic loosening after total joint replacement. We performed a study to illuminate the effect of ceramic particles with different diameters and concentrations on the mRNA expression of certain key regulators in particle-induced aseptic osteolysis (RANK, RANKL, OPG, and TNF-alpha) in THP-1 macrophage-like cells. Titanium particles were used as a positive control. RNA was analyzed by quantitative RTPCR. Our results demonstrate that alumina ceramic particles, regardless of particle size, caused only slight upregulations of RANK, TNF-alpha, and OPG mRNA, whose levels were significantly lower in comparison with those of titanium particles (p < 0.05). The continuous increasing tendency to time and particle-dependent mRNA expression of all the parameters stimulated by titanium particles was not found after stimulation with ceramic materials. Even after the concentration of ceramic particles was increased, only a mild upregulation of mRNA expression was found. Furthermore, we observed that the bioinert properties of ceramic particles did not change much in diameters ranging from 0.5 to 1.5 microm. At most of the measuring time points, there was no significant difference between the reactions of the large and small particles in this range. Our results support the theory about the relative bioinert properties of alumina ceramic particles.

Effects of NF-kappaB inhibitor on titanium particulate-induced inflammation in a murine model

BACKGROUND

Activation of nuclear factor kappa B (NF-kappaB) signaling in response to implant particulates may be critical in the pathogenesis of implant loosening after joint arthroplasty. The purpose of this study was to investigate the inhibitory effects of pyrrolidine dithiocarbamate (PDTC) in a murine model of inflammation induced by titanium (Ti) particulates.

MATERIALS AND METHODS

Ti particulates were introduced into established air pouches on C57BL/6J mice. Mice were injected intraperitoneally with either high-dose PDTC (100 mg/kg) or low-dose PDTC (50 mg/kg). Mice without drug treatment, as well as mice injected with saline alone were included. Each group consisted of sixteen mice. The membranes and lavage fluid were harvested 2 d or 7 d after injection of particulate suspension for histological and molecular analysis.

RESULTS

Histologic analysis showed that PDTC reduced inflammatory responses in air pouches, that is, thinner membrane and decreased cellular infiltration. In addition, PDTC reduced the release of inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in the lavage fluid or supernatant of homogenates as evaluated by ELISA.

CONCLUSION

These results suggest that PDTC inhibits Ti particulate-induced inflammatory responses in the murine model; thus it represents a promising therapeutic candidate for the prevention and treatment of implant loosening.

The induction of a catabolic phenotype in human primary osteoblasts and osteocytes by polyethylene particles

Polyethylene (PE) wear particles are associated with the osteolysis seen in aseptic loosening that leads to orthopaedic implant failure. While cells of the monocyte/macrophage lineage are implicated, evidence is now emerging that osteoblastic cells may also be affected by PE. In this study we investigated the effect of PE particles on osteoblasts, using a novel in vitro cell culture system that was developed to juxtapose cells and PE particles, replicating the 3-dimensional (3D) environment near implants. This system allowed normal human bone-derived cells (NHBC) to undergo differentiation into a mature osteocyte-like phenotype over a 21-28-day culture period. PE particles induced an increase in mRNA expression of the osteocyte markers E11, DMP-1 and SOST/sclerostin. NHBC responded to PE particles by increasing the mRNA expression of several genes associated with osteoclast formation and activity (RANKL, IL-8 and M-CSF) and decreased the expression of the osteoclast antagonist, OPG. PE also appeared to induce a switch in the RUNX2 control of gene expression from that of promoting matrix production (type I collagen) to inducing the expression of pro-osteoclastogenic genes. These results suggest that PE particles switch mature osteoblastic cells from an anabolic to a more catabolic phenotype. This concept was further supported by the finding that PE-induced expression of RANKL mRNA in the mouse osteocyte cell line, MLO-Y4. Overall, our results suggest that PE particles directly induce a change in the phenotype of mature osteoblasts and osteocytes, consistent with the net loss of bone near orthopaedic implants.

[Molecular pathways in aseptic loosening of orthopaedic endoprosthesis]

Operative joint replacement to treat disabling joint conditions secondary to degenerative and inflammatory arthritides has become one of the most efficacious and cost-effective procedures to relieve pain and restore joint function. However, prosthetic implants are not built to last forever and osteolysis and aseptic loosening has been associated with prosthetic arthroplasties since their introduction. The functional life of a synthetic joint is influenced by many factors including the material of the implant, operation procedures and the surgeon involved, as well as patient-related factors. Although promising developments have been achieved in this field, more than 10% of all implants still have to undergo operative revision within 15 years after the initial operation. Failure due to sepsis, fractures and dislocations has become rare; premature loosening of implants on the other hand is becoming much more important. Prosthetic loosening without concurrent infection or trauma is called aseptic loosening. It is generally accepted that small particles ("wear debris") and activated macrophages play a key role in aseptic loosening. The pathophysiology of this condition, however, is still not very well characterized. In this article, we review the molecular mechanisms and signal pathways that were unravelled as responsible factors for loosening orthopaedic implants. Finally, we discuss possible novel strategies for future therapeutic approaches.

Inhibiting wear particles-induced osteolysis with doxycycline

AIM

To study the effect of doxycycline (DOX) on osteoclastogenesis, mature osteoclast fate and function, wear particles-induced osteoeolysis, and to provide some foundation for treating aseptic loosening and osteolysis after joint arthroplasty.

METHODS

Osteoclasts were generated from mouse bone marrow monocytes with the receptor activator of NF-kappaB ligand and the macrophage colony stimulating factor. DOX at a concentration of 5, 10, 15, and 20 microg/mL was respectively added to the medium. Seven days later, the osteoclasts were determined through tartrate-resistant acid phosphatase (TRAP) staining. Mature osteoclasts were isolated from newborn rabbits and cultured for 3 d in 24-well plates or on bone slices. DOX at a concentration of 5, 10, 15, and 20 microg/mL was respectively added to the medium. After TRAP staining, the osteoclasts were counted, resorption on bone slices was quantified, and the area was calculated after toluidine blue and Mayer-hematoxylin staining. Polymethyl methacrylate (PMMA) or ultra-high molecular weight polyethylene (UHMWPE) particles were implanted on the calvariae of C57BL/J6 mice. DOX, at a dose of 2 and 10 mg x kg(-1) x d(-1), was respectively given intraperitoneally for 7 d. Seven days later, the calvariae were removed and processed for pathological analysis.

RESULTS

DOX treatment effectively inhibited in vitro osteoclastogenesis, affected the fate of mature osteoclasts, and inhibited mature osteoclasts, causing bone resorption. In vivo data indicated that DOX strongly inhibited PMMA or UHMWPE-induced osteolysis and osteoclastogenesis.

CONCLUSION

DOX can effectively inhibit osteoclastogenesis and affect mature osteoclast fate and suppress wear particles induced by osteolysis and osteoclastogenesis. DOX might be useful in the treatment or prevention of wear particles-induced osteolysis and aseptic loosening for its effect on osteoclast generation and mature osteoclast fate and function.

Biological options to enhance periprosthetic bone mass

There is a potential for the use of pharmacological agents to enhance the quality of bone around a total hip or knee prosthesis, reducing the risk of implant failure or periprosthetic fracture. Bisphosphonates are currently used for the management of postmenopausal osteoporosis and recent investigations also suggest a potential role for the management of postoperative periprosthetic bone loss. Current evidence suggests that the short-term gains may not be sustained in the long term. Teriparatide and parathyroid hormone 1-84 have been licensed to treat postmenopausal osteoporosis and may also be investigated for the potential to enhance periprosthetic bone mass. In addition, other agents such as calcitonin and strontium ranelate, non-anabolic agents such as doxycycline, and recombinant OPG adeno-associated virus (rAAV) gene therapy, may in the future provide solutions for enhancing periprosthetic bone mass.

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.

Nonsurgical management of osteolysis: challenges and opportunities

Osteolysis remains a common mode of total hip arthroplasty failure. In vitro and animal models have been used to determine the pathophysiology of osteolysis by carefully dissecting the biochemical pathways leading to particulate wear debris and periprosthetic bone loss. Numerous cytokines and inflammatory mediators, including TNF-alpha and IL-1, are critical participants in this cascade and may represent prime targets for pharmacologic intervention. Osteoclasts, the end effector cells involved in the osteolytic process, also represent potential targets. Cell surface receptors on osteoclast precursors, such as receptor activator of NF-kappaB (RANK) (on osteoclasts) and RANK-ligand (RANKL) (on stromal cells), provide opportunities to arrest osteoclast maturation. Enhancing the naturally occurring osteoprotegerin is another recent attempt at modulating osteoclast behavior and a possible target for pharmacologic therapies. Other nonoperative strategies include intercepting tumor necrosis factor-alpha activity, interfering with the RANK-RANKL interaction necessary for osteoclast development and maturation, bisphosphonate therapy, and using viral vectors to deliver genes. Although each of these approaches has potential benefits, there are substantial challenges to effective implementation. Until there is convincing evidence of efficacy in human clinical trials, we recommend vigilant screening and appropriate surgery with component loosening or substantial likelihood of loosening, periprosthetic fracture, or major bone loss.