Wear particulate species and bone loss in failed total joint arthroplasties

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.

Does Focal Osteolysis in a PRECICE Stryde Intramedullary Lengthening Nail Resolve after Explantation?

Concerns surrounding osteolysis near and around the modular junction of a stainless-steel intramedullary lengthening rod prompted a manufacturer recall from the United States market in early 2021. These actions were preceded by similar steps taken in Europe. A concomitant review of stainless-steel lengthenings at our institution demonstrated signs of adverse tissue reaction including periosteal reaction and osteolysis at the modular junction and/or male-sided locking screws. Nearly half of our patients presented with these findings on radiographic images. At the time of the previous review, only half of the nearly 60 implanted stainless-steel devices met a 6-month follow-up. At this juncture, many patients have had their devices explanted. Given the suspected adverse tissue reactions caused by a component of the internal device, we sought to examine the rate of osteolysis post-explantation following removal of a stainless-steel nail. We reviewed a consecutive series of patients who underwent implantation of a stainless-steel limb lengthening device in the femur and/or tibia at a single institution between December 2018 and December 2020. Patients were included if their device was explanted. Periosteal reaction and osteolysis was classified according to a novel and validated classification system, as analyzed by five fellowship-trained surgeons. In addition, changes observed prior to explantation were tracked post-explantation to assess for resolution. The incidence of periosteal reaction and osteolysis prior to explantation was 22/57 (39%) and 15/57 (26%), respectively. Of the 15 patients with osteolysis pre-explantation, 14 patients’ implants were explanted. Of these, eight patients had available follow-up films. Two patients were identified as having partial osteolysis resolution at mean 1-year follow-up, while six patients were identified as having complete osteolysis at mean 18-months follow-up. Periosteal tissue reaction and osteolysis largely resolved following explantation in a subset of patients. These results provide further support to the claim that the stainless-steel device contributed to the changes seen. Further follow-up is warranted to examine the longer-term effects of adverse tissue reaction in this patient population.

Bisphosphonates in Total Joint Arthroplasty: A Review of Their Use and Complications

Background

Considerable interest has been expressed in the use of bisphosphonates to treat periprosthetic osteoporosis with the clinical goals of reducing periprosthetic fractures and prolonging implant survival.

Methods

A systematic review was performed with the goal of identifying both basic science and clinical studies related to the risks and benefits of bisphosphonate use in total joint arthroplasty.

Results

Studies have shown that bisphosphonates may increase early bony ingrowth, decrease the postoperative loss of bone mineral density, and increase the longevity of implants by reducing the need for revisions secondary to aseptic loosening. Continuing bisphosphonates for 1 year postoperatively seems to provide the greatest benefit, with only marginal benefit being shown by continuing therapy for up to 2 years. Current data present some concerns for an increased risk of periprosthetic fractures especially in younger patients, and prolonged therapy is not recommended due to the potential risk of atypical femur fractures. Patients should be counseled regarding the risk of side effects of bisphosphonates, including the risk of osteonecrosis of the jaw, which is a rare but serious side effect. They should also be counseled on the risk of atypical femur fractures and gastrointestinal intolerance.

Conclusions

Orthopedic surgeons could consider bisphosphonates for up to 1 year postoperatively regardless of the patient’s prior bone mineral density, after discussion regarding the risks and benefits with the patient.

Biopsy Proven Focal Osteolysis in a Stainless-Steel Limb-Lengthening Device: A Report of Three Cases

Three pediatric patients presented with histologically confirmed osteolysis after limb lengthening with a magnetic, telescoping, stainless-steel device. The first patient's findings were discovered radiographically before routine removal of the device. In all cases, intraoperative histologic specimens taken from around the modular junction demonstrated particle-laden macrophages with suspicion for metal debris. Silicone debris was also identified.

We found definitive osteolysis secondary to metal at the modular junction of three stainless-steel lengthening implants. This process is not well-understood in the setting of limb lengthening and should be examined further.

The Synergistic Effect of Nicotine and Staphylococcus aureus on Peri-Implant Infections

Smoking is considered a key risk factor for implant survival; however, how it interacts with the pathogens in peri-implant infections is not clear. Here, we identified that nicotine, the key component of cigarette smoking, can interact with Staphylococcus aureus and synergistically induce peri-implant infections in a rat osteolysis model. The nicotine–S. aureus combination group increased the gross bone pathology, osteolysis, periosteal reactions, and bone resorption compared to the nicotine or S. aureus single treated group (p < 0.05). Nicotine did not promote the proliferation of S. aureus both in vitro and in vivo, but it can significantly upregulate the expression of staphylococcal protein A (SpA), a key virulence factor of S. aureus. The nicotine–S. aureus combination also synergistically activated the expression of RANKL (receptor activator of nuclear factor-kappa B ligand, p < 0.05) to promote the development of peri-implant infections. The synergistic effects between nicotine and S. aureus infection can be a new target to reduce the peri-implant infections.

Metal-induced delayed type hypersensitivity responses potentiate particle induced osteolysis in a sex and age dependent manner

It is widely recognized that innate macrophage immune reactions to implant debris are central to the inflammatory responses that drive biologic implant failure over the long term. Less common, adaptive lymphocyte immune reactions to implant debris, such as delayed type hypersensitivity (DTH), can also affect implant performance. It is unknown which key patient factors, if any, mediate these adaptive immune responses that potentiate particle/macrophage mediated osteolysis. The objective of this investigation was to determine to what degree known adaptive immune responses to metal implant debris can affect particle-induced osteolysis (PIO); and if this pathomechanism is dependent on: 1) innate immune danger signaling, i.e., NLRP3 inflammasome activity, 2) sex, and/or 3) age. We used an established murine calvaria model of PIO using male and female wild-type C57BL/6 vs. Caspase-1 deficient mice as well as young (12–16 weeks old) vs. aged (18–24 months old) female and male C57BL/6 mice. After induction of metal-DTH, and Cobalt-alloy particle (ASTM F-75, 0.4um median diameter) calvaria challenge, bone resorption was assessed using quantitative micro-computed tomography (micro-CT) analysis and immune responses were assessed by measuring paw inflammation, lymphocyte transformation test (LTT) reactivity and adaptive immune cytokines IFN-gamma and IL-17 (ELISA). Younger aged C57BL/6 female mice exhibited the highest rate and severity of metal sensitivity lymphocyte responses that also translated into higher PIO compared to any other experimental group. The absence of inflammasome/caspase-1 activity significantly suppressed DTH metal-reactivity and osteolysis in both male and female Caspase-1 deficient mice. These murine model results indicate that young female mice are more predisposed to metal-DTH augmented inflammatory responses to wear debris, which is highly influenced by active NLRP3 inflammasome/caspase-1 danger signaling. If these results are clinically meaningful for orthopedic patients, then younger female individuals should be appropriately assessed and followed for DTH derived peri-implant complications.

Vitamin E-infused highly cross-linked polyethylene did not reduce the number of in vivo wear particles in total knee arthroplasty

AIMS

Vitamin E-infused highly cross-linked polyethylene (E1) has recently been introduced in total knee arthroplasty (TKA). An in vitro wear simulator study showed that E1 reduced polyethylene wear. However there is no published information regarding in vivo wear. Previous reports suggest that newly introduced materials which reduce in vitro polyethylene wear do not necessarily reduce in vivo polyethylene wear. To assist in the evaluation of the newly introduced material before widespread use, we established an in vivo polyethylene wear particle analysis for TKA. The aim of this study was to compare in vivo polyethylene wear particle generation between E1 and conventional polyethylene (ArCom) in TKA.

METHODS

A total of 34 knees undergoing TKA (17 each with ArCom or E1) were investigated. Except for the polyethylene insert material, the prostheses used for both groups were identical. Synovial fluid was obtained at a mean of 3.4 years (SD 1.3) postoperatively. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined by scanning electron microscopy.

RESULTS

The total number of polyethylene wear particles obtained from the knees with E1 (mean 6.9, SD 4.0 × 10⁷ counts/knee) was greater than that obtained from those with ArCom (mean 2.2, SD 2.6 × 10⁷ counts/knee) (p = 0.001). The particle size (equivalent circle of diameter) from the knees with E1 was smaller (mean 0.5 μm, SD 0.1) than that of knees with ArCom (mean 1.5, SD 0.3 μm) (p = 0.001). The aspect ratio of particles from the knees with E1 (mean 1.3, SD 0.1) was smaller than that with ArCom (mean 1.4, SD 0.1) (p < 0.001 ).

CONCLUSION

This is the first report of in vivo wear particle analysis of E1. E1 polyethylene did not reduce the number of in vivo polyethylene wear particles compared with ArCom in early clinical stage. Further careful follow-up of newly introduced E1 for TKA should be carried out. Cite this article: Bone Joint J 2020;102-B(11):1527-1534.

Higher Activity Level Following Total Knee Arthroplasty Is Not Deleterious to Mid-Term Implant Survivorship

BACKGROUND

The impact of a patient's activity level following total knee arthroplasty (TKA) remains controversial, with some surgeons concerned about increased polyethylene wear, aseptic loosening, and revisions. The purpose of this study is to report on implant survivorship and outcomes of high activity patients compared to low activity patients after TKA.

METHODS

A retrospective review identified 1611 patients (2038 knees) that underwent TKA with 5-year minimum follow-up. Patients were divided in 2 groups based on their University of California Los Angeles (UCLA) activity level: low activity (LA) (UCLA ≤5) and high activity (HA) (UCLA ≥6). Outcomes included range of motion, Knee Society scores, complications, and reoperations. Parametric survival analysis was performed to evaluate the significance of activity level on survivorship while controlling for age, gender, preoperative pain, Knee Society clinical scores, Knee Society functional scores, and body mass index (BMI).

RESULTS

Mean follow-up was 11.4 years (range 5.1-15.9). The LA group had significantly more female patients, were older, had higher BMI, and had lower functional scores preoperatively (all with P < .001). The HA group had significantly higher improvements in Knee Society scores (P < .001) and pain postoperatively (P < .001). Revisions were performed in 4% of the LA group and 1.7% knees of the HA group (P = .003). After controlling for age, gender, preoperative pain, Knee Society clinical scores, Knee Society functional scores, and BMI, a higher postoperative activity level remained a significant factor for improved survivorship with an odds ratio of 2.4 (95% confidence interval 1.2-4.7, P = .011). The all-cause 12-year survivorship was 98% for the HA group and 95.3% for the LA group (P = .003). The aseptic 12-year survivorship was 98.4% for the HA group and 96.3% for the LA group (P = .02).

CONCLUSION

Highly active patients had increased survivorship at 5-year minimum follow-up compared to lower activity patients after TKA. Patient activity level after TKA may not need to be limited with modern implants.

Periprosthetic Osteolysis: Mechanisms, Prevention and Treatment

Clinical studies, as well as in vitro and in vivo experiments have demonstrated that byproducts from joint replacements induce an inflammatory reaction that can result in periprosthetic osteolysis (PPOL) and aseptic loosening (AL). Particle-stimulated macrophages and other cells release cytokines, chemokines, and other pro-inflammatory substances that perpetuate chronic inflammation, induce osteoclastic bone resorption and suppress bone formation. Differentiation, maturation, activation, and survival of osteoclasts at the bone-implant interface are under the control of the receptor activator of nuclear factor kappa-Β ligand (RANKL)-dependent pathways, and the transcription factors like nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Mechanical factors such as prosthetic micromotion and oscillations in fluid pressures also contribute to PPOL. The treatment for progressive PPOL is only surgical. In order to mitigate ongoing loss of host bone, a number of non-operative approaches have been proposed. However, except for the use of bisphosphonates in selected cases, none are evidence based. To date, the most successful and effective approach to preventing PPOL is usage of wear-resistant bearing couples in combination with advanced implant designs, reducing the load of metallic and polymer particles. These innovations have significantly decreased the revision rate due to AL and PPOL in the last decade.

Particulate and ion forms of cobalt-chromium challenged preosteoblasts promote osteoclastogenesis and osteolysis in a murine model of prosthesis failure

This study investigated the interactive behavior of the particulate and ion forms of cobalt-chromium (Co-Cr) alloy challenged preosteoblasts during the process of prosthetic implant loosening. Preosteoblasts were challenged with Co-Cr particles or Co(II) ions for 72 h, followed by the proliferation and PCR assays. For in vivo test, a titanium pin was implanted into proximal tibia of SCID mice to mimic knee replacement. Co-Cr particles or Co(II) ion challenged preosteoblasts (5 × 10⁵ ) were intra-articularly injected into the implanted knee. The animals were sacrificed 5 weeks post-op, and the prosthetic knees were harvested for biomechanical pin-pullout testing, histological evaluations, and microCT assessment. In vitro study suggested that Co-Cr particles and Co(II) ions significantly suppressed the proliferation of preosteoblasts in a dose-dependent manner. RT-PCR data on the challenged cells indicated overexpression of receptor activator of nuclear factor kappa-B ligand (RANKL) and inhibited osteoprotegerin (OPG) gene expression. Introduction of the differently challenged preosteoblasts to the pin-implant mouse model resulted in reduced implant interfacial shear strength, thicker peri-implant soft-tissue formation, more TRAP+ cells, lower bone mineral density, and bone volume fraction. In conclusion, both Co-Cr particles and Co(II) ions interfered with the growth, maturation, and functions of preosteoblasts, and provides evidence that the metal ions as well play an important role in effecting preosteoblasts in the pathogenesis of aseptic loosening. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 187-194, 2019.

Sequentially annealed highly cross-linked polyethylene reduced in vivo wear particle generation in total knee arthroplasty

INTRODUCTION

Sequentially annealed highly cross-linked polyethylene (HXLPE) was recently introduced to reduce the wear in total knee arthroplasty (TKA). However, an in vivo advantage of sequentially annealed HXLPE on wear particle generation is still controversial. The purpose of this study is to compare the characteristics of in vivo wear particles between sequentially annealed HXLPE and conventional polyethylene after TKA.

MATERIALS AND METHODS

Synovial fluid was obtained from the eight knees with sequentially annealed HXLPE and from eight knees with conventional polyethylene 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyzer.

RESULTS

Total number of wear particles in each knee was 2.1 ± 1.0 × 10⁷ with sequentially annealed HXLPE (mean ± standard deviation) and 4.9 ± 3.6 × 10⁷ with conventional polyethylene ( p = 0.036). Particle size (equivalent circle diameter) was 1.01 ± 0.26 μm with sequentially annealed HXLPE and 1.02 ± 0.20 μm with conventional polyethylene ( p = 0.674). Aspect ratio was 1.33 ± 0.04 with sequentially annealed HXLPE and 1.39 ± 0.10 with conventional polyethylene ( p = 0.462).

CONCLUSIONS

The sequentially annealed HXLPE reduced the in vivo polyethylene wear particles by 58% compared with conventional polyethylene without the significant change of particle size and shape.

Comparison of in vivo polyethylene wear particles between mobile- and fixed-bearing TKA in the same patients

PURPOSE

Polyethylene wear particle generation is one of the most important factors that affects the mid- to long-term results of total knee arthroplasties (TKA). Mobile-bearing total knee prostheses were developed to reduce polyethylene wear generation. However, whether mobile-bearing prostheses actually generate fewer polyethylene wear particles than fixed-bearing prostheses remains controversial. The aim of this study was to compare, within individual patients, the in vivo polyethylene wear particles created by a newly introduced mobile-bearing prosthesis in one knee and a conventional fixed-bearing prosthesis in other knee.

METHODS

Eighteen patients receiving bilateral TKAs to treat osteoarthritis were included. The synovial fluid was obtained from 36 knees at an average of 3.5 years after the operation. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined using a scanning electron microscope and an image analyser.

RESULTS

The size and shape of the polyethylene wear particles from the mobile-bearing prostheses were similar to those from the conventional fixed-bearing prostheses. Although the number of wear particles from the mobile-bearing prosthesis (1.63 × 10⁷ counts/knee) appeared smaller than that from the fixed-bearing prosthesis (2.16 × 10⁷ counts/knee), the difference was not statistically significant.

CONCLUSIONS

The current in vivo study shows that no statistically significant differences were found between the polyethylene wear particles generated by a newly introduced mobile-bearing PS prosthesis and a conventional fixed-bearing PS prosthesis during the early clinical stage after implantation.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Paresis of the Peroneal Nerve: A Rare But Severe Long-term Complication of Polyethylene Wear in Knee Arthroplasty

One of the most important limiting factors in the long-term success of total knee arthroplasty is polyethylene wear. Particles of the polyethylene inserts have been shown to elicit a foreign body response, which produces bone resorption and osteolysis, ultimately leading to loosening and component failure. The authors report on a case of an elderly patient who underwent a total knee arthroplasty almost 2 decades ago. Clinical and radiological checkups of the knee had not been performed recently. He now presented with a painful and swollen knee, recurrent joint effusion and swelling of the lower leg, and paresis of the peroneal nerve. Radiological examination showed asymmetric wear of the polyethylene insert and pronounced periprosthetic osteolysis of the proximal tibia and the distal femur. Furthermore, a large ganglion on the anterolateral aspect of the lower leg, resulting in pressure on the peroneal nerve, was detected on ultrasound examination. Open excision of the ganglion was performed initially, followed by 1-stage revision knee arthroplasty using a modular system a few weeks later. This case shows a rare but severe long-term complication of total knee arthroplasty and highlights the importance of regular clinical and radiological checkups after total joint replacements, even for asymptomatic patients and especially in the long term (ie, beyond 10 years after implantation). The current case shows that wear of the polyethylene insert may also lead to ganglion formation that causes paresis of the peroneal nerve. [Orthopedics. 2017; 40(3):e538-e540.].

Finite element study of the acetabulum in cemented hip arthroplasty investigating retention or removal of the subchondral bone plate

The importance of the subchondral bone plate of the acetabulum when preparing the pelvis for a cemented acetabular cup during total hip arthroplasty (THA) has been investigated using finite element analysis. The effect of retaining or removing the subchondral bone plate and the use of anchoring holes are compared. Loading was applied via both hip joint contact force and the activity of up to 22 muscles at five stages through the load bearing phase of the gait cycle. Removing the subchondral bone plate leads to decreased stresses in the cancellous bone and slightly increased stresses in the cortical shell superior to the acetabulum. The differences between the two cases are small, nevertheless there are indications that removal of the subchondral bone plate reduces the stresses. Increasing the cement penetration depth leads to a slightly more rigid structure, due to cement penetrating the cancellous bone. Adding anchoring holes moves the position of the highest cancellous bone strains from the bone-cement interface into the cancellous bone. Thus removal of the subchondral bone plate should lead to an increased potential for cement penetration into the cancellous bone which should be beneficial for cup fixation and thus improve long term implant survival.

Wear particles derived from metal hip implants induce the generation of multinucleated giant cells in a 3-dimensional peripheral tissue-equivalent model

Multinucleate giant cells (MGCs) are formed by the fusion of 5 to 15 monocytes or macrophages. MGCs can be generated by hip implants at the site where the metal surface of the device is in close contact with tissue. MGCs play a critical role in the inflammatory processes associated with adverse events such as aseptic loosening of the prosthetic joints and bone degeneration process called osteolysis. Upon interaction with metal wear particles, endothelial cells upregulate pro-inflammatory cytokines and other factors that enhance a localized immune response. However, the role of endothelial cells in the generation of MGCs has not been completely investigated. We developed a three-dimensional peripheral tissue-equivalent model (PTE) consisting of collagen gel, supporting a monolayer of endothelial cells and human peripheral blood mononuclear cells (PBMCs) on top, which mimics peripheral tissue under normal physiological conditions. The cultures were incubated for 14 days with Cobalt chromium alloy (CoCr ASTM F75, 1–5 micron) wear particles. PBMC were allowed to transit the endothelium and harvested cells were analyzed for MGC generation via flow cytometry. An increase in forward scatter (cell size) and in the propidium iodide (PI) uptake (DNA intercalating dye) was used to identify MGCs. Our results show that endothelial cells induce the generation of MGCs to a level 4 fold higher in 3-dimentional PTE system as compared to traditional 2-dimensional culture plates. Further characterization of MGCs showed upregulated expression of tartrate resistant alkaline phosphatase (TRAP) and dendritic cell specific transmembrane protein, (DC-STAMP), which are markers of bone degrading cells called osteoclasts. In sum, we have established a robust and relevant model to examine MGC and osteoclast formation in a tissue like environment using flow cytometry and RT-PCR. With endothelial cells help, we observed a consistent generation of metal wear particle- induced MGCs, which heralds metal on metal hip failures.

Molecular analysis of chromium and cobalt-related toxicity

Occupational and environmental exposure to Co and Cr has been previously linked to a wide array of inflammatory and degenerative conditions and cancer. Recently, significant health concerns have been raised by the high levels of Cr and Co ions and corrosion products released by biomedical implants. Herein, we set to analyze the biological responses associated with Co and Cr toxicity. Histological, ultrastructural, and elemental analysis, performed on Cr and Co exposed patients reveal the presence of corrosion products, metallic wear debris and metal ions at varying concentrations. Metallic ions and corrosion products were also generated in vitro following macrophage phagocytosis of metal alloys. Ex vivo redox proteomic mapped several oxidatively damaged proteins by Cr(III) and Co(II)-induced Fenton reaction. Importantly, a positive correlation between the tissue amounts of Cr(III) and Co(II) ions and tissue oxidative damage was observed. Immobilized- Cr(III) and Co(II) affinity chromatography indicated that metal ions can also directly bind to several metallo and non-metalloproteins and, as demonstrated for aldolase and catalase, induce loss of their biological function. Altogether, our analysis reveals several biological mechanisms leading to tissue damage, necrosis, and inflammation in patients with Cr and Co-associated adverse local tissue reactions.

The pathology of orthopedic implant failure is mediated by innate immune system cytokines

All of the over 1 million total joint replacements implanted in the US each year are expected to eventually fail after 15–25 years of use, due to slow progressive subtle inflammation at the bone implant interface. This inflammatory disease state is caused by implant debris acting, primarily, on innate immune cells, that is, macrophages. This slow progressive pathological bone loss or “aseptic loosening” is a potentially life-threatening condition due to the serious complications in older people (>75 yrs) of total joint replacement revision surgery. In some people implant debris (particles and ions from metals) can influence the adaptive immune system as well, giving rise to the concept of metal sensitivity. However, a consensus of studies agrees that the dominant form of this response is due to innate reactivity by macrophages to implant debris where both danger (DAMP) and pathogen (PAMP) signalling elicit cytokine-based inflammatory responses. This paper discusses implant debris induced release of the cytokines and chemokines due to activation of the innate (and the adaptive) immune system and the subsequent formation of osteolysis. Different mechanisms of implant-debris reactivity related to the innate immune system are detailed, for example, danger signalling (e.g., IL-1β, IL-18, IL-33, etc.), toll-like receptor activation (e.g., IL-6, TNF-α, etc.), apoptosis (e.g., caspases 3–9), bone catabolism (e.g., TRAP5b), and hypoxia responses (Hif1-α). Cytokine-based clinical and basic science studies are in progress to provide diagnosis and therapeutic intervention strategies.

No difference in in vivo polyethylene wear particles between oxidized zirconium and cobalt-chromium femoral component in total knee arthroplasty

PURPOSE

Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. Oxidized zirconium was introduced as a material for femoral components to reduce polyethylene wear generation. However, an in vivo advantage of oxidized zirconium on polyethylene wear particle generation is still controversial. The purpose of this study was to compare in vivo polyethylene wear particles between oxidized zirconium total knee prosthesis and conventional cobalt-chromium (Co-Cr) total knee prosthesis.

METHODS

Synovial fluid was obtained from the knees of 6 patients with oxidized zirconium total knee prosthesis and from 6 patients with conventional cobalt-chromium (Co-Cr) total knee prosthesis 12 months after the operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyser.

RESULTS

Total number of particles in each knee was 3.3 ± 1.3 × 10(7) in the case of oxidized zirconium (mean ± SD) and 3.4 ± 1.2 × 10(7) in that of Co-Cr (n.s.). The particle size (equivalent circle diameter) was 0.8 ± 0.3 μm in the case of oxidized zirconium and 0.6 ± 0.1 μm in that of Co-Cr (n.s.). The particle shape (aspect ratio) was 1.4 ± 0.0 in the case of oxidized zirconium and 1.4 ± 0.0 in that of metal Co-Cr (n.s).

CONCLUSIONS

Although newly introduced oxidized zirconium femoral component did not reduce the in vivo polyethylene wear particles in early clinical stage, there was no adverse effect of newly introduced material. At this moment, there is no need to abandon oxidized zirconium femoral component. However, further follow-up of polyethylene wear particle generation should be performed to confirm the advantage of the oxidized zirconium femoral component.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

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.

Creep and fatigue behavior of a novel 2-component paste-like formulation of acrylic bone cements

The fatigue and creep performance of two novel acrylic bone cement formulations (one bone cement without antibiotics, one with antibiotics) was compared to the performance of clinically used bone cements (Osteopal V, Palacos R, Simplex P, SmartSet GHV, Palacos R+G and CMW1 with Gentamicin). The preparation of the novel bone cement formulations involves the mixing of two paste-like substances in a static mixer integrated into the cartridge which is used to apply the bone cement. The fatigue performance of the two novel bone cement formulations is comparable to the performance of the reference bone cements. The creep compliance of the bone cements is significantly influenced by the effects of physical ageing. The model parameters of Struik's creep law are used to compare the creep behavior of different bone cements. The novel 2-component paste-like bone cement formulations are in the group of bone cements which exhibit a higher creep resistance.

Evidence for active antigen presentation by monocyte/macrophages in response to stimulation with particles: the expression of NFκB transcription factors and costimulatory molecules

BACKGROUND

The macrophage and lymphocyte response to wear debris contributes to the failure of some joint replacements. Costimulatory molecule expression by particle-containing macrophages is an evidence for antigen presentation. The NFκB transcription factors are regulators of costimulatory molecules and are present in tissue near failed joint prostheses. The tissue localisation of NFκB and the expression of these factors and costimulatory molecules by U937 cells stimulated with nano- and microparticles are reported, together with the effects of an NFκB inhibitor (sc514).

MATERIALS AND METHODS

The tissue localisation of RelA, RelB, c-rel, p50, p52 and NF-IL6 was examined by immunohistochemistry in samples from 15 patients with failure of metal against polyethylene total hip replacements. The expression of these NFκB factors by U937 cells stimulated with microparticles (CoCr, diamond) and nanoparticles (diamond) was examined by quantified RT-PCR. Lipopolysaccharide provided positive controls while negative controls had no additions to culture. Inhibition of NFκB activity by sc-514 was studied. The expression of costimulatory molecules (CD80, CD86 and HLA-DR) was evaluated in parallel cell culture studies by tricolour flow cytometry.

RESULTS AND DISCUSSION

Immunohistochemistry of tissue showed the highest expression for NF-IL6 (32.56 ± 11.61 per cent), RelA (33.66 ± 9.98 per cent) and p52 (32.07 ± 12.90 per cent), then RelB (22.63 ± 7.49 per cent), c-rel (14.07 ± 6.72 per cent) and p50 (13.07 ± 5.99 per cent). NF-IL6 was localised to macrophages, RelB to RFD1+ dendritic cells. U937 cells showed an increased expression of all NFκB factors (p < 0.01) in response to CoCr and diamond microparticles. Only RelA and c-rel (p < 0.01) were increased by one diamond nanoparticle and p52 and c-rel (p < 0.01) by another nanoparticulate diamond. Inhibition by sc-514 of RelA, c-rel and p50 expression occurred with all four particles, p52 was decreased for all diamond particles (but not CoCr) and RelB was not inhibited with any of the particles. CD86 and HLA-DR expression were upregulated by microparticles (CoCr, diamond) (p ≪ 0.01) with lower levels (significant) of these molecules found with diamond nanoparticles. CD80 expression was much less than CD86 and HLA-DR. Costimulatory molecule expression in the bone-implant interface indicates antigen presentation by macrophages. Functional studies with U937 monocytes show the same molecules expressed on exposure to micro- and nanoparticles. Highest values occur with CoCr while the smallest diamond nanoparticles are the least stimulatory. NFκB expression gives an insight into the immunogenic potential of the different particles.

A FULL NUMERICAL ANALYSIS OF ELASTOHYDRODYNAMIC LUBRICATION IN KNEE PROSTHESIS UNDER WALKING CONDITION

Lubrication plays an important role in reducing prosthetic wear. Time-dependent elastohydrodynamic lubrication simulation for total knee replacements was carried out under physiological loading and motions of a gait cycle. In numerical implement, a simplified ellipsoid-on-plane configuration was introduced to represent the artificial knee joint. Load and motions came from ISO standard, and both anterior–posterior displacement and flexion–extension rotation were considered to realize sliding and rolling motions of the knee. The governing Reynolds and elasticity equations were solved simultaneously using the multigrid technique. The elastic deformation was calculated based on the constrained column model. The results show that: (i) under the combination of entraining and squeeze-film actions throughout the walking cycle, the predicted central film thickness decreases during stance phase and keeps a relatively larger value in swing phase; (ii) high joint conformity helps to reduce hydrodynamic pressure and increase lubrication film thickness; (iii) the thickness of ultra-high molecular weight polyethylene layer and its properties also have influence on the lubrication performance in artificial knee replacement. Based on the aforementioned EHL analysis, potential surface damage of knee implants can be further evaluated.

Factors to consider in joint prosthesis systems

In joint reconstruction, the techniques and materials that provide the best outcomes for patients have been debated. The main points of controversy relate to the use of hemiarthroplasties versus total joint prostheses with metal-on-metal versus metal-on-polyethylene articulations. This article investigates these areas as well as the applicability of the techniques and materials and the complications that can occur. Hypersensitivity to materials used in joint prostheses is relatively common but often unrecognized. Although the discussion applies to all joints, the temporomandibular joint (TMJ) is emphasized. For TMJ reconstruction, metal-on-polyethylene articulation in total joint prostheses provides better treatment outcomes than metal-on-metal articulation.

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.

Distinct immunohistomorphologic changes in periprosthetic hip tissues from historical and highly crosslinked UHMWPE implant retrievals

Assessment of immune response to implant wear debris in periprosthetic tissue following total hip arthroplasty suggests that multiple factors are involved in the loss implant function. The current study investigated wear debris and the associated immunohistomorphologic changes in tissues from nine patients with historical (gamma air-sterilized) and nine highly crosslinked UHMWPE implant components. Paraffin embedded tissue sections were evaluated for the presence of histiocytes, giant cells, fibrocartilage/bone, and necrosis. To determine the incidence, degree and co-localization of immunohistomorphologic changes and wear, overlapping full-field tissue arrays were collected in brightfield and polarized light. The historical cohort tissues predominantly showed histiocytes associated with significant accumulations of small wear (0.5-2 microm), and giant cells associated with large wear (> or =2 microm). Frequently, focal regions of necrosis were observed in association with wear debris. For the highly crosslinked cohort, inflammation and associated wear debris were limited, but in tissues from patients revised after implantation times of >2 years a response was observed. Whereas significant amounts of fibrocartilage/bone were observed in patients at earlier implantation times. In both cohorts, tissue responses were more extensive in the retroacetabular or proximal femoral regions. The current findings suggest that wear debris-induced inflammation may be a major contributor to the loss of implant function for both the historical and highly crosslinked cohorts, but it is not the primary cause of early implant loosening. This study highlights the importance of using a more quantitative and standardized assessment of immunohistomorphologic responses in periprosthetic tissues, and emphasizes differences in specific anatomical regions of individual patient tissues.

Effects of orthopedic polymer particles on chemotaxis of macrophages and mesenchymal stem cells

Wear particles generated from total joint arthroplasty (TJA) stimulate macrophages to release chemokines. The role of chemokines released from wear particle-stimulated macrophages on the migration of macrophages and osteoprogenitor cells in vitro has not been elucidated. In this study, we challenged murine macrophages (RAW 264.7) with clinically relevant polymethyl methacrylate (PMMA, 1-10 microm) and ultra high molecular weight polyethylene (UHMWPE, 2-3 microm) particles. The chemotactic effects of the conditioned media (CM) were tested in vitro using human macrophages (THP-1) and human mesenchymal stem cells (MSCs) as the migrating cells. CM collected from both particle types had a chemotactic effect on human macrophages, which could be eliminated by monocyte chemotactic protein-1 (MCP-1) neutralizing antibody. Blocking the CCR1 receptor eliminated the chemotactic effect, while CCR2 antibody only partially decreased THP-1 cell migration. CM from PMMA but not UHMWPE-exposed macrophages led to chemotaxis of MSCs; this effect could be eliminated by macrophage inflammatory protein-1 alpha (MIP-1alpha) neutralizing antibody. Neither CCR1 nor CCR2 blocking antibodies showed an effect on the migration of MSCs. Chemokines released by macrophages stimulated by wear particles can have an effect on the migration of macrophages and MSCs. This effect seems to be dependent on the particle type, and may be modulated by MCP-1 and MIP-1alpha, however, more than one chemokine may be necessary for chemotaxis.

Friction properties of novel PVP/PVA blend hydrogels as artificial cartilage

In this work, novel polyvinylpyrrolidone (PVP)/polyvinylalcohol (PVA) blend hydrogels were prepared by repeated freezing-thawing cycles. The factors that influenced friction properties of blend hydrogels, such as PVP content, contact load, sliding speed, and lubrication condition, were mainly studied by sliding with stainless steel ball. The results showed that friction coefficients of the PVP/PVA blend hydrogels were definitely dependent on such influence factors. The friction system consisting of blend hydrogel and stainless steel ball nearly exhibited a mixed lubrication regime especially under bovine serum lubrication, and it can be proposed as a promising method to reduce wear of the prosthesis.

Bioactive ceramic-reinforced composites for bone augmentation

Biomaterials have been used to repair the human body for millennia, but it is only since the 1970s that man-made composites have been used. Hydroxyapatite (HA)-reinforced polyethylene (PE) is the first of the 'second-generation' biomaterials that have been developed to be bioactive rather than bioinert. The mechanical properties have been characterized using quasi-static, fatigue, creep and fracture toughness testing, and these studies have allowed optimization of the production method. The in vitro and in vivo biological properties have been investigated with a range of filler content and have shown that the presence of sufficient bioactive filler leads to a bioactive composite. Finally, the material has been applied clinically, initially in the orbital floor and later in the middle ear. From this initial combination of HA in PE other bioactive ceramic polymer composites have been developed.

Comparison of two methods of fatigue testing bone cement

Two different methods have been used to fatigue test four bone cements. Each method has been used previously, but the results have not been compared. The ISO 527-based method tests a minimum of 10 samples over a single stress range in tension only and uses Weibull analysis to calculate the median number of cycles to failure and the Weibull modulus. The ASTM F2118 test regime uses fewer specimens at various stress levels tested in fully reversed tension-compression, and generates a stress vs. number of cycles to failure (S-N) or Wöhler curve. Data from specimens with pores greater than 1mm across is rejected. The ISO 527-based test while quicker to perform, provides only tensile fatigue data, but the material tested includes pores, thus the cement is closer to cement in clinical application. The ASTM regime uses tension and compression loading and multiple stress levels, thus is closer to physiological loading, but excludes specimens with defects obviously greater than 1mm, so is less representative of cement in vivo. The fatigue lives between the cements were up to a factor 15 different for the single stress level tension only tests, while they were only a factor of 2 different in the fully reversed tension-compression testing. The ISO 527-based results are more sensitive to surface flaws, thus the differences found using ASTM F2118 are more indicative of differences in the fatigue lives. However, ISO 527-based tests are quicker, so are useful for initial screening.

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

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

Retrieval analysis of motion preserving spinal devices and periprosthetic tissues

This article reviews certain practical aspects of retrieval analysis for motion preserving spinal implants and periprosthetic tissues as an essential component of the overall revision strategy for these implants. At our institution, we established an international repository for motion-preserving spine implants in 2004. Our repository is currently open to all spine surgeons, and is intended to be inclusive of all cervical and lumbar implant designs such as artificial discs and posterior dynamic stabilization devices. Although a wide range of alternative materials is being investigated for nonfusion spine implants, many of the examples in this review are drawn from our existing repository of metal-on-polyethylene, metal-on-metal lumbar total disc replacements (TDRs), and polyurethane-based dynamic motion preservation devices. These devices are already approved or nearing approval for use in the United States, and hence are the most clinically relevant at the present time. This article summarizes the current literature on the retrieval analysis of these implants and concludes with recommendations for the development of new test methods that are based on the current state of knowledge of in vivo wear and damage mechanisms. Furthermore, the relevance and need to evaluate the surrounding tissue to obtain a complete understanding of the biological reaction to implant component corrosion and wear is reviewed.

In vivo comparison of wear particles between highly crosslinked polyethylene and conventional polyethylene in the same design of total knee arthroplasties

Reduction of wear with highly crosslinked polyethylene (HXLPE) has been reported in in vitro and in vivo studies of total hip prostheses. However, use of HXLPE in total knee prostheses is still controversial. The aim of this study was to compare in vivo polyethylene wear particle generation of HXLPE with that of conventional polyethylene in total knee prostheses of the same design. Synovial fluid was obtained from four knees with HXLPE inserts and three knees with conventional polyethylene inserts at 1 year after operation. Polyethylene particles were isolated and examined using a scanning electron microscope and image analyzer. The total number of particles in each knee was 0.28 +/- 0.12 x 10(6) in HXPLE group (mean +/- standard error) and 6.87 +/- 2.85 x 10(6) in conventional polyethylene group (p = 0.040). Particle size (equivalent circle diameter) was 0.64 +/- 0.07 microm in HXPLE group and 1.21 +/- 0.21 microm in conventional polyethylene group (p = 0.030). Particle shape (aspect ratio) was 1.33 +/- 0.10 in HXLPE and 1.88 +/- 0.19 in conventional polyethylene (p = 0.035). Thepercentage of particles of submicron size was greater than 90% in HXLPE group and 55% in conventional polyethylene group. Except for the material of the polyethylene insert, the design and material of prostheses were completely the same in both groups. The HXLPE insert generated fewer, smaller, and rounder polyethylene wear particles than the conventional polyethylene insert in the early stage after surgery.

Circulating blood monocytes traffic to and participate in the periprosthetic tissue inflammation

OBJECTIVE

To examine the trafficking of human circulating blood monocytes and their influence on the inflammation of periprosthetic tissues using a novel mouse-human chimera model.

METHODS

Periprosthetic tissue and bone chips from patients with aseptic prosthetic loosening were implanted into the muscles of immune-deficient SCID mice depleted of host macrophages by periodic intraperitoneal injection of anti-asialo GM1 rabbit sera (ASGM1). Autologous patient peripheral blood monocytes (PBMCs) were labeled with PKH2 fluorescent dye and injected intraperitoneally into the implanted animals. Mice were sacrificed 14 days after PBMC transfusion for molecular and histological analyses.

RESULTS

Patient periprosthetic tissues were well tolerated in SCID mice and preserved a high level of viability. Cell trafficking studies revealed the accumulation of fluorescent PBMC within the xenografts, with total cell counts in the xenografts significantly increased following the systemic PBMC infusion. PBMC infusion also promoted the expression of IL-1, IL-6, TNFalpha, and RANK within the periprosthetic tissue.

CONCLUSION

Systemic PBMC migrated to the implanted periprosthetic tissues and contributed to the local inflammation. The data provide evidence that circulating blood monocytes may play a role in pathologic process during aseptic loosening of total joint replacement.

Once-weekly oral medication with alendronate does not prevent migration of knee prostheses: A double-blind randomized RSA study

BACKGROUND AND PURPOSE

Early migration of joint replacements is an effect of poor fixation and can predict late loosening. By reducing the bone resorption after implantation of a joint replacement, it should be possible to enhance the initial fixation of the implant. We studied the effect of once-weekly treatment with alendronate after knee replacement.

PATIENTS AND METHODS

We recruited 60 patients (60 knees) with gonarthrosis who were scheduled for a total knee replacement. They were operated on with identical implants and uncemented fixation. 30 patients were treated with a bisphosphonate (alendronate) and 30 patients underwent placebo treatment. The treatment started postoperatively and continued on a weekly basis for 6 months. The fixation of the implants was measured with repeated radiostereometry for 2 years.

RESULTS

There was no difference in migration of implants between the two groups.

CONCLUSION

With uncemented fixation of knee implants, no benefit of once-weekly treatment with alendronate, starting postoperatively, could be seen during a 2-year follow-up period.

The combined role of wear particles, macrophages and lymphocytes in the loosening of total joint prostheses

This review considers the causes of loosening of prosthetic joint replacement paying attention to the biological mechanisms rather than other effects that are physical, such as component fracture and other failure related to mechanical problems. Infection accounts for approximately 1.5 per cent of joint loosening and when it occurs it is a cause of serious concern to the surgeon. The loosening of prosthetic joints in the absence of infection is by far the most common reason for revision surgery and is known as aseptic loosening. While this may be multifactorial in terms of causation, and non-biological factors may contribute significantly in a particular individual, a significant part is undoubtedly played by the generation of wear debris, mainly from the bearing surfaces of the joint, and the cellular reaction to this in the implant bed. Phagocytic cells (macrophages and multinucleated giant cells) are the ones that remove foreign material from the tissues, and the ways in which these cells function in the interface between implant and bone are described. Mediators produced locally include numerous cytokines, enzymes and integrins. There is evidence for interactions between macrophages and locally recruited lymphocytes, which may or may not give rise to an immunologically mediated process.Sensitization of individuals having metal implants in place has been shown by positive skin tests or blood lymphocyte transformation tests and in these cases has been accompanied by loosening and failure of the replacement joint. The question remains as to whether this process is also present in a proportion of individuals with aseptic loosening in the absence of clearly defined clinical evidence of sensitization.Numerous studies performed by the author's group and, latterly, by others suggest that the cellular reactions detected in the tissues in cases of aseptic loosening are indeed those of contact sensitization. There is good evidence to show that a type IV cell-mediated immune reaction is taking place, with TH1 cell involvement and active antigen presentation. The extent to which sensitization is present in individual cases of aseptic loosening remains a subject for further work and this needs all the sophisticated molecular methods now available to modern biology to be applied in appropriate prospective clinical studies coupled with experimental models in vitro and in vivo. Immunological processes may play a more important part in joint loosening than previously considered.

Preliminary tribological evaluation of nanostructured diamond coatings against ultra-high molecular weight polyethylene

BACKGROUND

Some loss of joint prostheses has been attributed to osteolytic loosening associated with debris from wear of polyethylene articulating against metal alloys. Reduced polyethylene wear has been reported with ceramics serving as an alternative counterface.

METHODS

Nanostructured Diamond (NSD) coatings were deposited onto Ti6Al4V by microwave plasma-assisted chemical vapor deposition, with both hydrogen-rich (H-NSD) and helium-rich (He-NSD) feedgas mixtures. Pin-on-disk wear tests of polyethylene against NSD and CoCr were performed in serum lubrication at body temperature. Scanning electron microscopy was used to examine surface morphology, and nanoindentation was used to determine hardness and modulus of the polyethylene wear surfaces. Raman spectroscopy, surface roughness, and wettability analyses of the NSD coatings were performed.

RESULTS

Raman spectroscopy confirmed sp(2) and sp(3) bonded carbon in the NSD coatings. No significant differences in wear factors were found between polyethylene on H-NSD, He-NSD, and CoCr, despite higher roughness and friction coefficients for the He-NSD and H-NSD coatings, compared with CoCr. Contact angles for the diamond coatings were reduced following the wear tests, indicating that these surfaces became more hydrophilic. Numerous small protuberances were observed on pins articulated against CoCr, and a single, large protuberance was observed in polyethylene-on-NSD. These features were conjectured to be reconsolidated polyethylene particles. Nanoindentation modulus and hardness of the worn polyethylene surfaces were lower for polyethylene-on-diamond than for polyethylene-on-CoCr.

CONCLUSIONS

As a counterface to polyethylene, NSD-coated Ti6Al4V produced wear factors comparable to CoCr in the present pin-on-disk tests, a promising step towards its use in joint replacement bearing applications.

Characteristics of Hylamer polyethylene particles isolated from peri-prosthetic tissues of failed cemented total hip arthroplasties

Polyethylene wear particles are one of the most important factors affecting the results of total hip arthroplasty. Hylamer, a highly crystalized ultra-high-molecular-weight polyethylene, has been used in total hip arthroplasty for wear reduction, but has exhibited high wear rate and excessive osteolysis. The aim of the present study was to examine Hylamer wear particles in peri-prosthetic tissues with osteolysis obtained from two cases of failed cemented total hip arthroplasty at 8 and 6 years after operation. Polyethylene particles were isolated, and examined using a scanning electron microscope and image analyzer. Total numbers of Hylamer polyethylene particles in the two cases were 5.6 x 10(9) and 8.0 x 10(9) g(-1). Particle sizes (in equivalent circle diameter) for the two cases were 1.07 +/- 0.06 microm and 1.16 +/- 0.05 microm, and particle shapes (roundness) were 3.05 +/- 0.22 and 3.76 +/- 0.28. The Hylamer polyethylene particles were larger in size and more elongated and their number was larger, compared with the corresponding reported values for particles generated from conventional polyethylene. This increase in particle number and elongation may lead to early osteolysis in total hip arthroplasty with Hylamer.

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.

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

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

Effect of ultra-high molecular weight polyethylene thickness on contact mechanics in total knee replacement

One of the important design parameters in current knee joint replacements is the thickness of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert, yet there is no clear definition of the upper limit of the ‘thick’ polyethylene insert. Using one design knee implant and subjecting it to the physiological loads encountered throughout the gait cycle, measurements of the lengths of contact imprints generated were compared with the corresponding theoretical predictions for different insert thicknesses under the same applied load. Multiple regression analysis was applied to test whether the dimensions of contact imprints are influenced by UHMWPE thickness. Good agreement was obtained between the theoretical predictions and the experimental measurements of the dimensions of contact imprints when the knee was at 60° flexion. Therefore, it was possible to estimate the contact pressure at the articulating surface using the theoretical model. Contact imprint dimensions increased with increasing applied load. Statistical analysis of the experimental data revealed that, at 0° flexion, the overall imprint dimensions increased as the UHMWPE thickness increased from 8 to 20 mm. However, the increment was not significant when the thickness subinterval 10-15 mm was considered. Furthermore, at 60° flexion, thickness was not a significant factor for the overall imprint dimensions. No evidence was found from the data to suggest that an increment in polyethylene thickness over 10 mm would significantly reduce the contact imprint dimensions. These findings suggest that thicker inserts can be avoided, as they require unnecessary bone resection.

Pin-on-disc evaluation of self-reinforced composite poly(methyl methacrylate) for total joint replacements

Femoral components of hip replacements are commonly anchored in the femur with bone cement or poly(methyl methacrylate) (PMMA). Wear or fracture of bone cement can lead to loosening of the femoral component, which drastically affects the success and longevity of hip replacements. Self-reinforced composite PMMA (SRC-PMMA) has been previously developed for potential use, as a precoat material for hip replacements. The composite consists of high strength fibers that have been shown to have greatly improved mechanical properties over bulk PMMA. The goal of this work was to examine SRC-PMMA for improved wear properties, as a function of processing temperature. Pin-on-disc tests were used to characterize and rank the wear rates of SRC-PMMA and PMMA. Composites made with higher processing temperatures had significantly lower wear rates than do PMMA at a significance level of p < or = 0.05. The lowest wear rate was 8.2 microg/m, at a processing temperature of 136 degrees C, compared to a wear rate for PMMA of 13.3 microg/m. At the lowest processing temperature (105 degrees C), a wear rate higher than PMMA was found, and failure was dominated by fiber delamination. In the more completely processed samples (122 degrees C < or = T < or = 150 degrees C), wear rates were equivalent to or better than PMMA, and smoother and more homogenous wear was noted in wear tracks. Fatigue cracks were prominent at higher processing temperatures or when the wear pin was riding orthogonal to fibers. Wear particles were collected and examined. Wear particle diameter and aspect ratio showed no correlation to processing temperature, but were similar to particles retrieved from human tissue samples.

In vitro and in vivo biological responses to a novel radiopacifying agent for bone cement

Iodixanol (IDX) and iohexol (IHX) have been investigated as possible radiopacification agents for polymethylmethacrylate (PMMA) bone cement, to replace the currently used barium sulphate and zirconia. IDX and IHX are both water-soluble iodine-based contrast media and for the last 20 years have been used extensively in clinical diagnostic procedures such as contrast media enhanced computed tomography, angiography and urography. One of the major reasons to remove the current radiopacifying agents is their well-documented cytotoxicity and their potential to increase bone resorption. Using in vitro bone resorption assays, the effect of PMMA particles plus IDX or IHX to induce osteoclast formation and lacunar resorption on dentine slices has been investigated. These responses have been compared with the in vitro response to PMMA particles containing the conventional radiopacifying agents, that is, barium sulphate and zirconia. In parallel, the in vivo reaction, in terms of new bone formation, to particles of these materials has been tested using a bone harvest chamber in rabbit tibiae. In vitro cell culture showed that PMMA containing IHX resulted in significantly less bone resorption than PMMA containing the conventional opacifiers. In vivo testing, however, showed no significant differences between the amounts of new bone formed around cement samples containing the two iodine-based opacifying agents in particulate form, although both led to fewer inflammatory cells than particles of PMMA containing zirconia. Our results suggest that a non-ionic radiopacifier could be considered as an alternative to the conventional radiopacifying agents used in biomaterials in orthopaedic surgery.