Macrophage exposure to polymethyl methacrylate leads to mediator release and injury

Comparative Evaluation of Two Glass Polyalkenoate Cements: An In Vivo Pilot Study Using a Sheep Model

Poly(methyl methacrylate) (PMMA) is used to manage bone loss in revision total knee arthroplasty (rTKA). However, the application of PMMA has been associated with complications such as volumetric shrinkage, necrosis, wear debris, and loosening. Glass polyalkenoate cements (GPCs) have potential bone cementation applications. Unlike PMMA, GPC does not undergo volumetric shrinkage, adheres chemically to bone, and does not undergo an exothermic setting reaction. In this study, two different compositions of GPCs (GPCA and GPCB), based on the patented glass system SiO₂-CaO-SrO-P₂O₅-Ta₂O₅, were investigated. Working and setting times, pH, ion release, compressive strength, and cytotoxicity of each composition were assessed, and based on the results of these tests, three sets of samples from GPCA were implanted into the distal femur and proximal tibia of three sheep (alongside PMMA as control). Clinical CT scans and micro-CT images obtained at 0, 6, and 12 weeks revealed the varied radiological responses of sheep bone to GPCA. One GPCA sample (implanted in the sheep for 12 weeks) was characterized with no bone resorption. Furthermore, a continuous bone-cement interface was observed in the CT images of this sample. The other implanted GPCA showed a thin radiolucent border at six weeks, indicating some bone resorption occurred. The third sample showed extensive bone resorption at both six and 12 weeks. Possible speculative factors that might be involved in the varied response can be: excessive Zn²⁺ ion release, low pH, mixing variability, and difficulty in inserting the samples into different parts of the sheep bone.

ASIA syndrome symptoms induced by gluteal biopolymer injections: Case-series and narrative review

Background

The number of plastic surgery procedures have been rising in the last few years. The morbi-mortality due to illegal use of biopolymers is a public health problem. One of the clinical consequences, foreign body modelling reaction, may be a precursor of ASIA (Autoimmune/Inflammatory disease induced by adjuvants) syndrome.The objective of this article is to present a case-series study of patients who developed ASIA syndrome following gluteal injection with biopolymers and emphasize the importance of toxic exposure in triggering autoimmune responses. A surgical technique used on some of the patients in the study is described.

Methods

A group of thirteen patients, diagnosed with foreign body modelling reaction, who developed ASIA syndrome confirmed by approved criteria was followed between May 2016 and May 2018. The "Butterfly Wings Technique," a new surgical procedure for patients who have medium to severe compromise, was used on five of them.A narrative literature review was done to look for subjects with ASIA syndrome and gluteal biopolymer infiltration.

Results

All the patients in the present case-series with foreign body modelling reaction developed ASIA syndrome. Some of them had a background of familial autoimmunity. Five of the patients were surgically treated and saw a clinical improvement after the extraction of the biopolymer with the proposed technique.The narrative literature review identified 7 articles related to the disease through the database search.

Conclusions

We suggest that foreign body modelling reaction should be considered a precursor to ASIA syndrome. New research projects will be needed in the future to evaluate the factors that determine when ASIA syndrome is triggered in a patient with this reaction.

Calcium sulfate-containing glass polyalkenoate cement for revision total knee arthroplasty fixation

Poly(methyl methacrylate) (PMMA) bone cement is used as a minor void filler in revision total knee arthroplasty (rTKA). The application of PMMA is indicated only for peripheral bone defects with less than 5 mm depth and that cover less than 50% of the bone surface. Treating bone defects with PMMA results in complications as a result of volumetric shrinkage, bone necrosis, and aseptic loosening. These concerns have driven the development of alternative bone cements. We report here on novel modified glass polyalkenoate cements (mGPCs) containing 1, 5 and 15 wt% calcium sulfate (CaSO₄ ) and how the modified cements' properties compare to those of PMMA used in rTKA. CaSO₄ is incorporated into the mGPC to improve both osteoconductivity and bioresorbability. The results confirm that the incorporation of CaSO₄ into mGPCs decreases the setting time and increases release of therapeutic ions such as Ca²⁺ and Zn²⁺ over 30 days of maturation in deionized (DI) water. Moreover, the compressive strength for 5 and 15 wt% CaSO₄ addition increased to over 30 MPa after 30 day maturation. Although the overall initial compressive strength of the mGPC (~ 30 MPa) is less than PMMA (~ 95 MPa), the compressive strength of mGPC is closer to that of cancellous bone (~ 1.2-7.8 MPa). CaSO₄ addition did not affect biaxial flexural strength. Fourier transform infrared analysis indicated no cross-linking between CaSO₄ and the GPC after 30 days. in vivo tests are required to determine the effects the modified GPCs as alternative on PMMA in rTKA.

Related Biological Research in the Interface between Bone Cement and Bone after Percutaneous Vertebroplasty

Percutaneous vertebroplasty (PVP) is widely used in the treatment of painful osteoporotic vertebral compression fractures with the injection of PMMA cement, and the controversy for PMMA damage to the osteoporotic bone tissue and to affect the fractures repairing never stops. 72 old female rabbits, each age 3.0~3.5 y, rabbits were assigned randomly to two groups of thirty-six each; PMMA cement were injected into vertebral body in rabbits via mimic PVP, sacrificed at 1 h, 24 h, 3 d, 7 d, 4 w, and 12 w. The expression VEGF and collagen type I, the tissue response, and repair reaction in the interface between PMMA and bone tissue were observed dynamically with RT-PCR and western blot technique; the osteocalcin expression were studied by immunohistochemistry. Compared with the control group, the expression of collagen I increased at 1 hour and was higher from 24 h to 3 d. From 4 weeks to 12 weeks after injection of PMMA. The expression of VEGF decreased at 1 hour and 24 hours, significantly increased at 3 days, decreased once again at 7 days, then increased significantly at 4-12 weeks. The osteocalcin expression continued to increase during 4 to 12 week. PMMA would not cause local bone permanent necrosis, and interface injury repairing cycle could be prolonged in a vertebroplasty.

Periprosthetic femoral fracture due to biodegradable cement restrictor

Biodegradable materials are gaining popularity in orthopedics. Despite finding use in different areas of orthopedic surgery, they do not come without disadvantages such as foreign body reactions, granulomatous reactions, and sterile sinus formation in bone. We report a case of a patient who sustained a periprosthetic fracture seen at the tip of a cemented femoral stem approximately 5 years postsurgery, secondary to the use of a biodegradable cement restrictor. There was no evidence of trauma or fall on the affected hip. To our knowledge, there has been no previous report describing periprosthetic fracture at the tip of cemented femoral stem secondary to the use of a biodegradable cement restrictor. We suggest abandoning use of these materials while performing cemented hip arthroplasties.

Enhancement of osteoblast differentiation that is inhibited by titanium particles through inactivation of NFATc1 by VIVIT peptide

Bone formation, which is inhibited by particulate wear debris, is a pathological factor that contributes to periprosthetic osteolysis. Although the nuclear factor of activated T cells c1 (NFATc1) is known to be involved in osteoblast differentiation, and its effect on osteoblasts in response to wear particles remains unclear. In this study, we investigated the role of NFATc1 in the regulation of osteoblastic differentiation of rat calvaria (RC) cells (a cell-culture model comprising many osteoprogenitors) that were challenged with titanium (Ti) particles. The results showed that the Ti particles inhibited osteoblastic differentiation and mineralization of RC cells. NFATc1 plays a critical role in the Ti-particle inhibition process of the osteoblastic differentiation in RC cells. Inactivation of NFATc1 by the 11R-VIVIT peptide potently enhanced osteoblast differentiation and mineralization inhibition by the Ti particles. The 11R-VIVIT peptide does not have a toxic effect on the RC cells. On the basis of these data, we conclude that inactivation of NFATc1 by the 11R-VIVIT peptide may provide a promising therapeutic target for the treatment of periprosthetic osteolysis by increasing bone formation.

Biofunctionalized magnetic hydrogel nanospheres of magnetite and kappa-carrageenan

Magnetic hydrogel kappa-carrageenan nanospheres were successfully prepared via water-in-oil (w/o) microemulsions combined with thermally induced gelation of the polysaccharide. The size of the nanospheres (an average diameter of about 50 and 75 nm) was modulated by varying the concentration of surfactant. The nanospheres contained superparamagnetic magnetite nanoparticles (average diameter 8 nm), previously prepared by co-precipitation within the biopolymer. Carboxyl groups, at a concentration of about 4 mmol g(-1), were successfully grafted at the surface of these magnetic nanospheres via carboxymethylation of the kappa-carrageenan. The carboxylated nanospheres were shown to be thermo-sensitive in the 37-45 degrees C temperature range, indicating their potential as thermally controlled delivery systems for drugs and/or magnetic particles at physiological temperatures. Finally, preliminary results have been obtained for IgG antibody conjugation of the carboxylated nanospheres and the potential of these systems for bio-applications is discussed.

Targeted lipid-coated nanoparticles: delivery of tumor necrosis factor-functionalized particles to tumor cells

Polymeric nanoparticles displaying tumor necrosis factor on their surface (TNF nanocytes) are useful carrier systems capable of mimicking the bioactivity of membrane-bound TNF. Thus, TNF nanocytes are potent activators of TNF receptor 1 and 2 leading to a striking enhancement of apoptosis. However, in vivo applications are hampered by potential systemic toxicity. Here, using TNF nanocytes as a model system, we developed a procedure to generate targeted lipid-coated particles (TLP) in which TNF activity is shielded. The TLPs generated here are composed of an inner single-chain TNF (scTNF)-functionalized, polymeric nanoparticle core surrounded by a lipid coat endowed with polyethylene glycol (PEG) for sterical stabilization and a single-chain Fv (scFv) fragment for targeting. Using a scFv directed against the tumor stroma marker fibroblast activation protein (FAP) we show that TLP and scTNF-TLP specifically bind to FAP-expressing, but not to FAP-negative cells. Lipid coating strongly reduced nonspecific binding of particles and scTNF-mediated cytotoxicity towards FAP-negative cells. In contrast, an increased cytotoxicity of TLP was observed for FAP-positive cells. Thus, through liposome encapsulation, nanoparticles carrying bioactive molecules, which are subject to nonselective uptake and activity towards various cells and tissues, can be converted into target cell-specific composite particles exhibiting a selective activity towards antigen-positive target cells. Besides safe and targeted delivery of death ligands such as TNF, TLP should be suitable for various diagnostic and therapeutic applications, which benefit from a targeted delivery of reagents embedded into the particle core or displayed on the core particle surface.

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.

Absence of lymphatics at the bone-implant interface: implications for periprosthetic osteolysis

BACKGROUND

Wear particles, found at the bone-implant interface surrounding a loose prosthesis, are commonly phagocytosed by macrophages. Wear particles and wear particle-containing macrophages are also found in regional lymph nodes draining arthroplasty tissues. The means by which wear particles are transported from arthroplasty tissues to lymph nodes is uncertain, as the presence or absence of lymphatic vessels in periprosthetic tissues has not been established.

METHODS

We determined immunophenotypic expression of LYVE-1 and podoplanin, two highly specific lymphatic endothelial cell markers, in the hip arthroplasty pseudocapsule surrounding the false joint and the bone-implant interface of the femoral and acetabular pseu-domembrane.

RESULTS

LYVE-1+/podoplanin+ lymphatic vessels were not identified in the pseudomembrane but were found in the pseudocapsule. Normal bone did not contain lymphatic vessels.

INTERPRETATION

Our findings suggest that the wear particles shed at the bone-implant interface are not transported to draining lymph nodes by lymphatics directly from the pseudomembrane, but via the pseudocapsule. The absence of a lymphatic clearance mechanism may contribute to accumulation of wear particles at the bone-implant interface and promote periprosthetic osteolysis through stimulation of osteoclast formation and activity.

Effects of synovial fluid from aseptic prosthesis loosening on collagen production in osteoblasts

Synovial fluid from a loose prosthesis may act as a vehicle for factors that regulate bone turnover. The effect of such synovial fluid on osteoblasts has been studied. Synovial fluid obtained from patients who underwent revision hip arthroplasty because of aseptic prosthesis loosening was studied regarding the effect on protein synthesis, procollagen I mRNA expression, the secretion of procollagen I carboxyterminal propeptide (PICP) and osteocalcin in MG63 osteoblasts. Protein synthesis was increased and procollagen I mRNA expression was decreased by synovial fluid from patients with prosthesis loosening. Synovial fluid stimulated the total PICP in cell medium, but there was no change after correction for cell protein content in the cells. Synovial fluid in patients with prosthesis loosening has a general stimulatory effect on collagen formation and osteoblast proliferation because of a stimulatory effect on cell growth. Aseptic prosthesis loosening may be associated with an increase in bone formation.

Kinetics of polymethylmethacrylate particle-induced inhibition of osteoprogenitor differentiation and proliferation

Periprosthetic bone loss induced by implant wear debris may be a combined effect of osteolysis and reduced bone formation resulting from particle-induced suppression of osteoprogenitor differentiation. This study investigated the time-dependent effects of polymethylmethacrylate (PMMA) particles on the osteogenic capability of bone marrow osteoprogenitor cells during the early phase of differentiation. Murine bone marrow cells were challenged with PMMA particles (0.30% v/v) on the first day of growth in osteogenic medium. Particles were removed from culture after 1, 3, and 5 days, respectively, after which cell growth in osteogenic medium was continued until the 15th day. Bone marrow osteoprogenitor cells exposed to particles during the first 5 days of differentiation showed complete, irreversible inhibition of proliferation, alkaline phosphatase expression, and mineralization. Osteoprogenitors exposed to particles for more than 5 days showed the same degree of inhibition, while those exposed to particles for less than 5 days showed a diminished inhibitory response. Conditioned medium from particle-treated cells did not suppress osteogenic development, demonstrating that suppression of osteogenesis was not due to secreted inhibitory factors. This study has shown that the early phase of osteoprogenitor differentiation is a crucial time period during which exposure to PMMA particles causes irreversible inhibition of osteogenesis.

Effects of titanium particle size on osteoblast functions in vitro and in vivo

The formation of titanium (Ti)-wear particles during the lifetime of an implant is believed to be a major component of loosening due to debris-induced changes in bone cell function. Radiographic evidence indicates a loss of fixation at the implant-bone interface, and we believe that the accumulation of Ti particles may act on the bone-remodeling process and impact both long- and short-term implant-fixation strengths. To determine the effects of various sizes of the Ti particles on osteoblast function in vivo, we measured the loss of integration strength around Ti-pin implants inserted into a rat tibia in conjunction with Ti particles from one of four size-groups. Implant integration is mediated primarily by osteoblast adhesion/focal contact pattern, viability, proliferation and differentiation, and osteoclast recruitment at the implant site in vivo. This study demonstrates the significant attenuation of osteoblast function concurrent with increased expression of receptor activator of nuclear factor kappaB ligand (RANKL), a dominant signal for osteoclast recruitment, which is regulated differentially, depending on the size of the Ti particle. Zymography studies have also demonstrated increased activities of matrix metalloproteinases (MMP) 2 and 9 in cells exposed to larger Ti particles. In summary, all particles have adverse effects on osteoblast function, resulting in decreased bone formation and integration, but different mechanisms are elicited by particles of different sizes.

A bioresorbable calcium phosphate delivery system with teicoplanin for treating MRSA osteomyelitis

To assess the effectiveness of calcium phosphate as a delivery system of teicoplanin, methicillin-resistant Staphylococcus aureus osteomyelitis was induced in 36 rabbits. Osteomyelitis was induced by inoculating 10 cfu of methicillin-resistant Staphylococcus aureus isolate into a 2-mm hole at the upper 1/3 of the femur for 3 weeks, when all animals had reoperations, and calcium phosphate cement with 3% teicoplanin was implanted. Animals were divided into six groups of six animals each, sacrificed at Weeks 1, 2, 3, 4, 5, and 6, respectively, after implantation. One rabbit in each group was used as a control. Substantial clinical improvement of the rabbits was observed after implantation, accompanied with sterile cultures of bone after the second week of treatment. Throughout the same period, 10 to 10 cfu/g of methicillin-resistant Staphylococcus aureus isolate was cultured from the control samples. Bacterial eradication signified a considerable decrease of the total histologic scores of osteomyelitis compared with controls, accompanied with newly growing host bone. The calcium phosphate with teicoplanin delivery system seems promising for treatment of bone infection attributable to methicillin-resistant Staphylococcus aureus. In addition, this mixture allows filling of bone defects by new host bone.

The Use of Bone Cement Induces an Increase in Serum Astroglial S-100B Protein in Patients Undergoing Total Knee Arthroplasty

Cerebral microemboli can occur during arthroplasty with the use of bone cement. Astroglial S-100B protein is a sensitive marker of cerebral damage. Therefore, we designed this study to determine the effect of bone cement on the brain by investigating serum levels of S-100B protein in patients undergoing bone surgery with or without bone cement. Fourteen patients undergoing knee arthroplasty (n = 7) or reamed intramedullary nailing for tibial fracture (n = 7) requiring a pneumatic tourniquet were enrolled in this study. Bone cement containing polymethyl methacrylate and methyl methacrylate was used for every patient undergoing knee arthroplasty. Serum samples were obtained from venous blood before the induction of general anesthesia, 15 min after deflation of a pneumatic tourniquet, and 3 days after the operation. The serum level of S-100B protein was significantly increased 15 min after a pneumatic tourniquet deflation in the knee arthroplasty group compared with the tibial fracture group (0.41 and 0.08 ng/mL, respectively; P < 0.05). In all patients studied, no neurological abnormalities were noted in the postoperative period. These results suggest that, in patients undergoing knee arthroplasty, bone cement may transiently induce astroglial injury, although it does not alter neurological outcome.

IMPLICATIONS

Serum S-100B protein was significantly increased 15 min after a pneumatic tourniquet deflation in patients undergoing knee arthroplasty with bone cement, but not in those undergoing reamed intramedullary nailing for tibial fracture without bone cement. These results suggest that bone cement may transiently induce astroglial injury.

Treatment of osteomyelitis with local antibiotics delivered via bioabsorbable polymer

The purpose of the current study was to show the efficacy and safety of an absorbable polymer (polycaprolactone) as an antibiotic delivery vehicle for treatment of osteomyelitis. An intramedullary osteomyelitis was induced in the femur of adult rabbits by Staphylococcus aureus inoculation after use of a sclerosing agent, and then treatment was done with intramedullary irrigation and implantation of a rod made of polycaprolactone, polycaprolactone plus 6% tobramycin, or polymethylmethacrylate plus 6% tobramycin. A control group received irrigation only. At defined intervals, the animals were euthanized and culture of the inoculated site was done. In addition, histologic sections of body tissues were made to look for signs of systemic toxicity of the implant. After 4 weeks of treatment, a statistically significant difference was found between the animals that were treated with irrigation alone and the animals that were treated with antibiotic-laden rods of polycaprolactone or polymethylmethacrylate. There was no difference between the antibiotic rod types. No histologic evidence of toxicity was found. Bioabsorbable rods of polycaprolactone are a safe and effective means of antibiotic delivery for treatment of osteomyelitis.

Particles and periimplant bone resorption

There is compelling evidence that the most important factor in late periprosthetic bone resorption is an inflammatory reaction to debris. Based on results from several laboratories, it seems likely that opsonized particles activate the macrophage nuclear factor-kappa B signal transduction system via membrane receptors, leading to release of tumor necrosis factor-alpha and other cytokines and growth factors. Tumor necrosis factor stimulates osteoblasts to release cytokines that recruit inflammatory cells and osteoclast precursors to the site and promote the differentiation of early osteoclasts. Tumor necrosis factor influences fibroblasts to release tissue metalloproteinases, and induces c-src in osteoclast precursors, the expression of which is necessary for additional bone resorption. Phagocytosis of debris by osteoblasts may reduce collagen synthesis, whereas phagocytosis by fibroblasts may induce chemokines that amplify inflammation. Bone has been partially protected from particle-induced resorption in animals with defective or inhibited tumor necrosis factor or nuclear factor-kappa B signaling. Many aspects of this inflammatory reaction require clarification, including identifying the factors that influence variability among patients, and testing the importance of costimulatory molecules such as bacterial endotoxin, but the fundamental importance of particles in most cases of aseptic loosening seems certain.

Osteosarcoma of the proximal humerus: long-term results with limb-sparing surgery

The purpose of the current study was to analyze the long-term oncologic and functional results and complications associated with limb-sparing surgery and endoprosthetic reconstruction for 23 patients with osteosarcoma of the proximal humerus. There was one Stage IIA lesion, 18 Stage IIB lesions, and four Stage III lesions in this study group. Twenty-two patients were treated with an extraarticular resection that included the deltoid and rotator cuff and one patient was treated with an intraarticular resection that spared the shoulder abductors. In all these patients, the proximal humerus was reconstructed with a cemented endoprosthetic replacement that was stabilized via a technique of static suspension (Dacron tapes) and dynamic suspension (muscle transfers). At latest followup (median, 10 years), 15 patients (65%) were alive without evidence of disease. There were no local recurrences. Prosthetic survival was 100% for the 15 survivors. The Musculoskeletal Tumor Society upper extremity functional score ranged from 24 to 27 (80%-90%). All shoulders were stable and pain-free. Elbow and hand function were preserved in all patients. The most common complication was a transient neurapraxia (n = 8). En bloc extraarticular resection and endoprosthetic reconstruction is a safe and reliable method of limb-sparing surgery for patients with high-grade extracompartmental osteosarcoma of the proximal humerus.

The effect of particle wear debris on NFkappaB activation and pro-inflammatory cytokine release in differentiated THP-1 cells

Orthopedic wear debris has been thought to be an important factor associated with osteolysis and loosening of total joint arthroplasties. Previous in vitro studies have reported that particles of wear debris induce the release of pro-inflammatory cytokines and other inflammatory mediators from macrophages and other cells. Several recent investigations, however, have suggested that the wear particles themselves may not be primarily responsible for the inflammatory cellular responses, but that the observed cytokine release in vitro may be caused by endotoxin adsorbed to commercially available particle preparations. The intracellular pathways involved in macrophage signal transduction also are poorly understood. The purposes of this study are to use isolated orthopedic wear debris particles to evaluate pro-inflammatory cytokine release and nuclear factor kappa B (NFkappaB) activation from macrophages. Cells from human monocyte/macrophage cell line (THP-1) were differentiated and incubated with particles of debris that had been isolated from a failed human total hip arthroplasty. The titanium-alloy particles did not evoke release of TNF-alpha or IL-1beta whereas lipopolysaccharide (LPS) or LPS-treated debris particles induced both TNF-alpha and IL-1beta. LPS-treated particles, but not particles alone, stimulated NFkappaB activation. Our results suggest that at the concentrations tested in this study, endotoxin-free wear debris particles may not themselves initiate inflammatory cellular responses in differentiated THP-1 cells. It is unclear whether adsorbed endotoxin is clinically associated with osteolysis and/or loosening in total joint arthroplasties, but several factors, including adsorbed endotoxin, need to be investigated to explore the cellular responses responsible for osteolysis and/or loosening.

Biochemical analyses of human macrophages activated by polyethylene particles retrieved from interface membranes after failed total hip arthroplasty

Human monocyte/macrophages (M/M) were exposed to retrieved ultra-high molecular weight polyethylene (UHMWPE) particles isolated after enzymatic digestion of revision total hip arthroplasty interface membrane tissue samples. The cellular response of human M/M to UHMWPE was compared with the response of these cells to latex particles and culture medium alone. We incubated macrophages in good contact with polyethylene particles using an inverted culture system. Chamber slides on which macrophages were attached were filled with polyethylene particle suspension and sealed with plastic sheets. After the slides were inverted, the incubation was completed. Retrieved UHMWPE particulate debris stimulated human M/M to secrete interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha. Human M/M exposed to retrieved UHMWPE particles secreted significantly more IL-1beta, IL-6, and TNF-alpha compared with M/M exposed to latex particles (P<.05).

Elution characteristics of tobramycin from polycaprolactone in a rabbit model

This study investigated the elution characteristics of tobramycin from polycaprolactone, a bioabsorbable polymer, in a rabbit model. Sixty rabbits were divided into two groups. Group 1 had polycaprolactone rods impregnated with 6% tobramycin surgically implanted into the proximal femoral intramedullary canal. Group 2 received polymethylmethacrylate rods of like size, shape, and antibiotic concentration. Serum and urine samples were obtained, and tobramycin levels were determined via fluorescent immunosorbent assay. Rabbits were sacrificed as long as 56 days after surgery. Local bone tobramycin concentration was determined using the agar diffusion method. Polycaprolactone delivered a significantly higher peak bone concentration of tobramycin (22.4 microg/mL) than did polymethylmethacrylate (13.59 microg/mL). Polycaprolactone also had a more gradual decrease in local tobramycin concentration than did polymethylmethacrylate. Neither polycaprolactone nor polymethylmethacrylate yielded consistently detectable (> 0.1 microg/mL) serum tobramycin levels. Urine concentrations mirrored those seen in bone, with polycaprolactone achieving significantly higher tobramycin concentrations than did polymethylmethacrylate. Polycaprolactone had superior elution characteristics compared with polymethylmethacrylate in this lapine model, suggesting that polycaprolactone might be a promising local antibiotic delivery vehicle for the treatment of osteomyelitis.

In vitro elution of tobramycin from bioabsorbable polycaprolactone beads

OBJECTIVES

To compare the in vitro elution characteristics of tobramycin impregnated beads made of polycaprolactone (PCL) and polymethylmethacrylate (PMMA).

DESIGN

Six-millimeter PCL and PMMA beads with 6% tobramycin were formed and placed in phosphate-buffered saline or newborn calf serum and incubated at room temperature or 37 degrees C. Aliquots were taken at intervals for eight weeks. Tobramycin levels were determined by fluorescent assay and antibacterial efficacy was assessed by measuring the zones of inhibition against Staphylococcus aureus and Pseudomonas aeruginosa on agar diffusion plates.

RESULTS

Tobramycin elution rates at room temperature were similar up to three weeks. At three weeks, elution rates from PCL beads were twice those from PMMA beads, and at eight weeks, elution from PCL was quadruple that from PMMA. At 37 degrees C, tobramycin elution rates from PCL were eight times greater than those from PMMA by eight weeks. Total tobramycin eluted from PCL beads was 38.9% and 20% in PMMA beads. All samples showed bacteriostatic activity against S. aureus and P. aeruginosa at eight weeks.

CONCLUSIONS

These in vitro results show that PCL has superior antibiotic elution characteristics compared with PMMA, and this may translate into a more effective antibiotic delivery vehicle. In addition, PCL is a bioabsorbable polymer, which may decrease the need for a second surgical procedure to remove retained beads.

Significance of the type and the size of biomaterial particles on phagocytosis and tissue distribution

Particulates generated by dissolution or wear of injected or implanted biomaterials may migrate into various tissues and lead to activation of the host's inflammatory and immune responses. The purpose of this study was to evaluate the relevance of size and chemical composition of biomaterial particles on the pattern of particle distribution in host tissues. Adult female B6C3F1 mice were injected intraperitoneally with polymethylmethacrylate (PMMA) particles (size 1.4 and 6.4 micro in diameter) and polystyrene (PS) particles (size 1.2, 5.2, and 12.5 micro in diameter), and euthanized 1, 7, and 28 days later. Peritoneal exudate cells (PECs) were collected and the number of cells and percentage of actively phagocytic cells was determined. Macroscopic examination of the tissues in the peritoneal cavity peritoneum revealed visible accumulations of the colored PS particles in the adipose tissues adjacent to the spleen and pancreas, and caudal to the stomach. Distribution of the PS particles appeared similar regardless of the particle size. The location of PMMA particles, which were not colored, could not be distinguished from host tissue and could not be observed in this manner. Intensive phagocytosis of the small and medium sized particles by peritoneal macrophages was observed on day 1, and was diminishing by day 7 after injection. The largest PS particles (12.5 micro) were not engulfed by the peritoneal macrophages. Histological examination of the spleen, lymph nodes, and the adjacent adipose tissues revealed a marked difference in the deposition patterns of the two polymers used. PS particles, regardless of size, were accumulated primarily in the white adipose tissues adjacent to the spleen and pancreas gland, but very few particles were observed in the splenic tissue. On the other hand, mice injected with PMMA particles of either size had enlarged and activated spleens with marked deposits of particles in the red pulp. These results indicate that these PS and PMMA particles induce different patterns and intensities of the host response. The chemical makeup of the particle is more important in the distribution pattern than is the size of the particle.

Effect of polymethylmethacrylate particles on mature bone in the optical bone chamber

Reaction of mature bone and its vasculature to 3.33 +/- 0.19 microm polymethylmethacrylate (PMMA) particles at a concentration of 2.5 x 10(8)/cc was measured using optical bone chamber implant intravital microscopy. Twelve adult female New Zealand White rabbits were divided into six receiving Healon alone (controls) and six receiving Healon plus PMMA. The particles were introduced to the bone chamber compartment after removing its overlying optical element, which was immediately reinstalled. Reaction was monitored weekly over a 6-week period using video and photographic imaging. Bone was labeled before treatment with oxytetracycline and after treatment with alizarin complexone. Perfusing blood was labeled with fluorescein isothiocyanate dextran-70 kDa (FITC-D70). Parameters measured were net bone resorption, from black and white images, bone turnover, from color images, vascularity, and average vessel caliber. Neither bone turnover nor vessel caliber were significantly affected at the p < or = 0.050 level over time. In contrast, bone resorption was significantly greater and vascularity significantly less in the presence of PMMA. It was inferred that any differences in bone turnover were masked by resorption of new bone. It was concluded that the lack of a PMMA effect on average vessel caliber meant that the vascularity effects were not due to angiogenesis, but to vessel recruitment (or its opposite), an effect more consistent with inflammation than repair. The lack of vascularity increase in PMMA-treated compartments also suggested that increased resorption was a local phenomenon, because blood supply had not increased to provide the extra osteoclasts required for observed net bone loss.

Influence of particle size in the effect of polyethylene on human osteoblastic cells

The influence of two different sizes of polyethylene particles (< 30 and 20-200 microm) on osteoblastic function has been studied in primary human bone cell cultures. Cells were obtained from trabecular bone fragments of patients undergoing knee reconstructive surgery. On reaching confluency, cells were subcultured in three flasks: < 30 microm polyethylene particles were added to the first flask, 20-200 microm particles to the second flask and none to the third flask, which was the control. The resulting subcultures were incubated until confluence. Osteoblastic function was evaluated by assaying the secretion of osteocalcin, alkaline phosphatase, and C-terminal type I procollagen (PICP), with or without 1.25(OH)2D3 stimulation in the cell-conditioned medium. Adding < 30 microm polyethylene particles to these osteoblastic cell cultures increased the levels of osteocalcin secreted after 1,25(OH)2D3 stimulation. Treating stimulated or basal osteoblastic cultures with either polyethylene particle size did not affect alkaline phosphatase secretion. However, the addition of <30 microm polyethylene particles decreased PICP levels in the basal and stimulated cultures. A parallel series of osteoblastic cultures was treated with < 30 microm polyethylene particles and stimulated or not with 1,25(OH)2D3 to determine the effect on osteocalcin mRNA expression using RT-PCR amplification. Polyethylene particle-treated cultures had higher osteocalcin mRNA expression regardless of whether they had been stimulated with 1,25(OH)2D3 or not. We conclude that particle size affects the influence of polyethylene on osteoblastic function markers. Particles with a diameter of less than 30 microm increase osteocalcin expression and secretion.

Effect of anti-inflammatory medication on monocyte response to titanium particles

Cytokines produced by macrophages in the periprosthetic membranes surrounding joint replacements have been implicated as causal agents in osteolysis and prosthetic loosening. The present study characterizes the response of human peripheral blood monocytes to titanium particles. Monocytes were obtained from donated blood and were cultured in the presence of different-sized titanium particles. Exposure to titanium-aluminum-vanadium particles significantly changed the release of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-1 (IL-1), whereas there was no significant effect on the release of prostaglandin E(2) (PGE(2)). When monocytes were cultured with particles, the titanium alloy particles induced significantly more release of TNF-alpha and less IL-1 secretion. Ciprofloxacin inhibited production of TNF-alpha, IL-6, IL-1, and PGE(2) in human monocytes exposed to titanium particles. In contrast to ciprofloxacin, indomethacin was not a potent inhibitor of TNF-alpha production but potentiated IL-6 production in titanium-stimulated monocytes. Indomethacin had no effect on the production of IL-1 and was a potent inhibitor of PGE(2) production in titanium-stimulated monocytes. Pentoxifylline had an inhibitor effect on TNF-alpha production in titanium-stimulated monocytes. Pentoxifylline potentiated IL-6 and IL-1 production in monocytes exposed to titanium particles and had a biphasic effect on the PGE(2) production. The results of this study support our hypothesis that human monocytes release bone resorption mediators after in vitro exposure to TiAlV alloy particles. The results also demonstrate the differences of bone-resorbing mediators in response to different wear particle size. The pharmacologic agents (ciprofloxacin, pentoxifylline, and indomethacin) that can modulate the release of bone resorbing mediators such as PGE(2), TNF-alpha, IL-1, and IL-6 release from human monocytes. The results help to elucidate the differences in cellular response to wear particles but may not be directly transposed to the human situation.

Clodronate prevents prosthetic migration: a randomized radiostereometric study of 50 total knee patients

In a double-blind study, we randomized 50 patients to receive peroral clodronate medication or placebo from 3 weeks before until 6 months after a total knee replacement with a cemented NexGen implant. Migration of the tibial components was measured by radiostereometry at 1 year. Clodronate reduced prosthetic migration, as measured by maximum total point motion, from 0.40 mm to 0.29 mm (p = 0.01). This confirms that the early postoperative migration is related to bone resorption and thus the biology of the bone bed. Since early migration is related to late loosening, 6 months of clodronate medication might reduce the risk of loosening.

Wear particle diffusion and tissue differentiation in TKA implant fibrous interfaces

In the context of mechanical loosening, we studied the hypothesis that wear-particle migration in the fibrous membrane under tibial plateaus after total knee arthroplasty can be explained by the pumping effects of the interstitial fluid in the tissue. Further, as a secondary objective we investigated the possibility that interface-tissue differentiation is influenced by interstitial fluid flow and strain, as mechanical effects of interface motions. For comparative reasons, we analyzed a previously published simplified two-dimensional finite-element model, this time assuming biphasic tissue properties. We wanted to determine hydrostatic pressure and flow velocities in the fluid phase, in addition to stresses and strains, for time-dependent loading of the plateau. We found that fluid flow in the interface was extremely slow, except in the periphery. Hence, loosening due to particle-induced bone resorption appears improbable. The results, however, do support the idea that particles migrate with fluid flow, when such flow occurs. Where fibrous tissue tends to be prominent in reality, the fluid is repeatedly extruded and reabsorbed in the model. Where these values are low, fibrocartilage is commonly found. When material properties were varied to subsequently represent fibrocartilage and two stages of mineralization, the strains and fluid velocities is reduced. Fluid pressure, however, did not change. Our results refute the hypothesis that wear particles are pumped through the interface tissue below a TKA but support the hypothesis that interface tissue type and loosening processes are influenced by mechanical tissue variables such as tissue strain and interstitial fluid velocity.

Synovial fluid from loose hip arthroplasties inhibits human osteoblasts

Aseptic loosening of prosthetic components in patients who have undergone total hip arthroplasty is a major clinical problem. Earlier studies on this topic have focused mainly on different aspects of bone resorption. The current study investigated the influence of synovial fluid from patients who underwent revision surgery because of aseptic loosening and synovial fluid from patients with osteoarthritis on the proliferation of primary cultures of human osteoblasts. Incubation of cells with 10% synovial fluid from patients who had revision surgery significantly inhibited [3H]thymidine incorporation into deoxyribonucleic acid in human osteoblasts compared with control conditions, whereas 10% synovial fluid from patients with osteoarthritis had a significant stimulatory effect. These findings correlate well with clinical features seen in these diseases, such as increased net bone resorption around the prosthesis in patients with loosening, and increased periarticular bone formation in patients with osteoarthritis.

The influence of hydroxyapatite particles on osteoclast cell activities

Aseptic loosening after total joint arthroplasty is a major problem in orthopedic surgery. Small particles from material wear have been reported as the main cause of implant failure. For this reason, investigation into possible wear particles from the materials used in the implant may lead to longevity after arthroplasty. Hydroxyapatite (HA) has been extensively investigated and reported as an excellent biomaterial with excellent biocompatibility. In this study, we used an in vitro osteoblast/osteoclast model to test the biocompatibility of various-sized HA particles. Primary osteoclasts/osteoblasts were co-cultured with different-sized HA particles (0.5-3.0 microm, 37-53 microm, 177-205 microm, and 420-841 microm) for 3 h, 1 day, 3 days, and 7 days. Cellular responses to the HA particles were evaluated by changes in cell counts and the secretion of transforming growth factor (TGF-beta1), alkaline phosphatase (ALP), tumor necrosis factor (TNF-alpha), prostaglandin (PGE2), and lactate dehydrogenase (LDH) in the supernatant of the culture media. The results showed that osteoblasts/osteoclasts co-cultured with HA particles smaller than 53 microm undergo the most significant changes. Cellular counts significantly decreased, and the changes were more obvious in the osteoblast population. There also was a significant decrease in TGF-beta1 concentration and a significant increase in PGE2 and LDH concentration, but there were no changes in the TNF-alpha or ALP titer. It can be concluded that larger HA particles may be quite compatible with bone cells while smaller-sized HA particles can both activate the osteoclasts and decrease the cell population of the osteoblasts. Justification for the additional expense incurred with the use of hydroxyapatite in primary total hip arthroplasty should be further evaluated.

Failure of partial cementation to achieve implant stability and bone ingrowth: a long-term roentgen stereophotogrammetric study of tibial components

Thirty patients with gonarthrosis were operated on with the PCA primary total knee prosthesis and had the tibial component fixed to the bone by partial cementation. In the first two groups of patients, cementation was by a peripheral rim of high and low-viscosity cement, respectively. In the third group, the pegs were cemented with the low-viscosity cement. Follow-up was performed with use of clinical parameters and roentgen stereophotogrammetric analysis. Clinically, the series was successful apart from a problem with tibial component wear, necessitating revision in five patients. At 8 years, the mean Hospital for Special Surgery score was 81 points. Venn-diagram scores revealed four failures and three acceptable cases; the remaining cases were satisfactory. Apart from one loose patellar component, there was no mechanical loosening. Roentgen stereophotogrammetric analysis showed that the tibial components moved relative to the bone; this indicated fibrous tissue fixation, which was corroborated histologically in two patients. The objective, to achieve bone ingrowth, was thus not successfully met. Radiolucent lines were consistently seen, and their size correlated with the migration as measured by roentgen stereophotogrammetric analysis. Furthermore, five continuously migrating prostheses showed significantly larger radiolucent zones than the prostheses that migrated only initially, and they were less well bonded to the bone at 1 year. In conclusion, partial cementation does not appear to be a way to achieve bone ingrowth in porous-coated implants under load.

Flow cytometric analysis of macrophage response to ceramic and polyethylene particles: effects of size, concentration, and composition

Using the J774 macrophage cell line, we designed an in vitro model to analyze by flow cytometry the effects of size, concentration, and composition of ceramic (Al2O3 and ZrO2) and high density polyethylene (HDP) particles on phagocytosis and cell mortality. Inflammatory mediator (TNF-alpha) also was measured by ELISA. Kinetic studies revealed that phagocytosis of the particles begins very early after cell exposure, increasing with time and particle concentration and reaching a plateau after 15 h. This implies that the optimum period to evaluate cellular response to particulate debris is between 15 and 24 h of incubation. Results also showed that phagocytosis increases with concentration for particles up to 2 microns. For larger particles (up to 4.5 microns), phagocytosis seems to reach a plateau independent of size and concentration, which suggests a saturation of phagocytosis that is most likely dependent on overall particle volume ingested. We did not detect any significant difference in phagocytosis between Al2O3 and ZrO2 at 0.6 microns. Al2O3 seems to be more easily phagocytosed than HDP at the same size (4.5 microns) and concentrations. Cytotoxicity studies revealed that macrophage mortality increases with particle size and concentration for sizes greater than 2 microns. Smaller particles (0.6 microns) cause cell mortality only at higher concentrations (from 1,250 particles per cell), but the mortality is still very low (10%). No significant difference in cell mortality and TNF-alpha release was found between Al2O3 and ZrO2. Effects of Al2O3 and HDP at 4.5 microns were compared by measuring TNF-alpha release. Results showed that TNF-alpha release increases with particle concentrations and is higher with HDP than with Al2O3.

The effects of cobalt chromium upon macrophages

The purpose of this study was to elucidate the mechanisms by which cobalt chromium particulate wear debris contribute to the aseptic loosening of total joint prostheses. Incubation of macrophages with cobalt chromium led to release of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2), but did not lead to release of interleukin-1 beta (IL-1 beta) or interleukin 6 (IL-6). Exposure of macrophages cocultured with osteoblasts to cobalt chromium also led to significant release of TNF-alpha and PGE2, but did not lead to significant IL-6 or IL-1 beta production. The release of PGE2 in the coculture system was greater than that detected when macrophages were exposed to cobalt chromium without the osteoblast contribution. Exposure of radiolabeled calvaria to media from macrophages incubated with cobalt chromium in coculture with osteoblasts led to release of 45Ca. In contrast, exposure of radiolabeled calvaria to media from isolated macrophages incubated with these particles did not result in release of 45Ca. Exposure of macrophages to cobalt chromium was toxic, as reflected by release of the intracellular enzyme lactate dehydrogenase. Macrophages play a role in the initiation of bone resorption at the interface through the phagocytosis of cobalt chromium particles and subsequent release of TNF-alpha and PGE2. The presence of osteoblasts at the interface may be required for amplification of the inflammatory response and ultimately for bone resorption.

Effect of particulate bioactive glass on human synoviocyte cultures

Bioglass is a resorbable glass material that has been shown to induce osteoblast proliferation as well as bone matrix production in vitro. Its physico-chemical properties have been reported to be suitable for use as an implant coating for arthroplasty. However, Bioglass is a ceramic material that can fragment into particulate debris in vivo. The effect of particulate Bioglass on tissue cells has not been defined. In order to determine the biologic response to particulate Bioglass, we tested its effect on human synoviocytes in a cell culture model. At the concentrations of 1.0 and 10, micrograms/mL, particulate Bioglass (sizes ranging from approximately 0.5 to 80 microns) had a low cytotoxic effect. However, these concentrations induced secretion of TNF alpha. The observation that particulate Bioglass elicits release of inflammatory cytokines suggests that the development of this bioceramic implant coating should address techniques that would minimize the generation of particulates.

Pathogenesis of bone loss after total hip arthroplasty

Bone loss with or without evidence of aseptic loosening is a long term complication after total hip arthroplasty (THA). It occurs with all materials and in all prosthetic systems in use or that have been used to date. Bone loss after THA can be a serious problem in revision surgery because bone deficiencies may limit reconstructive options, increase the difficulty of surgery, and necessitate autogenous or allogenic bone grafting. There are three factors adversely affecting maintenance of bone mass after THA: (1) bone loss secondary to particulate debris; (2) adaptive bone remodeling and stress shielding secondary to size, material properties, and surface characteristics of contemporary prostheses; and (3) bone loss as a consequence of natural aging. This chapter reviews the mechanisms of the primary causes of bone loss after THA.

Migration of hydroxyapatite onlays into the mandible and nasal bone and local bone turnover in growing rabbits

To determine the effects of local bone turnover on the migration of macroporous hydroxyapatite onlays in the nasal bone and mandibular ramus, we performed histomorphometric analyses of the underlying bone area in 41 New Zealand White rabbits from the age of 4 weeks. The hydroxyapatite implants were placed under the periosteum of the right nasal bone (a depository bone onto its periosteal surface and endosteal resorptive) and the mandibular ramus (resorptive onto its outer surface). The corresponding left sides were sham operated. Following fluorescence bone labeling, composite specimens of the hydroxyapatite block including both sides of the nasal bone and mandible were removed at 0 (n = 1), 3, 6, 9, 12, and 16 weeks postoperatively (n = 8, respectively) and processed to yield undecalcified sections. Bone-bone marrow interfaces in the entire area within 200 microns beneath the base of the hydroxyapatite and in the counter-area on the sham-operated side were measured under a light microscope. In all grafted specimens, the hydroxyapatite matrix was directly united with the underlying tissue by bone ingrowth. However, the sinking of the hydroxyapatite graft in the nasal bone was significant at 3 weeks postoperatively and gradually increased thereafter. In the mandible, the sinking became significant at 6 weeks. In the nasal bone, the bone area density beneath the graft showed a time-dependent decrease during the experimental period, but in the mandibular bone, the value was initially decreased at 3 weeks and then recovered to baseline level. In both bones, parameters of bone resorption, such as osteoclast number and osteoclast surface, were significantly increased from 3 weeks. While the parameters of bone formation, such as osteoblast surface and mineralizing surface, were significantly decreased from 3 weeks in the nasal bone, they were significantly increased in the mandible. Mineral apposition rate showed a significant decrease in both bones. Our data indicate that while the bone area density beneath the hydroxyapatite seemed to depend on bone formation, increased bone resorption would be more critical for the remodeling of underlying bony architecture in the migration of the hydroxyapatite graft.

The effect of surgical approach on femoral stem position in canine cemented total hip replacement

A prospective clinical study was designed to determine the effect of surgical approach on femoral stem position in canine cemented total hip replacement. Candidates for total hip replacement were randomly placed into one of two groups. In one group (n = 10), a craniolateral approach to the hip joint was made, incorporating a femoral trochanteric osteotomy. In the other group (n = 11), a craniolateral approach to the hip joint was made without performing a femoral trochanteric osteotomy. Radiographs obtained immediately after the operation were evaluated by two independent examiners for femoral stem position (neutral, varus, or valgus) and percentage of femoral canal fill, using a defined protocol. There was no statistical difference in femoral stem position between the study groups, whereas a greater percentage of canal fill was associated with the neutral femoral stem position.

The role of polyethylene wear in joint replacement failure

Aseptic loosening is the major cause of failure of joint replacement prostheses. Polyethylene implants removed at revision surgery regularly show wear. It is proposed that the polyethylene particles released into the tissues as a consequence of this wear induce a tissue response that precedes aseptic loosening. This paper presents the results of recent in vivo and in vitro studies of the biological response to polyethylene wear particles undertaken in the authors' laboratories. A clinical perspective is provided by the inclusion of the authors' recent observations of retrieval analyses of joint replacement implant wear and the tissue response to polyethylene in humans.

Titanium, chromium and cobalt ions modulate the release of bone-associated cytokines by human monocytes/macrophages in vitro

Osteolysis has become a major cause of aseptic loosening in total joint arthroplasty (TJA). Titanium, cobalt and chromium are commonly used in orthopaedic implants (e.g. joint prostheses). The release of bone-associated cytokines has been associated with the development of osteolysis in patients with prostheses. We evaluated the effects of these metals on the release of bone-associated cytokines (IL-1 beta, IL-6, TNF-alpha and TGF-beta 1) by human blood monocytes/macrophages and monocyte-like U937 cells upon lipopolysaccharide (LPS) stimulation, the cell proliferation, and their cytotoxic effects on these cells in vitro. We found that the release of IL-1 beta was enhanced by titanium, chromium and cobalt, the release of TNF-alpha was enhanced by titanium and chromium, and the release of IL-6 was enhanced by titanium. All three metal ions inhibited the release of TGF-beta 1. We also found that titanium and chromium, but not cobalt, enhanced blood monocyte/macrophage proliferation in response to LPS while only titanium enhanced U937 cell proliferation in response to LPS. The metals in concentrations ranging from 0.01 to 100 ngml-1 did not stimulate the cells to secrete detectable cytokines in the absence of LPS. Furthermore, a 4-h pre-exposure of blood monocytes/macrophages or U937 cells to the metals did not alter cytokine release when the metals were removed from the media prior to the addition of LPS. Similarly, a 4-h pre-exposure of blood monocytes/macrophages or U937 cells to LPS did not alter cytokine release when LPS was removed from the media prior to the addition of the metals. The metals did not reduce cell viability and induce cell injury after 72h incubation with the cells. The data suggest that the three metals at clinically relevant concentrations modulated cytokine expression, whereas they did not induce any cytotoxic effects. A metal-induced enhancement of bone-resorbing cytokine release with a concomitant inhibition of bone-forming cytokine release may be an important factor in the development of osteolysis, which can severely compromise the outcome of TJA.

Effect of size, concentration, surface area, and volume of polymethylmethacrylate particles on human macrophages in vitro

This study investigated effects of different sizes, concentrations, volumes, and surface areas of polymethylmethacrylate (PMMA) particles on human macrophages. Adherent peripheral blood monocytes isolated from five healthy individuals were exposed for 48 h to phagocytosable (0.325 micron and 5.5 microns) and nonphagocytosable (200 microns) spherical particles. Each particle size was tested over a range of concentrations (10(4)-10(11) particles per milliliter [0.325 micron], 10(2)-10(7) particles per milliliter [5.5 microns], 10(1)-10(4) particles per milliliter [200 microns]) to provide overlap in number, volume, and surface area. Primary human monocyte/macrophages were cultured in macrophage serum-free medium and 5% fetal calf serum. Macrophage viability was assessed by 3H-thymidine uptake and activation was quantified by release of interleukin-1 beta, interleukin-6, tumor necrosis factor-alpha, prostaglandin E2 (PGE2), and the lysosomal enzyme hexosaminidase. Medium alone served as a negative control; lipopolysaccharide (10 micrograms/mL) was also tested. PMMA particles were not toxic to human macrophages at any concentration tested. The smallest phagocytosable particles (0.325 micron) stimulated the release of interleukin-1 beta, interleukin-6, prostaglandin E2, and hexosaminidase at concentrations of 10(10)-10(11) particles/mL. The release of cytokines, PGE2, and hexosaminidase depended on the size, concentration, surface area, and volume of the phagocytosable particles. This study demonstrates that PMMA particle load Mi.e., the concentration of phagocytosable particles per tissue volume, characterized by size, surface area, and volume, rather than simply particle number-determines the degree of macrophage activation.

Role of tumor necrosis factor alpha in particulate-induced bone resorption

The purpose of this study was to determine the role of tumor necrosis factor alpha in bone resorption secondary to mediator release from macrophages exposed to cement particles. The J774 mouse macrophage cell line was exposed to polymethylmethacrylate particles for 24 hours and the resulting conditioned medium was analyzed for prostaglandin E2, tumor necrosis factor alpha, interleukin-1 alpha and beta, and the ability to stimulate release of prostaglandin E2 and 45Ca from radiolabeled mouse calvaria. Macrophage exposure to polymethylmethacrylate particles led to a 9-fold increase in release of tumor necrosis factor alpha (p < 0.01), but did not lead to a significant increase in release of prostaglandin E2, interleukin-1 alpha, or interleukin-1 beta when compared to unexposed cells. Exposure of the macrophages to polymethylmethacrylate particles over a time course from 30 minutes to 96 hours led to an increase in the release of tumor necrosis factor alpha that was initially detected at 30 minutes and was maximum at 48 hours. Incubation of the macrophage-polymethylmethacrylate conditioned medium with rat calvaria significantly increased the release of 45Ca and prostaglandin E2 from the bone. To study the role of release of tumor necrosis factor alpha in bone resorption, the macrophage-polymethylmethacrylate conditioned medium was then preincubated with anti-tumor necrosis factor alpha antibody prior to exposure of the conditioned medium to the calvaria. This preincubation was successful in significantly inhibiting 45Ca release by calvaria (p <0.01) to levels that were not significantly different from the levels of release by unexposed calvaria. Tumor necrosis factor alpha appears to play a critical role in initiating particulate-induced bone resorption. Exposure of macrophages to polymethylmethacrylate particles leads to a significant release of tumor necrosis factor alpha in a time-dependent fashion. This macrophage-polymethylmethacrylate conditioned medium stimulated release of prostaglandin E2 and bone resorption in bone organ culture. The addition of anti-tumor necrosis factor alpha antibody to this in vitro system inhibited the bone resorption stimulated by the macrophage-polymethylmethacrylate conditioned medium and partially suppressed the production of prostaglandin E2. The sequence of events in this model for particulate-induced bone resorption appears to be initiated by the production of tumor necrosis factor alpha by the macrophage, followed by production of prostaglandin E2 by cells in bone, and then by bone resorption.

Isolation and characterization of wear particles generated in patients who have had failure of a hip arthroplasty without cement

Wear particles from thirty-five membranes obtained during revision hip-replacement operations were studied after digestion of the soft tissue with papain. The particles were isolated and were characterized with use of light and scanning electron microscopic techniques, x-ray microanalysis, and an automated particle analyzer. The mean size of the polyethylene particles was 0.5 micrometer, and the metal particles were a mean of 0.7 micrometer, as determined with scanning electron microscopy. The automated particle analyzer revealed a mean particle diameter of 0.63 micrometer (more than 90 per cent of all particles were less than 0.95 micrometer) and a mean of 1.7 billion particles per gram of tissue, compared with only 143 million per gram of tissue for the control samples. X-ray microanalysis revealed metal debris in sixteen (46 per cent) of the thirty-five membranes after digestion. Thirteen (50 per cent) of the twenty-six membranes surrounding a titanium-alloy stem contained metal particles, compared with three of the nine membranes surrounding a chromium-cobalt stem. Metal debris was present in only one of the twelve membranes surrounding a titanium-alloy stem without a porous coating, compared with twelve of the fourteen membranes surrounding a titanium-alloy stem with a porous coating. This tenfold difference in prevalence was significant (p < 0.005). On the average, the total number of particles (expressed in millions per gram of tissue) associated with the bipolar acetabular components was twice that associated with the fixed acetabular components. In addition, there was a trend toward a larger mean size of the polyethylene particles in association with the bipolar cups. Our data indicate that particulate prosthetic debris in the tissues around failed femoral components that have been inserted without cement constitutes a class of particles that are predominantly less than one micrometer in size and are present in amounts of more than one billion particles per gram of tissue. Routine histological methods did not detect this class of wear debris and led to a gross underestimation of the amount of debris in these membranes.

Human monocyte response to particulate biomaterials generated in vivo and in vitro

We studied the ability of four clinically relevant particle species to stimulate human peripheral blood monocytes to release bone-resorbing agents, including interleukin-1 (both interleukin-1 alpha and interleukin-1 beta), interleukin-6, and prostaglandin E2. The species studied were titanium-6% aluminum-4% vanadium (TiAlV), commercially pure titanium, fabricated ultrahigh molecular weight polyethylene, and polyethylene retrieved from interfacial membranes of failed uncemented total hip arthroplasties. For all species, the mean size was less than 1 micron. Human peripheral blood monocytes were challenged with these particles in a uniform manner on the basis of surface area. Phorbol 12-myristate acetate, zymosan, and nonphagocytosable titanium particles served as controls. Stimulation of human monocytes is a function of the composition and concentration of particles. In this study, TiAlV particles appeared to be the most competent to elicit the synthesis and release of inflammatory mediators. Particles of commercially pure titanium and of fabricated ultrahigh molecular weight polyethylene also could induce the release of various cellular mediators, albeit at a lower level, whereas the particles of polyethylene retrieved from interfacial membranes were less stimulatory in these short-term in vitro experiments.