Release and excretion of metal in patients who have a total hip-replacement component made of titanium-base alloy

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.

Inhibition of T and B cell proliferation by titanium, cobalt, and chromium: role of IL-2 and IL-6

The mechanism by which an increased risk of prosthetic infection is induced in patients with total joint arthroplasties is poorly understood. The adverse effects of metallic corrosion products of a prosthesis on host defense mechanisms, particularly immune response and release of immunoregulatory cytokines, remain largely unknown. Titanium, cobalt, and chromium are the materials most often used for joint implantation. Therefore, this study was aimed at investigating the cytotoxicity of titanium, cobalt, and chromium and whether these metals affect T and B cell proliferation and the release of cytokines by human peripheral blood mononuclear cells (PBMC) in vitro. Metal cytotoxicity was not observed judging by cell viability and cell injury after PBMC was extensively exposed to the metals. Phytohemagglutinin (PHA)-induced T cell proliferation and lipopolysaccharide-induced B cell proliferation were significantly inhibited by titanium, chromium, and cobalt. The release of IL-2 and IL-6 by PHA-stimulated PBMC was significantly inhibited by titanium, chromium, and cobalt. Titanium did not alter IFN-gamma production, whereas chromium and cobalt significantly reduced IFN-gamma release by PHA-stimulated PBMC. The addition of IL-2 and IL-6 significantly restored the metal-induced inhibition of T cell and B cell proliferation, respectively. This study sheds light on how the metals impair immune response and cytokine release, suggesting that patients with an extensive exposure to the metals may develop immune dysfunctions. The compromised immune response induced by the metals might significantly contribute to an increased risk of infection in patients with joint prostheses.

In-vitro corrosion and wear of titanium alloys in the biological environment

Cyclic anodic polarization studies were undertaken for several titanium alloys of varying composition and phase structures. All materials were exposed to an accelerated corrosion test using a potentiostat and their electrochemical behaviour was analysed within a potential range of 0 to 5000 mV. The electrolyte used was a phosphate buffered saline (PBS) solution at pH = 5, 7.4 and 9. The polarization curves obtained represented both the passive and active regions of the materials and these curves were used to compare the resistance to pitting corrosion of each material. The sliding-wear of these materials was studied in both non-corrosive and corrosive environments. A simple pin-on-disc type wear apparatus was designed and built to simulate the co-joint action of corrosion and sliding-wear. Using this apparatus, it was also possible to evaluate the effect of wear-accelerated corrosion, which was also evaluated by wearing the surface of the specimens prior to corrosion. It was evident that the mixed phase alpha-beta alloys (Ti-6AI-4V and Ti-6AI-7Nb) possessed the best combination of both corrosion and wear resistance, although commercially pure titanium and the near-beta (Ti-13Nb-13Zr) and beta (Ti-15Mo) alloys displayed the best corrosion resistant properties.

Titanium serum and urine levels in rabbits with a titanium implant in the absence of wear

Although devices made of titanium and its alloy with 6% aluminium and 4% vanadium have been remarkably successful primarily in orthopaedic and dental applications, clinical reports have implicated the biological response to released metal from this class of metals as a cause of failure. It is our hypothesis that in the absence of wear, the amount of titanium released is small and will preferentially accumulate in local tissues. One important implication of this is that measurable quantities of titanium in serum and urine that have been observed in clinical studies result from mechanically induced or assisted release phenomena. In order to test this hypothesis, titanium levels in various tissues and fluids of animals both with and without titanium implants need to be determined. In this paper, we report the titanium concentration in serum and urine of rabbits in the absence of wear. Titanium fibre felts were implanted into the tibia of rabbits. At various time points, serum and urine samples were collected from these rabbits as well as from two groups of control rabbits. The samples were analysed for titanium concentration using electrothermal atomic absorption spectrophotometry. The data for the implant group show that titanium levels in serum and urine do not increase in comparison to controls up to one year after implantation. Some clinical studies have documented elevated titanium serum and urine levels in the presence of titanium-based prostheses. The different results from these studies can be resolved by considering titanium release mechanisms other than passive dissolution.

Titanemia from total knee arthroplasty. A case resulting from a failed patellar component

The subject of this case report is a patient with elevated serum levels of titanium (77 parts/billion [ppb]; normal, 3.3 ppb) and vanadium (0.38 ppb; normal, 0.17 ppb) resulting from excessive wear of a metal-backed patellar component in a total knee arthroplasty. The patellar component was worn through both its polyethylene and metal backing as a result of abnormal contact between the patellar and femoral components. Scanning electron microscopic examination of the ingrowth surface of the patellar component indicated that particle debonding occurred as a result of overloading of the sintered neck regions at the particle-substrate interface, suggesting a possible damage during initial insertion of the device, which may have predisposed it to loosening and abnormal contact with the femoral component. Wear particles resulted in staining of the tissues within the knee and an inflammatory and immune response in the synovium consisting of giant cells and T lymphocytes. The serum metal levels were reduced 22 weeks after replacing the patellar component; however, the titanium level was still slightly elevated (8 ppb).

A tapered titanium femoral stem inserted without cement in a total hip arthroplasty. Radiographic evaluation and stability

The results of 416 total hip arthroplasties performed in 372 patients with insertion of a Mallory-Head titanium femoral component without cement were reviewed retrospectively, to determine the stability and the radiographic parameters of stability for this type of stem. The average duration of clinical and radiographic follow-up was 3.7 years (range, 2.0 to 6.5 years). No revisions were performed to treat instability of the stem, pain, or osteolysis by the time of the latest follow-up examination. Although the clinical results were excellent, the radiographic signs of fixation that have been well described for chromium-cobalt stems were frequently absent. So-called endosteal spot welds, commonly seen in association with long, extensively coated stems, were seen infrequently. Resorptive bone-remodeling rarely extended beyond zones 1 and 7 of Gruen et al. Both endosteal and periosteal distal cortical hypertrophy was common, but the cause was unknown. Osteolysis of the distal aspect of the femur, shedding of the porous coating, and breakage of the stem were not seen. Forty-four stems (11 per cent) had initial subsidence; however, it nearly always stabilized within six months postoperatively and did not affect the eventual stability at the time of the short-term follow-up. The short-term clinical outcome confirmed the stability of these stems that had been determined from the radiographic findings and the lack of revisions. At the latest follow-up examination, 323 (87 per cent) of the patients (362 [87 per cent] of the hips) had no or slight pain in the lower limb over-all and only twenty-two (6 per cent) of the patients (twenty-seven [6 per cent] of the hips) had pain in the thigh. This tapered titanium femoral component appears to provide excellent short-term stability, without resorptive bone-remodeling, osteolysis, or a high prevalence of pain in the thigh. Radiographic evaluation of stability of this stem is clearly different from that of chromium-cobalt stems-particularly extensively coated anatomic medullary locking stems-in that so-called spot welds and severe resorptive bone changes were uncommon and distal cortical hypertrophy was common.

Cobalt and chromium concentrations in patients with metal on metal total hip replacements

There has been a resurgence of interest in the use of metal on metal bearings in total hip arthroplasty. Although the use of metal on metal bearing couples would eliminate or substantially reduce particulate polyethylene generation (depending on the presence or absence of polyethylene in the implant system), there is concern about the potential for increased particulate and ionic metal generation in comparison with polyethylene on metal bearings. These metallic degradation products may be transported away from the implant site and distributed systemically. Chromium concentrations in the serum and urine and cobalt concentrations in the serum were measured in subjects with cobalt chromium alloy metal on metal total hip replacements and in controls without implants. Eight subjects with long term (> 20 years) McKee-Farrar total hip replacements had 9-fold elevations in serum chromium, 35-fold elevations in urine chromium, and at least 3-fold elevations in serum cobalt concentrations in comparison with controls. Six subjects with short term (< 2 years) metal on metal surface replacement arthroplasties had 3-fold elevations in serum chromium, 4-fold elevations in urine chromium, and 4-fold elevations in serum cobalt concentrations in comparison with subjects with McKee-Farrar implants. Although the toxicologic importance of these trace metal elevations has not been established, serum and urine metal concentrations may be useful markers for the tribologic performance of metal on metal bearings.

Development of in vitro biocompatibility assays for surgical material

This work reports the development of a test to evaluate the biologic effects of implant material used in orthopaedics and traumatology based on the examination of inflammation and allergic reactions at the cellular level. The variation in arachidonic acid metabolite production by murine peritoneal macrophage cultures was studied using different powders of implant material. Macrophage activation by zymosan served as a control. Mouse peritoneal macrophages were labeled with 14C-arachidonic acid, and the synthesis of cyclooxygenase products (6-keto-prostaglandin F1 alpha; prostaglandins F2 alpha, E2, D2; and thromboxane B2) and lipoxygenase products (hydroxyeicosatetraenoic acids) was analyzed and quantified by chromatography. Results obtained through these assays support the reported clinical data that chrome and nickel increase the production of hydroxyeicosatetraenoic acids by mouse peritoneal macrophages. HXPATRI, titan oxide, and monoclinic zircon also increase the production of hydroxyeicosatetraenoic acids in contrast to other powders tested (alumina, HXPBL, chrome cobalt alloy, stainless steel 316L, titan, quadratic zircon), which have little effect on the production of arachidonic acid metabolites by the lipoxygenase pathway. It is concluded that determination of arachidonic acid metabolite production by murine peritoneal macrophage cultures is appropriate for evaluating implant material.

Cytocompatibility of Ti-6Al-4V and Ti-5Al-2.5Fe alloys according to three surface treatments, using human fibroblasts and osteoblasts

Titanium alloys are well known for their superior mechanical properties as well as for their good biocompatibility, making them desirable as surgical implant materials. However, these alloys have been proven to behave poorly in friction since wear particles were often detected in tissues and organs associated with titanium implants. In this paper, three surface treatments were investigated in order to improve the wear resistance and the hardness of Ti-6Al-4V and Ti-5Al-2.5Fe: (a) glow discharge nitrogen implantation (10(17) atoms cm-2), (b) plasma nitriding by plasma diffusion treatment (PDT) and (c) deposition of TiN layer by plasma-assisted chemical vapour deposition (PACVD) additionally to PDT. Surface characterization after the different treatments showed considerable improvement in surface hardness, especially after the two nitriding processes. Moreover, the good corrosion resistance of untreated alloys was maintained. A cell culture model using human cells was chosen to study the effect of such treatments on the cytocompatibility of these materials. The results showed that Ti-5Al-2.5Fe alloy was as cytocompatible as the Ti-6Al-4V alloy and the same surface treatment led to identical biological consequences on both alloys. Nitrogen implantation did not modify at all the cellular behaviour observed on untreated samples. After the two nitriding treatments, cell proliferation and viability appeared to be significantly reduced and the scanning electron microscopy study revealed somewhat irregular surface states. However, osteoblast phenotype expression and protein synthesis capacity were not affected. PDT and PACVD may be interesting alternatives to the physical vapour deposition technique.

Influence of biomaterial surface texture on bone ingrowth in the rabbit femur

The purpose of this study was to examine both the histologic and the mechanical characteristics of bone apposition to an experimental surface, arc-deposited titanium, in a rabbit model and to compare them with those of four previously studied surfaces: one layer of cobalt-chromium beads, three layers of cobalt-chromium beads, plasma-sprayed cobalt-chromium, and uncoated titanium alloy. Bilateral cylindrical implants were press-fit into the lateral femoral condyles of 70 adult New Zealand White rabbits, which were allowed unrestricted activity and then killed at 6 or 12 weeks. The distal femora were harvested, radiographed, and prepared for either mechanical or histologic evaluation. All of the implants with coated surfaces had significantly greater shear strength than the implants of grit-blasted titanium alloy after both 6 and 12 weeks. After 6 weeks, maximum bone apposition occurred in the beaded surfaces. After 12 weeks, the shear strengths and bone apposition of implants of arc-deposited titanium and of one and three layers of cobalt-chromium beads were significantly greater than those of implants of plasma-sprayed cobalt-chromium and grit-blasted titanium alloy. The histologic studies correlated with the mechanical results. After 12 weeks, the bone apposition and mechanical stability of arc-deposited titanium were similar to those of a single layer of beads. There appeared to be no advantage to multiple layers of beads, and the plasma-sprayed cobalt-chromium and grit-blasted titanium surfaces showed lower shear strength and bone apposition than the other groups.

Distribution of titanium and vanadium following repeated injection of high-dose salts

Titanium and its alloy of 6% aluminium and 4% vanadium are used extensively in orthopedic and dental surgery. However, in conditions of motion leading to wear, there is significant generation of wear products with deposition of black debris in the tissue. The questions remain as to how much of this debris is generated and to where it is transported. Previous studies have been hampered by low levels of detected elements giving values just above the background levels found in normal tissue and body fluids. The purpose of these experiments was to increase the body burden of titanium and vanadium by injecting larger doses of titanium and vanadium salts over an extended period of time. Each animal (Syrian hamster) received 100 micrograms of each element once a week for six weeks. The hamster was sacrificed on the seventh week and body fluids and tissue harvested. The results indicate that in the experimental animals there was transport of vanadium with levels above control in urine, plasma, liver, spleen, and the mineralized portion and organic portion of bone. Titanium had less transport but still showed levels in the experimental animals in plasma, kidney, liver, spleen, and both phases of bone above those in the control animals. Neither element was found above control levels in lung or red blood cells. The levels of titanium and vanadium in control bone were high, possibly indicating bone as a site for storage and accumulation of these elements when encountered in the activities of daily living.

The potential role of fibroblasts in periprosthetic osteolysis: fibroblast response to titanium particles

Periprosthetic osteolysis with or without aseptic loosening is a major clinical problem in total hip arthroplasty. While the macrophage response to prosthetic wear debris and its role in periprosthetic osteolysis has been extensively studied, information regarding other cell types (fibroblasts, osteoblasts) is limited. This study explored the response of fibroblasts to particulate wear debris. Fibroblasts isolated from interfacial membranes of patients with failed total hip replacements and normal synovial tissue, when challenged with small-sized ( < 3 microns) titanium (Ti) particles, responded with significantly enhanced expressions of collagenase, stromelysin and, to a much lesser extent, their tissue inhibitor of metalloproteinases (TIMP). These "regulated" expressions at both mRNA and protein levels were correlated with the size and composition of particles. De novo protein synthesis was required for the regulation of these mRNAs. A similar effect could be induced by the treatment of the cells with particle-free conditioned medium from Ti particle-stimulated fibroblasts. Furthermore, this conditioned medium significantly suppressed the mRNA levels of procollagen alpha 1 (I) and alpha 1 (III) in osteoblast-like MG-63 cells. It is concluded that fibroblasts stimulated with certain particle debris may play an important role in periprosthetic osteolysis by releasing bone-resorbing metalloproteinases and mediator(s) which resulted in suppressed collagen synthesis in osteoblasts.

Intraocular deposition of metallic fragments during phacoemulsification: possible causes and effects

We undertook a prospective slit lamp examination of 56 eyes which had undergone routine phacoemulsification, in order to determine the incidence of metallic intraocular foreign bodies. Characteristic small reflective particles were noted in 86%, with a mean of 5.1 particles per affected eye. No accompanying clinical problems were seen. The used phacoemulsification needles were examined with colour photography and scanning electron microscopy. A characteristic pattern of wear was observed, corresponding to an area under the plastic irrigating sleeve rather than at the tip. This suggests cavitation erosion rather than instrument contacts as the cause. Titanium alloy contains 6% aluminium, 4% vanadium and 0.25% iron. All its constituents may corrode and leach from the surface of the metal when in contact with body fluids and have been implicated in numerous adverse biological processes.

Nitric acid passivation of Ti6Al4V reduces thickness of surface oxide layer and increases trace element release

Passivation of Ti6Al4V and cpTi implants using methods based on the ASTM-F86 nitric acid protocol are used with the intention of reducing their surface reactivity, and consequently the corrosion potential, in the highly corrosive biologic milieu. The ASTM-F86 passivation protocol was originally developed for surgical implants made of stainless steel and chrome cobalt alloy. Using X-ray photoelectron spectroscopy (XPS) to examine the effect of nitric acid passivation on the surface oxide layer of mill-annealed Ti6Al4V and cpTi, we have found that such treatment actually reduced the oxide thickness on the alloy while having no significant effect on the pure metal. These results correlated with observations obtained using graphite furnace atomic absorption spectrophotometry (GFAAS) to detect trace element release from solid, mill-annealed, Ti6Al4V and cpTi into serum-containing culture medium. We detected significantly greater levels of Ti, Al, and V in the presence of passivated compared to nonpassivated Ti6Al4V. In contrast, nitric acid passivation did not influence Ti release from mill-annealed cpTi. These results, derived from two mill-annealed Ti-based metals, would indicate that re-examination of ASTM-F86-based passivation protocols with respect to Ti6Al4V should be considered in view of the widespread use of this alloy for biomedical devices.

Aluminum levels and stores in patients with total hip endoprostheses from TiAIV or TiAINb alloys

Aluminum ranks as a potentially hazardous agent. Pathologic findings in different organs show that it can accumulate in brain, muscle, liver and bone. Therefore, we investigated whether patients with cementless total hip endoprostheses made out of titanium alloys containing aluminum are at risk. In order to determine the complete aluminum body loading in patients who have had their hip replacement for a long period of time (mean 58 months), we mobilized possible stores of aluminum with desferoxamine (DFO). Electrothermal atomic absorption spectroscopy was used to quantify the level of aluminum in serum and urine before and after DFO treatment. A serum aluminum value of 10 micrograms/l or less is internationally accepted as safe. The average serum aluminum level in this study was 14.2 micrograms/l, which is slightly above the limit, but clearly below those levels which can lead to disease (> 50 micrograms/l). No relevant storage of aluminum was found. This latter finding is more important since chronically elevated aluminum levels lead to cellular deposits, which affect the cellular biochemistry. The values before and after DFO mobilization did not differ substantially, indicating that aluminum in alloys for biomaterials can be regarded as safe as far as the risk of aluminum release in vivo is concerned. Histologic studies of bone from the bone-metal interface also showed no deposits of local aluminum release.

Increased metal release from cemented femoral components made of titanium alloy. 19 hip prostheses followed with radiostereometry (RSA)

In 19 patients the concentrations of metal were measured in serum, urine and joint fluid 2 years after implantation of uncemented commercially pure titanium acetabular cups and cemented or uncemented femoral components made of titanium alloy. A ceramic against the polyethylene articulation was used. The fixation of the components was followed with radiostereometry (RSA). Samples from 12 patients scheduled for hip or knee prostheses and without any metallic implant were used as controls. High levels of titanium were found in cemented hips and when large acetabular cups had been inserted. Increased aluminum levels were also noted in the cemented hips. Vanadium was not detected in any of the samples. Micromotions were detected in most of the implants, but the magnitude of these movements could not be used to predict the release of metal into the synovial fluid.

Migration of corrosion products from modular hip prostheses. Particle microanalysis and histopathological findings

Migration of solid corrosion products from the modular head-neck junction of fifteen total hip replacements to the periprosthetic tissues was studied. The devices and tissues were recovered at the time of a revision procedure or at autopsy after a mean of sixty-four months (range, eight to ninety-seven months). The prostheses had a cobalt-chromium-alloy head coupled with a cobalt-chromium-alloy or a titanium-alloy stem. The solid corrosion product was identified by electron microprobe analysis and Fourier transform infrared microprobe spectroscopy as a chromium orthophosphate hydrate-rich material. The product was present at the junction of the modular head and neck and as particles within the periprosthetic tissues as early as eight months postoperatively. In several hips, it was also present on the polyethylene bearing surface. The particles in the tissues ranged in size from less than one to 500 micrometers. They were present within histiocytes or were surrounded by foreign-body giant cells in the pseudocapsule of the hip joint; in the membranes of the femoral bone-implant interface; and at sites of femoral endosteal erosions, with and without loosening of the femoral component.

Theories of wear and loosening in hip prostheses. Wear-induced loosening vs loosening-induced wear--a review

The observation of perioprosthetic granulomas containing wear debris around apparently well-fixed as well as around loose-fitting prosthetic components has led to the development of the hypothesis of wear-induced loosening. However, the hypothesis of wear-induced loosening can neither explain the rapid early prosthetic migration detected by roentgen stereophotogrammetry nor the epidemiology of clinical failure without supplementary ad hoc-assumptions. By contrast, apart from explaining the rapid early prosthetic migration detected by roentgen stereophotogrammetry, the theory of early loosening can explain the development of wear granulomas as well as to a great extent the epidemiology of clinical failure.

Clinical comparison of the Miller Galante I and AMK total knee systems

One hundred patients with primary osteoarthritis of the knee were prospectively randomized to assess the clinical outcome between two contemporary knee designs, namely the Anatomic Modular Knee (AMK, DePuy, Warsaw, IN) and the Miller Galante I (MG I, Zimmer, Warsaw, IN). In addition, patients were stratified by surgeon. While the clinical outcome measured by the Hospital for Special Surgery knee scores was similar for both groups, there was a difference in the number of complications requiring further surgery. Extensor mechanism complications requiring further surgery occurred in four patients (3 MG I and 1 AMK); three patients in the MG I group required a distal realignment procedure for patellar dislocation, while none of the AMK patients had this complication. There was, however, one patellar fracture in the AMK group that required an open reduction. The authors postulate that the major difference contributing to patellofemoral complications relates to the patellofemoral design and patellar tracking, with the more anatomic AMK femoral component having better patellar tracking and stability clinically.

Cellular uptake of titanium and vanadium from addition of salts or fretting corrosion in vitro

The use of titanium and titanium-6% aluminum-4% vanadium alloy for dental and orthopedic implants has increased in the last decade. The implants are presumed to be compatible because osseointegration, bony apposition, and cell attachment are known. However, the cellular association of titanium and vanadium have remained unknown. This study examined the uptake of salts or fretting corrosion products. Titanium was not observed to be toxic to the cells. Vanadium was toxic at levels greater than 10 micrograms/mL. The percentage of cellular association of titanium was shown to be about 10 times that of vanadium. The percentage of cellular association of either element was greater from fretting corrosion than from the addition of salts. The presence of vanadium did not affect the cellular uptake of titanium. The presence of titanium decreased the cell association of vanadium.

Reduction of fretting corrosion of Ti-6Al-4V by various surface treatments

Titanium and titanium-6% aluminum-4% vanadium (Ti-6Al-4V) are known to be biocompatible and corrosion resistant. However, there have been numerous reports of elevated tissue levels of titanium due to passive dissolution, wear, or fretting corrosion of implants. Studies were undertaken to determine whether the fretting corrosion of Ti-6Al-4V could be reduced by surface treatment of one or both surfaces in a fretting situation. Three different surface treatments were studied: ion implantation, physical vapor deposition nitriding, and plasma ion nitriding. The specimens used were screws fretting against the countersinks of a two-hole plate. Fretting corrosion was assessed by weight loss, by chemical analysis of test solutions, and by scanning electron microscopy. Surface treatment of one component, the screws, resulted in reduction in the release of titanium to only 18-32% of that seen with the untreated controls. Weight loss of the untreated plates fretted against physical vapor deposition nitrided screws and plasma ion nitrided screws was reduced to 31 and 38% of the control, respectively. The weight loss of plasma nitrided screws was only 30% that of the control. Nitriding of both plates and screws resulted in a further decrease in plate weight loss and metal release. Plasma ion nitriding of both components had the most significant effect, with the weight loss and titanium release being only 11 and 2% of the control values, respectively.

A method for production and characterization of metal prosthesis wear particles

The wear of joint prostheses generates wear particles that produce an inflammatory response in the surrounding tissues and may contribute to bone resorption resulting in prosthetic loosening. Although the effects of particles produced from prosthetic materials have been studied extensively in vitro and in vivo, little attention has been paid to the standardisation of methods for the generation and characterization of these particles. This paper describes a reproducible method for generation of metal particles by the abrasive shaking of joint replacement components. Particular attention was given to the production of metal particles that closely resembled particles found around solid and loose human prostheses. To achieve this, particle size, size distribution, chemical composition, and shape were characterized. Particles that were 0.5-3.0 microns in diameter were isolated by differential sedimentation, and the distribution of particle sizes was determined with use of a Coulter Multisizer. Chemical composition was measured by atomic absorption spectrophotometry, and transmission electron microscopy was used to characterize particle shape. The techniques were shown to be reproducible, since there was little variation between batches over a lengthy time period. These or similar methods of particle production and characterization should be an essential part of future in vitro and in vivo studies of wear particles.

Polyethylene wear in total hip arthroplasty in patient-matched groups. A comparison of stainless steel, cobalt chrome, and titanium-bearing surfaces

Osteolysis and component loosening secondary to polyethylene (PE) debris are of paramount concern to today's joint replacement surgeon. This retrospective clinical study measures linear wear in 568 implanted total hip prostheses in which three different metals were used as bearing surfaces (307 stainless steel T-28 [Zimmer, Warsaw, IN], 162 cobalt chrome Tr-28 [Zimmer], and 99 nonion implanted titanium Miami Orthopedic Surgical Consultants [Biomet, Warsaw, IN] prostheses) implanted by a single surgeon over an 8-year period. The acetabular component in all cases was nonmetal-backed compression-molded PE, and all components were cemented. Linear wear was measured using the radiographic technique described by Livermore et al. (The effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg 72A:518, 1990) in which change in acetabular component thickness is determined from serial radiographs. A separate evaluation of this technique confirmed accuracy to within 0.18 mm. Radiographs were also evaluated for femoral and acetabular radiolucencies, femoral subsidence, and osteolysis. Patients were matched for sex, age, weight, and length of follow-up period to eliminate these retrospective variables for comparison of wear. The patient-matched groups consisted of 77 patients from each group (43 women, 34 men) with the following demographics: age, 66 years; weight, 158.9 lbs.; follow-up period, 7.9 years. Results revealed linear wear rates of 0.06 stainless steel, 0.05 cobalt chrome, and 0.08 titanium in the patient-matched groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibroblast response to metallic debris in vitro. Enzyme induction cell proliferation, and toxicity

Bovine synovial fibroblasts in primary monolayer culture were exposed to particulate metallic debris. The effects of the metallic particles on the synthesis and secretion of proteolytic enzymes and on cell proliferation and viability were examined. Uniform suspensions of titanium, titanium-aluminum, cobalt, and chromium particles, ranging in size from approximately 0.1 to ten micrometers (average, one to three micrometers), were prepared; the particle concentrations (the volume of particles divided by the total volume of the suspension) ranged from 0.0005 to 5 per cent. Aliquots of the particle suspensions were added to the synovial fibroblast cultures. The final particle concentrations in the media ranged from 0.0000083 to 0.83 per cent. After seventy-two hours of exposure, each medium was harvested and was assayed for proteolytic and collagenolytic activity and for hexosaminidase levels. Neutral metalloproteases, quantified by collagenolytic and caseinolytic (proteolytic) activity, represent enzymes, secreted by cells, that are capable of degrading extracellular matrix. Hexosaminidase is a marker for lysosomal enzyme activity that can include more than thirty enzymes, such as proteases, lipases, nucleases, and phosphatases. Cell proliferation was quantified by uptake of 3H-thymidine. Cell morphology was examined by scanning electron microscopy. Titanium, titanium-aluminum, and chromium significantly stimulated 3H-thymidine uptake at low particle concentrations (p < 0.01, p < 0.002, and p < 0.002, respectively). Exposure to cobalt, even at the lowest particle concentration, resulted in a significant decrease in thymidine uptake (p = 0.027). At the highest particle concentrations, all particles were toxic, as evidenced by the absence of thymidine uptake. At high particle concentrations, all of the metals caused a decrease in caseinolytic (proteolytic) and collagenolytic activity in the culture media. Titanium elevated the lysosomal enzyme marker, hexosaminidase, except at high concentrations. Chromium and titanium-aluminum had no significant effect on hexosaminidase at any particle concentration, while cobalt decreased all enzyme markers at mid-particle to high-particle concentrations. Scanning electron microscopy demonstrated that the morphological response of fibroblasts to titanium included membrane-ruffling and extension of filopodia, typical of active fibroblasts. In contrast, exposure to cobalt at the same concentration resulted in cell crenation, indicative of cell death.

Storage and elimination of titanium, aluminum, and vanadium salts, in vivo

Hamsters were injected with titanium, aluminum, and vanadium salts either intraperitoneally or intramuscularly to study the transport, storage, and elimination of these metals. Blood samples were taken at 4 h or 24 h, and urine samples were taken at 24, 48, and 72 h. The hamsters were then injected weekly for 5 weeks after the initial injection. Blood and portions of the kidneys, liver, lung, and spleen were taken at sacrifice. All samples were analyzed for titanium, aluminum, and vanadium concentrations using graphite furnace atomic absorption spectroscopy (GFAAS). Titanium was found not to be excreted in the urine, was found in low levels in the blood, and was elevated over control in the kidney, liver, and spleen. Aluminum detection via GFAAS showed wide standard deviations and high levels in controls; however, aluminum was found to be excreted in the urine, and to be transported by the blood in the experimental animals. A small amount accumulated in the liver and spleen. Vanadium was excreted in high levels in the urine. A small amount was found in the blood, and the level in the organs was below the reliable detection limits. The rapid excretion of vanadium might be related to its solubility in physiological conditions, while the limited excretion of titanium may be related to its being insoluble in the physiologic environment.