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This study aimed to investigate the long-term serum metal ion levels of patients who received metal-on-metal hip resurfacing arthroplasty (MoM HRA). We conducted a retrospective study of 99 patients (110 hips) from March 2006 to May 2017 who underwent MoM HRA. The Harris Hip Score (HHS) and the University of California at Los Angeles (UCLA) activity score were measured, and the patients underwent clinical and radiological management. Serum levels of cobalt (Co), chromium (Cr), and molybdenum (Mo) were measured using inductively coupled plasma mass spectrometry (ICPMS) at 1, 6, and 12 months, and each year follow-up after prosthesis implantation. Patients were followed up from 1 to 156 months, with a mean of 98 months. No complications occurred. Metal ion analysis revealed significantly elevated levels compared to preoperative levels. The metal ions levels increased and reached a peak after surgery, and then the levels began to decline gradually. Approximately 84-108 months after surgery, the metal ion levels increased again to approximately peak levels. Then, up to 156 months after surgery, the metal ions levels will drop approximately to preoperative levels. The serum levels of Cr in women were higher than those in men, with the difference being statistically significant. Patients with a body mass index (BMI) of ≥24.9 kg/m2 Co levels were significantly higher than those of normal-weight patients. The serum levels of metal ions showed no significant differences between the prostheses. The use of the MoM HRA was clinically effective, and the Co, Cr, and Mo levels increased significantly after HRA; however, upon long-term follow-up, serum metal ion levels tended to decrease to preoperative levels. Longer follow-up periods and larger study samples are needed to establish the long-term outcome of patients undergoing HRA with MoM bearings. Level IV, Therapeutic Study.

Adverse Reaction to Metal Debris (ARMD) is a major cause of implant failure leading to revision surgery in patients with metal-on-metal (MoM) hip arthroplasties. However, the pathogenesis and its association to implant wear are poorly understood and previous studies have yielded discrepant results. We sought to investigate the associations between histological findings, whole blood and synovial fluid metal ion concentrations and periprosthetic tissue metal concentrations in patients with MoM total hip replacements and hip resurfacings revised for ARMD. 107 hips in total were included in our study. Of these, 87 were total hip replacements and 20 were hip resurfacings, respectively. We found that whole blood, synovial fluid and periprosthetic tissue metal concentrations correlated poorly with histological findings. We suggest that the lack of a clear association between histological findings and wear measures in the present study as well as in previous studies is mostly influenced by variability in patient susceptibility. However, patients presenting with perivascular lymphocytic infiltration had lower chromium concentration in their periprosthetic tissues than patients with no perivascular lymphocytic infiltration. This may reflect the role of metal hypersensitivity in implant failure in these patients. Patients with total hip replacements evinced more necrosis and lymphocytic infiltration in their tissues than patients with hip resurfacings. This suggests that trunnion wear debris is more cytotoxic and/or immunogenic than bearing wear debris leading to higher failure rates seen in patients with total hip replacements.

Background: In recent time, metal ion debris and adverse local tissue reaction have reemerged as an area of clinical concern with the use of large femoral heads after total hip arthroplasty (THA)., Methods: Between June 2014 and January 2015, 60 patients with a noncemented THA using a titanium (titanium, molybdenum, zirconium, and iron alloy) femoral stem and a V40 trunnion were identified with a minimum 5-year follow-up. All THAs had a 32- or 36-mm metal (n = 30) or ceramic (n = 30) femoral head coupled with highly cross-linked polyethylene. Cobalt, chromium, and nickel ions were measured., Results: Patients with metal heads had detectable cobalt and chromium levels. Cobalt levels were detectable in 17 (56.7%) patients with a mean of 2.0 μg/L (range: <1.0-10.8 μg/L). Chromium levels were detectable in 5 (16.7%) patients with a mean of 0.3 μg/L (range: <1.0-2.2 μg/L). All patients with a ceramic head had nondetectable cobalt and chromium levels. Cobalt and chromium levels were significantly higher with metal heads compared to ceramic heads (P < .01). Cobalt levels were significantly higher with 36-mm metal heads compared with 32-mm heads (P < .01). Seven patients with metal femoral heads had mild hip symptoms, 4 of whom had positive findings of early adverse local tissue reaction on magnetic resonance imaging. All ceramic THA was asymptomatic., Conclusion: The incidence and magnitude of cobalt and chromium levels is higher in metal heads compared to ceramic heads with this implant system (P < .01). Thirty-six millimeter metal femoral heads result in larger levels of cobalt compared with 32-mm metal heads., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: Recent registry data reveal that modular-neck hip prostheses are associated with increased revision rates compared to fixed-neck stems. Poor implant survival has been associated to corrosion at the neck-stem junction, inducing metal ion release and subsequently adverse local tissue reactions. Data on metal ion release on the neck-stem junction of such stems are scarce. The purpose of this study was to evaluate corrosion at this interface by determining metal ion release., Methods: Serum and whole blood metal ion levels of 40 patients after 1 year of implantation of a modular-neck stem (titanium stem and cobalt-chromium neck) were compared with 10 patients with a monobloc version of the stem (all titanium) and 10 patients having no implant at all., Results: Seven of 40 patients (18%) with a modular-neck stem had cobalt or chromium concentrations >2 μg/L. These patients underwent magnetic resonance imaging using metal artifact reduction sequences, which revealed a pseudotumor in 1 patient., Conclusion: Corrosion at the neck-stem junction of modular-neck stems is a reported phenomenon, which is in part reflected by elevated systemic ion levels. The use of such implants should be restricted to a minimum, and screening algorithms of patients with such implants must be developed., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: The aim of our study was to investigate the clinical results and serum metal ion levels in a cohort of patients who received total hip arthroplasty (THA) with ceramic-on-metal (CoM) bearings., Methods: From September 2009 to December 2011, 78 patients (89 hips) who underwent THA with CoM bearings were involved in this study. Harris Hip Score, Short-Form 12, and Western Ontario and McMaster Universities Osteoarthritis Index scores were measured and radiographs were taken for radiographic analysis. Serum metal ion levels of cobalt (Co), chromium (Cr), molybdenum (Mo), and titanium (Ti) were measured using high-resolution inductively coupled plasma-mass spectrometry., Results: Severy-four patients (85 hips) were followed up at a mean of 50 months. At the end of follow-up, HSS, Short-Form 12, and Western Ontario and McMaster Universities Osteoarthritis Index scores were improved significantly compared with preoperative values. No intraoperative and postoperative complications occurred, and no radiolucency, osteolysis, and loosening was found from radiographic examination. Metal ion analysis showed that serum metal ions levels were significantly elevated compared with normal values. Spearman correlation analysis revealed that there was a correlation between 3 metal ion levels and body mass index(Co: r = 0.49, P < .01; Cr: r = 0.47, P < .01; Mo: r = 0.36, P = .04). No correlation was found between metal ion levels and age, cup abduction angle, cup anteversion angle, acetabular version, bilateral arthroplasty, cup screw used, hip stem implant type, or femoral head size., Conclusion: Our study concluded that the use of a CoM THA is effective clinically, but the systemic metal ion levels are significantly elevated at midterm follow-up. Whether the elevated metal ion levels will induce an adverse reaction is unknown and long-term follow-up is need., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: The potential risks associated with hip resurfacing arthroplasty (HRA) are controversial and underestimated. The aim of this study was to explore intermediate-term trends for the levels of cobalt (Co), chromium (Cr), and molybdenum (Mo) ions after HRA., Methods: Forty patients who underwent HRA from October 2005 to December 2010 were recruited to this study. The serum levels of metal ions were examined preoperatively and 3, 12, 24, and 60 months after surgery. Trends and differences in levels of metal ions with respect to sex, operated side, and body mass index (BMI) were analyzed., Results: There were no significant differences in levels of Cr, Co, and Mo at each time point with respect to sex, operated side, and BMI (p > 0.05). The postoperative levels of Cr, Co, and Mo ions were significantly higher than the preoperative levels across sex, operated side, and BMI groups. Postoperative levels of Cr, Co, and Mo peaked at 12, 24, and 60 months, respectively. Cr levels peaked earlier (at 12 months) in the overweight (BMI ≥25 kg/m(2)) group compared to the normal-weight group (BMI <25 kg/m(2)), Co levels (at 12 months) peaked in women compared to men, and Mo levels (at 3 months) peaked in the bilateral HRA group compared to the unilateral HRA group., Conclusions: Serum levels of Cr, Co, and Mo increased significantly after HRA. Cr levels peaked earlier in the overweight patients, Co levels peaked in women, and Mo levels peaked in patients who underwent bilateral HRA. However, there were no significant differences with respect to sex, operated side, and BMI.

Background: Despite the theoretical advantages of ceramic-on-metal (CoM) bearings observed in laboratory settings, limited clinical data are available to support in vitro results. Our present study prospectively investigated the clinical results, serum metal ion levels, inflammatory factor levels, and liver-kidney function in a cohort of patients who received total hip arthroplasty (THA) with CoM bearings., Methods: The cohort comprised 82 THAs in 71 patients (41 men and 30 women), with a mean age of 54 (range 22-77) years. The mean follow-up was four years. All patients completed pre- and postoperative clinical assessment using the Harris Hip Score, Short Form-12, Western Ontario and McMaster Universities Osteoarthritis Index, and radiographic analysis. The serum metal ion levels of cobalt, chromium, molybdenum, and titanium were measured using high-resolution inductively coupled plasma mass spectrometry, and were compared with normal reference values. Inflammatory factors including C-reactive protein, erythrocyte sedimentation, and interleukin-6 levels, and liver-kidney function including alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, and blood urea nitrogen, were measured in our hospital clinical key laboratory., Results: At the end of the follow-up period, all clinical assessments showed a statistically significant improvement. Although the inflammatory factor levels and liver-kidney function were within normal ranges, the serum levels of metal ion were significantly elevated compared with normal values: cobalt, 2.8 μg/L; chromium, 2.2 μg/L; molybdenum, 0.9 μg/L; and titanium, 2.1 μg/L. Spearman's correlation analysis showed an association between cobalt, chromium, and titanium metal ion levels and BMI values., Conclusions: Our study demonstrated that the use of a CoM THA was clinically effective and that metal ion levels were significantly elevated at midterm follow-up. Whether the elevated metal ion levels may reduce adverse reactions is unknown, and long-term follow-up is needed.

Metal-on-metal resurfacing arthroplasty of the hip has been used increasingly over the last 10 years in younger active patients. The dissolution of the metal wear particles results in measurable increases in cobalt and chromium ions in the serum and urine of patients with a metal-on-metal bearing. We measured the cobalt, chromium, and molybdenum ion levels in urine; serum; and breast milk in a young and active patient with a metal-on-metal hip prosthesis after a pathologic fracture of the femoral neck. Metal-on-metal hip prosthesis leads to increasing levels of molybdenum in breast milk in the short-term follow-up. There are no increasing levels of chromium and cobalt ions in breast milk. Besides the already known elevated concentrations in serum of chromium and cobalt after implantation of a metal-on-metal hip prosthesis, we found no increasing levels of chromium and cobalt in urine., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Metal-on-metal (MoM) total hip arthroplasty (THA) has been introduced in an attempt to reduce the wear rate and the consequent osteolysis around implants. The aim of this study was to present the intermediate to long-term clinical and radiological outcomes and to investigate the metal ion levels in the blood of patients who had undergone primary uncemented MoM THA in our institution. Between July 1997 and November 2003, 166 patients (193 hips), with a mean age of 50 years (range, 18-65 years), underwent primary MoM THA. Clinical data, radiographs, and blood samples were obtained at regular follow-up visits. Cobalt (Co), chromium (Cr), and molybdenum (Mo) ions were measured by inductively coupled plasma-mass spectrometry (ICP-MS) from the patient's whole blood. All patients were prospectively followed for a minimum of 5 years (mean, 7 years; range, 5-11 years). The mean Harris hip score (HHS) and the University of California at Los Angeles (UCLA) activity score at the latest follow-up was 88 ± 11 and 7 ± 1.8 points, respectively. Thirteen hips have been revised. Ten acetabular components had early failure, due to factory manufacturing problems. All other implants have been found stable, with no signs of aseptic loosening. The probability of survival at 11 years, if the hips that were revised due to manufacturing problems were excluded, was 98.4%. The Co and Cr metal ion levels, after increasing significantly during the first 4 to 5 years post-surgery, remained stable, with a tendency to decrease thereafter, but not significantly. During the same follow-up period, Mo ion levels remained stable. In this 5-to-11 year follow-up study of MoM THA patients, excellent survivorship, with low complications rates, was found. Results of longer follow-up studies are necessary to clarify the possible long-term effects of metal ion release.

Background: Metal-on-metal Birmingham hip resurfacing (MOM-BHR) is an alternative to metal-on-metal total hip arthroplasty (MOM-THA), especially for young and/or active patients. However, wear resulting in increased serum ion levels is a concern., Questions/purposes: We asked whether (1) serum chromium (Cr), cobalt (Co), and molybdenum (Mo) concentrations would differ between patients with either MOM-BHR or MOM-THA at 5 years, (2) confounding factors such as gender would influence ion levels; and (3) ion levels would differ at 2 and 5 years for each implant type., Patients and Methods: Ions were measured in two groups with either MOM-BHR (n = 20) or MOM-THA (n = 35) and a mean 5-year followup, and two groups with either MOM-BHR (n = 15) or MOM-THA (n = 25) and a mean 2-year followup. Forty-eight healthy blood donors were recruited for reference values., Results: At 5 years, there were no differences in ion levels between patients with MOM-BHR or MOM-THA. Gender was a confounding factor, and in the MOM-BHR group at 5 years, Cr concentrations were greater in females compared with those of males. Mean ion levels were similar in patients with 2 and 5 years of followup for each implant type. Ion levels in patients were sevenfold to 10-fold higher than in controls., Conclusions: As the metal ion concentrations in the serum at 5 years were in the range reported in the literature, we do not believe concerns regarding excessive metal ion levels after MOM-BHR are justified., Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of level of evidence.

The main components (Ti, V, Cr, Co, Ni, and Mo) of metallic alloys currently used in hip and knee articular prostheses have been simultaneously determined in human whole blood and urine of implanted people by a (HR)-ICP-MS method previously developed in our laboratory. The determination of those elements has been carried out in patients with knee and hip prosthesis and in a group of pre-operation patients without any metallic device in their bodies, used as controls, demonstrating the usefulness of this technique to perform multielement analysis at ppt levels in complex matrices. The concentrations of V, Cr, Co, Ni, and Mo in urine and blood of implanted people turned out to be very similar to those obtained in control patients. However, raised Ti levels could be found both in urine and blood of patients with articular prostheses made or coated with a titanium alloy (Ti(6)Al(4)V).

Background: Metal ion toxicity, metal hypersensitivity, and metal carcinogenicity are causes for concern for patients with metal-on-metal hip replacements. Thus, understanding the biological fate of metal ions, and consequently their long-term systemic effects, is of great interest to patients and surgeons alike., Methods: Inductively coupled plasma mass spectrometry was used to measure the levels of cobalt, chromium, and molybdenum ions in the blood of control patients (preoperative control pre-resurfacing patients), patients with a metal-on-polyethylene total hip prosthesis, patients with a metal-on-metal total hip prosthesis with either a 28 or 36-mm femoral head, and patients with a hip resurfacing prosthesis. Since cobalt and chromium ions have the potential to induce oxidative stress through irreversible biochemical damage to macromolecules, the levels of ions were correlated to the concentration of three oxidative stress markers in the plasma of these patients., Results: The median cobalt level was significantly lower (p < 0.001) in the 36-mm metal-on-metal total hip arthroplasty group (1.8 parts per billion [1.8 microg/L]) compared with the 28-mm metal-on-metal total hip arthroplasty group (2.5 parts per billion [2.5 microg/L]) and the hip resurfacing group (2.3 parts per billion [2.3 microg/L]) at six months postoperatively. The median chromium level was also significantly lower (p < 0.01) in the 36-mm metal-on-metal total hip arthroplasty group (0.25 parts per billion [0.25 microg/L]) compared with the 28-mm metal-on-metal total hip arthroplasty group (0.35 parts per billion [0.35 microg/L]) and the hip resurfacing group (0.50 parts per billion [0.50 microg/L]) at six months postoperatively. However, neither the median cobalt levels nor the median chromium levels were significantly different among the three metal-on-metal groups at one year. The median levels of molybdenum were not significantly different among the three groups at either six months or one year. In addition, there was no significant difference in the plasma concentration of oxidative stress markers in patients with metal-on-metal bearings compared with that in control patients., Conclusions: The blood metal ion levels in the hip resurfacing group were similar to those in the 28 and 36-mm-head metal-on-metal total hip arthroplasty groups. This study suggests that the increased metal ion levels had no effect on oxidative stress markers in the blood of these patients.

Background: Metal-on-metal total hip resurfacing arthroplasty is increasingly being performed in young and active patients. Preclinical in vitro testing of implants is usually performed with use of hip simulators, and the serum metal ion concentration is determined for the purpose of monitoring the patients. The goal of this study was to characterize the early running-in period in vivo and in vitro by characterizing metal ion levels., Methods: A well-functioning total hip resurfacing prosthesis was implanted in fifteen consecutive patients, and the serum metal ion concentrations in these patients were then determined preoperatively and at intervals during the first postoperative year (at one, six, twelve, twenty-four, and fifty-two weeks). The number of walking cycles was measured with use of a computerized accelerometer in order to compare walking cycles to hip simulator cycles. In vitro, five similar components were investigated for 3 million cycles with use of a hip simulator. Serum samples were obtained at different time points, and wear was measured by quantifying wear particles and ions in the samples. All patient and simulation serum samples were analyzed with use of inductively coupled plasma-mass spectrometry. One simulator implant was investigated with use of scanning electron microscopy., Results: The serum chromium and cobalt levels of the patients continuously increased during the first six months and showed an insignificant decrease thereafter. The molybdenum concentration was unchanged compared with preoperative values. In contrast, the simulator measurements showed a different wear pattern with a high-wear running-in period and a low-wear steady-state phase. The running-in period was delayed by 300,000 cycles and lasted up to 1 million cycles. Scanning electron microscopic analysis showed a carbon-rich protein film predominantly in the early phases of simulation. Scratches were detected originating from pits filled with aluminum oxide and silicon oxide and from pulled-out carbides that were causing third-body wear., Conclusions: The simulator study allowed an exact characterization of the running-in period and showed a delayed onset of running-in wear. In contrast, the clinical data showed a slow increase in measured ion concentrations. These different wear patterns are probably due to the effects of distribution, accumulation, and excretion of particles and ions in vivo.

Unlabelled: Modern metal-on-metal hip resurfacing was introduced as a bone-preserving method of joint reconstruction for young and active patients; however, the large diameter of the bearing surfaces is of concern for potential increased metal ion release. We hypothesized there were no differences in serum concentrations of chromium, cobalt, and molybdenum between patients who had metal-on-metal hip resurfacing (Group A; average head diameter, 48 mm; median followup, 24 months) and patients who had 28-mm metal-on-metal THA (Group B; median followup, 25 months). Serum concentrations also were compared with concentrations in healthy subjects. We identified no differences in ion levels between Groups A and B. A distinction was made according to gender. Women showed a higher chromium release in Group A whereas men had a higher cobalt release in Group B. Values obtained from Group A were higher than those of the control subjects. Our data suggest metal-on-metal bearings for THA should not be rejected because of concern regarding potential increased metal ion release; however, patients with elevated ion levels, even without loosening or toxicity, could be at higher risk and should be followed up periodically., Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Background: All metal implants--and metal-on-metal bearings in particular--corrode and cause a release of metal ions. Because cobalt and chromium have been shown to be carcinogenic and mutagenic in human and animal models, systemic toxicity and cancer risk are considered to be possible disadvantages of the metal-on-metal articulation. This study was designed to investigate the serum concentration profiles of chromium, cobalt and molybdenum after implantation of a Birmingham hip resurfacing arthroplasty (BHR) and a cementless total hip replacement with a 28-mm Metasul articulation (MTHR), over the first 2 years after implantation., Methods: We analyzed profiles of metal ion serum levels in 111 patients implanted with a BHR, in 74 patients implanted with an MTHR, and in 130 implant-free probands control subjects using atomic absorption spectrophotometry., Results: Chromium and cobalt concentrations (in microg/L) of all BHR and MTHR patients differed significantly from those of control subjects (chromium: < 0.25; cobalt: 0.25). The median chromium and cobalt concentrations in BHR patients had increased to 5.1 and 4.3 microg/L 2 years after surgery. Concentrations in BHR patient exceeded those in the unilateral MTHR patients. Molybdenum serum concentrations hardly changed over time in either group and were not significantly different from the concentrations seen in the control subjects., Interpretation: During the first 2 years after surgery, the Birmingham hip resurfacing arthroplasty leads to a significantly greater increase in serum chromium and cobalt levels than the 28-mm metal-on-metal MTHR. Observation of patients over a longer period will be necessary in order to evaluate any chronic adverse effects to the system due to elevated chromium and cobalt serum concentrations.

A prospective study was performed to investigate changes in metal levels and chromosome aberrations in patients within 2 years of receiving metal-on-metal hip arthroplasties. There was a statistically significant increase of cobalt and chromium concentrations, with a small increase in molybdenum, in whole blood at 6, 12, and 24 months after surgery. There was also a statistically significant increase of both chromosome translocations and aneuploidy in peripheral blood lymphocytes at 6, 12, and 24 months after surgery. The changes were generally progressive with time, but the change in aneuploidy was much greater than in chromosome translocations. No statistically significant correlations were found in secondary analyses between chromosome translocation indices and cobalt or chromium concentration in whole blood. Although the clinical consequences of these changes, if any, are unknown, future epidemiological studies could usefully include direct comparisons of patients with implants of different composition.

Purpose of the Study: Component wear and dissemination of wear debris, particularly with metal-on-metal combinations, is the predominant long-term complication of total hip arthroplasty. The purpose of our work was to search for metal pArticles released when using the metal-on-polyethylene combination by analyzing serum levels of chromium (Cr), cobalt (Co), nickel (Ni), and molybdium (Mo) in patients with a metal-on-polyethylene chromium-cobalt total hip arthroplasty. We compared the observed levels with those observed in a control population and studied changes as a function of signs of loosening., Material and Methods: During a thirty-Month period, 53 patients with degenerative hip disease underwent total hip arthroplasty. The same implant, PVL, being used for all hips. Forty-eight patients were available for analysis at a minimum follow-up of 32 Months. Results of the clinical and radiological examination of the operated hip were recorded. Serum metal levels were assayed by mass spectrometry on total blood samples. Patient activity was determined with the Devane classification and hip function with the Postel-Merle-d'Aubligné score; walking distance was recorded in kilometers. Signs of prosthetic loosening were identified on plain radiograms (AP and lateral views) searching for femoral and/or acetabular lucent lines, cement fracture, granuloma. The control group included 56 patients scheduled for total hip arthroplasty. Non-parametric statistical analysis was used to search for correlations between the clinical, radiological, and biological parameters., Results: At mean 44 Months follow-up, 17% of the patients had a fair or mediocre function score and 37% had radiological signs of femoral component loosening. Serum cobalt increased significantly in the implanted group (serum cobalt >or=0.60 microg/L in 50% of patients) compared with the control group (serum cobalt >or=0.60 microg/L in 9%) (P<0.001, Mann-Whittney test). Increased serum cobalt was highest in patients with radiographic signs of loosening. This significant difference was not found for other metals. Patient activity, hip function, and follow-up were not correlated with serum levels., Discussion: Serum cobalt appears to be a good biological marker of prosthetic function although intra- and inter-individual variations are influenced by assay technique, metal ion solubility, and metal dissemination in the organism. The metal-on-metal combination does not appear to be the only friction couple which increases the serum level of metal ions. Our results do not allow defining a time of latency between onset of radiographic signs and increased serum levels.

Polyethylene (PE) wear has been shown to be a problem in long-term joint replacement using metal-on-PE bearing. The use of metallic heads articulating with metallic cups could solve this problem: success will be enhanced if wear and corrosion of the articulating surfaces are maintained at a low level. New models with metal-on-metal bearing have been proposed, to be used mainly for young subjects: such coupling seems to have a reduced release, but it is unclear yet if the medium-term corrosion rate is really negligible or, on the contrary, it is significantly higher than in the metal-on-PE bearing. Aim of our study was the comparison of ion release in the serum of two groups of patients who had the same type of stable cementless prosthesis, but different bearing: twenty-six patients with metal-on-metal (Group A) and fifteen patients with metal-on-PE bearing (Group B) were examined. The follow-up was 14-38 months for group A and 18-34 months for group B. The serum concentration of chromium (Cr), cobalt (Co) and molybdenum (Mo) was measured. Twenty-two patients before surgery were used for comparison (Group C). The reference values were obtained from a population of twenty-two healthy subjects (Group D). Our findings indicate that metal-on-metal bearings produce a significantly higher systemic release of cobalt and chromium (ng/ml) when compared with levels found in metal-on-PE, pre-surgery and reference groups. Such a high release should induce to improve the bearing materials or, at least, to study the biologic fate of metal ions and consequently their long-term effects. In such a way a risk-to-benefit ratio for the patient could be established., (Copyright 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 467-474, 2002)