The purpose of this study was to evaluate whether concerns about the release of metal ions in metal-on-metal total hip replacements (THR) should be extended to patients with metal-bearing total disc replacements (TDR). Cobalt and chromium levels in whole blood and serum were measured in ten patients with a single-level TDR after a mean follow-up of 34.5 months (13 to 61) using inductively-coupled plasma mass spectrometry. These metal ion levels were compared with pre-operative control levels in 81 patients and with metal ion levels 12 months after metal-on-metal THR (n = 21) and resurfacing hip replacement (n = 36). Flexion-extension radiographs were used to verify movement of the TDR. Cobalt levels in whole blood and serum were significantly lower in the TDR group than in either the THR (p = 0.007) or the resurfacing group (p < 0.001). Both chromium levels were also significantly lower after TDR versus hip resurfacing (p < 0.001), whereas compared with THR this difference was only significant for serum levels (p = 0.008). All metal ion levels in the THR and resurfacing groups were significantly higher than in the control group (p < 0.001). In the TDR group only cobalt in whole blood appeared to be significantly higher (p < 0.001). The median range of movement of the TDR was 15.5° (10° to 22°). These results suggest that there is minimal cause for concern about high metal ion concentrations after TDR, as the levels appear to be only moderately elevated. However, spinal surgeons using a metal-on-metal TDR should still be aware of concerns expressed in the hip replacement literature about toxicity from elevated metal ion levels, and inform their patients appropriately

We report serum metal ion level data in patients with unilateral and bilateral hip resurfacing over a ten-year period. In these patients there is an increase in both cobalt and chromium levels above the accepted reference ranges during the first 18 months after operation. Metal ion levels remain elevated, but decline slowly for up to five years. However, the levels then appear to start rising again in some patients up to the ten-year mark. There was no significant difference in cobalt or chromium levels between men and women. These findings appear to differ from much of the current literature. The clinical significance of a raised metal ion level remains under investigation

Aims. This study compared the cobalt and chromium serum ion concentration of patients treated with two different metal-on-metal (MoM) hinged total knee arthroplasty (TKA) systems, as well as a titanium nitride (TiN)-coated variant. Methods. A total of 63 patients (65 implants) were treated using either a MoM-coated (n = 29) or TiN-coated (n = 7) hinged TKA (GenuX mobile bearing, MUTARS; Implantcast, Germany) versus the BPKS (Brehm, Germany) hinged TKA (n = 27), in which the weight placed on the MoM hinge is diffused through a polyethylene (PE) inlay, reducing the direct load on the MoM hinge. Serum cobalt and chromium ion concentrations were assessed after minimum follow-up of 12 months, as well as functional outcome and quality of life. Results. No differences in mean age (69 years, 40 to 86), mean age adapted Charlson Comorbidity Index (3.1 (SD 1.4)), mean BMI (29.2 kg/m. 2. (SD 5.8)), or number of other implants were observed between groups. Significant improvements in outcome scores and pain levels were achieved for all groups, and there was no difference in quality of life (12-Item Short-Form Health Survey questionnaire (SF-12)). Mean cobalt and chromium ion levels were significantly higher for the GenuX versus the BPKS hinged TKA (GenuX vs BPKS: cobalt: 16.3 vs 9.4 µg/l; chromium: 9.5 vs 5.2 µg/l). The TiN-coated implants did not appear to confer improvement in the metal ion levels. Metal ion concentrations above 7 µg/l were detected in 81%(29/36) of GenuX patients versus 41% (11/27) in the BPKS group. No GenuX patients had normal levels under 2 µg/l, versus 22% of BPKS patients. No significant reduction in outcome scores was observed regardless of the metal ion levels, whereas higher work-related activity was correlated with higher chromium concentrations. Conclusion. Hinged TKA, using MoM hinges, resulted in critically high cobalt and chromium ion concentrations. The BPKS hinged TKA showed significantly lower metal ion concentrations compared with the GenuX TKA. No benefits were observed using TiN coating. The different weightbearing mechanics might influence the wear of the component materials. Higher workloads and physical activity could influence chromium levels. Cite this article: Bone Joint J 2022;104-B(3):376–385

Aims. We have previously demonstrated raised cobalt and chromium levels in patients with larger diameter femoral heads, following metal-on-polyethylene uncemented total hip arthroplasty. Further data have been collected, to see whether these associations have altered with time and to determine the long-term implications for these patients and our practice. Methods. Patients from our previous study who underwent Trident-Accolade primary total hip arthroplasties using a metal-on-polyethylene bearing in 2009 were reviewed. Patients were invited to have their cobalt and chromium levels retested, and were provided an Oxford Hip Score. Serum ion levels were then compared between groups (28 mm, 36 mm, and 40 mm heads) and over time. Results. Metal ion levels were repeated in 33 patients. When comparing the results of serum metal ion levels over time, regardless of head size, there was a significant increase in both cobalt and chromium levels (p < 0.001). Two patients with larger head sizes had undergone revision arthroplasty with evidence of trunnion damage at surgery. Two patients within the 40 mm subgroup had metal ion levels above the MHRA (Medicines and Healthcare Products Regulatory Agency) threshold for detailed investigation. The increase in cobalt and chromium, when comparing the 36 mm and 40 mm groups with those of the 28 mm group, was not significant (36 mm vs 28 mm; p = 0.092/p = 0.191; 40 mm vs 28 mm; p = 0.200/p = 0.091, respectively). There was no difference, between femoral head sizes, when comparing outcome as measured by the Oxford Hip Score. Conclusion. This study shows an increase in cobalt and chromium levels over time for all modular femoral head sizes in patients with metal-on-polyethylene bearings, with two patients demonstrating ion levels above the MHRA threshold for failure, and a further two patients requiring revision surgery. These results may have clinical implications regarding longer term follow-up of patients and future implant choice, particularly among younger patients. Cite this article: Bone Joint J 2020;102-B(7):832–837

Objectives. Alarm over the reported high failure rates for metal-on-metal (MoM) hip implants as well as their potential for locally aggressive Adverse Reactions to Metal Debris (ARMDs) has prompted government agencies, internationally, to recommend the monitoring of patients with MoM hip implants. Some have advised that a blood ion level >7 µg/L indicates potential for ARMDs. We report a systematic review and meta-analysis of the performance of metal ion testing for ARMDs. Methods. We searched MEDLINE and EMBASE to identify articles from which it was possible to reconstruct a 2 × 2 table. Two readers independently reviewed all articles and extracted data using explicit criteria. We computed a summary receiver operating curve using a Bayesian random-effects hierarchical model. Results. Our literature search returned 575 unique articles; only six met inclusion criteria defined a priori. The discriminative capacity of ion tests was homogeneous across studies but that there was substantial cut-point heterogeneity. Our best estimate of the “true” area under curve (AUC) for metal ion testing is 0.615, with a 95% credible interval of 0.480 to 0.735, thus we can state that the probability that metal ion testing is actually clinically useful with an AUC ≥ 0.75 is 1.7%. Conclusion. Metal ion levels are not useful as a screening test for identifying high risk patients because ion testing will either lead to a large burden of false positive patients, or otherwise marginally modify the pre-test probability. With the availability of more accurate non-invasive tests, we did not find any evidence for using blood ion levels to diagnose symptomatic patients. Cite this article: M. Pahuta, J. M. Smolders, J. L. van Susante, J. Peck, P. R. Kim, P. E. Beaule. Blood metal ion levels are not a useful test for adverse reactions to metal debris: a systematic review and meta-analysis. Bone Joint Res 2016;5:379–386. DOI: 10.1302/2046-3758.59.BJR-2016-0027.R1

We retrospectively analysed concentrations of chromium and cobalt ions in samples of synovial fluid and whole blood taken from a group of 92 patients with failed current-generation metal-on-metal hip replacements. We applied acid oxidative digestion to our trace metal analysis protocol, which found significantly higher levels of metal ion concentrations in blood and synovial fluid than a non-digestive method. Patients were subcategorised by mode of failure as either ‘unexplained pain’ or ‘defined causes’. Using this classification, chromium and cobalt ion levels were present over a wider range in synovial fluid and not as strongly correlated with blood ion levels as previously reported. There was no significant difference between metal ion concentrations and manufacturer of the implant, nor femoral head size below or above 50 mm. There was a moderately positive correlation between metal ion levels and acetabular component inclination angle as measured on three-dimensional CT imaging. Our results suggest that acid digestion of samples of synovial fluid samples is necessary to determine metal ion concentrations accurately so that meaningful comparisons can be made between studies

Aims. We investigated whether blood metal ion levels could effectively identify patients with bilateral Birmingham Hip Resurfacing (BHR) implants who have adverse reactions to metal debris (ARMD). Patients and Methods. Metal ion levels in whole blood were measured in 185 patients with bilateral BHRs. Patients were divided into those with ARMD who either had undergone a revision for ARMD or had ARMD on imaging (n = 30), and those without ARMD (n = 155). Receiver operating characteristic analysis was used to determine the optimal thresholds of blood metal ion levels for identifying patients with ARMD. Results. The maximum level of cobalt or chromium ions in the blood was the parameter which produced the highest area under the curve (91.0%). The optimal threshold for distinguishing between patients with and without ARMD was 5.5 µg/l (83.3% sensitivity, 88.4% specificity, 58.1% positive and 96.5% negative predictive values). Similar results were obtained in a subgroup of 111 patients who all underwent cross-sectional imaging. Between 3.2% and 4.3% of patients with ARMD were missed if United Kingdom (7 µg/l) and United States (10 µg/l) authority thresholds were used respectively, compared with 2.7% if our implant specific threshold was used, though these differences did not reach statistical significance (p ≥ 0.248). Conclusion. Patients with bilateral BHRs who have blood metal ion levels below our implant specific threshold were at low-risk of having ARMD. Cite this article: Bone Joint J 2016;98-B:1455–62

A retrospective study was conducted to investigate the changes in metal ion levels in a consecutive series of Birmingham Hip Resurfacings (BHRs) at a minimum ten-year follow-up. We reviewed 250 BHRs implanted in 232 patients between 1998 and 2001. Implant survival, clinical outcome (Harris hip score), radiographs and serum chromium (Cr) and cobalt (Co) ion levels were assessed. Of 232 patients, 18 were dead (five bilateral BHRs), 15 lost to follow-up and ten had been revised. The remaining 202 BHRs in 190 patients (136 men and 54 women; mean age at surgery 50.5 years (17 to 76)) were evaluated at a minimum follow-up of ten years (mean 10.8 years (10 to 13.6)). The overall implant survival at 13.2 years was 92.4% (95% confidence interval 90.8 to 94.0). The mean Harris hip score was 97.7 (median 100; 65 to 100). Median and mean ion levels were low for unilateral resurfacings (Cr: median 1.3 µg/l, mean 1.95 µg/l (< 0.5 to 16.2); Co: median 1.0 µg/l, mean 1.62 µg/l (< 0.5 to 17.3)) and bilateral resurfacings (Cr: median 3.2 µg/l, mean 3.46 µg/l (< 0.5 to 10.0); Co: median 2.3 µg/l, mean 2.66 µg/l (< 0.5 to 9.5)). In 80 unilateral BHRs with sequential ion measurements, Cr and Co levels were found to decrease significantly (p < 0.001) from the initial assessment at a median of six years (4 to 8) to the last assessment at a median of 11 years (9 to 13), with a mean reduction of 1.24 µg/l for Cr and 0.88 µg/l for Co. Three female patients had a > 2.5 µg/l increase of Co ions, associated with head sizes ≤ 50 mm, clinical symptoms and osteolysis. Overall, there was no significant difference in change of ion levels between genders (Cr, p = 0.845; Co, p = 0.310) or component sizes (Cr, p = 0.505; Co, p = 0.370). Higher acetabular component inclination angles correlated with greater change in ion levels (Cr, p = 0.013; Co, p = 0.002). Patients with increased ion levels had lower Harris hip scores (p = 0.038). In conclusion, in well-functioning BHRs the metal ion levels decreased significantly at ten years. An increase > 2.5 µg/l was associated with poor function. Cite this article: Bone Joint J 2013;95-B:1332–8

Plasma levels of cobalt and chromium ions and Metal Artefact Reduction Sequence (MARS)-MRI scans were performed on patients with 209 consecutive, unilateral, symptomatic metal-on-metal (MoM) hip arthroplasties. There was wide variation in plasma cobalt and chromium levels, and MARS-MRI scans were positive for adverse reaction to metal debris (ARMD) in 84 hips (40%). There was a significant difference in the median plasma cobalt and chromium levels between those with positive and negative MARS-MRI scans (p < 0.001). Compared with MARS-MRI as the potential reference standard for the diagnosis of ARMD, the sensitivity of metal ion analysis for cobalt or chromium with a cut-off of > 7 µg/l was 57%. The specificity was 65%, positive predictive value was 52% and the negative predictive value was 69% in symptomatic patients. A lowered threshold of > 3.5 µg/l for cobalt and chromium ion levels improved the sensitivity and negative predictive value to 86% and 74% but at the expense of specificity (27%) and positive predictive value (44%). Metal ion analysis is not recommended as a sole indirect screening test in the surveillance of symptomatic patients with a MoM arthroplasty. The investigating clinicians should have a low threshold for obtaining cross-sectional imaging in these patients, even in the presence of low plasma metal ion levels

Aims. In metal-on-polyethylene (MoP) total hip arthroplasty (THA), large metal femoral heads have been used to increase stability and reduce the risk of dislocation. The increased size of the femoral head can, however, lead to increased taper corrosion, with the release of metal ions and adverse reactions. The aim of this study was to investigate the relationship between the size of the femoral head and the levels of metal ions in the blood in these patients. Methods. A total of 96 patients were enrolled at two centres and randomized to undergo MoP THA using either a 32 mm metal head or a femoral head of between 36 mm and 44 mm in size, being the largest possible to fit the thinnest available polyethylene insert. The levels of metal ions and patient-reported outcome measures (Oxford Hip Score, University of California, Los Angeles Activity Scale) were recorded at two and five years postoperatively. Results. At five years, the median levels of chromium, cobalt, and titanium were 0.5 μg/l (interquartile range (IQR) 0.50 to 0.62), 0.24 μg/l (IQR 0.18 to 0.30), and 1.16 μg/l (IQR 1.0 to 1.68) for the 32 mm group, and 0.5 μg/l (IQR 0.5 to 0.54), 0.23 μg/l (IQR 0.17 to 0.39), and 1.30 μg/l (IQR 1 to 2.05) for the 36 mm to 44 mm group, with no significant difference between the groups (p = 0.825, p = 1.000, p = 0.558). There were increased levels of metal ions at two years postoperatively in seven patients in the 32 mm group, compared with four in the 36 mm to 44 mm group, and at five years postoperatively in six patients in the 32 mm group, compared with seven in the 36 mm to 44 mm group. There was no significant difference in either the OHS (p = 0.665) or UCLA (p = 0.831) scores between patients with or without an increased level of metal ions. Conclusion. In patients who underwent MoP THA, we found no differences in the levels of metal ions five years postoperatively between those with a femoral head of 32 mm and those with a femoral head of between 36 mm and 44 mm, and no corrosion-related revisions. As taper corrosion can start after five years, there remains a need for longer-term studies investigating the relationship between the size of the femoral head size and corrosion in patients undergoing MoP THA. Cite this article: Bone Joint J 2024;106-B(3 Supple A):31–37

Metal-on-metal bearings for total hip replacement (THR) are becoming increasingly popular. Improved wear characteristics mean that these articulations are being inserted into younger patients in the form of THR and resurfacing procedures. This has led to concerns regarding potential carcinogenicity because of the increased exposure to metal ions that the procedure brings. We have studied the serum cobalt and chromium concentrations in patients who had primary, well-fixed Ring metal-on-metal THRs for more than 30 years. The levels of cobalt and chromium were elevated by five and three times, respectively compared with those in our reference groups. Metal-on-metal articulations appear to be the source of metal ions throughout the life of the prosthesis. In three patients who had undergone revision of a previous metal-on-metal THR to a metal-on-polyethylene replacement the levels of metal ions were within the normal range. The elevations of cobalt and chromium ions seen in our study were comparable with those in patients with modern metal-on-metal THRs

Metal-on-metal hip bearings are being implanted into younger patients. The consequence of elevated levels of potentially carcinogenic metal ions is therefore a cause for concern. We have determined the levels of cobalt (Co), chromium (Cr), titanium (Ti) and vanadium (Va) in the urine and whole blood of patients who had had metal-on-metal and metal-on-polyethylene articulations in situ for more than 30 years. We compared these with each other and with the levels for a control group of subjects.

We found significantly elevated levels of whole blood Ti, Va and urinary Cr in all arthroplasty groups. The whole blood and urine levels of Co were grossly elevated, by a factor of 50 and 300 times respectively in patients with loose metal-on-metal articulations when compared with the control group. Stable metal-on-metal articulations showed much lower levels. Elevated levels of whole blood or urinary Co may be useful in identifying metal-on-metal articulations which are loose.

We examined the relationships between the serum levels of chromium and cobalt ions and the inclination angle of the acetabular component and the level of activity in 214 patients implanted with a metal-on-metal resurfacing hip replacement. Each patient had a single resurfacing and no other metal in their body. All serum measurements were performed at a minimum of one year after operation. The inclination of the acetabular component was considered to be steep if the abduction angle was greater than 55°. There were significantly higher levels of metal ions in patients with steeply-inclined components (p = 0.002 for chromium, p = 0.003 for cobalt), but no correlation was found between the level of activity and the concentration of metal ions. A highly significant (p < 0.001) correlation with the arc of cover was found. Arcs of cover of less than 10 mm were correlated with a greater risk of high concentrations of serum metal ions. The arc of coverage was also related to the design of the component and to size as well as to the abduction angle of the acetabular component. Steeply-inclined acetabular components, with abduction angles greater than 55°, combined with a small size of component are likely to give rise to higher serum levels of cobalt and chromium ions. This is probably due to a greater risk of edge-loading

This is a longitudinal study of the daily urinary output and the concentrations in whole blood of cobalt and chromium in patients with metal-on-metal resurfacings over a period of four years.

Twelve-hour urine collections and whole blood specimens were collected before and periodically after a Birmingham hip resurfacing in 26 patients. All ion analyses were carried out using a high-resolution inductively-coupled plasma mass spectrometer. Clinical and radiological assessment, hip function scoring and activity level assessment revealed excellent hip function.

There was a significant early increase in urinary metal output, reaching a peak at six months for cobalt and one year for chromium post-operatively. There was thereafter a steady decrease in the median urinary output of cobalt over the following three years, although the differences are not statistically significant. The mean whole blood levels of cobalt and chromium also showed a significant increase between the pre-operative and one-year post-operative periods. The blood levels then decreased to a lower level at four years, compared with the one-year levels. This late reduction was statistically significant for chromium but not for cobalt.

The effects of systemic metal ion exposure in patients with metal-on-metal resurfacing arthroplasties continue to be a matter of concern. The levels in this study provide a baseline against which the in vivo wear performance of newer bearings can be compared.

A prospective study of serum and urinary ion levels was undertaken in a triathlete who had undergone a metal-on-metal resurfacing arthroplasty of the hip four years previously. The one month study period included the final two weeks of training, the day of the triathlon, and the two weeks immediately post-race. Serum cobalt and chromium levels did not vary significantly throughout this period, including levels recorded on the day after the 11-hour triathlon. Urinary excretion of chromium increased immediately after the race and had returned to pre-race levels six days later. The clinical implications are discussed.

We describe the findings at six years in an ongoing prospective clinicoradiological and metal ion study in a cohort of 26 consecutive male patients with unilateral Birmingham Hip Resurfacing arthroplasties with one of two femoral head sizes (50 mm and 54 mm). Their mean age was 52.9 years (29 to 67). We have previously shown an early increase in the 24-hour urinary excretion of metal ions, reaching a peak at six months (cobalt) and one year (chromium) after operation. Subsequently there is a decreasing trend in excretion of both cobalt and chromium. The levels of cobalt and chromium in whole blood also show a significant increase at one year, followed by a decreasing trend until the sixth year.

Aims. To establish the survivorship, function, and metal ion levels in an unselected series of metal-on-metal hip resurfacing arthroplasties (HRAs) performed by a non-designer surgeon. Methods. We reviewed 105 consecutive HRAs in 83 patients, performed by a single surgeon, at a mean follow-up of 14.9 years (9.3 to 19.1). The cohort included 45 male and 38 female patients, with a mean age of 49.5 years (SD 12.5). Results. At the time of review 13 patients with 15 hips had died from causes unrelated to the hip operation, and 14 hips had undergone revision surgery, giving an overall survival rate of rate of 86.7% (95% confidence interval (CI) 84.2 to 89.1). The survival rate in men was 97.7% (95% CI 96.3 to 98.9) and in women was 73.4% (95% CI 70.6 to 75.1). The median head size of the failed group was 42 mm (interquartile range (IQR) 42 to 44), and in the surviving group was 50 mm (IQR 46 to 50). In all, 13 of the 14 revised hips had a femoral component measuring ≤ 46 mm. The mean blood levels of cobalt and chromium ions were 26.6 nmol/l (SD 24.5) and 30.6 nmol/l (SD 15.3), respectively. No metal ion levels exceeded the safe limit. The mean Oxford Hip Score was 41.5 (SD 8.9) and Harris Hip Score was 89.9 (14.8). In the surviving group, four patients had radiolucent lines around the stem of the femoral component, and one had lysis around the acetabular component; eight hips demonstrated heterotopic ossification. Conclusion. Our results confirm the existing understanding that HRA provides good long-term survival and function in patients with adequate-sized femoral heads. This is evidenced by a 97.7% survival rate among men (larger heads) in our series at a mean follow-up of 14.9 years. Failure is closely related to head sizes ≤ 46 cm. Cite this article: Bone Jt Open 2022;3(1):68–76

Aims. Dual mobility (DM) implants have been shown to reduce the dislocation rate after total hip arthroplasty (THA), but there remain concerns about the use of cobalt chrome liners inserted into titanium shells. The aim of this study was to assess the clinical outcomes, metal ion levels, and periprosthetic femoral bone mineral density (BMD) at mid-term follow-up in young, active patients receiving a modular DM THA. Methods. This was a prospective study involving patients aged < 65 years, with a BMI of < 35 kg/m. 2. , and University of California, Los Angeles activity score of > 6 who underwent primary THA with a modular cobalt chrome acetabular liner, highly cross-linked polyethylene mobile bearing, and a cementless titanium femoral stem. Patient-reported outcome measures, whole blood metal ion levels (μg/l), and periprosthetic femoral BMD were measured at baseline and at one, two, and five years postoperatively. The results two years postoperatively for this cohort have been previously reported. Results. A total of 43 patients were enrolled. At minimum follow-up of five years, 23 (53.4%) returned for clinical and radiological review, 25 (58.1%) had metal ion analysis performed, 19 (44.2%) underwent dual energy x-ray absorptiometry scans, and 25 (58%) completed a pain-drawing questionnaire. The mean modified Harris Hip Scores improved significantly from 54.8 (SD 19) preoperatively to 93.08 (SD 10.5) five years postoperatively (p < 0.001). One patient was revised for aseptic acetabular loosening. The mean cobalt levels increased from 0.065 μg/l (SD 0.03) to 0.08 (SD 0.05) and the mean titanium levels increased from 0.35 (SD 0.13) to 0.78 (SD 0.29). The femoral BMD ratio decreased in Gruen Zone 1 (91.9%) at five years postoperatively compared with the baseline scores at six weeks potoperatively. The femoral BMD ratio was maintained in Gruen zones 2 to 7. Conclusion. The use of a modular DM component and a cementless, tapered femoral stem shows excellent mid-term survivorship with minimal concerns for corrosion and metal ion release in a cohort of young, active patients undergoing primary THA. Cite this article: Bone Joint J 2021;103-B(7 Supple B):73–77

Aims. Modular dual-mobility (DM) articulations are increasingly used during total hip arthroplasty (THA). However, concerns remain regarding the metal liner modularity. This study aims to correlate metal artifact reduction sequence (MARS)-MRI abnormalities with serum metal ion levels in patients with DM articulations. Methods. A total of 45 patients (50 hips) with a modular DM articulation were included with mean follow-up of 3.7 years (SD 1.2). Enrolled patients with an asymptomatic, primary THA and DM articulation with over two years’ follow-up underwent MARS-MRI. Each patient had serum cobalt, chromium, and titanium levels drawn. Patient satisfaction, Oxford Hip Score, and Forgotten Joint Score-12 (FJS-12) were collected. Each MARS-MRI was independently reviewed by fellowship-trained musculoskeletal radiologists blinded to serum ion levels. Results. Overall, two patients (4.4%) had abnormal periprosthetic fluid collections on MARS-MRI with cobalt levels > 3.0 μg/l. Four patients (8.9%) had MARS-MRI findings consistent with greater trochanteric bursitis, all with cobalt levels < 1.0 μg/l. A seventh patient had a periprosthetic fluid collection with normal ion levels. Of the 38 patients without MARS-MRI abnormalities, 37 (97.4%) had cobalt levels < 1.0 μg/l, while one (2.6%) had a cobalt level of 1.4 μg/l. One patient (2.2%) had a chromium level > 3.0 μg/l and a periprosthetic fluid collection. Of the 41 patients with titanium levels, five (12.2%) had titanium levels > 5.0 μg/l without associated MARS-MRI abnormalities. Conclusion. Periprosthetic fluid collections associated with elevated serum cobalt levels in patients with asymptomatic DM articulations occur infrequently (4.4%), but further assessment is necessary due to implant heterogeneity. Cite this article: Bone Joint J 2024;106-B(3 Supple A):89–96