Serum metal ion concentration: comparison between small and large head metal-on-metal total hip arthroplasty

Immunoglobulin A Nephropathy in a Patient With Bilateral Metal-on-Metal Hip Arthroplasty

Immunoglobulin A (IgA) nephropathy in the presence of a metal-on-metal (MoM) hip arthroplasty is a rare condition that requires close monitoring. A 61-year-old male with bilateral hip osteoarthritis underwent resurfacing hip arthroplasty with MoM articulating surfaces. Prior to his four-year postoperative visit, the patient was diagnosed with IgA nephropathy. During this visit, the patient reported clicking in the left resurfacing hip arthroplasty, and serum metal ions were significantly elevated. Consequently, the patient underwent conversion to bilateral ceramic-on-cross-linked polyethylene total hip arthroplasty, which resulted in the restoration of metal ion levels to normal. This case highlights that IgA nephropathy played a critical role in impeding the clearance of metal ions. Routine metal ion counts are warranted in patients with MoM articulating interfaces and a newly diagnosed nephropathy.

Metal Ion Release, Clinical and Radiological Outcomes in Large Diameter Metal-on-Metal Total Hip Arthroplasty at Long-Term Follow-Up

Total hip arthroplasty (THA) with metal-on-metal (MoM) bearings have shown problems of biocompatibility linked to metal ion release at the local level causing an adverse reaction to metal debris (ARMD) and at a systemic level. The aim of this study was to evaluate clinical and radiological outcomes, and metal ion concentrations in the blood and urine of patients who underwent THA with the LIMA Met-Met hip system. Patients with ceramic-on-ceramic (CoC) bearings were included as a control group. In this study, 68 patients were enrolled: 34 with MoM THAs and 34 with CoC THAs. Patients were evaluated clinically (Harris Hip Score, SF-36) and radiologically at a median of 7.4 years after surgery. Whole blood and urinary cobalt and chromium levels were also assessed. Both types of implants were comparable in terms of clinical and functional results. Ion levels were significantly higher in the MoM group compared with CoC group 7 years after surgery. No correlations were found between metal ion levels and patient demographics, functional and radiological outcomes, and prosthesis features. Patient monitoring is thus advised to establish if prosthesis revision is necessary, especially in the case of MoM THA.

Pseudotumours, cobalt and clinical outcome in small head metal-on-metal versus conventional metal-on-polyethylene total hip arthroplasty

BACKGROUND

Metal-on-metal total hip arthroplasty (MoM THA) is associated with the formation of pseudotumours. Studies mainly concern pseudotumour formation in large head MoM THA. We performed a long-term follow-up study, comparing pseudotumour incidence in small head metal-on-metal (SHMoM) THA with conventional metal-on-polyethylene (MoP) THA. Predisposing factors to pseudotumour formation were assessed.

METHODS

From a previous randomised controlled trial comparing SHMoM (28 mm) cemented THA with conventional MoP cemented THA, patients were screened using a standardised CT protocol for the presence of pseudotumours. Serum cobalt levels and functional outcome were assessed.

RESULTS

56 patients (33 MoP and 23 MoM) were recruited after mean follow-up of 13.4 years (SD 0.5). The incidence of pseudotumours was 1 (5%) in the SHMoM THA cohort and 3 (9%) in the MoP THA cohort. Prosthesis survival was 96% for both SHMoM and MoP THAs. Serum cobalt levels did not exceed acceptable clinical values (<5 µg/L) whereas no differences in cobalt levels were detected at follow-up between both groups. Oxford and Harris Hip Scores were good and did not differ between SHMoM and MoP THA.

CONCLUSIONS

This long-term follow-up study shows a low incidence of pseudotumour formation and good functional outcome in cemented head-taper matched SHMoM and MoP THA.

The value of serial metal ion levels in following up patients with metal-on-metal hip arthroplasty

BACKGROUND

The sensitivity of cobalt (Co) and chromium (Cr) ion-levels in detecting poorly performing metal-on-metal hip implants is low. This study proposes that serial changes in ion-levels are a more accurate marker of arthroplasties at risk.

METHODS

Serial metal ion-levels and implant data of 285 patients with ASR resurfacing or replacement were studied. Patient and implant characteristics were analysed using univariate and multivariate analyses.

RESULTS

111 (39%) had revision surgery. Time since index surgery (p<0.001), acetabular inclination (p<0.001), their interaction (p<0.001) and femoral head size (p = 0.01) were significant variables. Head size (≤51 mm) had lower Co and Cr levels (p = 0.01). Cr/Co showed marginal decrease over time in the unrevised group and no decrease prerevision.

CONCLUSIONS

Repeated measurement of ion-levels were higher in the revision group suggesting that serial measurements rather than absolute values may have a role to play in predicting implant failure.

Comparison between component designs with different femoral head size in metal-on-metal total hip arthroplasty; multicenter randomized prospective study

BACKGROUNDS/AIMS

We prospectively studied 78 prostheses with conventional femoral head and 86 prostheses with large head (Magnum) of metal-on-metal total hip arthroplasty (MoM THA) with two years follow-up.

METHODS

Clinical outcomes and blood metal ion were evaluated.

RESULTS

There were no significant differences of clinical outcomes between groups. 1.17 ± 1.01 μg/L of blood cobalt ion in Magnum was significantly lower than 1.99 ± 2.34 μg/L in conventional group. No dislocation was observed in Magnum while one dislocation in conventional group. MoM THA with large head is useful if the implants are positioned in appropriate alignment, however longer follow-up will be necessary.

CLINICAL TRIAL REGISTRATION

NCT01010763 (registered on ClinicalTrials.gov).

What are the predictors and prevalence of pseudotumor and elevated metal ions after large-diameter metal-on-metal THA?

BACKGROUND

Soft tissue masses, or "pseudotumors," around metal-on-metal total hip arthroplasty (MoM THA) have been reported frequently; however, their prevalence remains unknown. Several risk factors, including elevated metal ion levels, have been associated with the presence of pseudotumor, although this remains controversial.

QUESTIONS/PURPOSES

The goals of this study were to (1) determine the prevalence of pseudotumors after large-diameter head MoM THA; (2) identify risk factors associated with pseudotumor formation and elevated metal ion levels; and (3) determine the early failure rate of large-diameter MoM THA.

METHODS

Between December 2005 and November 2012, 258 hips (215 patients) underwent large-diameter head primary MoM THA at our institution. Clinical followup was obtained in 235 hips (91%). Using an inclusion criteria of a minimum followup of 1 year, a subset of 191 hips (mean followup, 4 years; range, 1-7 years) was recruited for high-resolution ultrasound screening for the presence of pseudotumor. Whole blood cobalt and chromium ion levels, UCLA activity level, WOMAC score, patient demographics as well as surgical, implant, and radiographic data were collected. Bivariate correlations and multivariate log-linear regression models were used to compare the presence of pseudotumor and elevated metal ions with all other factors.

RESULTS

Ultrasound detected a solid, cystic, or mixed mass in 20% hips (38 of 191). No correlation was found between the presence of pseudotumor and any risk factor that we examined. After controlling for confounding variables, elevated cobalt ions were correlated (p<0.001, R=0.50, R2=0.25) with smaller femoral head size, the presence of bilateral MoM THA, and female sex. Elevated chromium ions were correlated (p<0.001, R=0.59, R2=0.34) with smaller femoral head size, presence of bilateral MoM THA, and lower body mass index. The overall survival of MoM THA was 96% at a mean followup of 4.5 years (range, 2-8 years).

CONCLUSIONS

With the numbers available, we found no associations between the presence of pseudotumor and the potential risk factors we analyzed, including elevated metal ion levels. Further work is needed to explain why larger femoral head sizes resulted in lower metal ion levels despite being associated with higher early failure rates in joint registry data.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Metal ion levels and revision rates in metal-on-metal hip resurfacing arthroplasty: a comparative study

Metal-on-metal (MoM) bearings in hip surgery are related to increased blood levels of metal ions. The nature of the relationship between ion levels and failure is still not fully understood. This study compares three cohorts of patients, 120 patients in each cohort, treated with a hip resurfacing arthroplasty, grouped by brand and diameter of femoral component on average four years postoperatively: Birmingham Hip Resurfacing ≥50 mm, Durom resurfacing ≥50 mm and Durom resurfacing <50 mm. The median blood ion levels of cobalt and chromium were significantly lower in the cohort with the large Durom resurfacing than the other two cohorts (P<0.05). The large BHR and large Durom HRA had revision rates of 3.3%. The small Durom HRA had a revision rate of 8.3%. Elevated blood ion levels can indicate a failing MoM bearing. The large BHR and large Durom HRA have similar revision rates yet the large Durom HRA had significantly lower metal ion levels. When similar ion levels were reported for BHR and small Durom the latter had significantly higher revision rates. This suggests ion levels do not absolutely predict the rate of HRA failure. Since MoM generation of metal ions is not the sole reason of failure, regular clinical and radiographic follow-up should also be in place for patients with these joints.

Does bearing size influence metal ion levels in large-head metal-on-metal total hip arthroplasty? A comparison of three total hip systems

BACKGROUND

The purpose of the study was twofold: first, to determine whether there is a statistically significant difference in the metal ion levels among three different large-head metal-on-metal (MOM) total hip systems. The second objective was to assess whether position of the implanted prostheses, patient demographics or factors such as activity levels influence overall blood metal ion levels and whether there is a difference in the functional outcomes between the systems.

METHODS

In a cross-sectional cohort study, three different metal-on-metal total hip systems were assessed: two monoblock heads, the Durom socket (Zimmer, Warsaw, IN, USA) and the Birmingham socket (Smith and Nephew, Memphis, TN, USA), and one modular metal-on-metal total hip system (Pinnacle, Depuy Orthopedics, Warsaw, IN, USA). Fifty-four patients were recruited, with a mean age of 59.7 years and a mean follow-up time of 41 months (12 to 60). Patients were evaluated clinically, radiologically and biochemically. Statistical analysis was performed on all collected data to assess any differences between the three groups in terms of overall blood metal ion levels and also to identify whether there was any other factor within the group demographics and outcomes that could influence the mean levels of Co and Cr.

RESULTS

Although the functional outcome scores were similar in all three groups, the blood metal ion levels in the larger monoblock large heads (Durom, Birmingham sockets) were significantly raised compared with those of the Pinnacle group. In addition, the metal ion levels were not found to have a statistically significant relationship to the anteversion or abduction angles as measured on the radiographs.

CONCLUSIONS

When considering a MOM THR, the use of a monoblock large-head system leads to higher elevations in whole blood metal ions and offers no advantage over a smaller head modular system.

Metal ion concentrations in body fluids after implantation of hip replacements with metal-on-metal bearing--systematic review of clinical and epidemiological studies

INTRODUCTION

The use of metal-on-metal (MoM) total hip arthroplasty (THA) increased in the last decades. A release of metal products (i.e. particles, ions, metallo-organic compounds) in these implants may cause local and/or systemic adverse reactions. Metal ion concentrations in body fluids are surrogate measures of metal exposure.

OBJECTIVE

To systematically summarize and critically appraise published studies concerning metal ion concentrations after MoM THA.

METHODS

Systematic review of clinical trials (RCTs) and epidemiological studies with assessment of metal ion levels (cobalt, chromium, titanium, nickel, molybdenum) in body fluids after implantation of metalliferous hip replacements. Systematic search in PubMed and Embase in January 2012 supplemented by hand search. Standardized abstraction of pre- and postoperative metal ion concentrations stratified by type of bearing (primary explanatory factor), patient characteristics as well as study quality characteristics (secondary explanatory factors).

RESULTS

Overall, 104 studies (11 RCTs, 93 epidemiological studies) totaling 9.957 patients with measurement of metal ions in body fluids were identified and analyzed. Consistently, median metal ion concentrations were persistently elevated after implantation of MoM-bearings in all investigated mediums (whole blood, serum, plasma, erythrocytes, urine) irrespective of patient characteristics and study characteristics. In several studies very high serum cobalt concentrations above 50 µg/L were measured (detection limit typically 0.3 µg/L). Highest metal ion concentrations were observed after treatment with stemmed large-head MoM-implants and hip resurfacing arthroplasty.

DISCUSSION

Due to the risk of local and systemic accumulation of metallic products after treatment with MoM-bearing, risk and benefits should be carefully balanced preoperatively. The authors support a proposed "time out" for stemmed large-head MoM-THA and recommend a restricted indication for hip resurfacing arthroplasty. Patients with implanted MoM-bearing should receive regular and standardized monitoring of metal ion concentrations. Further research is indicated especially with regard to potential systemic reactions due to accumulation of metal products.