The sensitivity, specificity and predictive values of raised plasma metal ion levels in the diagnosis of adverse reaction to metal debris in symptomatic patients with a metal-on-metal arthroplasty of the hip

Assessing brain integrity in patients with long-term and well-functioning metal-based hip implants

Production of metal debris from implant wear and corrosion processes is now a well understood occurrence following hip arthroplasty. Evidence has shown that metal ions can enter the bloodstream and travel to distant organs including the brain, and in extreme cases, can induce sensorial and neurological diseases. Our objective was tosimultaneously analyze brain anatomy and physiology in patients with long-term and well-functioning implants. Included were subjects who had received total hip or hip resurfacing arthroplastywith an implantation time of a minimum of 7 years (n = 28) and age- and sex-matched controls (n = 32). Blood samples were obtained to measure ion concentrations of cobalt and chromium, and the Montreal Cognitive Assessment was performed. 3T MRI brain scans were completed with an MPRAGE sequence for ROI segmentation and multiecho gradient echo sequences to generate QSM and R2* maps. Mean QSM and R2* values were recorded for five deep brain and four middle and cortical brain structures on both hemispheres: pallidum, putamen, caudate, amygdala, hippocampus, anterior cingulate, inferior temporal, and cerebellum. No differences in QSM or R2* or cognition scores were found between both groups (p > 0.6654). No correlation was found between susceptibility and blood ion levels for cobalt or chromium in any region of the brain. No correlation was found between blood ion levels and cognition scores. Clinical significance: Results suggest that metal ions released by long-term and well-functioning implants do not affect brain integrity.

Outcome of revision surgery for adverse local tissue reactions in patients with recalled total hip arthroplasty

INTRODUCTION

Recalls of total hip arthroplasty (THA) implants, including metal-on-metal (MoM) THA and dual taper stems, due to increased risk of adverse local tissue reaction (ALTR), represent a challenge for both surgeons and patients. This study aims to analyze the revision surgery outcomes for ALTR in patients with recalled THA implants.

METHODS

A total of 118 consecutive patients who underwent revision surgery due to ALTR with recalled THA were analyzed. Sub-group analysis was performed for recalled MoM THAs, head-neck modular stems, and dual taper neck-stems.

RESULTS

At a mean follow-up of 6.6 years, the complication and reoperation rates of the recalled THAs were 32.2% and 25.4% respectively. The most common post-revision complication was dislocation (16%). Revision of modular taper corrosion THA and high-grade intraoperative tissue damage were risk factors associated with post-revision complications.

CONCLUSION

This study reports high complication and reoperation rates of recalled THAs at mid-term follow-up. The high revision surgery complication rates in both groups suggest the importance of a systematic evaluation of all THA patients with at-risk implants.

LEVEL OF EVIDENCE

Level III, case control retrospective analysis.

Predictive factors affecting long-term survivorship of ASR metal-on-metal total hip arthroplasty

INTRODUCTION

We present the outcome of 154 ASR (Articular Surface Replacement) hips performed at the P.D Hinduja Hospital and Medical Research Centre in terms of revision rate, metal ion levels, and factors affecting survivorship. Further, determined the importance of serial metal ion estimation over single value with poorly functioning arthroplasties.

METHODS

A retrospective study of 154 ASR arthroplasties (136 patients) performed from April 2005 till March 2010 was conducted. Ninety-seven patients were available for final analysis. All patients were assessed for symptoms, radiographs, blood metal (chromium and cobalt), metal artefact reduction sequence (MARS), magnetic resonance imaging (MRI), and computerized tomography (CT).

RESULTS

Female gender, smaller femoral head, patients with a rising level of metal ion levels were more likely to have revision surgery. However, abnormal acetabular inclination/anteversion was not associated with the occurrence of raised metal ion levels, ARMD (adverse reaction to metal debris) or revision surgery. Patients with raised metal ion levels were more likely to have periprosthetic lucency, ARMD, and revision surgery. Median metal levels increased initially for the first three years. Still, patients who required revision surgery continued to have a metal ion rise until the point when revision surgery was performed. In contrast, patients who had a fall in metal ion levels did not require revision.

CONCLUSION

A single metal ion value is less predictive of failing arthroplasties; instead, a rising trend of metal ion levels can better delineate arthroplasties which will require revision. ASR hips whose blood ion levels fell after an initial rise and showed a declining trend did well.

Whole blood chromium concentration is very rarely elevated independently of whole blood cobalt

Due to the risk of adverse reactions to metal debris resulting from increased wear of the arthroplasty more than one million metal-on-metal (MoM) hip replacements worldwide are in active follow-up. Follow-up usually includes measurement of both whole blood cobalt (Co) and chromium (Cr) concentrations. Our experience is that Cr is seldom independently elevated. We wanted to ascertain whether blood Cr measurements could be omitted from follow-up protocols without lowering the quality of follow-up. We identified 8438 whole blood Co and Cr measurements performed without or prior to revision surgery. When the cut-off levels 5 µg/L and 7 µg/L were used, Cr was independently elevated in only 0.5% (95% confidence interval, CI, 0.3 to 0.6) and 0.2% (CI 0.1 to 0.3) of the measurements. The models with continuous variables showed that the higher the blood metal concentrations are the lower the percentage of measurements with Cr higher than Co. Our results suggest that whole blood Cr is very rarely independently elevated and therefore the authorities should consider omitting Cr measurements from their screening guidelines of MoM hip replacements. We believe this change in practice would simplify follow-up and lead to cost savings without decreasing the quality of follow-up.

Retention of metals in periprosthetic tissues of patients with metal-on-metal total hip arthroplasty is reflected in the synovial fluid to blood cobalt transfer ratio in the presence of a pseudotumour

Background

Modern metal-on-metal (MOM) arthroplasties were performed for over a decade before alarming reports of adverse metal reactions dramatically reduced their use. Failures are seen more often with high-wearing implants, but also well-positioned components with more favourable wear patterns can cause problems. There are no specific clinical indicators that could help us to predict the prognosis of these implants. For this reason, we still need more information on the effect of underlying factors that contribute to this process.

Methods

In this prospective cohort study, we investigated how cup orientation and type of pseudotumour determined by the Hart classification effect the distribution of metals in blood, synovial fluid and tissues surrounding the metal-on-metal hip prosthesis in revision surgery patients. One thousand two hundred twenty-nine metal-on-metal hip patients were screened and of those, 60 patients that had a revision surgery due to adverse metal reaction were included. Whole blood, synovial fluid and synovial/pseudotumour tissue samples were analysed for metal ion concentrations (Co, Cr, Mo and Ti).

Results

The lowest metal concentrations were found when both cup anteversion and inclination were optimal, and the highest when both were suboptimal. Suboptimal anteversion alone raised Cr-ion concentrations more than suboptimal inclination. The concentrations of metals in blood, synovial fluid or synovial soft tissue were the same in patients with and without a pseudotumour, but the relative transfer percentage of cobalt from synovial fluid to blood was higher in patients with a pseudotumour.

Conclusions

The implant orientation alone does not explain the metal concentrations found in tissues or distribution of metals between different tissues. The accumulation of metals in periprosthetic soft tissues increase the total metal load, and in the presence of a pseudotumour this is reflected in the transfer ratio of Co from synovial fluid to the blood. The total metal load of the pseudotumour tissue should be defined in future studies to determine if this will provide new insights for clinical practice.

Correlation of MARS MRI findings with cup position, metal ion levels and function in metal-on-metal total hip arthroplasty

INTRODUCTION

Metal-on-metal (MoM) total hip arthroplasties (THAs) have been linked with increased incidence of pseudotumours and revision rate. magnetic resonance imaging (MRI) is useful in diagnosing adverse reaction to metal debris (ARMD) disease but it is not known if MRI findings correlate with cup position.

PATIENTS AND METHODS

From a cohort of 79 MoM THA, 34 MRI studies were available. MRI was classified according to Anderson classification. Mean follow-up was 7.1 years. Evaluation included cup position including margin of safety, measurement of metal ion levels and evaluation of function.

RESULTS

44% of patients had definite ARMD. We did not find any correlation between MRI stage and Co, Cr, margin of safety (MOS) or functional scores. However, patients with a margin of safety angle < 21° had more severe findings in MRI.

CONCLUSIONS

Patients with MoM THA experience high degree of ARMD. In our study, the disease did not correlate with metal ion levels but correlated with cup position, evaluated with the MOS angle.

Establishing thresholds for metal ion levels in patients with bilateral Articular Surface Replacement hip arthroplasty

INTRODUCTION

The primary aim of the current study was to determine whether metal ion levels could identify well- from poorly-functioning implants in patients after undergoing bilateral Articular Surface Replacement (ASR) Hip System. The secondary aim was to establish threshold values for Co and Cr that could be used to predict clinical problems in these patients.

MATERIALS AND METHODS

The study included 125 patients treated with bilateral ASR hip resurfacing (HRA) and 93 patients treated with bilateral ASR XL total hip arthroplasty (THA) at a mean follow-up of 7.1 years post-surgery. Patients were labelled as well- or poorly-functioning based on strict criteria. We calculated the Co and Cr safe upper ion limits (SUL) for ASR HRA and ASR XL THA separately and assessed these cutoffs ability to predict clinical problems.

RESULTS

In patients with bilateral ASR HRA, the well-functioning group had lower ions than the poorly-functioning. In ASR THA patients, there was no difference in blood Co or Cr levels between well- and poorly-functioning implant groups (p = 0.118 and p = 0.379, respectively). Both Co and Cr could effectively discriminate between well-functioning and poorly-functioning ASR HRA implants (p < 0.001 and p < 0.001, respectively), but not for ASR THA implants (p = 0.118 and p = 0.564, respectively). SULs of 4.0 ppb for Co and 4.0 ppb for Cr could differentiate between well- and poorly-functioning implants with high specificity.

CONCLUSIONS

Metal ion levels are a more reliable tool in MoM HRA than THA when discriminating well- from poorly-functioning implants in bilateral patients. For patients treated with bilateral ASR HRA, ion levels above 4.0 ppb are highly specific for the detection of clinical problems.

The Outcome of Revision Surgery for Failed Metal-on-Metal Total Hip Arthroplasty

BACKGROUND

Metal-on-metal total hip arthroplasties (MoM THAs) are frequently revised, though there is a paucity of functional outcome data. We report on outcomes and prognostic factors predictive of outcome from the largest series of MoM THA revisions to date.

METHODS

A single-center consecutive series of revisions from MoM THAs was identified. The cohort was divided by the presence or absence of symptoms prior to revision. The primary outcome was functional outcome (Oxford Hip Score [OHS]). Secondary outcomes were complication data, pre-revision and post-revision blood metal ions, and modified Oxford classification of pre-revision magnetic resonance imaging.

RESULTS

One hundred eighty revisions at median follow-up of 5.48 years were identified. Median OHS improved from 29 to 37 with revision (P < .001). Symptomatic patients experienced the greatest functional benefit (ΔOHS 6.5 vs 1.4, P = .012), while the function of asymptomatic patients was unaffected by revision (P = .4). Use of a cobalt-chromium-containing bearing surface at revision and increased body mass index were predictive of poor functional outcome.

CONCLUSION

Symptomatic patients experience greater functional benefit from revision surgery but do not regain the same level of function as patients who were asymptomatic prior to revision. Body mass index and use of cobalt-chromium-containing bearing surfaces are prognostic for poor functional outcome.

Mechanisms of Adverse Local Tissue Reactions to Hip Implants

Adverse Local Tissue Reactions (ALTRs) are one of the main causes of hip implant failures. Although the metal release from the implants is considered as a main etiology, the mechanisms, and the roles of the released products are topics of ongoing research. The alloys used in the hip implants are considered biocompatible and show negligible corrosion in the body environment under static conditions. However, modularity and its associated mechanically assisted corrosion have been shown to release metal species into the body fluids. ALTRs associated with metal release have been observed in hip implants with metal-on-metal articulation initially, and later with metal-on-polyethylene articulation, the most commonly used design in current hip replacement. The etiological factors in ALTRs have been the topics of many studies. One commonly accepted theory is that the interactions between the metal species and body proteins and cells generate a delayed type IV hypersensitivity reaction leading to ALTRs. However, lymphocyte reactions are not always observed in ALTRS, and the molecular mechanisms have not been clearly demonstrated. A more accepted mechanism is that cell damage generated by metal ions may trigger the secretion of cytokines leading to the inflammatory reactions observed in ALTRs. In this inflammatory environment, some patients would develop hypersensitivity that is associated with poor outcomes. Concerns over ALTRS have brought significant impact to both the clinical selection and development of hip implants. This review is focused on the mechanisms of ALTRs, specifically, the metal release process and the roles of the metal species released in the etiology and pathogenesis of the disease. Hopefully, our presentation and discussion of this biological process from a material perspective could improve our current understanding on the ALTRs and provide useful guidance in developing preventive solutions.

The 10-year outcomes of the ASR XL Acetabular System: a single-center experience from China

Background

The revision rate of articular surface replacement (ASR) implants continues to rise in China because of metal debris. However, there are few reports on the clinical results of ASR implants with prolonged follow-up time in China. This study investigated the clinical outcomes and the risk factors of revision surgery in patients with ASR implants.

Methods

In total, 74 patients (74 hips) who underwent primary total hip arthroplasty (THA) with ASR implants over the past 4 to 10 years were retrospectively analyzed. Relevant clinical, radiographic, and biochemical data were examined.

Results

The average follow-up time was 88.46 (range 23–114) months, and the ASR implants of 18 hips (24.3%) were revised. Patients who received revision surgery had worse joint function with significantly lower Harris Hip Score and Western Ontario and McMaster Universities index than non-revision patients (61.11 ± 6.68 vs 85.30 ± 9.16, p < 0.001; 61.00 ± 3.83 vs 79.04 ± 14.49, p < 0.001; respectively). Higher acetabular abduction angle and serum Co and Cr concentration were significantly relevant to worse joint function as measured by HSS (p = 0.018, 0.009, 0.043, respectively). ROC curve analysis was applied to categorize the optimal cutoff values of acetabular abduction angle and serum Cr and Co concentration for revision surgery, which were settled as 47.80°, 98.44 μg/L, and 6.95 μg/L, respectively. Overall survival of the prostheses with high acetabular abduction angle (> 47.80°, HR = 70.145, 95% CI 1.558–3158.213, p = 0.029), high serum Cr concentration (98.44 μg/L, HR = 58.956, 95% CI 1.294–2685.203, p = 0.036), and high serum Co concentration (> 6.95 μg/L, HR = 179.511, 95% CI 2.360–13656.941, p = 0.019) decreased significantly than the lower groups.

Conclusions

Evaluation of the DePuy ASR XL articulation demonstrated increased rates of revision following a longer follow-up period. High acetabular abduction angle and serum Cr and Co concentration correlated with worse clinical outcomes and high revision rate. Therefore, we advocate that patients with DePuy ASR XL implants be followed up more closely than those with other implants, especially with high acetabular abduction angle and serum Cr or Co concentration.

Long-term results of the M2A-38-mm metal-on-metal articulation

Background

Large-diameter head metal-on-metal (MoM) bearings in total hip arthroplasty (THA) are associated with increased whole blood levels of chromium (Cr) and cobalt (Co), adverse reactions to metal debris (ARMD) and poor survival rates. The prevalence of high metals concentrations, ARMD and the risk of revision surgery may vary significantly among different prostheses and long-term studies are few. This single-center study reports the long-term results of the 38-mm MoM bearing system.

Materials and methods

Between 2003 and 2009, 80 patients received primary cementless THA using the large head metal-on-metal articulating surface M²A-38 cup (Biomet, Inc., Warsaw, IN, USA) at a single institution. Forty-five patients (53 hips) were retrospectively reviewed for a mean follow-up of 127 months.

Results

Two cups were revised. The cumulative implant survival rate was 98% at 10 years and 74% at 13 years. In the whole sample, the median Co and Cr concentrations were 4.8 µg/L (IQR 1.2–4.9 µg/L) and 2.5 µg/L (IQR 0.6–3.0 µg/L), respectively. The incidence of Co or Cr levels > 7 μg/L was 15.5% and the incidence of ARMD was 3.8%. Co and Cr levels showed no correlation with cup inclination, Harris Hip Score, or total Hip Disability and Osteoarthritis Outcome score.

Conclusions

Our results confirm that the problems of release of metal ions with the possible increase of metal circulating levels and of adverse reactions may also occur in the long term with this brand of MoM large head, and that a structured follow-up program is mandatory.

Levels of evidence

Level 4.

Liner dissociation leading to catastrophic failure of an Oxinium femoral head

Oxinium is an alternative bearing surface designed to emulate the superior wear and scratch properties of ceramic femoral heads in total hip arthroplasty while minimizing the risk for brittle fracturing. However, recent studies have indicated that hip dislocation following total hip arthroplasty may be a risk factor for catastrophic failure of the femoral head. Here, we report on a novel case of a catastrophic Oxinium head and polyethylene liner failure in the absence of previous hip dislocation or trauma and review the probable failure mechanism. This report underscores the need to be vigilant about proper acetabular cup and liner seating, particularly in the setting of Oxinium femoral head use. In the event of Oxinium head failure, metallosis may compromise stabilizing soft tissues including the abductors. Dual-mobility articulation, which was successful in this case, is one option to consider when the risk for chronic redislocation is elevated.

What is appropriate surveillance for metal-on-metal hip arthroplasty patients?

The unexpected high revision rates of large-diameter (femoral head sizes of 36 mm or greater) metal-on-metal hip arthroplasties (MoMHAs) have led to worldwide regulatory authorities recommending regular surveillance, even for asymptomatic individuals. However, these recommendations are not evidence-based and are very costly. The rapidly evolving evidence base requires an update regarding the investigation and management of MoMHA patients. This article is the first of 2 (the second article in this series will consider the threshold for performing revision, and the outcomes following ARMD revision surgery: Matharu et al., Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris: A clinical update. Acta Orthop 2018; in press), and considers the various investigative modalities used during surveillance, with specific focus on blood metal ion sampling and cross-sectional imaging. No single investigation can universally be used during MoMHA patient surveillance. Recent studies have now provided important information on interpreting blood metal ions (effective in identifying patients at low risk of problems), clarifying the roles of cross-sectional imaging (reserve combined ultrasound and MARS-MRI for complex cases), and providing parameters to safely exclude many asymptomatic patients from regular surveillance. This information will be useful when designing future surveillance protocols for MoMHA patients.

Blood Metal Ion Levels Have Limited Utility in the Surveillance of Asymptomatic Large-Head Metal-on-Metal Total Hip Arthroplasties

BACKGROUND

Blood cobalt (Co) and chromium (Cr) ion levels have been used as surveillance tools for adverse reaction to metal debris (ARMD) in metal-on-metal (MoM) articulations with varying thresholds in different countries. The aim of our study is to present the serial 12-year blood Co and Cr levels in a cohort of MoM total hip arthroplasties (THAs) with femoral head size ≥36 mm and analyze their utility in asymptomatic patients at current thresholds.

METHODS

A total of 256 patients with unilateral MoM THA with femoral head size ≥36 mm were included in this study with data collected prospectively. The implants used were Birmingham hip resurfacing cup-Freeman stem (BHR-F) or an Articular Surface Resurfacing cup-Corail/S-ROM stem. Annual follow-up with blood Co and Cr measurements was done as per Medicines and Healthcare Products Regulatory Agency (MHRA) of the United Kingdom guidelines. Receiver operating characteristic curve was plotted based on the sensitivity and specificity of blood metal ion values to detect ARMD. The metal ion levels in asymptomatic patients were analyzed separately.

RESULTS

Receiver operating characteristic curves showed poor discriminatory ability for both Co and Cr values in predicting ARMD at 7 μg/L. The sensitivity of Co and Cr was 82.1% and 53.5%, respectively, and their positive predictive values were 43.8% and 67.6%, respectively. After 7 years, there was no significant change in Co values, and there was a decline in Cr value after 9 years in asymptomatic patients.

CONCLUSION

To the best of our knowledge, this is the first study to describe the behavior of serial blood metal ion levels in asymptomatic large-diameter MoM THA. We suggest that annual blood Co and Cr have limited discriminant capacity in diagnosing the occurrence of metallosis and their measurement beyond 7 years is of limited utility in asymptomatic patients.

Comparison of metal ion concentrations and implant survival after total hip arthroplasty with metal-on-metal versus metal-on-polyethylene articulations

Background and purpose - Large metal-on-metal (MoM) articulations are associated with metal wear and corrosion, leading to increased metal ion concentrations and unacceptable revision rates. There are few comparative studies of 28-mm MoM articulations with conventional metal-on-polyethylene (MoP) couplings. We present a long-term follow-up of a randomized controlled trial comparing MoM versus MoP 28-mm articulations, focused on metal ions and implant survival. Patients and methods - 85 patients with a mean age of 65 years at surgery were randomized to a MoM (Metasul) or a MoP (Protasul) bearing. After 16 years, 38 patients had died and 4 had undergone revision surgery. 13 patients were unavailable for clinical follow-up, leaving 30 patients (n = 14 MoM and n = 16 MoP) for analysis of metal ion concentrations and clinical outcome. Results - 15-year implant survival was similar in both groups (MoM 96% [95% CI 88-100] versus MoP 97% [95% CI 91-100]). The mean serum cobalt concentration was 4-fold higher in the MoM (1.5 μg/L) compared with the MoP cohort (0.4 μg/L, p < 0.001) and the mean chromium concentration was double in the MoM (2.2 μg/L) compared with the MoP cohort (1.0 μg/L, p = 0.05). Mean creatinine levels were similar in both groups (MoM 93 μmol/L versus MoP 92 μmol/L). Harris hip scores differed only marginally between the MoM and MoP cohorts. Interpretation - This is the longest follow-up of a randomized trial on 28-mm MoM articulations, and although implant survival in the 2 groups was similar, metal ion concentrations remained elevated in the MoM cohort even in the long term.

Blood Metal Ion Thresholds to Identify Patients with Metal-on-Metal Hip Implants at Risk of Adverse Reactions to Metal Debris: An External Multicenter Validation Study of Birmingham Hip Resurfacing and Corail-Pinnacle Implants

BACKGROUND

The authors of recent studies have reported newly devised implant-specific blood metal ion thresholds to predict adverse reactions to metal debris (ARMD) in patients who have undergone unilateral or bilateral metal-on-metal (MoM) hip arthroplasty. These thresholds were most effective for identifying patients at low risk of ARMD. We investigated whether these newly devised blood metal ion thresholds could effectively identify patients at risk of ARMD after MoM hip arthroplasty in an external cohort of patients.

METHODS

We performed a validation study involving 803 MoM hip arthroplasties (323 unilateral Birmingham Hip Resurfacing [BHR], 93 bilateral BHR, and 294 unilateral Corail-Pinnacle implants) performed in 710 patients at 3 European centers. All patients underwent whole-blood metal ion sampling, and were divided into 2 groups: those with ARMD (leading to revision or identified on imaging; n = 75) and those without ARMD (n = 635). Previously devised implant-specific blood metal ion thresholds (2.15 μg/L of cobalt for unilateral BHR; 5.5 μg/L for the maximum of either cobalt or chromium for bilateral BHR; and 3.57 μg/L of cobalt for unilateral Corail-Pinnacle implants) were applied to the validation cohort, and receiver operating characteristic curve analysis was used to establish the discriminatory characteristics of each threshold.

RESULTS

The area under the curve, sensitivity, specificity, and positive and negative predictive values for the ability of each implant-specific threshold to distinguish between patients with and without ARMD were, respectively, 89.4% (95% confidence interval [CI] = 82.8% to 96.0%), 78.9%, 86.7%, 44.1%, and 96.9% for unilateral BHR; 89.2% (CI = 81.3% to 97.1%), 70.6%, 86.8%, 54.5%, and 93.0% for bilateral BHR; and 76.9% (CI = 63.9% to 90.0%), 65.0%, 85.4%, 24.5%, and 97.1% for unilateral Corail-Pinnacle implants. Using the implant-specific thresholds, we missed 20 patients with ARMD (2.8% of the patients in this series). We missed more patients with ARMD when we used the fixed thresholds proposed by regulatory authorities: 35 (4.9%) when we used the U.K. threshold of 7 μg/L for both cobalt and chromium (p = 0.0003), 21 (3.0%) when we used the U.S. threshold of 3 μg/L for both cobalt and chromium (p = 1.0), and 46 (6.5%) when we used the U.S. threshold of 10 μg/L for both cobalt and chromium (p < 0.0001).

CONCLUSIONS

This external multicenter validation study confirmed that patients with blood metal ion levels below new implant-specific thresholds have a low risk of ARMD after MoM hip arthroplasty. Using these implant-specific thresholds, we missed fewer patients with ARMD compared with when the thresholds currently proposed by regulatory authorities were used. We therefore recommend using implant-specific blood metal ion thresholds when managing patients who have undergone MoM hip arthroplasty.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.

The Utility of Metal Ion Trends in Predicting Revision in Metal-on-Metal Total Hip Arthroplasty

BACKGROUND

There is a paucity of data examining metal ion levels over time.

METHODS

We retrospectively reviewed 59 patients (69 hips) with an articular surface replacement total hip arthroplasty. We reviewed prerevision cobalt and chromium concentrations over time.

RESULTS

Seventy-one percent of patients who were revised and had multiple ion measurements (12/17) demonstrated increasing cobalt ion levels or elevated ion levels over time. There was a trend toward an elevated risk of revision for increasing cobalt and chromium levels starting at 12 and 4 ppb, respectively; this was significant for chromium levels above 7 ppb (hazard ratio 22.35, P = .001). Similarly, there was a trend toward an elevated risk of pseudotumor formation for increasing cobalt and chromium levels starting at 5 and 2.5 ppb, respectively; this was significant for cobalt levels above 7 ppb (hazard ratio 6.88, P = .027).

CONCLUSION

In this paper, cobalt and chromium levels levels above 5 and 2.5 ppb started to demonstrate an increased risk of ARMD, and should be considered as a lower cutoff for discussion with patients about the potential for future revision.

Correlation between serum metal ion levels and adverse local tissue reactions after Conserve® Plus hip resurfacing arthroplasty

BACKGROUND

Adverse local tissue reactions (ALTR) have been associated with the use of metal-on-metal (MoM) bearings and the monitoring of cobalt (Co) and chromium (Cr) ion levels in blood or serum may be the best way to evaluate in vivo the wear of these bearings. However, the relationship between Co and Cr ion concentrations and the formation of ALTR remains unclear.

METHODS

We investigated the relationship between ALTR and serum Co and Cr ion levels and identified the clinical factors influencing the formation of ALTR in patients treated with MoM hip resurfacing arthroplasties. 228 patients with unilateral Conserve® Plus MoM hip resurfacing had serum metal ion studies performed more than 1 year after surgery. Metal artifact reduction sequence magnetic resonance imaging (MARS MRI) was performed on subjects at risk for ALTR as determined by a screening protocol.

RESULTS

12 patients had ALTR. Logistic regression showed a strong association of ALTR with elevated ion levels and with low (<10 mm) contact patch to rim distance.

CONCLUSIONS

MoM bearings require enough functional coverage of the socket by design and then precise implantation to maximise functional coverage of the femoral ball, enhance lubrication, and avoid edge-loading wear.

Risk factors for wear-related failures after hip resurfacing in patients with a low contact patch to rim distance

Aims

A contact patch to rim (CPR) distance of < 10 mm has been associated with edge-loading and excessive wear. However, not all arthroplasties with a low CPR distance show problems with wear. Therefore, CPR distance may not be the only variable affecting the post-operative metal ion concentrations.

Patients and Methods

We used multiple logistic regression to determine what variables differed between the patients who had high and low cobalt (CoS) and chromium (CrS) serum ion concentrations within a cohort of patients with low (< 10 mm) CPR distances. A total of 56 patients treated with unilateral hip resurfacing arthroplasty (HRA) had CoS and CrS ion studies performed more than one year after surgery. The mean age of the patients at the time of surgery was 51.7 years (29 to 70), with 38 women (68%) and 18 men (32%).

Results

It was seen that 47 patients had low ion levels (< 7µg/L) and nine had high ion levels (≥ 7µg/L). We found increased risks of high wear with decreasing CPR distance.

Conclusion

The use of CPR distance measurements to predict hips at risk for elevated wear is needed for all patients with HRA. We recommend that patients with low CPR distances have at least one serum ion study performed while patients with CPR distance > 10 mm do not need routine ion studies. We believe that patients with low CPR distance and low ions do not need repeat ion studies unless the patient becomes symptomatic or has substantial radiographic changes. Cite this article: Bone Joint J 2017;99-B:865–71.

Cobalt toxicity in humans-A review of the potential sources and systemic health effects

Cobalt (Co) and its compounds are widely distributed in nature and are part of numerous anthropogenic activities. Although cobalt has a biologically necessary role as metal constituent of vitamin B₁₂, excessive exposure has been shown to induce various adverse health effects. This review provides an extended overview of the possible Co sources and related intake routes, the detection and quantification methods for Co intake and the interpretation thereof, and the reported health effects. The Co sources were allocated to four exposure settings: occupational, environmental, dietary and medical exposure. Oral intake of Co supplements and internal exposure through metal-on-metal (MoM) hip implants deliver the highest systemic Co concentrations. The systemic health effects are characterized by a complex clinical syndrome, mainly including neurological (e.g. hearing and visual impairment), cardiovascular and endocrine deficits. Recently, a biokinetic model has been proposed to characterize the dose-response relationship and effects of chronic exposure. According to the model, health effects are unlikely to occur at blood Co concentrations under 300μg/l (100μg/l respecting a safety factor of 3) in healthy individuals, hematological and endocrine dysfunctions are the primary health endpoints, and chronic exposure to acceptable doses is not expected to pose considerable health hazards. However, toxic reactions at lower doses have been described in several cases of malfunctioning MoM hip implants, which may be explained by certain underlying pathologies that increase the individual susceptibility for Co-induced systemic toxicity. This may be associated with a decrease in Co bound to serum proteins and an increase in free ionic Co²⁺. As the latter is believed to be the primary toxic form, monitoring of the free fraction of Co²⁺ might be advisable for future risk assessment. Furthermore, future research should focus on longitudinal studies in the clinical setting of MoM hip implant patients to further elucidate the dose-response discrepancies.

What Are Normal Metal Ion Levels After Total Hip Arthroplasty? A Serologic Analysis of Four Bearing Surfaces

BACKGROUND

The recent experiences with adverse local tissue reactions have highlighted the need to establish what are normal serum levels of cobalt (Co), chromium (Cr), and titanium (Ti) after hip arthroplasty.

METHODS

Serum Co, Cr, and Ti levels were measured in 80 nonconsecutive patients with well-functioning unilateral total hip arthroplasty and compared among 4 bearing surfaces: ceramic-on-ceramic (CoC); ceramic-on-polyethylene (CoP); metal-on-polyethylene (MoP), and dual mobility (DM). The preoperative and most recent University of California, Los Angeles (UCLA) and Western Ontario and McMaster Universities Arthritis Index (WOMAC) scores were compared among the different bearing surfaces.

RESULTS

No significant difference was found among serum Co and Cr levels between the 4 bearing surface groups (P = .0609 and P = .1577). Secondary analysis comparing metal and ceramic femoral heads demonstrated that the metal group (MoP, modular dual mobility (Stryker Orthopedics, Mahwah, NJ) [metal]) had significant higher serum Co levels compared with the ceramic group (CoC, CoP, MDM [ceramic]) (1.05 mg/L ± 1.25 vs 0.59 mg/L ± 0.24; P = .0411). Spearman coefficient identified no correlation between metal ion levels and patient-reported outcome scores.

CONCLUSION

No serum metal ion level differences were found among well-functioning total hip arthroplasty with modern bearing couples. Significantly higher serum Co levels were seen when comparing metal vs ceramic femoral heads in this study and warrants further investigation. Metal ion levels did not correlate with patient-reported outcome measures.

Mid-term changes in blood metal ion levels after Articular Surface Replacement arthroplasty of the hip

AIMS

Our first aim was to determine whether there are significant changes in the level of metal ions in the blood at mid-term follow-up, in patients with an Articular Surface Replacement (ASR) arthroplasty. Secondly, we sought to identify risk factors for any increases.

PATIENTS AND METHODS

The study involved 435 patients who underwent unilateral, metal-on-metal (MoM) hip resurfacing (HRA) or total hip arthroplasty (THA). These patients all had one measurement of the level of metal ions in the blood before seven years had passed post-operatively (early evaluation) and one after seven years had passed post-operatively (mid-term evaluation). Changes in ion levels were tested using a Wilcoxon signed-rank test. We identified subgroups at the highest risk of increase using a multivariable linear logistic regression model.

RESULTS

There were significant increases in the levels of metal ions for patients who underwent both MoM HRA (Chromium (Cr): 0.5 parts per billion (ppb); Cobalt (Co): 1.1 ppb) and MoM THA (Cr: 0.5 ppb; Co: 0.7 ppb). In a multivariable model considering MoM HRAs, the change in the levels of metal ions was influenced by female gender (Co: Odds Ratio (OR) 1.42; p = 0.002 and Cr: OR 1.08; p = 0.006). The change was found to be irrespective of the initial level for the MoM HRAs, whereas there was a negative relationship between the initial level and the change in the level for those with a MoM THA (Co: OR -0.43; p < 0.001 and Cr: OR -0.14; p = 0.033).

CONCLUSION

The levels of metal ions in the blood increase significantly over the period until mid-term follow-up in patients with both a MoM HRA and those with a MoM THA. We recommend that the levels of metal ions be measured most frequently for women with a MoM HRA. While those with a MoM THA appear to stabilise at a certain level, the accuracy of this trend is not yet clear. Vigilant follow-up is still recommended. Cite this article: Bone Joint J 2017;99-B(4 Supple B):33-40.

601 metal-on-metal total hip replacements with 36 mm heads a 5 minimum year follow up: Levels of ARMD remain low despite a comprehensive screening program

BACKGROUND

We conducted a retrospective study to assess the clinical outcome, failure rate, and reason for failure of a large consecutive series of 36 mm MoM Corail/Pinnacle total hip replacements (THRs).

METHODS

Between 2006 and 2011, 601 consecutive 36 mm MoM THRs were performed (585 patients). Patients were followed according to the UK Medicines and Healthcare Products Regulatory Agency (MHRA) guidelines. All patients were accounted for and 469 patients (78%) were clinically and radiographically assessed. 328 females and 141 males with a median age of 73 (range 36-94 years) and a median follow up of 7.2 years (range 5.2-9.7 years) were followed. Clinical data included blood cobalt and chromium, Oxford Hip Score (OHS), plain radiograph, ultrasound of hip and intra-operative findings in those patients who had revision surgery.

RESULTS

56 patients died of causes unrelated to their hip replacement. The mean survivorship of the implant was 92.8% (range 91.6-94%, 95% CI) at a median time to follow up of 84 months (62-113 months). The functional outcome was good with a median OHS of 38 out of 48 (23-44). The dislocation rate was 0.99%, with all these 6 cases requiring revision. 476 patients had blood tests. 100 patients (21%) had elevated levels of either cobalt above MHRA guidelines of 7 parts per billion (120 and 135 nmol/L respectively for cobalt and chromium). Cobalt was elevated independently of chromium in 75% of the cases (but never vice versa). The mean cup inclination angle was 42°. Each incremental stem size increase resulted in a decrease in cobalt by 11 nmol/L. The most common reason for revision was adverse reaction to metal debris (ARMD) (12 cases).

CONCLUSION

This paper is the largest and longest follow up of 36 mm MoM THRs. Using the MHRA guidelines for follow up, the revision rates of this cohort has remained low compared to other studies, but unacceptably higher than that of other bearing surfaces.

LEVEL OF EVIDENCE

III.

Recall of the ASR XL Head and Hip Resurfacing Systems

At the beginning of the 21st century, use of large-diameter, metal-on-metal devices was a popular procedure for hip replacement in young and physically active patients; however, within a few years, the number of revisions increased, resulting in a worldwide recall for the articular surface replacement (ASR) system. Complication rates for the ASR devices implanted at the authors' department are reported, with revision rates of 32% and 30% in the ASR XL Head and ASR Resurfacing groups, respectively. Reasons for revision surgery were serum metal ion elevation, luxation or subluxation, aseptic loosening, soft tissue compromise (adverse reactions to metal debris [ARMD]), and infection. The calculated implant survival for the ASR XL Head system and the ASR Resurfacing device (DePuy Orthopaedics Inc, Warsaw, Indiana) in the current series was 79% and 90%, respectively, at 60 months. Symptomatic patients with metal-on-metal devices, with or without elevated metal ion concentrations, should undergo cross sectional imaging to exclude ARMD. In cases of increased metal ion concentrations, local pain, or ARMD, revision surgery has to be evaluated. In the future, closer monitoring of new implants is needed to prevent high failure rates, as seen with the ASR design. Furthermore, the withdrawal of the device highlights the importance of national implant registries. [Orthopedics. 2017; 40(2):e340-e347.].

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.

Can blood metal ion levels be used to identify patients with bilateral Birmingham Hip Resurfacings who are at risk of adverse reactions to metal debris?

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.

Outcomes of the Recalled Articular Surface Replacement Metal-on-Metal Hip Implant System: A Systematic Review

BACKGROUND

The aim of this review was to synthesize the main findings of clinical studies that have evaluated outcomes of the articular surface replacement (ASR) Hip System.

METHODS

We performed a systematic literature search to identify all articles published between January 2008 and June 2015 that included ASR hip resurfacing arthroplasty (ASR HRA) or ASR total hip arthroplasty (ASR XL THA) outcomes according to the PRISMA statement.

RESULTS

A total of 56 studies were assessed. The prevalence of adverse local tissue reactions (ALTRs) and revision rates were found to be high. ALTR prevalence varied from 12.5% to 69% (mean, 33.5%). Mean revision rate for any reason at 4-year to 7-year follow-up was 13.8% (range, 5.6%-31%) for ASR HRA and 14.5% (range, 0%-37%) for ASR XL THA. Femoral head size <53 mm was found to correlate with higher blood metal ion levels. Femoral head size >44 mm was not associated with higher ALTR prevalence or revision rates in ASR XL THA. High blood metal ion levels (>7 μg/L Co, >7 μg/L Cr) were associated with higher failure rates and bearing-related complications. The role of cup positioning was found to be controversial.

CONCLUSION

ALTR prevalence and failure rates were high. High blood metal ion levels were a risk factor for ALTR and failure. Surprisingly, the role of cup positioning and large femoral head size in ASR XL THA were controversial. These findings should be considered in the clinical follow-up and risk stratification of patients with the ASR Hip System.

Cobalt Cardiomyopathy

Cobalt can cause a distinctive, rapidly progressive and reversible depression of cardiac systolic function, which is readily distinguished from other causes of cardiomyopathy. Patients present with the subacute onset of severe heart failure, which is accompanied by hypotension and cyanosis, pericardial effusion, low voltage on the electrocardiogram, marked elevation of serum enzymes, and lactic acidosis. They typically have a history of lethargy, anorexia, and weight loss in the months preceding the illness and exhibit other evidence of cobalt’s effects on the body (eg, polycythemia and goiter). The course of cobalt-related cardiomyopathy may be progressive and fatal, but those who survive and cease exposure generally demonstrate complete resolution of symptoms and recovery of cardiac function. Patients presenting with rapid onset of cardiomyopathy, who also exhibit polycythemia, pericardial effusion, or goiter should be evaluated for cobalt exposure. Exposure can be confirmed by the measurement of cobalt in the serum, but serum levels of the ion are not reliably predictive of clinical cardiotoxicity. The clinical emergence of cobalt cardiomyopathy seems to require the coexistence of one or more cofactors, particularly a low-protein diet, thiamine deficiency, alcoholism, and hypothyroidism. As the medicinal use of cobalt has waned and measures to reduce industrial exposure have been implemented, subacute cobalt-related cardiomyopathy had become rare. However, reports describing classical features of the disease have recently surged among patients with a malfunctioning cobalt-alloy hip prosthesis.

Platelet-lymphocyte ratios: a potential marker for pulmonary tuberculosis diagnosis in COPD patients

BACKGROUND

In recent decades, morbidity and mortality have been found to be significantly increased in patients with chronic obstructive pulmonary disease (COPD) complicated with pulmonary tuberculosis (PTB). Platelet-lymphocyte ratio (PLR) is an indicator for inflammatory diseases. This study aims to investigate whether PLR could act as a potential marker for patients with COPD complicated with PTB.

METHODS

In this retrospective study, laboratory characteristics of 87 COPD patients complicated with PTB (determined by Mycobacterium tuberculosis positive culture from sputum or bronchial lavage fluid) and 83 COPD patients (as the control group, determined by M. tuberculosis culture negativity from sputum or bronchial lavage fluid) were investigated. Data obtained on the day of admission were analyzed.

RESULTS

PLR >216.82 was identified as the optimal cutoff value for discriminating COPD patients with PTB (sensitivity 92.4%, specificity 84.5%, positive-predictive value 91.6%, negative-predictive value 86.2%, and area under the curve [AUC] was 0.87) from patients with COPD alone. The AUC of PLR was significantly greater than that of neutrophil-lymphocyte count ratio (AUC, 0.74; 95% confidence interval, 0.67-0.81; P<0.01).

CONCLUSION

PLR could be developed as a valuable maker for identifying tuberculosis infection in COPD patients.

Predicting high blood metal ion concentrations following hip resurfacing

PURPOSE

To determine whether gender, femoral head size, acetabular inclination, and time since surgery predicted high blood metal ion concentrations following Birmingham Hip Resurfacing (BHR).

METHODS

BHR patients with unilateral bearings at one specialist centre with blood cobalt and chromium concentrations measured up to May 2013 were included. This comprised a mixed (at-risk) group including symptomatic patients and asymptomatic individuals with specific clinical and/or radiological findings. Blood sampling was at a mean of 7.5 years (range 1-15.4 years) postoperatively.

RESULTS

Of 319 patients (mean age 49.3 years; 53% male), blood metal ions greater than 7 µg/l were observed in 9% (n = 28). Blood metal ions were significantly higher in females (p&lt;0.001), femoral head sizes ≤48 mm (p&lt;0.01), and cup inclinations &gt;55° (p&lt;0.001). Linear regression demonstrated femoral head size was responsible for the highest proportion of variance in blood metal ions (cobalt p&lt;0.001, R2 = 8%; chromium p&lt;0.001, R2 = 11%). Analysis of femoral head size and inclination together demonstrated 36% of BHRs with head sizes of 38-44 mm and inclination &gt;55° had blood metal ions &gt;7 µg/l. BHR 10-year survival for this at-risk group was 91% (95% confidence intervals 86.0%-95.0%) with 30 hips revised.

CONCLUSIONS

If blood metal ions are used to screen hip resurfacing patients for adverse reactions to metal debris it is recommended those with small femoral head sizes (38-44 mm) and high acetabular inclinations (&gt;55°) are targeted. These findings require validation in other cohorts as they may not be applicable to all hip resurfacing devices given the differences in radial clearance, coverage arc, and metallurgy.

A Comparison of Blood Metal Ions in Total Hip Arthroplasty Using Metal and Ceramic Heads

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.

Blood metal ion levels are not a useful test for adverse reactions to metal debris: A systematic review and meta-analysis

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.

What Is the Natural History of "Asymptomatic" Pseudotumours in Metal-on-Metal Hip Arthroplasty? Minimum 4-Year Metal Artifact Reduction Sequence Magnetic Resonance Imaging Longitudinal Study

BACKGROUND

Metal Artifact Reduction Sequence Magnetic Resonance Imaging (MARS-MRI) is an important cross-sectional imaging modality in detection of metal-on-metal (MoM) hip arthroplasty (HA) pseudotumours. Potential evolution of pseudotumours detected by MARS-MRI in "asymptomatic" patients with MoMHA arthroplasty beyond 2 years remains largely unknown. The aims of this longitudinal study were to (1) determine the natural history of pseudotumours in "asymptomatic" MoMHA patients under MARS-MRI surveillance and (2) characterize MRI feature(s) associated with progressive pseudotumours.

METHODS

A total of 37 MoMHA (32 patients, mean 56 years old) with pseudotumours on MARS-MRI were evaluated longitudinally using a standardized MARS-MRI protocol. Serum cobalt and chromium levels, pseudotumour size, thickness of the cyst wall, and MRI signal intensity of the abnormality were recorded and analyzed.

RESULTS

At minimum of 4-year follow-up (range 49-54 months), 4 Type II pseudotumours (11%) demonstrated MRI evidence of progression. Five Type I pseudotumours (14%) were found to have "regressed." No measurable MRI progression was detected in remaining patients (75%). MRI features associated with progressive pseudotumours included the presence of increased cystic wall thickness and "atypical" mixed fluid signal. MRI pseudotumour progression was not associated with metal ion levels.

CONCLUSION

The natural history of type I cystic pseudotumours continues to be nonprogressive in most "asymptomatic" MoMHA patients at minimum 4 years, suggesting the importance of patient symptoms and MRI characteristic features in the clinical decision-making process. Routine follow-up MARS-MRI evaluation of "asymptomatic" patients with low-grade cystic pseudotumours in the absence of interval clinical changes may not be indicated.

Hip resurfacing: history, current status, and future

Hip resurfacing arthroplasty (HRA) presents several advantages over conventional total hip arthroplasty (THA), including conservation and preservation of bone, reduced risk of dislocation, easy replication of hip biomechanics and easy revision if needed. It is a particularly appealing procedure for young patients. HRA has been performed for over 40 years following the same technological advances as THA. The bearing material used by most designs is metal-on-metal (MoM), which has the best compromise between strength and wear properties. However, MoM HRA has a specific set of possible complications. Aseptic femoral failures were initially the most prevalent cause for revision but progress in patient selection and surgical technique seem to have resolved this problem. Wear-related failures (high metal ion levels and adverse local tissue reactions) are now the main concern, and are essentially associated with poor acetabular component design and orientation, to which MoM is more sensitive than other bearing materials. The concept of functional coverage is key to understanding how MoM bearings are affected by edge wear. Only a 3-D assessment of cup position (e.g., the contact patch to rim distance) provides the necessary information to determine the role of cup positioning in relationship with abnormal bearing wear.The concept of hip resurfacing is more valid today than ever as the age of the patients in need of hip arthroplasty keeps getting lower. The recent publication of several excellent long-term survivorship results suggests that selection of a well-designed resurfacing system and accuracy in the placement of the cup can achieve long-term durability.

The Effectiveness of Blood Metal Ions in Identifying Patients with Unilateral Birmingham Hip Resurfacing and Corail-Pinnacle Metal-on-Metal Hip Implants at Risk of Adverse Reactions to Metal Debris

BACKGROUND

We investigated whether blood metal ions could effectively identify patients with metal-on-metal hip implants with two common designs (Birmingham Hip Resurfacing [BHR] and Corail-Pinnacle) who were at risk of adverse reactions to metal debris.

METHODS

This single-center, prospective study involved 598 patients with unilateral hip implants (309 patients with the BHR implant and 289 patients with the Corail-Pinnacle implant) undergoing whole blood metal ion sampling at a mean time of 6.9 years. Patients were classified into two groups, one that had adverse reactions to metal debris (those who had to undergo revision for adverse reactions to metal debris or those with adverse reactions to metal debris on imaging; n = 46) and one that did not (n = 552). Three metal ion parameters (cobalt, chromium, and cobalt-chromium ratio) were compared between groups. Optimal metal ion thresholds for identifying patients with adverse reactions to metal debris were determined using receiver operating characteristic analysis.

RESULTS

All ion parameters were significantly higher (p < 0.0001) in the patients who had adverse reactions to metal debris compared with those who did not. Cobalt maximized the area under the curve for patients with the BHR implant (90.5%) and those with the Corail-Pinnacle implant (79.6%). For patients with the BHR implant, the area under the curve for cobalt was significantly greater than that for the cobalt-chromium ratio (p = 0.0005), but it was not significantly greater than that for chromium (p = 0.8483). For the patients with the Corail-Pinnacle implant, the area under the curve for cobalt was significantly greater than that for chromium (p = 0.0004), but it was similar to that for the cobalt-chromium ratio (p = 0.8139). Optimal blood metal ion thresholds for identifying adverse reactions to metal debris varied between the two different implants. When using cobalt, the optimal threshold for identifying adverse reactions to metal debris was 2.15 μg/L for the BHR group and 3.57 μg/L for the Corail-Pinnacle group. These thresholds had good sensitivities (88.5% for the BHR group and 80.0% for the Corail-Pinnacle group) and specificities (84.5% for the BHR group and 76.2% for the Corail-Pinnacle group), high negative predictive values (98.8% for the BHR group and 98.1% for the Corail-Pinnacle group), and low positive predictive values (34.3% for the BHR group and 20.0% for the Corail-Pinnacle group). The authority thresholds proposed by the United States (3 μg/L and 10 μg/L) and the United Kingdom (7 μg/L) missed more patients with adverse reactions to metal debris at 2.0% to 4.7% (twelve to twenty-eight patients) compared with our implant-specific thresholds at 1.2% (seven patients missed).

CONCLUSIONS

Patients who underwent metal-on-metal hip arthroplasty performed with unilateral BHR or Corail-Pinnacle implants and who had blood metal ions below our implant-specific thresholds were at low risk of adverse reactions to metal debris. These thresholds could be used to rationalize follow-up resources in asymptomatic patients. Analysis of cobalt alone is acceptable. Implant-specific thresholds were more effective than currently recommended fixed authority thresholds for identifying patients at risk of adverse reactions to metal debris requiring further investigation.

LEVEL OF EVIDENCE

Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Systemic cobalt toxicity from total hip arthroplasties

As adverse events related to metal on metal hip arthroplasty have been better understood, there has been increased interest in toxicity related to the high circulating levels of cobalt ions. However, distinguishing true toxicity from benign elevations in cobalt levels can be challenging. The purpose of this review is to examine the use of cobalt alloys in total hip arthroplasty, to review the methods of measuring circulating cobalt levels, to define a level of cobalt which is considered pathological and to review the pathophysiology, risk factors and treatment of cobalt toxicity. To the best of our knowledge, there are 18 published cases where cobalt metal ion toxicity has been attributed to the use of cobalt-chromium alloys in hip arthroplasty. Of these cases, the great majority reported systemic toxic reactions at serum cobalt levels more than 100 μg/L. This review highlights some of the clinical features of cobalt toxicity, with the goal that early awareness may decrease the risk factors for the development of cobalt toxicity and/or reduce its severity.

Take home message: Severe adverse events can arise from the release of cobalt from metal-on-metal arthroplasties, and as such, orthopaedic surgeons should not only be aware of the presenting problems, but also have the knowledge to treat appropriately.

Cite this article: Bone Joint J 2016;98-B:14–20.

The Interchangeability of Plasma and Whole Blood Metal Ion Measurement in the Monitoring of Metal on Metal Hips

One hundred and twenty six paired samples of plasma and whole blood were measured with inductively coupled plasma mass spectrometry technique for metal ions analysis to determine a relationship between them. There was a significant difference between the mean plasma and whole blood concentrations of both cobalt (Co) and chromium (Cr) (p < 0.0001 for both Co and Cr). The mean ratio between plasma and whole blood Cr and Co was 1.56 (range: 0.39-3.85) and 1.54 (range: 0.64-18.26), respectively, but Bland and Altman analysis illustrated that this relationship was not universal throughout the range of concentrations. There was higher variability at high concentrations for both ions. We conclude that both these concentrations should not be used interchangeably and conversion factors are unreliable due to concentration dependent variability.

Intraoperative Fluoroscopy Improves Component Position During Anterior Hip Arthroplasty

The goal of this retrospective review was to determine whether fluoroscopic guidance improves acetabular cup abduction and anteversion alignment during anterior total hip arthroplasty. The authors retrospectively reviewed 199 patients (fluoroscopy group, 98; nonfluoroscopy group, 101) who underwent anterior total hip arthroplasty at a single center with and without C-arm fluoroscopy guidance. Included in the study were patients of any age who underwent primary anterior approach total hip arthroplasty performed by a single surgeon, with 6-month postoperative anteroposterior pelvis radiographs. Acetabular cup abduction and anteversion angles were measured and compared between groups. Mean acetabular cup abduction and anteversion angles were 43.4° (range, 26.0°-57.4°) and 23.1° (range, 17°-28°), respectively, in the fluoroscopy group. Mean abduction and anteversion angles were 45.9° (range, 29.7°-61.3°) and 23.1° (range, 17°-28°), respectively, after anterior total hip arthroplasty without the use of C-arm guidance (nonfluoroscopy group). The use of fluoroscopy was associated with a statistically significant difference in cup abduction (P=.002) but no statistically significant difference in anteversion angles. In the fluoroscopy group, 80% of implants were within the combined safe zone compared with 63% in the nonfluoroscopy group. A significantly higher percentage of both acetabular cup abduction angles and combined anteversion and abduction angles were in the safe zone in the fluoroscopy group. Fluoroscopy is not required for proper anteversion placement of acetabular components, but it may increase ideal safe zone placement of components.

A longitudinal study of MARS MRI scanning of soft-tissue lesions around metal-on-metal total hip arthroplasties and disease progression

We investigated the changes seen on serial metal artefact reduction magnetic resonance imaging scans (MARS-MRI) of metal-on-metal total hip arthroplasties (MoM THAs). In total 155 THAs, in 35 male and 100 female patients (mean age 70.4 years, 42 to 91), underwent at least two MRI scans at a mean interval of 14.6 months (2.6 to 57.1), at a mean of 48.2 months (3.5 to 93.3) after primary hip surgery. Scans were graded using a modification of the Oxford classification. Progression of disease was defined as an increase in grade or a minimum 10% increase in fluid lesion volume at second scan. A total of 16 hips (30%) initially classified as ‘normal’ developed an abnormality on the second scan. Of those with ‘isolated trochanteric fluid’ 9 (47%) underwent disease progression, as did 7 (58%) of ‘effusions’. A total of 54 (77%) of hips initially classified as showing adverse reactions to metal debris (ARMD) progressed, with higher rates of progression in higher grades. Disease progression was associated with high blood cobalt levels or an irregular pseudocapsule lining at the initial scan. There was no association with changes in functional scores. Adverse reactions to metal debris in MoM THAs may not be as benign as previous reports have suggested. Close radiological follow-up is recommended, particularly in high-risk groups.

Cite this article: Bone Joint J 2015;97-B:1328–37.

Corrosion and Adverse Local Tissue Reaction in One Type of Modular Neck Stem

Modular neck stems allow for optimization of joint biomechanics by restoring anteversion, offset, and limb length. A potential disadvantage is the generation of metal ions from fretting and crevice corrosion. We identified 118 total hip arthroplasty implanted with one type of dual-modular femoral component. Thirty-six required revision due to adverse local tissue reaction. Multivariate analysis isolated females and low offset necks as risk factors for failure. Kaplan-Meir analysis revealed small stem sizes failed at a higher rate during early follow-up period. Although the cobalt/chrome levels were higher in the failed group, these tests had low diagnostic accuracy for ALTR, while MRI scan was more sensitive. We conclude that the complications related to the use of dual modular stems of this design outweigh the potential benefits.

Follow-Up of Metal-on-Metal Hip Arthroplasty Patients Is Currently Not Evidence Based or Cost Effective

Over one-million patients worldwide have received metal-on-metal (MoM) hip arthroplasties with a significant proportion requiring revision surgery in the short-term for adverse reaction to metal debris (ARMD). Worldwide authorities have subsequently issued follow-up guidance for MoM hip patients. This article compares follow-up guidelines for MoM hips published by five worldwide authorities, analyses these protocols in relation to published evidence, and assesses the financial implications of these guidelines. A number of major differences exist between authorities regarding patient follow-up, with vast cost differences between protocols (£84 to £988/patient/year for stemmed MoM hips and £0 to £988/patient/year for hip resurfacing). Current worldwide guidance is neither evidence-based nor financially sustainable with most protocols lacking the sensitivity to detect asymptomatic ARMD lesions.

Blood metal ions after hybrid metal-on-polyethylene Exeter-Trident total hip replacement

Background

Metal-on-metal total hip replacements (THRs) with large femoral heads have been associated with elevated levels of cobalt (Co) and chromium (Cr), which have been attributed to high levels of wear at the articular surface. Our unit recently published data showing a significant increase in the mean levels of Co ions in patients with a 36-mm diameter femoral head with the metal-on-polyethylene Trident−Accolade system. The aim of this study is to assess the levels of Co and Cr in the Exeter−Trident hybrid system, as similar findings would raise concern over the V40 taper trunnion.

Materials and methods

The study included 83 patients (45 male and 38 female with a mean age of 75.6 years) who received Exeter−Trident hybrid metal-on-polyethylene THRs. The patients were then divided into two groups according to the diameter of the femoral head used—38 patients in the 28-mm group (control), and 45 in the 36-mm (experimental) group. Serum levels of blood Co and Cr were analysed for all recruited patients.

Results

In the control group (28-mm femoral head) all Co and Cr values were normal (under the abnormal threshold), as were the experimental group (36-mm femoral head). The data values were below <10 nmol and <40 nmol for Co and Cr, respectively.

Conclusion

Since the National Joint Registry (NJR) states that the Exeter femoral stem is the commonest cemented femoral stem prosthesis used in the UK, we found it imperative that these results are documented given the corresponding findings in the Trident−Accolade system in our previous study. This study provides relative reassurance that the issue does not lie with the V40 taper trunnion, but raises suspicion that the issue may be with the titanium Accolade stem with large diameter femoral heads.

Level of evidence III.

High failure rate of the R3 metal-on-metal total hip arthroplasty

We report our failures with the use of the R3 metal-on-metal bearing. Forty six patients had an R3 acetabular system metal-on-metal THR in our centre between March 2007 and March 2009. All operations were performed using femoral components and appropriately matched femoral heads manufactured by Smith and Nephew. Twelve patients underwent revision surgery for adverse reaction to metal debris (ARMD). The median acetabular inclination was 40 degrees (range 21.1-49.1) and the median acetabular anteversion was 7.5 degrees (range 3.3-10.4). The median serum Cobalt was 9.9 µg/L (range 3.1-45) and the median serum Chromium was 5.8 µg/L (range 1.8-19.3). The time to revision was 39.2 months (range 13-53). Our current failure rate is 24%.

Influence of implant design on blood metal ion concentrations in metal-on-metal total hip replacement patients

PURPOSE

Most factors considered to affect blood metal ions following metal-on-metal hip replacement are based on hip resurfacing patients. The study aims were to determine which factors affect blood metal ion concentrations following metal-on-metal total hip replacement (MoM THR).

METHODS

All unilateral MoM THR patients at one centre with whole-blood cobalt (Co) and chromium (Cr) concentrations measured up to May 2013 were included. Blood sampling was at a mean of 4.5 years (range 1.1-11.8 years) postoperatively.

RESULTS

Of 496 patients (mean age 59.1 years; 52.8% male), blood metal ions >7 μg/l were observed in 9.7% (n = 48). Large femoral head sizes (≥38 mm) had significantly higher (p < 0.0001) blood metal ions than smaller sizes (28/36 mm). Corail-Pinnacle implants produced significantly lower blood metal ions compared to other implant designs (p < 0.01 Co and Cr). Univariate linear regression demonstrated the only significant predictors of both blood Co and Cr concentrations were femoral head size (R(2) = 8.6% Co and R(2) = 3.3% Cr, both p < 0.0001) and implant design (R(2) = 8.8%, p = 0.005 Co and R(2) = 5.1%, p = 0.003 Cr). When the three THR implant design groups (Corail-Pinnacle, Synergy, Other) were analysed separately, femoral head size no longer significantly affected blood metal ions in any of the three implant design groups.

CONCLUSIONS

Implant design was the most important factor affecting blood metal ion concentrations. We recommend the regularity of follow-up be tailored to survival rates of various MoM THR designs rather than according to femoral head size.

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.

Clinical results of the conserve plus metal on metal hip resurfacing: an independent series

The purpose of the present study was to report the clinical and radiographic results of an independent series of the Conserve Plus hip resurfacing. Five hundred forty-eight consecutive hip resurfacings were performed using the Conserve Plus prosthesis in 458 patients (350 males) with a mean age of 48.3 years (range 19 to 66). No patients were lost to follow-up. At a mean follow-up of 6.6 years (3.9 to 11.9) thirty (5.4%) hips required conversion to a total hip arthroplasty (THA) (20 males, 10 females, mean age=48.3±7.3 years). Five-year survival with as revision endpoint was 94.5% (95% CI: 93.5% to 95.5%). This study confirms the good clinical results previously reported with the Conserve Plus hip resurfacing device.

Metal ion levels and functional results following resurfacing hip arthroplasty versus conventional small-diameter metal-on-metal total hip arthroplasty; a 3 to 5year follow-up of a randomized controlled trial

We present an update of a randomized controlled trial on 71 patients (<65 years) who received either a resurfacing hip arthroplasty (RHA) (n=38) or cementless 28-mm metal-on-metal (MoM) total hip arthroplasty (THA) (n=33). Metal ion levels and functional outcome scores were analyzed with a mean follow-up of 58 months (SD 8.1). No clear shifts in relatively good outcome was encountered between RHA and THA. Metal ion levels appear to equalize between groups after 3 years. Median cobalt and chromium remained below 1.3 μg/L throughout follow-up in both groups. Six revisions were performed, of which three for pseudotumor formation (one THA, two RHA). In conclusion there were no clinical differences between the two groups and metal ion levels were lower than other series remained low, however, pseudotumor formation was not eliminated.

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.