Pseudotumors in association with well-functioning metal-on-metal hip prostheses: a case-control study using three-dimensional computed tomography and magnetic resonance imaging

MRI of THA Correlates With Implant Wear and Tissue Reactions: A Cross-sectional Study

BACKGROUND

MRI is predictive of adverse local tissue reactions (ALTRs) after THA but how MRI directly relates to implant surface wear, fretting, and trunnion corrosion at different articulations between implant components remains unclear. MRI generates high-contrast images to display soft tissues around arthroplasty and may provide a surgeon the means to distinguish and differentiate host-related synovial patterns as a response to either polyethylene wear or metal wear and corrosion products.

QUESTIONS/PURPOSES

The purposes of this study were (1) to correlate findings from MRI in patients who have undergone THA with direct assessment of implant wear, corrosion, and fretting from retrieved components; and (2) to distinguish the unique synovial responses on MRI in patients who have undergone THA based on bearing materials.

METHODS

In this prospective study, patients undergoing THA (181 patients, 187 hips) with metal-on-metal (MoM), hip resurfacing (HRA), metal-on-polyethylene (MoP), ceramic-on-polyethylene, ceramic-on-ceramic, or modular neck designs having revision surgery (between October 2013 and June 2017) underwent preoperative MRI. A single reader blinded to the bearing surface made an assessment of the synovial response (Gwet's AC1, 0.65-0.97); these data were compared with semiquantitative histology of tissue samples by a single reader (Gwet's AC1, 0.92) and semiquantitative wear, corrosion, and fretting analysis of retrieved components using Goldberg scoring (Gwet's AC1, 0.60-0.79). Direct noncontact measurements of implant wear were also made. Correlations and analyses of variance were used to assess associations between metrics and differences by implant type, respectively.

RESULTS

Correlations were found between MRI synovial thickness with severity of fretting and corrosion damage of the female head-neck trunnion of femoral stems in modular designs (ρ = 0.26 [95% confidence interval {CI}, 0.12-0.39]; p = 0.015, n = 185) and ALTR grade and volumetric wear in MoM bearings (ρ = 0.93 [95% CI, 0.72-0.98]; p < 0.001, n = 10). MRI synovial thickness was highest in patients identified with aseptic lymphocyte-dominated vasculitis-associated lesions and diffuse tissue necrosis. On MRI, MoP hips demonstrated a distinct polymeric synovial response, whereas HRA, MoM, and modular hips more commonly demonstrated ALTR. Hips classified as having a polymeric synovial response on MRI had a greater number of particles present in tissue samples.

CONCLUSIONS

In this study, we demonstrated that MRI of THA can distinguish synovial responses that reflect the bearing type of the implanted THA and correlate to direct measurements of implant wear, corrosion, and fretting and histologic assessment of wear particles in periprosthetic tissues. MRI provides a means of direct, noninvasive visualization of the host-generated synovial response. Patients presenting with painful arthroplasties may be evaluated for the cause of their discomfort, specifically highlighting any concerning synovial reactions that would warrant more prompt surgical intervention. Future studies would benefit from a prospective evaluation of different implants to assess the natural longitudinal history of arthroplasty complications, including the development and prevalence of ALTR across bearing constructs.

LEVEL OF EVIDENCE

Level III, diagnostic study.

The correlation between activity level, serum-ion concentrations and pseudotumours in patients with metal-on-metal hip articulations and metal-on-polyethylene total hip articulations

Purpose

Young and physically active patients have mainly received metal-on-metal (MoM) total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA). However, the correlation between daily physical activity (PA) levels, serum-ion concentrations of chromium and cobalt and pseudotumours formation of patients who underwent MoM THA/RHA is insufficiently explored.

Methods

Ninety-nine patients with 134 hip articulations, 71 MoM THA/RHA and 63 MoP THA participated in a cross-sectional study at XXX University Hospital, Denmark, at mean 7.3 (range: 0.4–21.7) years after surgery. Patients' daily PA was monitored during a two-week period using a triaxial accelerometer. Metal artefact reduction sequence magnetic resonance imaging scans, estimation of serum-ion concentrations of chromium and cobalt and the Copenhagen Hip and Groin Outcome Score (HAGOS) questionnaire were completed on Day 14.

Results

Patients with a pseudotumour who underwent MoM THA/RHA had a higher average cadence of median 101.4 [interquartile range (IQR: 95.5–105)] steps/min than patients without a pseudotumor, median 96.7 (IQR: 92.2–103) steps/min (p = 0.02). Serum-ion concentrations of chromium and cobalt were higher in patients with a pseudotumour who underwent MoM THA/RHA, median 2.57 (IQR: 1.4–3.4) μg/L and 1.80 (IQR: 1.2–2.6) μg/L, respectively, than in patients without a pseudotumour, median 1.85 (IQR: 1.1–3.2) μg/L and 1.34 (IQR: 0.9–2.2) μg/L in MoM THA/RHA (p = 0.04 and p = 0.03). There was no statistical difference in these parameters between patients with and without a pseudotumour who underwent MoP THA. Daily PA levels of patients who underwent MoM THA/RHA were significantly correlated with serum-ion concentrations of chromium (p = 0.0002, r = 0.44) and cobalt (p = 0.005, r = 0.34), whereas no correlations were seen among patients who underwent MoP THA (p > 0.12).

Conclusion

The daily PA level of patients who underwent MoM THA/RHA influences the serum-ion concentrations of chromium and cobalt and the risk of pseudotumour formation.

Translational potential of this article

Results of this article add important knowledge on potential recommendations of prosthesis selection for patients with a high level of physical activity.

Surface integrity of polyethylene liners following trunnionosis of a dual modular neck total hip implant

BACKGROUND

There has been a trend in the evolution of total hip arthroplasty towards increased modularity; with this increase in modularity come some potentially harmful consequences. Modularity at the neck shaft junction has been linked to corrosion, adverse reaction to metal debris and pseudotumour formation.

AIM

The aim of this retrieval study is to assess whether the surface integrity of the polyethylene (PE) liner is affected by metal wear debris in a single implant design series of THA revised for trunnionosis.

METHODS

A retrieval analysis of thirty dual-taper modular neck hip prostheses was performed; the mean time from implantation to revision was 2.7 years (1.02-6.2). PE liners were analysed using a scanning electron microscope with an energy dispersive spectrometer to assess for metal particles embedded on the liner surface. Serum metal ion levels and inflammatory markers were also analysed.

RESULTS

There were small numbers of metal particles present on the PE liners. The mean number of metal particles per liner was four and the particles varied in size from 0.5 µm to 122 µm mean 16 µm. All patients had elevated metal ion levels: cobalt 6.02 µg/l, chromium 1.22 µg/l, titanium 3.11 µg/l. The cobalt:chromium ratio was 7.55:1. Inflammatory markers were also marginally raised (ESR 17; CRP 10).

CONCLUSION

These results suggest that retention of PE liners may be reasonable when performing isolated revision of the femoral component in cases of failure at the modular neck stem junction, especially when the inner diameter of the liner is already optimised for head size and stability.

Implant Failure After Motec Wrist Joint Prosthesis Due to Failure of Ball and Socket-Type Articulation-Two Patients With Adverse Reaction to Metal Debris and Polyether Ether Ketone

We describe 2 cases of articulation-related failures resulting in revision surgery after a Motec total wrist arthroplasty: one with an adverse reaction to metal debris and the other with an adverse reaction to polyether ether ketone. In the first patient, blood cobalt and chrome levels were elevated and magnetic resonance imaging showed clear signs of a pseudotumor. The other patient had an extensive release of polyether ether ketone particles into the surrounding synovia due to adverse wear conditions in the cup, leading to the formation of a fluid-filled cyst sac with a black lining and diffuse lymphocyte-dominated inflammation in the synovia. We recommend regular follow-up including x-rays, monitoring of cobalt and chrome ion levels, and a low threshold for cross-sectional imaging in patients who have undergone total wrist arthroplasty with a Motec joint prosthesis. Wear-related problems can also develop in implants in which polyether ether ketone is the bulk material.

Adverse reaction to metal debris after small-head diameter metal-on-metal total hip arthroplasty: an increasing concern

INTRODUCTION:

Failures due to adverse reaction to metal debris (ARMD) have become an area of common focus among surgeons performing hip replacements. Several authors have reported data on the prevalence of these masses, in both symptomatic and asymptomatic patients after either large-diameter head metal-on-metal (MoM) total hip arthroplasty (THA) or hip resurfacing arthroplasty, with a large variability of rate. To our knowledge, few data are reported on the association of this lesion with the use of small-head diameter MoM.

METHODS:

15 hips that were revised for ARMD in small-head MoM THA were included in this study. We focused our attention on the difficulties of diagnosis and treatment and also on the histologic aspects of the harvested pathologic tissue.

RESULTS:

The histological examination of our cases showed a presence of lymphocytic infiltrate suggesting a delayed hypersensitivity reaction to the metal of type IV (ALVAL), but different from each other in term of the prevalence of the cellular component. Osteolysis and severe soft tissue damage were also observed. Revision resulted in remission of the lesion and successful implant.

CONCLUSIONS:

Our observation suggests that the evidence of ARMD should be considered even in case of small-head MoM arthroplasty and therefore these patients should be followed scrupulously with 2nd level diagnostic tools such as magnetic resonance imaging with metal artifact reduction sequence (MARS-MRI) and metal ion levels at least once. Further investigations are necessary to establish the real prevalence of this phenomenon in the whole population of small-head MoM THAs.

Pleomorphic clinical spectrum of metallosis in total hip arthroplasty

PURPOSE

To summarize the biological effects of metal debris from hip arthroplasties which characterize a polymorphic clinical spectrum of local and remote manifestation.

METHODS

Retrospective study. Patient, implant, and surgical characteristics were collected, including implant survival, clinical manifestations, cause of arthroplasty revision or implant failure, and peri- and intra-operative complications. The primary endpoint was implant survivorship. Hip revision arthroplasty was decided considering clinical signs and symptoms, abnormal imaging (XR, MR, TC, echotomography, scintigraphy), and blood metal ion level. An ad hoc electronic form was used to collect demographic, epidemiological, and clinical variables. In-between group comparisons of quantitative variables were performed with the Student t test and the Mann-Whitney for parametric and non-parametric variables, respectively. Logistic regression analyses were carried out to assess the relationship between clinical and radiographic characteristics and stem and cup revision. Radiographic measurements of implant positioning validity and reliability were assessed using Krippendorff's alpha reliability coefficient. The statistical software STATA version 15 (StatsCorp, TX) was used to perform statistical computations.

RESULTS

In this MoM THA series, the most incident cause of implant failure was ARMD in 11 out of 14 (78.6%) patients. All clinical failure manifestations, revision surgery highlights, and intra-operative findings are reported.

CONCLUSIONS

The local adverse reactions include lesions of different clinical relevance from small asymptomatic soft tissue lesions to dramatic osteolysis, necrosis, effusion, and growing masses which can cause secondary pathological effects. Symptoms of systemic toxicity are rarely described but may have been largely unreported in literature. Despite the extensive literature on the topic, the patient's management is still uncertain and challenging. Every metallic implant (e.g., screws, plates, spinal instrumentations) has a potential local or systemic adverse effect. Organizing a national registry of arthroplasty should be mandatory, in order to collect data about the patients, the surgery, the implanted device (with a careful post-marketing tracking), and the follow-up for all the procedures performed at a national level. The data collected in the registry will allow to analyze the implant survival and to better recognize the undesirable and sometimes unexpected effects of different biomaterials on the whole body.

Physical Activity Is Associated With the Level of Chromium but Not With Changes in Pseudotumor Size in Patients With Metal-on-Metal Hip Arthroplasty

BACKGROUND

Metal-on-metal (MoM) total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA) were previously considered an excellent option for young and physically active patients. However, the relationship between MoM THA/RHA patients' daily physical activity (PA), metal ion measurements of chromium and cobalt, and pseudotumor dynamic is insufficiently explored.

METHODS

One hundred eleven patients with 148 hip articulations, 77 MoM THA/RHA and 71 MoP THA, participated in a prospective cohort study, with 5 cross-sectional analyses during a 1-year follow-up. Baseline follow-up was at mean 7.1 (range: 0.2-21.5) years postoperative. At baseline and every 3 months thereafter, patients' daily PA was monitored during a 2-week period using a triaxial accelerometer, and next metal artifact reducing sequence magnetic resonance imaging scans, metal ion measurements of chromium and cobalt, and the Copenhagen Hip and Groin Outcome Score questionnaire were completed.

RESULTS

We found a statistically significant relationship between daily PA and metal ion measurements of chromium at all follow-ups in MoM THA/RHA patients (P ≤ .03) but not in MoP THA patients (P > .35). Patients' daily PA was not related to changes in pseudotumor size at any follow-up (P > .30). Ten of 26 (38%) pseudotumors in MoM THA/RHA and 8 of 29 (28%) pseudotumors in MoP THA changed classification according to the Anderson grading. No pseudotumors transformed in appearance or changed anatomical location.

CONCLUSION

The daily PA of MoM THA/RHA patients is associated with metal ion measurements of chromium but not with changes in pseudotumor size. This is new and important knowledge, which may be useful for hip surgeons in recommendation and monitoration of the consequences of PA in active patients with MoM THA/RHA.

Indications for MARS-MRI in Patients Treated With Articular Surface Replacement XL Total Hip Arthroplasty

BACKGROUND

The purpose of this study was to identify which patient and clinical factors are predictive of adverse local tissue reaction (ALTR) and to use these factors to create a highly sensitive algorithm for indicating metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) in Articular Surface Replacement (ASR) XL total hip arthroplasty patients. Our secondary aim was to compare our algorithm to existing national guidelines on when to take MARS-MRI in metal-on-metal total hip arthroplasty patients.

METHODS

The study consisted of 137 patients treated with unilateral ASR XL implants from a prospective, multicenter study. Patients underwent MARS-MRI regardless of clinical presentation at a mean of 6.2 (range, 3.3-10.4) years from surgery. Univariate and multivariate analyses were conducted to determine which variables were predictive of ALTR. Predictors were used to create an algorithm to indicate MARS-MRI. Finally, we compared our algorithm's ability to detect ALTR to existing guidelines.

RESULTS

We found a visual analog scale pain score ≥2 (odds ratio [OR] = 2.53; P = .023), high blood cobalt (OR = 1.05; P = .023), and male gender (OR = 2.37; P = .034) to be significant predictors of ALTR presence in our cohort. The resultant algorithm achieved 86.4% sensitivity and 60.2% specificity in detecting ALTR within our cohort. Our algorithm had the highest area under the curve and was the only guideline that was significantly predictive of ALTR (P = .014).

CONCLUSION

Our algorithm including patient-reported pain and sex-specific cutoffs for blood cobalt levels could predict ALTR and indicate MARS-MRI in our cohort of ASR XL metal-on-metal patients with high sensitivity.

LEVEL OF EVIDENCE

Level II, diagnostic study.

What role does metal allergy sensitization play in total knee arthroplasty revision?

Background

Clinicians are often faced with the decision whether to revise a painful total knee replacement in patients who have chronic vague pain with no apparent explanation. A sensitive metal testing assay called the lymphocyte stimulation test has been used to detect nickel sensitization in patients with orthopedic implants. We hypothesize that nickel sensitization plays a role in the pathology of failed joint arthroplasty in patients with unexplained dissatisfaction.

Methods

32 patients with symptomatic total knee arthroplasty without obvious mechanical findings were tested prior to revision surgery. 19 nickel-sensitized and 13 non-sensitized patients were compared by cell counts of synovium surgical specimens for CD4⁺ and CD8⁺ cell lines. Patients were then revised with ceramic-coated implants. Secondary evaluation of functional outcomes, range of motion, and pain relief were assessed.

Results

Nickel-sensitive patients showed a statistical increase in CD4⁺ reactivity compared to CD8⁺ reactivity. The ratio of CD4⁺/CD8⁺ T lymphocytes was 1.28 in nickel-sensitive patients versus 0.76 in the control (p = 0.009). There was no difference in functional scores, clinical scores, or range of motion after revision.

Conclusions

This study provides objective data via histological analysis in support of a nickel allergic sensitization in failed arthroplasties where clinical and/or radiographic abnormalities may not be apparent. Biopsy for CD4⁺/CD8⁺ cell counts may provide further proof of the existence of nickel sensitization in lymphocyte stimulation test positive patients, and more importantly, may implore the surgeon to consider low nickel implant design in these patients.

Long-Term Outcomes After Metal-on-Metal Total Hip Arthroplasty With a 28-mm Head: A 17- to 23-Year Follow-Up Study of a Previous Report

BACKGROUND

Second-generation, metal-on-metal total hip arthroplasty (MoM THA) using a 28-mm head has shown favorable results compared with large head MoM THA. The purpose of this study is to evaluate the long-term outcomes of cementless primary MoM THA with a 28-mm head and the incidence of osteolysis using computed tomography.

METHODS

A total of 92 patients (53 men and 39 women) who underwent primary cementless MoM THA (114 hips) with a 28-mm head were enrolled in this study. Their mean age was 46.2 years at the time of surgery. The mean follow-up duration was 20 years. The Harris hip score, presence of thigh or groin pain, radiographic results, presence of peri-implant osteolysis, histologic analysis, and Kaplan-Meier survival curves were evaluated.

RESULTS

The mean preoperative Harris hip score of 50.5 improved to 85.1 at the final follow-up. Eight patients (8 hips) experienced groin pain, but none had thigh pain. Twelve revisions (6.2%) were performed including 10 hips for aseptic loosening with osteolysis and 2 hips for periprosthetic fracture around the stem. At 23 years, 91% of patients were free from revision of the acetabular component due to aseptic loosening and 90.1% were free from revision of both femoral and acetabular components due to any reason. Osteolysis was identified around the cup in 12 cases (10.5%) and around the stem in 7 cases (6.1%).

CONCLUSION

MoM THA with a 28-mm head showed a relatively low rate of aseptic implant loosening at a mean follow-up of 20 years.

Differential proteomic analysis of synovial fluid from hip arthroplasty patients with a pseudotumor vs. Periprosthetic osteolysis

Adverse tissue reactions to metal implants, including pseudotumors, can compromise implant functionality and survivorship. The identification of specific proteins in the synovial fluid (SF) of hip arthroplasty patients with a pseudotumor may lead to a better understanding of the underlying pathomechanisms. The objective of the present study was to compare the protein content of SF from patients with a short-term metal-on-metal hip implant associated with a pseudotumor and patients with a long-term metal-on-polyethylene hip implant associated with periprosthetic osteolysis. Discovery proteomics was used to identify differentially abundant proteins in albumin-depleted SF. In toto, 452 distinct proteins (present in at least half of the patients in one or both groups) were identified. Thirty of these 452 proteins were differentially abundant between the two groups, including two potential biomarkers: 6-phosphogluconate dehydrogenase (which plays a major protective role against oxidative stress) for the pseudotumor group, and scavenger receptor cysteine-rich type 1 protein M130 (which is involved in low-grade inflammation) for the periprosthetic osteolysis group. Other differentially abundant proteins identified suggest the presence of an adaptive immune response (particularly a type-IV hypersensitivity reaction), necrosis, and greater oxidative stress in patients with a pseudotumor. They also suggest the presence of an innate immune response, oxidative stress, tissue remodeling, and apoptosis in both patient groups, although differences in the specific proteins identified in each group point to differences in the pathomechanisms. Overall, results provide insights into the molecular mechanisms underlying metal-related pseudotumors and periprosthetic osteolysis, and may ultimately help elucidate pseudotumor etiology and assess the risk that asymptomatic pseudotumors will develop into an aggressive lesion. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1849-1859, 2018.

Higher Prevalence of Mixed or Solid Pseudotumors in Metal-on-Polyethylene Total Hip Arthroplasty Compared With Metal-on-Metal Total Hip Arthroplasty and Resurfacing Hip Arthroplasty

BACKGROUND

Pseudotumors are a common finding in metal-on-metal (MoM) total hip arthroplasty (THA) and resurfacing hip arthroplasty (RHA). However, information on pseudotumors in metal-on-polyethylene (MoP) THA is limited.

METHODS

One hundred eleven patients with 148 hip articulations-30 MoM THA, 47 MoM RHA, and 71 MoP THA-participated in a cross-sectional study at mean 7.1 (range: 0.2-21.5) years postoperatively. Patients were evaluated with metal artifact reducing sequence magnetic resonance imaging, measurements of metal ions, clinical scores of Harris Hip Score, Oxford Hip Score, the Copenhagen Hip and Groin Outcome Score, and conventional radiographs.

RESULTS

Pseudotumors were present in 13 of 30 (43%) MoM THA, 13 of 47 (28%) MoM RHA, and 29 of 71 (41%) MoP THA patients, which was a similar prevalence (P = .10). The prevalence of mixed or solid pseudotumors was significantly higher in patients with MoP THA (n = 10) compared to MoM THA (n = 3) and MoM THA (n = 0), (P = .01). Hips with a mixed or solid pseudotumor had significantly poorer scores of Harris Hip Score (P = .01) and OHS (P = .002) and higher metal ion levels of cobalt (P = .0009) compared to hips without a pseudotumor or with a cystic pseudotumor.

CONCLUSION

Pseudotumors have primarily been associated with MoM hip articulations, but we found a similar pseudotumor prevalence in MoP THA, which is the most common bearing worldwide. Mixed or solid pseudotumors were more often seen in MoP THA compared with MoM hip articulations, and patients with a mixed or solid pseudotumor had poorer clinical scores and higher metal ion levels than patients without a pseudotumor or with a cystic pseudotumor.

Association Between Pseudotumor Formation and Patient Factors in Metal-on-Metal Total Hip Arthroplasty Population

BACKGROUND

Pseudotumor formation from metal-on-metal (MoM) hip implants is associated with implant revision. The relationship between pseudotumor type and patient outcomes is unknown.

METHODS

We retrospectively reviewed patients with a MoM total hip arthroplasty and metal artifact reduction sequence magnetic resonance imaging. Pseudotumors were graded using a validated classification system by a fellowship-trained radiologist. Patient demographics, metal ion levels, and implant survival were analyzed.

RESULTS

Pseudotumors were present in 49 hips (53%). Thirty-two (65%) pseudotumors were cystic thin walled, 8 (16%) were cystic thick walled, and 9 (18%) were solid masses. Patients with pseudotumors had high offset stems (P = .030) but not higher metal ion levels. Patients with thick-walled cystic or solid masses were more likely to be symptomatic (P = .025) and were at increased risk for revision (P = .004) compared to patients with cystic lesions.

CONCLUSION

Pseudotumor formation is present in 53% of patients with a MoM total hip arthroplasty, of which 40% were asymptomatic. Patients with thick-walled cystic and solid lesions were more likely to be symptomatic and undergo revision.

Revision for Symptomatic Pseudotumor After Primary Metal-on-Polyethylene Total Hip Arthroplasty with a Standard Femoral Stem

BACKGROUND

Pseudotumor formation following total hip arthroplasty (THA) is a well-known complication mainly associated with metal-on-metal (MoM) bearings and taper corrosion on modular-neck femoral stems. The purpose of this study was to determine the prevalence of revision surgery for symptomatic pseudotumors in a large cohort of patients treated with primary THA with a standard stem and a non-MoM articulation.

METHODS

We included 2,102 patients treated with a total of 2,446 THAs from 1999 until May 2016 in a prospective, observational cohort study. All patients underwent THA with the same uncemented, non-modular-neck femoral stem and metal-on-polyethylene (MoP) (n = 2,409) or ceramic-on-polyethylene (n = 37) articulation. All patients were followed by means of a combination of surgical and medical chart review, follow-up visits, and the Swedish Hip Arthroplasty Register. Metal artifact reduction sequence magnetic resonance imaging (MARS MRI) was used for diagnosis of the pseudotumors, and serum metal ion levels and inflammatory marker levels were measured for all patients who underwent a revision due to pseudotumor.

RESULTS

The prevalence of revision for symptomatic pseudotumor formation was 0.5% (13 cases) at a mean follow-up time of 7 years. The incidence rate was 0.9 case per 1,000 person-years. All 13 revisions were done in patients with an MoP articulation.

CONCLUSIONS

This study demonstrated a 0.5% prevalence of revision due to symptomatic pseudotumor formation in a cohort of patients who underwent THA with a non-MoM construct. Surgeons should be aware that symptomatic pseudotumor formation requiring revision surgery is a tangible complication even after standard MoP THA.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Revision surgery of metal-on-metal hip arthroplasties for adverse reactions to metal debris

Background and purpose - The initial outcomes following metal-on-metal hip arthroplasty (MoMHA) revision surgery performed for adverse reactions to metal debris (ARMD) were poor. Furthermore, robust thresholds for performing ARMD revision are lacking. This article is the second of 2. The first article considered the various investigative modalities used during MoMHA patient surveillance (Matharu et al. 2018a ). The present article aims to provide a clinical update regarding ARMD revision surgery in MoMHA patients (hip resurfacing and large-diameter MoM total hip arthroplasty), with specific focus on the threshold for performing ARMD revision, the surgical strategy, and the outcomes following revision. Results and interpretation - The outcomes following ARMD revision surgery appear to have improved with time for several reasons, among them the introduction of regular patient surveillance and lowering of the threshold for performing revision. Furthermore, registry data suggest that outcomes following ARMD revision are influenced by modifiable factors (type of revision procedure and bearing surface implanted), meaning surgeons could potentially reduce failure rates. However, additional large multi-center studies are needed to develop robust thresholds for performing ARMD revision surgery, which will guide surgeons' treatment of MoMHA patients. The long-term systemic effects of metal ion exposure in patients with these implants must also be investigated, which will help establish whether there are any systemic reasons to recommend revision of MoMHAs.

Association between periprosthetic tissue metal content, whole blood and synovial fluid metal ion levels and histopathological findings in patients with failed metal-on-metal hip replacement

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

[Mid-term effectiveness of large-head metal-on-metal total hip arthroplasty]

Objective

To explore the mid-term effectiveness of large-head metal-on-metal total hip arthroplasty (THA).

Methods

A retrospective analysis was made on the clinical date of 40 patients (43 hips) who were treated with the large-head metal-on-metal THA between April 2009 and June 2010. There were 18 males (20 hips) and 22 females (23 hips) with an average age of 55.1 years (range, 20-85 years). Unilateral hip was involved in 37 cases and bilateral hips in 3 cases. The disease causes included osteonecrosis of the femoral head in 14 cases (15 hips), osteoarthritis in 6 cases (7 hips), rheumatoid arthritis in 4 cases (4 hips), femoral neck fracture in 4 cases (4 hips), and developmental dysplasia of the hip in 12 cases (13 hips). Before operation, the Harris score and University of California Los Angeles (UCLA) score were 38.51±5.62 and 4.21±1.43, respectively. The visual analogue scale (VAS) score was 6.78±0.95.

Results

All patients were followed up 6.7-8.3 years (mean 7.5 years). All incisions healed primarily and no neurovascular injury, infection, and hip dislocation occurred. At last follow-up, the Harris score and UCLA score were 93.33±3.21 and 7.32±1.45, respectively, showing significant differences when compared with preoperative scores ( t=51.753, P=0.000; t=23.232, P=0.000). The thigh pain occurred in 3 cases (3 hips) in whom the inflammatory pseudotumor of soft tissues was found in 1 case (1 hip). Postoperative X-ray films showed that the acetabular abduction angle and anteversion angle were (46.5±3.2)° and (14.8±3.6) °, respectively. The initial stability of femoral stem prosthesis was excellent in 39 hips and good in 4 hips according to Mulliken standard. Osteolysis occurred in 2 hips and revision was performed in 1 hip of secondary loosening of prosthesis. The rest patients had no prosthesis loosening or sinking.

Conclusion

The mid-term effectiveness of large-head mental-on-mental THA in treatment of the terminal diseases of hips are good.

Systemic and local toxicity of metal debris released from hip prostheses: A review of experimental approaches

Despite the technological improvements in orthopedic joint replacement implants, wear and corrosion products associated with the metal components of these implants may result in adverse local tissue and perhaps systemic reactions and toxicities. The current review encompasses a literature review of the local and systemic toxicity studies concerning the effect of CoCrMo wear debris released from wear and corrosion of orthopedic implants and prostheses. Release of metallic debris is mainly in the form of micro- and nano-particles, ions of different valences, and oxides composed of Co and Cr. Though these substances alter human biology, their direct effects of these substances on specific tissue types remain poorly understood. This may partially be the consequence of the multivariate research methodologies employed, leading to inconsistent reports. This review proposes the importance of developing new and more appropriate in-vitro methodologies to study the cellular responses and toxicity mediated by joint replacement wear debris in-vivo.

Frank Stinchfield Award: Identification of the At-risk Genotype for Development of Pseudotumors Around Metal-on-metal THAs

BACKGROUND

Once touted as the future of hip arthroplasty, metal-on-metal (MoM) bearing surfaces have fallen sharply from favor with the emergence of a strong body of evidence demonstrating unacceptably high premature implant failure rates. The previously unpredictable development of adverse local tissue reactions (ALTRs) has been a substantive contributor to this. Although the underlying pathophysiology of these so-called "pseudotumors" is now well understood, the fundamental predisposing patient risk factors have remained elusive.

QUESTIONS/PURPOSES

The aim of this research, as a clinical-genotype correlation analysis, was to identify specific alleles (genes) associated with the development of ALTRs in patients with in situ MoM THAs.

METHODS

A case-control study of patients who received a large-head, primary MoM THA between 2005 and 2008 was performed with a minimum followup of 5 years. Twenty-six patients who had undergone revision of a primary MoM THA secondary to symptomatic ALTRs were recruited. The mean timeframe from primary MoM THA to symptomatic revision was 5.5 years (range, 1-10 years). Twenty-eight control subjects were randomly selected asymptomatic patients with no evidence of ALTRs on protocol-specific screening. Baseline demographics and high-resolution genotype (human leukocyte antigen [HLA] Class II) were collected for all patients. Cohorts were similar with respect to age at the time of primary MoM THA (mean, 54.8 versus 54.9 years, p = 0.95) and serum cobalt (mean, 5.5 versus 8.5 μg/L, p = 0.09) and chromium concentrations (mean, 2.9 versus 4.2 μg/L, p = 0.27). The association between genotype and revision surgery secondary to ALTRs was determined with gender as a covariate.

RESULTS

The prevalence of the risk genotype was 30% (16 of 54) among the entire cohort. Adjusting for sex, the odds of revision were 6.1 times greater among patients with the risk genotype present than among patients without (95% confidence interval [CI], 1.5-25.4; p = 0.01). Among females, the specificity of the risk genotype was 1.0 (95% CIexact, 0.5-1.0; pexact = 0.03), and for males, it was 0.8 (95% CIexact, 0.6-0.9; pexact < 0.01).

CONCLUSIONS

The findings of this study suggest that, among patients with a primary MoM THA, allelic variation within the HLA Class II loci may be a strong, independent risk factor associated with the need for subsequent revision surgery secondary to pseudotumor formation.

CLINICAL RELEVANCE

Given the hypothesis-generating nature of this novel undertaking, confirmatory prospective clinical studies are required to further elucidate this correlation and to explore the clinical utility of targeted genetic screening in this specific population. This research may, however, represent a key missing piece in the puzzle that is metal ion-induced pseudotumor formation.

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.

Pseudotumor in metal-on-metal hip arthroplasty: a comparison study of three grading systems with MRI

OBJECTIVE

Pseudotumors, a well-known complication of metal-on-metal total hip arthroplasty (MoM THA), are well identified on metal artifact-reducing sequences magnetic resonance imaging (MARS-MRI). Several MRI grading systems are described in the orthopedic literature, but their validity is unknown in large clinical studies. Our study was undertaken to describe the classification of pseudotumors in a preselected cohort divided into high- and low-risk patients, using three pseudotumor grading systems applied on MARS-MRI, and to determine the interobserver reliability of the grading systems.

PATIENTS AND METHODS

A retrospective study was performed on 377 consecutive patients (240 MRI scans) treated with an M2a-38 and Taperloc stem combination (Biomet, Warsaw, IN, USA). Patients were divided into a high-risk and a low-risk group based on previous published risk factors. Two observers determined the presence of pseudotumors using three different pseudotumor grading systems for classifying MARS-MRI results.

RESULTS

The prevalence of pseudotumors as determined with MARS-MRI was 59% in our high-risk group, 0% in the low-risk group and 43% in the control group. Serum cobalt values were increased in the high-risk group. The kappa values of the Anderson, Hauptfleisch and Matthies grading system scores were 0.43, 0.44, and 0.49 respectively.

CONCLUSIONS

High-risk patients are at a high risk for pseudotumor development. No pseudotumor development was found in low-risk patients. Interobserver reliability scored best with the Matthies system, but all three grading systems showed only a moderate agreement.

Analysis of bearing wear, whole blood and synovial fluid metal ion concentrations and histopathological findings in patients with failed ASR hip resurfacings

BACKGROUND

Adverse Reaction to Metal Debris (ARMD) is still a major reason for revision surgeries in patients with metal-on-metal (MoM) hip replacements. ARMD consists of a wide range of alterations in periprosthetic tissues, most important of which are metallosis, inflammation, pseudotumors and necrosis. Studies investigating histopathological findings and their association to implant wear or indirect measures of wear have yielded inconsistent results. Therefore, we aimed to investigate bearing surface wear volume, whole blood and synovial fluid metal ion concentrations, histopathological findings in periprosthetic tissues and their associations.

METHODS

Seventy-eight patients with 85 hips revised for ARMD were included in the study. Prior to revision surgery, all patients had whole blood chromium and cobalt ion levels assessed. In revision surgery, a synovial fluid sample was taken and analyzed for chromium and cobalt. Periprosthetic tissue samples were taken and analyzed for histopathological findings. Explanted implants were analyzed for bearing wear volume of both acetabular cup and femoral head components.

RESULTS

Volumetric wear of the failed components was highly variable. The total wear volume of the head and cup had a strong correlation with whole blood chromium and cobalt ion concentrations (Cr: ρ = 0.80, p < 0.001 and Co: ρ = 0.84, p < 0.001) and a bit weaker correlation with fluid chromium and cobalt ion concentrations (Cr: ρ = 0.50, p < 0.01 and Co: ρ = 0.41, p = 0.027). Most tissues displayed only low-to-moderate amounts of macrophages and lymphocytes. Total wear volume correlated with macrophage sheet thickness (ρ = 0.25, p = 0.020) and necrosis (ρ = 0.35, p < 0.01). Whole blood chromium and cobalt ion concentrations had similar correlations. Lymphocyte cuff thickness did not correlate with either total wear volume or whole blood metal ion concentrations, but correlated with the grade of necrosis.

CONCLUSIONS

Bearing wear volume correlated with blood metal ion levels and the degree of necrosis and macrophage infiltration in periprosthetic tissues suggesting a dose-response relationship. Whole blood metal ion levels are a useful tool for clinician to estimate bearing wear and subsequent tissue response.

Modularity in Total Hip Arthroplasty: Benefits, Risks, Mechanisms, Diagnosis, and Management

Modular implants are currently widely used in total hip arthroplasty because they give surgeons versatility during the operation, allow for easier revision surgery, and can be adjusted to better fit the anatomy of the specific patient. However, modular implants, specifically those that have metal-on-metal junctions, are susceptible to crevice and fretting corrosion. This can ultimately cause implant failure, inflammation, and adverse local tissue reaction, among other possible side effects. Surgeons should be aware of the possibility of implant corrosion and should follow a set of recommended guidelines to systematically diagnose and treat patients with corroded implants. Ultimately, surgeons will continue to use modular implants because of their widespread benefits. However, more research is needed to determine how to minimize corrosion and the negative side effects that have been associated with modular junctions in total hip arthroplasty. [Orthopedics. 2017; 40(6):355-366.].

MRI Findings in Patients After Small-Head Metal-on-Metal Total Hip Arthroplasty with a Minimum Follow-up of 10 Years

BACKGROUND

Concern has been raised about the late onset of adverse reactions to metal debris (ARMD) in patients with a small-head metal-on-metal total hip replacement. The aims of this study were to assess the frequency and characteristic appearance of ARMD in patients with a small-head (28-mm) metal-on-metal total hip replacement and elevated blood ion levels (>1 μg/L) after a minimum follow-up of 10 years and to analyze the possible risk factors associated with the prevalence of these lesions.

METHODS

In the present study, we used metal artifact reduction sequence magnetic resonance imaging (MARS MRI) to investigate the cases of 53 patients (66 hips) with a small-head (28-mm) metal-on-metal total hip replacement and elevated blood ion levels at a mean follow-up interval of 15.5 years (range, 10.6 to 19.3 years). Whole blood metal ion levels (cobalt and chromium), clinical outcome scores (Harris hip score), and radiographs were obtained for each patient. Tissue samples from patients who had revision surgery were histologically examined.

RESULTS

MARS MRI revealed ARMD in 27 hips (41%). Most hips with ARMD (67%) were asymptomatic. ARMD were generally small, with a median lesion size of 2.3 cm (range, 0.3 to 71.4 cm) and predominantly cystic in nature. Multivariate regression analysis revealed positive correlation between cobalt ion levels and the presence of ARMD. In this case series, the risk for the development of ARMD was 2.87 times higher for every 1 μg/L increase of blood cobalt ion concentration (95% confidence interval, 1.01 to 8.17; p = 0.048).

CONCLUSIONS

In this case series, ARMD were seen in 41% of the hips following small-head metal-on-metal total hip arthroplasty at long-term follow-up, and most patients with ARMD were asymptomatic. Blood cobalt ion levels could be identified as a risk factor for ARMD. However, ARMD also occurred in patients with low metal ion levels. Further studies are necessary to investigate the role of ARMD in asymptomatic patients with this bearing type.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

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.

Long-term results of Birmingham hip resurfacing arthroplasty in Asian patients

Several reports have shown good long-term results with the Birmingham hip resurfacing (BHR) arthroplasty, but little is known about the results in Asian countries where there is a high prevalence of osteonecrosis and developmental dysplasia of the hip, and many females with small femoral head sizes. Therefore, we retrospectively evaluated the long-term clinical results of the BHR in 112 Japanese patients (53 males and 59 females-130 hips) with an average age of 52 years. Implant survivorship was analyzed using the Kaplan-Meier method with the endpoint being revision for any reason. Factors such as sex, femoral component size, and type of hip disease were analyzed as predictors of implant survivorship. With a median follow-up of 12 years, six cases were revised (two for femoral component aseptic loosening, two for infection, one for cup aseptic loosening, and one for femoral neck fracture), and the overall survival rate was 96.5% (95% CI 90.9-98.7) at 10 years and 93.6% (95% CI 83.4-97.7) at 15 years. When septic revisions were excluded, the implant survival rate was 98.2% (95% CI 92.9-99.6) at 10 years and 95.3% (95% CI 83.9-98.7) at 15 years. Sex, femoral component size, and type of hip disease were not predictors of implant survivorship. In conclusion, good clinical results were obtained with the BHR at 10- and 15-year follow-up in Japanese patients who have different stature and types of hip diseases as compared with patients in Western countries.

Risk factors for failure of the 36 mm metal-on-metal Pinnacle total hip arthroplasty system: a retrospective single-centre cohort study

Aims

To determine ten-year failure rates following 36 mm metal-on-metal (MoM) Pinnacle total hip arthroplasty (THA), and identify predictors of failure.

Patients and Methods

We retrospectively assessed a single-centre cohort of 569 primary 36 mm MoM Pinnacle THAs (all Corail stems) followed up since 2012 according to Medicines and Healthcare Products Regulation Agency recommendations. All-cause failure rates (all-cause revision, and non-revised cross-sectional imaging failures) were calculated, with predictors for failure identified using multivariable Cox regression.

Results

Failure occurred in 97 hips (17.0%). The ten-year cumulative failure rate was 27.1% (95% confidence interval (CI) 21.6 to 33.7). Primary implantation from 2006 onwards (hazard ratio (HR) 4.30; 95% CI 1.82 to 10.1; p = 0.001) and bilateral MoM hip arthroplasty (HR 1.59; 95% CI 1.03 to 2.46; p = 0.037) predicted failure. The effect of implantation year on failure varied over time. From four years onwards following surgery, hips implanted since 2006 had significantly higher failure rates (eight years 28.3%; 95% CI 23.1 to 34.5) compared with hips implanted before 2006 (eight years 6.3%; 95% CI 2.4 to 15.8) (HR 15.2; 95% CI 2.11 to 110.4; p = 0.007).

Conclusion

We observed that 36 mm MoM Pinnacle THAs have an unacceptably high ten-year failure rate, especially if implanted from 2006 onwards or in bilateral MoM hip patients. Our findings regarding implantation year and failure support recent concerns about the device manufacturing process. We recommend all patients undergoing implantation since 2006 and those with bilateral MoM hips undergo regular investigation, regardless of symptoms.

Cite this article: Bone Joint J 2017;99-B:592–600.

Adverse reaction to metal debris in a consecutive series of DUROM™ hip resurfacing: pseudotumour incidence and metal ion concentration

INTRODUCTION

The aim of this study was to evaluate the incidence of adverse reactions to metal debris (ARMD) in a consecutive series of DUROM™ Hip Resurfacing Arthroplasty (HRA) at mid-term follow-up.

METHODS

Between October 2003 and March 2007 a total of 134 consecutive DUROM™ HRA in 121 patients were performed at our institution. Follow-up could be obtained in 101 unrevised patients (83%) at a mean time of 8.51 ± 0.97 years postoperatively and included patient-related outcome measurement, plain radiographs, MARS-MRI as well as whole blood metal ion assessment.

RESULTS

17 (16.5%) out of 103 hips revealed pseudotumour occurrence in MRI investigation, 1 (10.6%) with a diameter of ≥2 cm. Higher incidence of pseudotumours was found patients with femoral component size <50 mm. 38 patients had elevated cobalt levels, 36 of them (35%) in the range of 2-7 μg/l and 2 patients (1.9%) at a rate of >7 μg/l. In contrast to cobalt determination, only elevated chromium values showed a positive association with pseudotumour occurrence and size.

DISCUSSION

A significant proportion of patients developed pseudotumours and metal ion elevation in a consecutive cohort of DUROM™ HRA after mid-term follow-up. The incidence, however, seems not to differ from results of other well performing resurfacing brands; clinical relevance of our findings is unclear. Regarding potential local as well as systemic effects of metal particle release, close follow-up of patients is essential, even with clinically well-performing implants.

Diffuse B Cell Non-Hodgkin's Lymphoma Presenting Atypically as Periprosthetic Joint Infection in a Total Hip Replacement

The occurrence of extranodal primary B cell non-Hodgkin's lymphoma is rare. Total hip replacement is one of the most common orthopaedic procedures performed. There has been an increased incidence of primary lymphomas involving periprosthetic sites. Chronic inflammation due to metal debris arising from the prosthetic implants has been evidenced as one of the causes for the development of soft tissue lymphomas albeit rarely. We describe a case report of a 77-year-old patient who had underwent a cemented total hip replacement in the past who further developed large B cell primary non-Hodgkin's lymphoma. She presented initially with signs and symptoms highly suggestive of underlying periprosthetic infection. The radiological imaging was also indicative of periprosthetic infection. The diagnosis was eventually confirmed after an open biopsy. This case underlines the importance of considering and including soft tissue malignancy in the differential diagnosis of suspected chronic periprosthetic infection.

Metal Ion Levels in Young, Active Patients Receiving a Modular, Dual Mobility Total Hip Arthroplasty

BACKGROUND

Dual mobility total hip arthroplasty (THA) components improve stability, yet use of a modular cobalt alloy acetabular liner may be associated with metal ion release. This study's purpose was to measure blood metal ion levels in young, active patients receiving a dual mobility THA prosthesis.

METHODS

This is a prospective study of young, active patients undergoing primary THA. Twenty-six patients received a 22-mm cobalt alloy (n = 10) or a 28-mm ceramic (n = 16) femoral head, a modular cobalt chrome acetabular liner, with a highly cross-linked polyethylene insert (dual mobility). Seventeen control patients received a 32-mm cobalt alloy (n = 6), oxidized zirconium (n = 5), or ceramic (n = 6) femoral head and polyethylene acetabular liner (conventional). All patients received a cementless, titanium femoral stem. Blood metal ion levels (μg/L) were measured preoperatively and at 1 year postoperatively.

RESULTS

No difference was present for age or body mass index (P = .5 and .9). At 1 year postoperatively, mean cobalt levels were greater in the dual mobility cohort (0.23 ± 0.39 vs 0.15 ± 0.07, P < .001). Four patients in the dual mobility cohort had a cobalt level outside the reference range (0.03-0.29), with values from 0.34 to 1.81 μg/L. One patient in the conventional cohort had a cobalt level outside the reference range with a value of 0.39 μg/L.

CONCLUSION

The presence and clinical significance of increased cobalt levels in 4 patients with the use of a modular dual mobility prosthesis demonstrates the necessity of continued surveillance.

Ultrasound findings in asymptomatic patients with modular metal on metal total hip arthroplasty

OBJECTIVE

The use of metal-on-metal and modular total hip arthroplasty is associated with potentially serious local and systemic complications. The primary aim of this study was to identify the prevalence of a pseudotumor in asymptomatic patients with a particular metal-on-metal hip prosthesis after a minimum follow-up of 5 years using ultrasound evaluation. A secondary purpose was to identify associations between the presence of pseudotumor and serum metal ion levels following implantation.

METHODS

We prospectively evaluated data collected from 36 asymptomatic patients who underwent implantation of a Profemur Z metal-on-metal total hip arthroplasty from January 2004 to January 2010. Serum metal ion levels were collected in 2012 and 2015. Hip ultrasounds were performed in 2015.

RESULTS

Pseudotumors were found in 7/36 patients (19.4%). The average pseudotumor size measured 38.2 cm³ (range 7.35 cm³-130.81 cm³). Elevated metal ion levels were found in all patients at all time points. No statistical correlation was found between the presence of pseudotumor and patient age, age of the implant, component design, and any of the serum metal ion levels or ratios.

CONCLUSIONS

One in every five asymptomatic patients with metal-on-metal implants was found to have a periarticular pseudotumor. There was no dose-dependent relationship found between elevated serum metal ion levels and the development of a pseudotumor. Our findings suggest that in patients with known elevated metal ion levels, continued monitoring of ion levels may not be a reliable predictor of pseudotumor formation, and ultrasound surveillance can and should be routinely used to document the presence and progression of pseudotumor.

Metal Artifact Reduction Sequence MRI Abnormalities in Asymptomatic Patients with a Ceramic-on-Polyethylene Total Hip Replacement

BACKGROUND

Magnetic resonance imaging (MRI) is a commonly utilized screening modality in patients with a metal-on-metal (MoM) total hip replacement. The prevalence of clinically important fluid collections may be overestimated since these collections have been reported to occur in asymptomatic patients with MoM and other bearing surfaces. The purpose of this study was to determine the frequency and types of MRI-documented adverse local tissue reactions in asymptomatic patients with a ceramic-on-polyethylene (CoP) total hip replacement.

METHODS

Forty-four patients (50 hips) with a minimum 2-year follow-up after total hip arthroplasty with CoP implants and a Harris hip score of >90 were enrolled in this study. The inclusion criteria were the absence of hip pain and the availability of appropriate follow-up radiographs. All patients underwent a metal artifact reduction sequence (MARS) MRI scan to determine the presence of fluid collections in asymptomatic patients with a CoP bearing surface.

RESULTS

Fluid collections were observed in 9 (18%) of 50 asymptomatic hips in this cohort. There were 5 hips with intracapsular synovitis, and 2 of these hips had a thickened synovium. Extra-articular fluid collections with direct intracapsular communication were identified in 4 additional hips. Two of these hips had a thickened synovium. No signs of osteolysis or evidence of adverse local tissue reactions were noted on radiographs at the most recent follow-up.

CONCLUSIONS

This study revealed that fluid collections are not uncommon after total hip arthroplasty with CoP implants. Synovial thickening may be present and is more prevalent than has been reported in previous studies involving metal-on-polyethylene (MoP) bearing surfaces. The clinical importance and natural history of these findings remain unknown.

LEVEL OF EVIDENCE

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

Advances in MRI around metal

The prevalence of orthopedic metal implants is continuously rising in the aging society. Particularly the number of joint replacements is increasing. Although satisfying long-term results are encountered, patients may suffer from complaints or complications during follow-up, and often undergo magnetic resonance imaging (MRI). Yet metal implants cause severe artifacts on MRI, resulting in signal-loss, signal-pileup, geometric distortion, and failure of fat suppression. In order to allow for adequate treatment decisions, metal artifact reduction sequences (MARS) are essential for proper radiological evaluation of postoperative findings in these patients. During recent years, developments of musculoskeletal imaging have addressed this particular technical challenge of postoperative MRI around metal. Besides implant material composition, configuration and location, selection of appropriate MRI hardware, sequences, and parameters influence artifact genesis and reduction. Application of dedicated metal artifact reduction techniques including high bandwidth optimization, view angle tilting (VAT), and the multispectral imaging techniques multiacquisition variable-resonance image combination (MAVRIC) and slice-encoding for metal artifact correction (SEMAC) may significantly reduce metal-induced artifacts, although at the expense of signal-to-noise ratio and/or acquisition time. Adding advanced image acquisition techniques such as parallel imaging, partial Fourier transformation, and advanced reconstruction techniques such as compressed sensing further improves MARS imaging in a clinically feasible scan time. This review focuses on current clinically applicable MARS techniques. Understanding of the main principles and techniques including their limitations allows a considerate application of these techniques in clinical practice. Essential orthopedic metal implants and postoperative MR findings around metal are presented and highlighted with clinical examples.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017;46:972-991.

Systematic Screening of Adverse Reactions to Metal Debris after Recap-M2A-Magnum Metal-on-Metal Total Hip Arthroplasty

Background and Aims:

An adverse reaction to metal debris is a known complication after large diameter head metal-on-metal total hip arthroplasty. However, the failure rate varies depending on the implant design. Therefore, we investigated the prevalence of adverse reaction to metal debris, as well as the symptoms and risk factors after undergoing a ReCap-M2a-Magnum large diameter head metal-on-metal total hip arthroplasty.

Materials and Methods:

Between 2005 and 2012, 1188 patients (1329 hips) underwent ReCap-M2a-Magnum total hip arthroplasty at our institution. Systematic screening for adverse reaction to metal debris was arranged using the Oxford Hip Score questionnaire, hip and pelvic radiographs, and assessments of the serum chromium and cobalt ion levels. Clinical evaluation and magnetic resonance imaging were performed for the symptomatic patients, as well as those with either chromium or cobalt ion levels ⩾5 µg/L. The prevalence of adverse reaction to metal debris after ReCap-M2a-Magnum total hip arthroplasty was assessed, and the risk factors for adverse reaction to metal debris were evaluated using logistic regression. The mean follow-up time was 5.2 (0.003–9.1) years. This study was an extension of a previous study conducted at our institution with 80 patients.

Results:

In total, 33 patients (33 hips, 2.5% of all hips) required a revision operation due to adverse reaction to metal debris. Moreover, 157 hips exhibited definitive adverse reaction to metal debris, but a revision operation was not performed (157 of 1329 hips, 11.8% of all hips). Overall, 190 out of 1329 (14.3%) hips had definitive adverse reaction to metal debris. Pain, subluxation sensation, clicking, swelling, a small head size, and a fair/poor Oxford Hip Score were associated with definitive adverse reaction to metal debris.

Conclusion:

We found a high prevalence of adverse reaction to metal debris in the ReCap-M2a-Magnum total hip arthroplasty patients in this study; however, most of the patients did not require revision operations.

Inflammatory pseudotumor after ceramic-on-ceramic total hip arthroplasty

We present a unique case of a symptomatic adverse local tissue reaction in a patient with a ceramic-on-ceramic total hip bearing surface. To our knowledge, this pathological finding has not yet been described in a ceramic-on-ceramic articulation without a cobalt-chromium alloy trunnion or modular neck component as a source of metal wear. We conclude that despite its mechanical mostly benign wear characteristics, ceramic wear debris is not entirely inert and may lead to the development of adverse local tissue reaction.

What Is the Natural History of Asymptomatic Pseudotumors in Metal-on-metal THAs at Mid-term Followup?

BACKGROUND

The risk of early revision because of pseudotumors in patients who have undergone large-head metal-on-metal (MoM) total hip arthroplasty (THA) is well documented. However, the natural history of asymptomatic pseudotumors or of MoM articulations without pseudotumors is less well understood. The aim of our study was to investigate the natural history of primary MoM THA at mid-term followup.

QUESTIONS/PURPOSES

The purposes of this study were: (1) Did previously detected pseudotumors persist or worsen in asymptomatic patients at mid-term followup; and if so, did any of them require revision THA? (2) Did new pseudotumors form in asymptomatic patients at mid-term followup? (3) What happened to serum trace metal ions at mid-term followup? (4) Were postoperative patient-reported outcome measures (PROMs) maintained at mid-term followup?

METHODS

Seventy-one patients who underwent a MoM THA using a Metasul LDH implant with a Durom acetabular cup and an M/L Taper stem between September 2005 and October 2008 were reviewed. All patients for this study were part of two previously published studies from our early followup. Data from the previous studies were used for comparison only. Two of the 71 patients (2.8%) were lost to followup. The mean age at operation was 56 years (range, 34-68 years). There were 24 female patients. All patients had serum trace metal ions testing, ultrasound imaging, and PROMs at a mean 3.5 years (early followup) after the index operation (range, 3-5 years) and delayed followup at a mean 7 years (range, 6.5-9 years). The indication to undertake revision THA was based on clinical evaluation and not solely on the investigation results.

RESULTS

Twenty-three of 71 patients (32%) had a positive ultrasound scan for pseudotumor at early followup. Of these, eight patients underwent revision THA (11% of MoM THA or 35% of patients with an early positive ultrasound scan). The mean time between positive ultrasound scan and revision surgery was 13 months (range, 5-22 months). Of the remaining 15 patients with pseudotumor noted on early ultrasound, 12 had persistent pseudotumor, two resolved, and one was lost to followup. Six patients (13%) with a normal ultrasound scan at early followup showed new ultrasound findings at delayed followup. Of these, four (8%) were conclusively diagnosed as pseudotumor and one was revised. Serum trace metal ion increased at mid-term followup in the seven cases that showed an increase in volume of pseudotumor. Of the five patients in whom the volume of pseudotumor decreased on ultrasound at mid-term followup, three showed a decrease in serum trace ions levels, whereas two showed an increase. New-onset pseudotumors at mid-term followup was associated with an increase in serum trace metal ions at mid-term followup only in two of six cases. PROMs at mid-term followup of patients in this study remain high.

CONCLUSIONS

At mid-term followup, approximately 35% of patients who develop an early pseudotumor undergo revision arthroplasty, whereas the remaining are asymptomatic. The incidence of new-onset ultrasound findings suggestive of pseudotumors at mid- to long-term followup is approximately 8% and these require continued surveillance.

LEVEL OF EVIDENCE

Level II, prognostic study.

The Role of Metal-on-Metal Bearings in Total Hip Arthroplasty and Hip Resurfacing: Review Article

BACKGROUND

The current role of metal-on-metal (MoM) bearings in hip arthroplasty remains controversial. The low wear offered by MoM bearings compared to metal-on-polyethylene and the possibility of a lower risk of dislocation with larger head sizes, encouraged a trend towards the re-introduction of the MoM bearing couple. However, recent evidence has shown that not all designs of the MoM bearing have been successful.

QUESTIONS/PURPOSES

The purpose of this paper is to provide an update on the use of MoM bearings and address the following issues: (1) the reintroduction of metal-on-metal bearings in total hip arthroplasty, (2) the failure of metal-on-metal bearings in stemmed total hip arthroplasty, (3) the role of metal-on-metal hip resurfacing in modern orthopaedics and (4) metal-on-metal hip resurfacing versus total hip arthroplasty.

METHODS

A literature search strategy was conducted using various search terms in MEDLINE and Embase. The highest quality articles that met the inclusion criteria and best answered the topics of focus of this review were selected. Key search terms included 'metal-on-metal', 'total hip arthroplasty' and 'hip resurfacing'.

RESULTS

The initial search retrieved 1240 articles. Twenty-two articles were selected and used in the review.

CONCLUSION

Metal-on-metal hip resurfacing is still a suitable treatment option in specific patient populations with the appropriate implant design and surgical skill, while stemmed metal-on-metal total hip arthroplasty should be avoided in all patient populations. Continued follow-up of patients undergoing metal-on-metal hip resurfacing is critical in order to further understand the long-term outcomes of these patients and why certain complications tend to occur with this procedure.

Pseudotumour formation and subsequent resolution in metal-on-metal total hip arthroplasty following revision: Instructional review and an illustrative case report with revision using a dual mobility design

The use of large-diameter metal-on-metal (MoM) components in total hip arthroplasty (THA) is associated with an increased risk of early failure due to adverse local tissue reaction to metal debris (ARMD) in response to the release of metal ions from the bearing couple and/or head-neck taper corrosion. The aim of this paper was to present a review of the incidence and natural history of ARMD and the forms of treatment, with a focus on the need for and extent of resection or debulking of the pseudotumour. An illustrative case report is presented of a patient with an intra-pelvic pseudotumour associated with a large diameter MoM THA, which was treated successfully with revision of the bearing surface to a dual mobility couple and retention of the well-fixed acetabular and femoral components. The pseudotumour was left in situ Resolution of the intra-pelvic mass and normalisation of metal ion levels was observed seven months post-operatively. Cite this article: Bone Joint J 2016;98-B:736-40.

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.

A 5-year survival analysis of 160 Biomet Magnum M2 metal-on-metal total hip prostheses

BACKGROUND

Large-head metal-on-metal (MoM) total hip arthroplasties (THA) are associated with high failure rates and possible pseudotumour formation. This study reports the first results of 160 Biomet Magnum M2 large-head MoM total hip articulations.

PATIENTS AND METHODS

From 2006 to 2010 the Reinier de Graaf Hospital implanted 160 large-head Magnum M2 MoM THAs (Biomet Inc. Warsaw, Indiana, USA) in 150 patients. These patients were recalled after a warning from the Dutch Orthopaedic Association. Patients were offered a clinical and radiographic assessment of the hip prosthesis, serum control on cobalt and chromium ions, and an ultrasound of the hip. If indicated, additional MARS-MRI or CT scan was performed. Descriptive statistical analysis, correlations, t-tests, non-parametric tests and implant survival were calculated.

RESULTS

The mean follow-up was 6.1 years (4.8-8.4). A cumulative survival rate of 93.1% (95% CI: 88.3-98%) was found after 5 years. Reasons for revision were loosening, pain, infection and pseudotumour formation. The prevalence of pseudotumour formation around the prostheses was 8.75%.

CONCLUSIONS

This study reports the first results of 160 MoM THAs implanted in our clinic from 2006-2010. In total, 13 (8.1%) of the THAs were eligible for revision after the recall. In most patients the reason for revision was pseudotumour formation. A total of 14 (8.75%) pseudotumours were diagnosed at the first recall. These results show that a comprehensive follow-up strategy is essential for MoM THAs to promptly identify and manage early complications.

Management Guidelines for Metal-on-metal Hip Resurfacing Arthroplasty: A Strategy on Followup

Despite the initial promise of metal-on-metal (MoM) implants as the ideal bearing surface for hip replacements and resurfacings, high short term failure rates due to an adverse reaction to metal debris (ARMD) have led to a dramatic reduction in the number of MoM implants used in the modern era. With over one million patients worldwide having undergone hip operations utilizing a MoM bearing surface, the long term outcomes for such patients remains unknown, and there is much debate as to the most effective management of these patients. Although several regulatory bodies have released guidelines on the management of patients with MoM hips, these recommendations remain open to interpretation, and the most effective management for these patients remains unclear. The aim of this review is to compare the current guidelines for managing patients with MoM hips and also to discuss established ARMD risk factors, evidence regarding the optimum management for patients with MoM hips, and the indications for revision surgery. Furthermore, although specialized laboratory tests and imaging can be used to facilitate clinical decision making, over-reliance on any single tool should be avoided in the decision making process, and surgeons should carefully consider all findings when determining the most appropriate course of action.

Does a titanium sleeve reduce the frequency of pseudotumors in metal-on-metal total hip arthroplasty at 5-7years follow-up?

INTRODUCTION

Little is known about pseudotumor frequency and risk factors for pseudotumor formation among different types of metal-on-metal (MoM) hip arthroplasties. A lower release of chromium and cobalt have been reported in MoM hip arthroplasties with a titanium sleeve compared to MoM designs without a titanium sleeve, but yet it is unknown whether a titanium sleeve reduces the pseudotumor frequency. We conducted a cross-sectional study to investigate: 1) pseudotumor frequency, 2) risk factors of pseudotumor formation 3) and correlations between pseudotumors, serum metal-ions, implant position, and clinical symptoms.

HYPOTHESIS

We expected a lower pseudotumor frequency in MoM hip articulation with a titanium sleeve than reported in MoM hip articulation designs using chromium-cobalt sleeve.

MATERIALS AND METHOD

A consecutive series of 41 patients/49 hips (31 males), mean age 52 (28-68) years, participated in a 5.5±0.5 (4-6.5) year follow-up study of their M2a_Magnum hip articulation (Biomet Inc., Warsaw, Indiana, USA). Patients were evaluated with magnetic resonance imaging (MRI), measurements of serum metal-ions, plain radiographs, and clinical outcome measures of Harris Hip Score (HHS) and Oxford Hip Score (OHS).

RESULTS

Eighteen of 47 hips (38%) had MRI-verified pseudotumors, all cystic, with a mean dimension of 10.6×25.6×41mm. Digital measurements on plain radiographs revealed a higher cup anteversion in patients with a pseudotumor of mean 28.4°±5.05° compared to mean 23.5°±6.5° in patients without a pseudotumor (P=0.009). Serum metal-ion concentrations, acetabular cup inclination and measures of HHS and OHS were similar between patients with and without a pseudotumor (P>0.46).

CONCLUSION

At 5.5±0.5years after surgery, MRI-verified cystic pseudotumors were frequently observed in M2a_Magnum hip articulations despite the use of titanium sleeves. The pseudotumors were related to high cup anteversion angles but not related to high serum metal-ions or clinical symptoms.

LEVEL OF EVIDENCE

IV: cross-sectional study.

Scoring the Current Risk Stratification Guidelines in Follow-up Evaluation of Patients After Metal-on-Metal Hip Arthroplasty: A Proposal for a Metal-on-Metal Risk Score Supporting Clinical Decision-Making

BACKGROUND

In the follow-up evaluation of patients with metal-on-metal (MoM) hip replacements, current evidence suggests that orthopaedic surgeons should avoid reliance on any single investigative tool. Current risk stratification guidelines can be difficult to interpret because they do not provide guidance when there are several risk factors in different groups (high and low risk). To improve the clinical utility of risk stratification guidelines, we designed a scoring system to assess the risk of revision.

METHODS

The study population consisted of 1,709 patients (1,912 hips) enrolled in a multicenter follow-up study of a recalled MoM hip replacement. Eleven scoring criteria were determined on the basis of existing follow-up algorithm recommendations and consisted of patient-related factors, symptoms, clinical status, implant type, metal ion levels, and radiographic imaging results. Forward stepwise logistic regression was conducted to determine the minimum set of predictive variables for the risk of revision and to assign variable weights. The MoM risk score for each hip was then created by averaging the weighted values of each predictive variable.

RESULTS

Receiver operating characteristic curve analysis yielded good discrimination between all revised and unrevised hips, with an area under the curve of 0.82 (p < 0.001). The odds of revision for the group with a high MoM risk score were increased by 5.8-fold (95% confidence interval [CI], 3.1 to 11.0) relative to the moderate risk group and by 21.8-fold (95% CI, 9.9 to 48.0) compared with the low risk group.

CONCLUSIONS

Although the use of MoM hip arthroplasty has been limited since 2010, we continue to be faced with the follow-up and risk assessment of thousands of patients who have not had a revision. As more knowledge about risk stratification is gained, the complexity of the algorithms is expected to increase. We propose the use of the MoM risk score as a tool to aid in the clinical decision-making process.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

What is the natural history of asymptomatic pseudotumours in metal-on-metal hip resurfacing patients?

PURPOSE

We assessed the natural history of asymptomatic pseudotumours associated with metal-on-metal hip resurfacings (MoMHRs), and factors associated with future revision.

METHODS

In 2007-2008, we identified 25 MoMHRs (21 patients; mean age 59.9 years; 76% female) with asymptomatic pseudotumours. All patients underwent identical initial assessment (ultrasound, blood metal ions, radiographs, Oxford Hip Score [OHS]) and were considered asymptomatic because they denied experiencing hip symptoms, were satisfied with their MoMHR surgery, and had good or excellent OHSs (≥34). In 2012-2013, repeat assessments were performed in all non-revised patients.

RESULTS

Revision for pseudotumour was performed/recommended in 15 MoMHRs (60%) at a mean 2.7 years (range 0.4-6.4 years) from initial assessment, with 14 developing symptoms before revision. Non-revised MoMHRs (n = 10) underwent repeat ultrasound at a mean 5.1 years (range 4.0-6.5 years) later, with no changes in pseudotumour volume (p = 0.956) or OHS (p = 0.065) between assessments. High blood cobalt (p = 0.0048) and chromium (p = 0.0162), large pseudotumours (p = 0.0458), low OHS (p = 0.0183), and bilateral MoMHRs (p = 0.049) predicted future revision. Patients with blood metal ions above established unilateral/bilateral thresholds and/or initial pseudotumours &gt;30 cm3 had an 86.7% sensitivity, 70.0% specificity, 81.2% positive predictive value, and 77.8% negative predictive value for future revision.

CONCLUSIONS

MoMHR patients with initially asymptomatic pseudotumours often become symptomatic and require revision. Patients with high blood metal ions and/or pseudotumours &gt;30 cm3 should remain under annual surveillance or be considered for revision (especially in patients also having lower initial OHSs, bilateral MoMHRs, and/or those becoming symptomatic). Less regular surveillance of patients outside these parameters appears acceptable.

Factors associated with symptomatic pseudotumors following metal-on-metal total hip arthroplasty

Background

Pseudotumors associated with metal-on-metal hips can be symptomatic or asymptomatic. The purpose of this study was to identify the characteristics of pseudotumors associated with pain.

Methods

A total of 239 large-diameter, metal-on-metal total hip arthroplasties (THAs) were performed in 222 patients. Screening for pseudotumors was performed using magnetic resonance imaging (MRI) in all patients who underwent metal-on-metal THA, and 57 patients with 62 affected hips showed pseudotumors. There were 45 women with 49 hips and 12 men with 13 hips affected, with a mean age of 64 years and a mean body mass index (BMI) of 23.9 kg/m². Sixteen hips had symptomatic pseudotumors with pain, and 46 hips were asymptomatic. Pseudotumor size was determined. The anatomical position of pseudotumors was divided into anterior position and posterolateral position. Types of pseudotumors were divided into two types: cystic type; and mixed solid cystic and solid type without a cystic component. The follow-up study of pseudotumors was determined using MRI in 33 patients. The serum cobalt and chromium ion levels were measured in 38 patients after unilateral THA. Univariate and multivariate analyses were performed comparing symptomatic and asymptomatic patients to identify the characteristics of symptomatic pseudotumors.

Results

The mean BMI was 25.4 kg/m² in symptomatic patients and 23.4 kg/m² in asymptomatic patients; a higher BMI was associated with symptoms (P = 0.036). Symptomatic pseudotumors were significantly larger (three-fold) than asymptomatic pseudotumors (1812 mm² vs 642 mm², P = 0.003). Pseudotumors located in the anterior position were associated with symptoms (P = 0.032), and mixed solid cystic and solid type pseudotumors were associated with symptoms (P = 0.007). A multivariate analysis showed significant differences only in size (R² = 0.298, P = 0.031). No asymptomatic patients with pseudotumors became symptomatic during the follow-up period of MRI evaluation.

Conclusion

Larger size was a significant factor for pain on multivariate analysis.

Metal in Total Hip Arthroplasty: Wear Particles, Biology, and Diagnosis

Total hip arthroplasty (THA) has been performed for nearly 50 years. Between 2006 and 2012, more than 600,000 metal-on-metal THA procedures were performed in the United States. This article reviews the production of metal wear debris in a metal-on-metal articulation and the interaction of cobalt and chromium ions that ultimately led to a dramatic decline in the use of metal-on-metal THA articulations. Additionally, the article reviews mechanisms of metal wear, the biologic reaction to cobalt and chromium ions, the clinical presentation of failing metal-on-metal articulations, and current diagnostic strategies. Further, the article discusses the use of inflammatory markers, metal ion levels, radiographs, metal artifact reduction sequence magnetic resonance imaging, and ultrasound for failed metal-on-metal THA procedures. When adopting new technologies, orthopedic surgeons must weigh the potential increased benefits against the possibility of new mechanisms of failure. Metal-on-metal bearings are a prime example of the give and take between innovation and clinical results, especially in the setting of an already successful procedure such as THA. [Orthopedics. 2016; 39(6):371-379.].

Asymptomatic Pseudotumors in Patients with Taper Corrosion of a Dual-Taper Modular Femoral Stem: MARS-MRI and Metal Ion Study

BACKGROUND

Modularity in total hip arthroplasty facilitates intraoperative restoration of patient anatomy. Although dual-taper modular total hip arthroplasty offers potential advantages for optimizing the hip center of rotation, it has been associated with modular taper corrosion. This corrosion has led to adverse local tissue reactions (pseudotumors) at the neck-stem junction and elevated metal-ion levels. However, the occurrence of taper-corrosion-related pseudotumors in patients who remain asymptomatic following total hip arthroplasty with a dual-taper modular femoral stem remains largely unknown. The aims of this study were (1) to determine the prevalence of asymptomatic pseudotumors by utilizing metal artifact reduction sequence magnetic resonance imaging (MARS-MRI) and (2) compare serum metal-ion levels between symptomatic and asymptomatic patients with a dual-taper modular stem total hip replacement.

METHODS

We performed a retrospective cross-sectional study of 97 consecutive patients who had been treated with a dual-taper modular femoral stem total hip arthroplasty. Eighty-three patients were stratified into symptomatic and asymptomatic groups and evaluated with MARS-MRI, measurement of serum metal-ion levels, and the University of California at Los Angeles (UCLA) functional hip score.

RESULTS

The prevalence of pseudotumors as determined with MARS-MRI was 15% in our asymptomatic patients and 36% in the overall cohort. The median serum cobalt level and cobalt/chromium ratio were significantly higher in patients with a pseudotumor than in those without a pseudotumor (8.0 versus 2.0 μg/L [p = 0.004] and 10.3 versus 2.4 μg/L [p = 0.012], respectively). However, there was no significant difference in the serum cobalt level or cobalt/chromium ratio between symptomatic patients with a pseudotumor and asymptomatic patients with a pseudotumor (7.6 versus 6.2 μg/L [p = 0.37] and 8.3 versus 10.6 μg/L [p = 0.46], respectively). The UCLA scores of asymptomatic patients with a pseudotumor were similar to those of patients without a pseudotumor (6.7 versus 6.6).

CONCLUSIONS

The prevalence of asymptomatic taper-corrosion-related pseudotumors on MARS-MRI in this study demonstrated that the absence of symptoms does not exclude the presence of adverse local tissue reactions. Elevated cobalt levels and cobalt/chromium ratios were associated with the presence of pseudotumors in asymptomatic and symptomatic patients. Cross-sectional imaging such as MARS-MRI is indicated for patients with elevated metal-ion levels. A longitudinal study is required to determine whether asymptomatic patients with taper-corrosion-related pseudotumors will develop symptoms with time.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

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.