Large diameter metal on metal articulations. Comparison of total hip arthroplasty and hip resurfacing arthroplasty

Long-term clinical outcomes of the Biomet M2a-38: a retrospective review of 335 total hip arthroplasty cases

BACKGROUND

At the turn of the century, over one-third of total hip arthroplasties comprised metal-on-metal bearings. As this patient population and their implants age, it is crucial to understand associated late failure modes and expected long-term functional outcomes. We report the long-term results of a large metal-on-metal uncemented total hip arthroplasty system with unique design characteristics compared to others that have been reported with high failure rates.

METHODS

We retrospectively analyze our prospective clinical database to determine overall implant survivorship and functional outcomes. Further, we compare these results to the clinical outcomes reported in orthopedic registries and in other published studies with similar metal-on-metal total hip arthroplasty cohorts.

RESULTS

Implant survivorship at 10 years was 99.1% and continued to 97.6% survivorship at 20 years. Implant survivorship at 20 years did not vary significantly between sexes (Male: 98.3%, Female: 97.2%; log-rank p-value = 0.46). Mean whole blood cobalt levels were 2.6 µg/L in unilateral cases, 5.3 µg/L in bilateral patients, and 3.4 µg/L for the combined cohort. Average blood chromium levels were 1.4 µg/L in unilateral patients, 2.9 µg/L in bilateral patients, and 1.8 µg/L for group combined. We observed a 0.9% rate of failure due trunnion corrosion at a mean of 13.1 years postoperatively (10.6-15.6 years) but had no bearing wear failures.

CONCLUSIONS

Our 20-year implant survivorship of 97.6% with the M2a-38 bearing surpassed registry benchmarks for THA. This large-bearing (38 mm), full hemisphere coverage metal-on-metal system had no bearing wear failures, one failure of instability, one failure of fixation, and three trunnion failures, perhaps suggesting an optimum balance between stability of the joint and the trunnion.

International Registries: U.K. National Joint Registry, Nordic Registries, and Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR)

National-level joint arthroplasty registries were among the first large orthopaedic surgery databases and represent some of the longest-running and most influential big databases in our profession. Nordic registries were among the first registries and were followed by excellent registries in the United Kingdom and Australia. In this article, we describe each of these registries and highlight the data elements collected, the data points that can be obtained by linking the national arthroplasty registries to other national registries or databases, the completeness of data, and the strengths and weaknesses of each database. Each of these registries publishes an annual report that is available online, and each also can do more detailed analysis of certain aspects of its data for special studies.When evaluating and interpreting data from national joint registries, the user should be aware that, despite the power of huge numbers, there remain numerous limitations to the observational data. Strong selection biases exist with regard to which patients are chosen for which procedure. Surgeons of different skill levels may use one technique or implant differentially compared with another. The end points that registries collect differ widely: for example, some report only hip dislocations leading to revision rather than all dislocations. Registries in countries in which there are long wait times for revision surgery may report artificially low revision rates compared with countries in which revision surgery is more easily accessible. Despite these limitations, registries have the merit of reporting the actual results of huge numbers of surgical procedures performed across the spectrum of hospitals, surgeons, and patients, making the data extremely powerful for identifying trends, identifying early signs of problems related to certain implants or implant classes, and identifying associations between variables that can be further studied to determine if the effect is causal.

Harris Hip Score and SF-36 following metal-on-metal total hip arthroplasty and hip resurfacing - a randomized controlled trial with 5-years follow up including 75 patients

Background

The metal-on-metal large-diameter-head (MoM-LDH) hip replacements increased in popularity during the start of the twenty-first century. Subsequently reports raised concerns regarding adverse reactions due to elevated chromium (Cr) and cobalt (Co) concentrations as well as high rates of other complications and revisions.

The purpose was to compare Harris Hip Score and SF-36 at 5-years follow up following MoM-LDH total hip arthroplasty (MoM-LDH-THA) or MoM hip resurfacing (MoM-HR).

Methods

The study was conducted between November 2006 to January 2012 in a tertiary health care center in Denmark. Patients with primary or secondary osteoarthritis were randomly assigned to receive a Magnum (MoM-LDH-THA) or a Recap (MoM-HR) prosthesis. Randomization was computer generated and allocation was concealed in an opaque envelope. Neither patients nor care provider were blinded. Primary outcome was Harris Hip Score at 5-years follow up.

Results

Seventy-five were included and allocated to the MoM-LDH-THA (n = 39) and MoM-HR (n = 36) group. The study was prematurely stopped due to numerous reports of adverse events in patients with MoM hip replacements. Thirty-three in the MoM-LDH-THA and 25 in the MoM-HR group were available for primary outcome analysis.

Median Harris Hip Score was 100 (IQR: 98–100) for MoM-LDH-THA and 100 (IQR: 93–100) for MoM-HR (p = 0.486). SF-36 score was high in both groups with no significant difference between groups.

Conclusion

Harris Hip Score and SF-36 score was excellent in both groups with no significant difference at 5-years follow up. Our findings suggest that there is no clinical important difference between the two prostheses implanted 5 years after implantation.

Trial registration

ClinicalTrials.gov, NCT04585022, Registered 23 September 2020 – Retrospectively registered.

This study was not prospectively registered in a clinical trial database since it was not an entirely implemented standard procedure in the international orthopedic society when the study was planned.

Midterm outcomes of total hip arthroplasty with a modular Birmingham head

INTRODUCTION

Birmingham Hip Resurfacing (BHR) implants may be combined with a conventional femoral stem to create a modular metal-on-metal total hip arthroplasty (BHR MoM THA). There is little outcome data regarding this construct. This study examines midterm outcomes of BHR MoM THA compared to oxidised zirconium total hip arthroplasty (THA).

METHODS

A retrospective institutional review identified all patients receiving BHR MoM THA between April 2005 and February 2011 and a matched control cohort of zirconium THA patients. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Harris Hip Score (HHS), and SF-12 Health status scores were obtained. Revisions and complications were collected from clinical records. Radiographs were assessed for evidence of component malposition, loosening, osteolysis, or heterotopic ossification.

RESULTS

63 modular BHR MoM THA were identified in 61 patients (36 with BHR cups, 27 with R3 cups) and 63 zirconium THA in 58 matched controls. Mean follow-up was 58 months. 14 BHR MoM THA hips (22.2%) were revised (4 infections, 1 dislocation, 9 soft tissue reactions) compared to 3 (4.8%) zirconium THA (all infections). At latest follow-up, 18.4% of surviving BHR MoM THA hips were painful compared to 0.5% of zirconium THA controls (p < 0.001). WOMAC, HHS, and SF-12 did not differ significantly between surviving members of the 2 groups.

DISCUSSION

BHR MoM THA demonstrated a high revision rate, largely for adverse local soft tissue reaction and pain. Among those not revised, many reported some residual pain despite similar quality of life measures to those who received zirconium THA.

Femoral Fixation Methods in Hip Resurfacing Arthroplasty: An 11-Year Retrospective Comparison of 4013 Cases

BACKGROUND

The optimal femoral fixation method remains unclear. To evaluate the role of femoral fixation techniques in hip resurfacing, we present a comparison of 2 consecutive groups: group 1 (739 hips) with cemented femoral components; group 2 (3274 hips) with uncemented femoral components.

METHODS

We retrospectively analyzed our clinical database to compare failures, reoperations, complications, clinical results, and radiographic measurements. Groups were consecutive, so cemented cases had longer follow-up. However, all patients from both groups were at least 2 years out from surgery. Two-year clinical and radiographic data were compared. Longer-term comparison data as well as Kaplan-Meier implant survivorship curves specifically focusing on femoral failure modes were analyzed.

RESULTS

Kaplan-Meier 10-year implant survivorship using nontraumatic femoral failure as an end point was 98.9% for the cemented and 100% for the uncemented femoral component. The uncemented, group 2 cases showed a significantly lower raw failure rate (1.1% vs 4.6%), 2-year failure rate (0.8% vs 2.8%), 2-year femoral failure rate (0.4% vs 0.9%), and a lower combined rate of femoral complications and failures (0.6% vs 1.8%). In cases that did not fail, patient mean clinical scores, pain scores, and combined range of motion were all significantly better for group 2.

CONCLUSION

We have demonstrated that in the fully porous-coated ReCap device, uncemented femoral fixation is superior to cemented fixation at 11 years follow-up (0.0% vs 1.1% late femoral loosening) in this single-surgeon cohort. Early femoral fractures also reduced from 0.8% to 0.3%, but this may be partially or completely due to a new bone density management program. This study demonstrates better femoral implant survivorship for the uncemented device compared to the cemented femoral resurfacing component for this implant design.

Surgically Relevant Morphological Parameters of Proximal Human Femur: A Statistical Analysis Based on 3D Reconstruction of CT Data

Objectives

Recently, more accurate description of the femoral geometry has become of interest to engineers and orthopedic surgeons. However, an appropriate database is lacking. Therefore, the aim of this study is to present morphological parameters and their correlations, which are relevant for medical issues such as impingement after total hip replacement, as well as for implant design and the etiology of hip fractures.

Methods

We investigated 12 well‐known morphological parameters of the femur in 169 healthy human subjects through evaluation of 3D‐reconstructed CT scans. Pearson's coefficients of correlations were calculated using a statistical t‐test method for each pair of parameters.

Results

The mean, maximum, minimum, median, and standard deviation values are reported for all parameters. Histograms showing the distribution of each morphological parameter are also presented. It is shown that absolute and horizontal offsets, total femur length, and NCVD parameters are normally distributed, but NCDF and NCDS are not. Furthermore, an inter‐correlation matrix was reported to reveal statistical correlations between these parameters. The strongest positive correlation existed between absolute offset (OSA) and horizontal offset (OSH), while the least positive correlation was found between NCDF and total femur length (TFL), and also between NCDS and NCDF. Anteversion angle (ATA) and OSA showed the least negative correlation. However, the strongest negative correlation was found between neck‐shaft angle (NSA) and greater trochanter height (GTH), as well as between OSA and NCVD.

Conclusions

Comprehending patients’ native bone morphology, including the variations and correlations, is essential for orthopedic surgeons to undertake preoperative planning and surgery as well as to appropriately design medical devices. Thus, more population‐based detailed databases are necessary. We investigated an extensive set of proximal femoral morphology parameters using a statistically standardized method to expand the existing knowledge. The results of our study can be used for diverse medical and biomechanical purposes.

Predictive factors for metal ion levels in metal-on-metal total hip arthroplasty

INTRODUCTION

Although metal-on-metal (MoM) total hip arthroplasty (THA) and hip resurfacings (HR) have similar bearing surfaces and comparable wear rates, metal ion levels and risk of failure are higher for MoM-THA. The mechanism behind the increased metal ion levels in large head MoM-THA is not completely understood. The current study aims to identify predictive factors for increased metal ion levels in unilateral and bilateral large head MoM-THA.

MATERIALS AND METHODS

99 Birmingham modular MoM-THA in 87 patients with metal ion levels at least 36 months after index procedure were analyzed. Mean follow-up time was 61.3 months (range 37-108) and the relationship of the following variables (gender, age, BMI, follow-up time, UCLA Activity Score, cup inclination, femoral head size, bilateral surgery) on metal ion levels were analyzed with multivariate regression models.

RESULTS

Multivariate regression analysis revealed that bilateral MoM-THA surgery (p < 0.001) had a positive predictive effect on cobalt serum levels, while BMI had a negative (p = 0.018). Female gender (p = 0.012), activity (p = 0.001) and bilateral MoM-THA (p = 0.004) were positively correlated with chromium levels. Positive independent predictors for the cobalt-chromium ratio in the multivariate analysis were overall follow-up time (p = 0.004), bilateral MoM-THA (p < 0.001) and femoral head size (p = 0.007).

CONCLUSIONS

The data of the current study suggest that bilateral MoM-THA, increased patient activity levels and female gender are associated with increased chromium levels. Patients with larger component size, longer follow-up time and bilateral MoM-THAs have an increased cobalt-chromium ratio. These patients might be at increased risk for adverse local soft tissue reactions secondary to corrosion. Continuous close monitoring is recommended and bearing-surface change should be discussed if local tissue reactions occur.

Biological effects of metal degradation in hip arthroplasties

Metals and metal alloys are the most used materials in orthopedic implants. The focus is on total hip arthroplasty (THA) that, though well tolerated, may be associated with local and remote adverse effects in the medium-long term. This review aims to summarize data on the biological consequences of the metal implant degradation that have been attributed predominantly to metal-on-metal (MoM) THA. Local responses to metals consist of a broad clinical spectrum ranging from small asymptomatic tissue lesions to severe destruction of bone and soft tissues, which are designated as metallosis, adverse reactions to metal debris (ARMD), aseptic lymphocytic vasculitis associated lesion (ALVAL), and pseudotumors. In addition, the dissemination of metal particles and ions throughout the body has been associated with systemic adverse effects, including organ toxicity, cancerogenesis, teratogenicity, and immunotoxicity. As proved by the multitude of studies in this field, metal degradation may increase safety issues associated with THA, especially with MoM hip systems. Data collection regarding local, systemic and long-term effects plays an essential role to better define any safety risks and to generate scientifically based recommendations.

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.].

[What can we learn in future from the data of the German Arthroplasty Registry (EPRD) in comparison to other registries?]

The German Arthroplasty Registry (EPRD) was founded in 2010 and has been in full operation since 2014. Previous attempts at a systematic data collection of elective and non-elective knee and hip replacement in Germany failed mainly because of the long-term lack of funding. The EPRD is an interdisciplinary collaborative partnership between the German Association of Orthopedics and Orthopedic Surgery (DGOOC), all implant manufacturers of the German Medical Technology Association (BVMed), health insurers (AOK and the Association of Additional Healthcare Insurance) and hospitals (German Hospital Federation). As part of this cooperation a worldwide unique implant database has been set up, which includes all relevant components and a detailed description of implant specifications. This implant library enables a detailed evaluation of implant survival, revision rates and possible inferior implant performance of knee and hip replacements in Germany. At the end of 2015 the EPRD encompassed over 200,000 registered operations. Due to the high number of hip and knee arthroplasties in Germany with many different implants from different manufacturers there will be a rapid growth of data that are available for a national and also international comparison of the results.

Hip resurfacing: history, current status, and future

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

Reducing the failure rate of hip resurfacing in dysplasia patients: a retrospective analysis of 363 cases

BACKGROUND

Arthritis secondary to developmental hip dysplasia often mandates implant surgery at a relatively young age. Hip resurfacing arthroplasty (HRA), compared with standard stemmed total hip arthroplasty (THA), affords a more active lifestyle including extreme-motion activities but stimulates concerns pertaining to implant failure.

METHODS

We addressed the primary modes of failure through a series of interventions, including a new guideline for achieving proper implant alignment through intraoperative x-rays. We then compared two sequential cohorts in a single-surgeon practice: patients with developmental dysplasia who underwent HRA before (Group 1; 121 hips in 105 patients) and after (Group 2; 242 hips in 210 patients) June 2008, at which time the four interventions were all in place.

RESULTS

Implants in Group 2 failed less frequently within two years (0.8 % vs. 6.6 %, p = 0.002) and were more likely to have projected seven-year Kaplan-Meier survivorship (99 % vs. 89 %, p < 0.0001 by log-rank test). Patients in Group 2 were more likely to have normal metal ion levels (77 % vs. 56 %, p = 0.0008) and optimum metal ion levels (99 % vs. 86 %, p = 0.0008). Patients in Group 2 also benefited from a 19-min decrease in mean operation time, a 45 % decrease in mean estimated blood loss, and a 0.9-day decrease in mean hospital stay (p < 0.0001 in each instance).

CONCLUSIONS

We believe the interventions reported here, combined with sufficient surgeon experience and properly designed implants, afford patients with mild developmental dysplasia a more active lifestyle with favorable implant survival.

Prevalence of Failure due to Adverse Reaction to Metal Debris in Modern, Medium and Large Diameter Metal-on-Metal Hip Replacements--The Effect of Novel Screening Methods: Systematic Review and Metaregression Analysis

Metal-on-metal (MoM) hip replacements were used for almost a decade before adverse reactions to metal debris (ARMD) were found to be a true clinical problem. Currently, there is a paucity of evidence regarding the usefulness of systematic screening for ARMD. We implemented a systematic review and meta-analysis to establish the prevalence of revision confirmed ARMD stratified by the use of different screening protocols in patients with MoM hip replacements. Five levels of screening were identified: no screening (level 0), targeted blood metal ion measurement and/or cross-sectional imaging (level 1), metal ion measurement without imaging (level 2), metal ion measurement with targeted imaging (level 3) and comprehensive screening (both metal ions and imaging for all; level 4). 122 studies meeting our eligibility criteria were included in analysis. These studies included 144 study arms: 100 study arms with hip resurfacings, 33 study arms with large-diameter MoM total hip replacements (THR), and 11 study arms with medium-diameter MoM THRs. For hip resurfacing, the lowest prevalence of ARMD was seen with level 0 screening (pooled prevalence 0.13%) and the highest with level 4 screening (pooled prevalace 9.49%). Pooled prevalence of ARMD with level 0 screening was 0.29% and with level 4 screening 21.3% in the large-diameter MoM THR group. In metaregression analysis of hip resurfacings, level 4 screening was superior with regard to prevalence of ARMD when compared with other levels. In the large diameter THR group level 4 screening was superior to screening 0,2 and 3. These outcomes were irrespective of follow-up time or study publication year. With hip resurfacings, routine cross-sectional imaging regardless of clinical findings is advisable. It is clear, however, that targeted metal ion measurement and/or imaging is not sufficient in the screening for ARMD in any implant concepts. However, economic aspects should be weighed when choosing the preferred screening level.

A new universal, standardized implant database for product identification: a unique tool for arthroplasty registries

INTRODUCTION

Every joint registry aims to improve patient care by identifying implants that have an inferior performance. For this reason, each registry records the implant name that has been used in the individual patient. In most registries, a paper-based approach has been utilized for this purpose. However, in addition to being time-consuming, this approach does not account for the fact that failure patterns are not necessarily implant specific but can be associated with design features that are used in a number of implants. Therefore, we aimed to develop and evaluate an implant product library that allows both time saving barcode scanning on site in the hospital for the registration of the implant components and a detailed description of implant specifications.

MATERIALS AND METHODS

A task force consisting of representatives of the German Arthroplasty Registry, industry, and computer specialists agreed on a solution that allows barcode scanning of implant components and that also uses a detailed standardized classification describing arthroplasty components. The manufacturers classified all their components that are sold in Germany according to this classification. The implant database was analyzed regarding the completeness of components by algorithms and real-time data.

RESULTS

The implant library could be set up successfully. At this point, the implant database includes more than 38,000 items, of which all were classified by the manufacturers according to the predefined scheme. Using patient data from the German Arthroplasty Registry, several errors in the database were detected, all of which were corrected by the respective implant manufacturers.

CONCLUSIONS

The implant library that was developed for the German Arthroplasty Registry allows not only on-site barcode scanning for the registration of the implant components but also its classification tree allows a sophisticated analysis regarding implant characteristics, regardless of brand or manufacturer. The database is maintained by the implant manufacturers, thereby allowing registries to focus their resources on other areas of research. The database might represent a possible global model, which might encourage harmonization between joint replacement registries enabling comparisons between joint replacement registries.

Femoral diameter and stem type are independent risk factors for ARMD in the large-headed ASR THR group

Background

Adverse soft-tissue reaction to metal debris (ARMD) continues to be major source of concern in metal-on-metal (MoM) hip replacements. In our earlier study we were able to establish several risk factors for ARMD in patients who had received a small-diameter (<50 mm) Articular Surface Replacement (ASR, DePuy, Warsaw, IN, USA). The aims of the present study were to analyze whether these previously established risk factors also apply to patients who have received a large-headed (>50 mm) ASR™ XL THR.

Methods

Large-headed ASR total hip replacements were used in 225 operations (196 patients) at our institution. 176 patients (203 hips) attended a screening programme, consisting of a clinical evaluation, whole blood cobalt and chromium measurements, and cross-sectional imaging.

Results

Revision surgery was performed on 84 hips (37%) in 75 patients. ARMD was diagnosed in the majority (n = 73 [87%]) of these revisions. Cumulative 8-year survivorship was 52%. The previously established risk factors for ARMD were not applicable. Interestingly, increasing femoral diameter and stem type were identified as independent risk factors for ARMD but reduced cup coverage had no significant association with ARMD.

Conclusions

Stem type and increasing femoral size as independent risk factors for ARMD in the cohort of ASR XL THR patients, support the importance of taper failure in the development of ARMD. The present results suggest that the degree of taper failure may be variable and dependent on the taper design.

Factors affecting squeaking in metal on metal hip resurfacings

We reviewed 380 hip resurfacings cases between December 1999 and Dec 2012. 11 cases (2.89%) squeaked postoperatively. Mean follow-up was 88.6 months (19-130 months). Mean time to squeak was 11.3 months (3-22 months). Ten (91%) cases were male and nine (81%) cases had a Birmingham hip resurfacing. Cases were matched for age, gender, BMI and implant to three controls. Radiographs were analysed using EBRA (Einzel-Bild-Roentgen-Analysis, University of Innsbruck, Austria) software to evaluate cup orientation. There was no significant difference between the mean inclination angle of the cups (p = 0.26) or the mean anteversion angle (p = 0.29). There was no difference in serum cobalt (p = 0.20) or serum chromium (p = 0.45) levels at latest follow-up. Three of the 11 (27.3%) cases had revision surgery at a mean follow-up of 101 months (72-117 months). Squeaking was not influenced by patient demographic parameters and resolved in all cases that did not undergo revision surgery. Males with a resurfacing head size <50 mm had significantly increased odds of squeaking when compared to controls (odds ratio = 26.6; 95% CI = 1.2-573.3; p<0.05). Based on our findings, we do not recommend that squeaking on its own should be an indication for revision of hip resurfacing components.

Large-diameter metal-on-metal total hip arthroplasty: dislocation infrequent but survivorship poor

BACKGROUND

Use of large-diameter metal-on-metal (MoM) articulations in THA increased, at least in part, because of the possibility of achieving improved joint stability and excellent wear characteristics in vitro. However, there have been subsequent concerning reports with adverse reactions to metal debris (ARMD), pseudotumors, and systemic complications related to metal ions.

QUESTIONS/PURPOSES

The purpose of this study was to determine at a minimum of 2 years' followup (1) the proportion of patients who experienced a dislocation; (2) the short-term survivorship obtained with these implants; (3) the causes of failure and the proportion of patients who developed ARMD; and (4) whether there were any identifiable risk factors for revision.

METHODS

We reviewed the results of 1235 patients who underwent 1440 large-diameter MoM primary THAs at our institution using two acetabular devices from a single manufacturer with minimum 2-year followup. Large-diameter MoM devices were used in 48% (1695 of 3567) of primary THAs during the study period. We generally used these implants in younger, more active, higher-demand patients, in patients considered at higher risk of instability, and in patients with adequate bone stock to achieve stable fixation without use of screws. Clinical records and radiographs were reviewed to determine the incidence and etiology of revision. Patients whose hips were revised were compared with those not revised to identify risk factors; Kaplan-Meier survivorship analysis was performed as was multivariate analysis to account for potential confounding variables when evaluating risk factors. Minimum followup was 2 years (average, 7 years; range, 2-12 years); complete followup was available in 85% of hips (1440 of 1695).

RESULTS

Dislocation occurred in one hip overall (<1%; one of 1440). Kaplan-Meier analysis revealed survival free of component revision was 87% at 12 years (95% confidence interval, 84%-90%). The two most common indications for revision were ARMD (48%; 47 of 108 hips revised) and loosening or failure of ingrowth (31%; 34 of 108). Risk factors for component revision were younger age at surgery (relative risk [RR] 0.98 per each increased year; p=0.02), higher cup angle of inclination (RR 1.03 per each increased degree; p=0.04), and female sex (RR 1.67; p=0.03).

CONCLUSIONS

Large-diameter MoM THAs are associated with a very low dislocation rate, but failure secondary to ARMD and loosening or lack of ingrowth occur frequently. Patients with MoM THA should be encouraged to return for clinical and radiographic followup, and clinicians should maintain a low threshold to perform a systematic evaluation. Early diagnosis and appropriate treatment are recommended to prevent the damaging effects of advanced ARMD.

LEVEL OF EVIDENCE

Level IV, Therapeutic study.

No functional benefit of larger femoral heads and alternative bearings at 6 months following primary hip replacement

BACKGROUND AND PURPOSE

There has been a recent trend towards the use of greater femoral head sizes in an attempt to improve function and enhance stability after primary hip replacement. This has been associated with the use of alternative bearings, theoretically to reduce wear and improve implant longevity.

METHODS

We examined the influence of these variables on patient-reported outcome measures (PROMs) for a consecutive series of primary hip replacements using National Joint Registry (NJR) and PROMs-linked data. To minimize the confounding influence of implant design factors, the single most commonly used brand in England and Wales (DePuy Corail Pinnacle) was examined. Improvement in patient hip-specific outcomes (Oxford hip score, OHS), general health outcomes (Euroqol, EQ-5D), and rates of self-reported complications (bleeding, wound problems, re-admission, and reoperation) were compared for different head sizes (28-mm, 32-mm, and 36-mm) and bearings (metal-on-polyethylene (MoP), ceramic-on-polyethylene (CoP), and ceramic-on-ceramic (CoC)), adjusting for differences in case mix.

RESULTS

At a mean follow-up of 7 months, improvements in OHS and EQ5D index were similar for 28-mm and 36-mm heads. A 32-mm head was associated with poorer function (OHS: 20, 99% CI: 19-21, p = 0.002; EQ5D index: 0.39, 99% CI: 0.36-0.42, p = 0.004), although these small differences may not be of clinical importance. There were no statistically significant benefits of either CoP or CoC bearings compared to a MoP bearing. Complication rates were similar within comparisons of head sizes or bearings.

INTERPRETATION

In this short-term study, we did not find any functional benefits of larger head sizes or alternative bearings, after adjusting for other influences. We question their use in routine primary hip replacement given the lack of evidence of improved long-term survival in the literature.

Two-year serum metal ion levels in minimally invasive total conservative hip resurfacing: preliminary results of a prospective study

BACKGROUND

Metal-on-metal (MoM) hip resurfacings have been associated with the potential development of metallic debris and its associated pathology. Serum cobalt and chromium levels are a reliable surrogate marker of wear rates in MoM bearings. The aim of the study was to examine the trend in serum metal ion levels in the initial 2-year post-operative period following implantation of the minimally invasive total conservative hip MoM hip resurfacing and to determine whether head size, acetabular component orientation, clinical outcome scores or post-operative range of movement would affect these levels.

METHODS

In this prospective cohort study, serum cobalt and chromium ion levels were measured pre- and post-operatively in 25 patients who underwent minimally invasive total conservative hip MoM hip resurfacing. The results were correlated with acetabular component orientation, head size, outcome scores and post-operative range of movement.

RESULTS

The mean serum cobalt and chromium levels at 2 years were 1.2 ppb (0.4-4.4 ppb) and 2.1 ppb (0.7-5.7 ppb). The mean cup inclination was 43° (30°-60°) and anteversion was 18° (1°-47°). There was no clear relationship between serum ions and acetabular component orientation, outcome scores or range of movement. Patients with a head size ≤52 mm had significantly higher metal ion levels (cobalt P = 0.02, chromium P = 0.045).

CONCLUSION

Our preliminary results show all patients had cobalt and chromium levels below those indicating a high-risk implant, suggesting successful early outcome from minimally invasive total conservative hip resurfacing surgery.

What causes unexplained pain in patients with metal-on metal hip devices? A retrieval, histologic, and imaging analysis

BACKGROUND

Adverse tissue reactions associated with metal-on-metal (MOM) hips are common in resurfacing and total hip arthroplasty (THA) designs. The etiology of these reactions in painful, well-positioned arthroplasties is inconsistently described.

QUESTIONS/PURPOSES

The purposes of this study were to compare the (1) articular wear rates; (2) histologic findings; (3) synovial response on MRI; and (4) graded intraoperative tissue damage between well-positioned, MOM hips revised for unexplained pain and MOM hips revised for other reasons and to (5) determine whether the presence of a taper junction on a MOM articulation affects these four parameters in unexplained pain.

METHODS

We retrospectively studied 88 patients (94 hips) who had undergone revision of either a hip resurfacing or a large-head (> 36 mm) THA. Thirty-five hips revised for unexplained pain were compared with a control group of 59 hips revised for other causes. Articular wear was measured using three-dimensional contactless metrology and histologic analysis was performed using the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) score. Preoperative MRI was performed on 57 patients to determine synovial volumes and thicknesses. Tissue damage was graded from intraoperative reports.

RESULTS

Articular wear rates in the unexplained pain group were lower than in the control group (median 2.6 μm/year versus 12.8 μm/year, p < 0.001). Sixty-six percent of patients in the unexplained pain group had histologic confirmation of ALVAL compared with 19% in the control group (p < 0.001). The synovial thickness on MRI was higher in the unexplained pain group (p = 0.04) and was highly predictive of ALVAL. Severe intraoperative tissue damage was noted in more cases in the unexplained pain group (p = 0.01). There were no differences in articular wear, histology, MRI, and tissue damage between resurfacings and THAs revised for unexplained pain.

CONCLUSIONS

Unexplained pain in patients with well-positioned MOM hips warrants further investigation with MRI to look for features predictive of ALVAL. Tissue destruction in these cases does not appear to be related to high bearing wear or the presence of a taper.