The influence of the size of the component on the outcome of resurfacing arthroplasty of the hip

The assessment of implant shape-dependent failure mechanisms in primary total hip arthroplasty using finite element analysis

The three mechanisms known to be responsible for the failure of uncemented femoral stems in primary total hip arthroplasty (THA) are the stress shielding, excessive bone-implant interface stress, and excessive initial micromotion. Since implant designers usually have to sacrifice two mechanisms to improve the other one, the aim of this study was to assess which of them plays a more important role in the failure of uncemented stems. Two hip implant stems which are widely used in the primary THA and their mid-term clinical outcomes are available, were selected. Then, the amount of the three failure mechanisms created by each stem during the normal walking gait cycle was determined for a 70 kg female patient using the finite element method. The results indicated that the stem with better clinical outcome induced an average of 36.6% less stress shielding in the proximal regions of femur bone compared with the other stem. However, the maximum bone-implant interface stress and maximum initial micromotion were, respectively, 30 and 155% higher for the stem with better clinical outcomes. It was therefore concluded that the stress shielding has a more significant impact on the mid-term life of uncemented stems. However, care must be taken to ensure that the other two failure mechanisms do not exceed a certain threshold. It was also observed that the thinner and shorter stem created a smaller amount of stress shielding in the femur bone. The outcomes of this study can be used to design new hip implant stems that can potentially last longer.

Incidence, risk factors, and prognostic consequences of femoroacetabular cup impingement following hip resurfacing arthroplasty

PURPOSE

Hip resurfacing arthroplasty (HRA) is recommended for younger patients seeking higher levels of activity. However, femoroacetabular cup impingement (FACI) between the femoral neck and acetabular prosthesis remains a concern. This study aimed to determine the incidence, risk factors, and prognostic consequences of FACI after HRA.

METHODS

This study included 242 HRAs performed at a single institution. Three types of implants with different cup articular arc angle (CAAA) values were used. FACI was defined as indentation or spur formation at the femoral neck corresponding to the ridge of the acetabular cup. Multivariate regression analyses were conducted to identify risk factors for FACI. Clinical outcomes were compared between groups with and without impingement. The mean follow-up duration was 12 years (range, 2‒19).

RESULTS

FACI was identified in 87 out of 242 HRAs (36%). Multivariate regression analysis showed that FACI was associated with the use of implants with a greater CAAA (P < 0.001). At the latest evaluation, the mean Harris Hip Score (94 vs. 93; P = 0.405) and the incidence of groin pain (16.1% vs. 14.8%; P = 0.795) were similar between the groups with and without FACI. Implant survivorship free of any revision was 94.5% in the FACI group and 89.8% in the non-FACI group at 12 years (log-rank, P = 0.165).

CONCLUSION

This study identified that the incidence of FACI after HRA was 36%. Implants with greater CAAA were associated with a higher risk of impingement. However, radiographic FACI was not associated with adverse clinical outcomes of HRA after a mean follow-up of 12 years.

Clinical outcomes and return to dance after total hip arthroplasty or hip resurfacing in professional dancers

Aims

Professional dancers represent a unique patient population in the setting of hip arthroplasty, given the high degree of hip strength and mobility required by their profession. We sought to determine the clinical outcomes and ability to return to professional dance after total hip arthroplasty (THA) or hip resurfacing arthroplasty (HRA).

Methods

Active professional dancers who underwent primary THA or HRA at a single institution with minimum one-year follow-up were included in the study. Primary outcomes included the rate of return to professional dance, three patient-reported outcome measures (PROMs) (modified Harris Hip Score (mHHS), Hip disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS-JR), and Lower Extremity Activity Scale (LEAS)), and postoperative complications.

Results

A total of 49 hips in 39 patients (mean age 56 years (SD 13); 80% female (n = 39)) were included. Mean follow-up was 4.9 years (SD 5.1). Of these 49 hips, 37 THAs and 12 HRAs were performed. In all, 96% of hips returned to professional dance activities postoperatively. With regard to PROMs, there were statistically significant improvements in mHHS, HOOS-JR, and LEAS from baseline to ≥ one year postoperatively. There were complications in 7/49 hips postoperatively (14%), five of which required revision surgery (10%). There were no revisions for instability after the index procedure. Two complications (5.4%) occurred in hips that underwent THA compared with five (42%) after HRA (p = 0.007), though the difference by procedure was not significantly different when including only contemporary implant designs (p = 0.334).

Conclusion

Active professional dancers experienced significant improvements in functional outcome scores after THA or HRA, with a 96% rate of return to professional dance. However, the revision rate at short- to mid-term follow-up highlights the challenges of performing hip arthroplasty in this demanding patient population. Further investigation is required to determine the results of THA versus HRA using contemporary implant designs in these patients.

Long-Term Outcomes of Birmingham Hip Resurfacing Arthroplasty: A Systematic Review of Independent Series with At Least 10 Years of Follow-up

Background

Hip resurfacing arthroplasty (HRA) provides an attractive alternative to total hip arthroplasty (THA) for the management of osteoarthritis in younger, more active patients; however, concerns persist over complications specific to HRA. The aims of this systematic review were to assess the documented long-term survival rates of the metal-on-metal BIRMINGHAM HIP Resurfacing System at a follow-up of at least 10 years and to analyze the functional outcomes and cause of failures.

Methods

A systematic review was undertaken of all published cohort studies available in the MEDLINE, Cochrane, Embase, and PubMed research databases up to December 2021, as recommended by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data extraction was focused on survival rates, causes of failure, and functional outcomes. Survival estimates at 10 years were pooled in a meta-analysis, with each series weighted by its variance. Causes of failure were presented as a percentage of the pooled revisions.

Results

A total of 11 studies were identified, encompassing 3,129 cases. Across the 9 studies that had reported a mean follow-up, the mean follow-up was 11.7 years (range, 9.55 to 13.7 years). We found a pooled 10-year survival rate of 95.5% (95% confidence interval, 93.4% to 97.1%). There were 149 revisions among the studies (range, 4 to 38 revisions per study), a rate of 4.8% of the total procedures performed. The 2 main causes of revision were aseptic loosening (20.1% of revisions) and adverse reactions to metal debris (20.1%). There were no revisions for dislocation. Of the studies that reported preoperative functional scores, all reported significant improvement in mean scores postoperatively except for 1 study in which the mean Tegner activity score did not significantly improve.

Conclusions

When performed for appropriate indications, patients undergoing an HRA with use of the BIRMINGHAM HIP Resurfacing System can expect good implant survivorship at 10 years with acceptable functional results and low rates of dislocation and infection. This systematic review, however, confirms concerns regarding adverse reactions to metal debris as a leading cause of revision.

Level of Evidence

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

Birmingham Hip Resurfacing at 20 years

Aims

The Birmingham Hip Resurfacing (BHR) arthroplasty has been used as a surgical treatment of coxarthrosis since 1997. We present 20-year results of 234 consecutive BHRs performed in our unit.

Methods

Between 1999 and 2001, there were 217 patients: 142 males (65.4%), mean age 52 years (18 to 68) who had 234 implants (17 bilateral). They had patient-reported outcome measures collected, imaging (radiograph and ultrasound), and serum metal ion assessment. Survivorship analysis was performed using Kaplan-Meier estimates. Revision for any cause was considered as an endpoint for the analysis.

Results

Mean follow-up was 20.9 years (19.3 to 22.4). Registry data revealed that 19 hips (8.1%) had been revised and 26 patients (12%) had died from causes unrelated to the BHR. Among the remaining 189 hips, 61% were available for clinical follow-up at 20 years (n = 115) and 70% of patients had biochemical follow-up (n = 132). The cumulative implant survival rate at 20 years for male patients was 96.5% (95% confidence interval (CI) 93.5 to 99.6), and for female patients 87% (95% CI 79.7 to 94.9). The difference was statistically significant (p = 0.029). The mean Oxford Hip Score, Hip disability and Osteoarthritis Outcome Score, and Forgotten Joint Score were 45 (29 to 48), 89 (43 to 100), and 84 (19 to 100), respectively. The mean scores for each of the five domains of the EuroQol five-dimension three-level questionnaire were 1.2, 1.0, 1.2, 1.3, and 1.1, and mean overall score 82.6 (50 to 100). Ultrasound showed no pseudotumour. Mean cobalt and chromium levels were 32.1 nmol/l (1 to 374) and 45.5 nmol/l (9 to 408), respectively.

Conclusion

This study shows that BHRs provide excellent survivorship and functional outcomes in young male patients. At 20 years, soft-tissue imaging and serum metal ion studies suggest that a metal-on-metal resurfacing implant can be well tolerated in a group of young patients.

Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing

Objectives

Modern metal-on-metal (MoM) hip resurfacing arthroplasty (HRA), while achieving good results with well-orientated, well-designed components in ideal patients, is contraindicated in women, men with head size under 50 mm, or metal hypersensitivity. These patients currently have no access to the benefits of HRA. Highly crosslinked polyethylene (XLPE) has demonstrated clinical success in total hip arthroplasty (THA) and, when used in HRA, potentially reduces metal ion-related sequelae. We report the early performance of HRA using a direct-to-bone cementless mono-bloc XLPE component coupled with a cobalt-chrome femoral head, in the patient group for whom HRA is currently contraindicated.

Methods

This is a cross-sectional, observational assessment of 88 consecutive metal-on-XLPE HRAs performed in 84 patients between 2015 and 2018 in three centres (three surgeons, including the designer surgeon). Mean follow-up is 1.6 years (0.7 to 3.9). Mean age at operation was 56 years (sd 11; 21 to 82), and 73% of implantations were in female patients. All patients were individually counselled, and a detailed informed consent was obtained prior to operation. Primary resurfacing was carried out in 85 hips, and three cases involved revision of previous MoM HRA. Clinical, radiological, and Oxford Hip Score (OHS) assessments were studied, along with implant survival.

Results

There was no loss to follow-up and no actual or impending revision or reoperation. Median OHS increased from 24 (interquartile range (IQR) 20 to 28) preoperatively to 48 (IQR 46 to 48) at the latest follow-up (48 being the best possible score). Radiographs showed one patient had a head-neck junction lucency. No other radiolucency, osteolysis, component migration, or femoral neck thinning was noted.

Conclusion

The results in this small consecutive cohort suggest that metal-on-monobloc-XLPE HRA is successful in the short term and merits further investigation as a conservative alternative to the current accepted standard of stemmed THA. However, we would stress that survival data with longer-term follow-up are needed prior to widespread adoption.

Cite this article: R. B. C. Treacy, J. P. Holland, J. Daniel, H. Ziaee, D. J. W. McMinn. Preliminary report of clinical experience with metal-on-highly-crosslinked-polyethylene hip resurfacing. Bone Joint Res 2019;8:443–450. DOI: 10.1302/2046-3758.810.BJR-2019-0060.R1

Origins of material loss in highly worn acetabular cups of metal-on-metal total hip replacements

Excessive wear has been one of the major failure modes of metal-on-metal hip implants. From a collection of 541 retrieved ASR metal-on-metal implants, we selected those head-cup pairs with combined wear >100 mm³ , (N = 42) to assess the distributions of wear volume on cups, and non-conformance in the worn areas at the head-cup interfaces. All 42 had severe cup edge wear (average maximum wear depth 500 μm). On average, 58% of wear volume of cups occurred at the edge areas, whereas 42% occurred well inside the socket, indicating that substantial wear volume of cups was generated well inside the socket. Particularly, in eight cups, more than half of the wear volume occurred well inside the socket. The head-cup conformance in the worn areas was deteriorated. On average, in worn areas, head-cup clearance was approximately eight times greater than in unworn areas, and the sphericity of heads and cups was approximately 36 times and 84 times higher, respectively, than in unworn areas. The radius of curvature of the worn surfaces of heads and cups varied widely, with an average variation of 3 mm (0.6-7 mm) and 11 mm (2-47 mm) for heads and cups, respectively. The severely deteriorated conformance at the edge areas and the areas well inside the socket, due to edge contact, could be the major factor for excessive wear of these 42 pairs. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Microstructure and Surface Damage in Retrieved Metal-on-Metal Hip Arthroplasties

BACKGROUND

Besides promising results of metal-on-metal (MOM) hip arthroplasty (HA), frequent failures have been reported even in the short term. Many host, surgical, design, metallurgical, and processing factors have been evoked in the base of these events. We have tried to characterize and to evaluate metallurgical and processing features present in this type of implants.

METHODS

The acetabular and femoral components of 20 MOM HAs collected from a multicenter retrieval program were examined. All the specimens were inspected with naked eye, with confocal microscopy and vertical scanning interferometry, scanning electron microscopy, back-scattered electron imaging, and energy-dispersive X-ray spectroscopy, in 25 zones of each articular component.

RESULTS

Gas pores, shrinkage voids and holes of detached carbides, carbides on surface, embedded particles, scratches and marks of wear, surface discoloration, surface deposits, and tribochemical reaction layers were widely dispersed through a substantial percentage of the total bearing surface in all the implanted components. Surface cup and head voids, and cup scratches showed significant correlation with the clearance of pair. A higher surface damage of the cup and head was observed mainly in the low clearance prostheses. There was no other significant correlation or difference in the incidence and importance of any of these defects between resurfacing hip arthroplasties and total hip arthroplasties, or according to the pair diameter.

CONCLUSION

Some metallurgical features and surface damage were significantly present in the retrieved implants of MoM HAs. It would be desirable to improve the structure and metallurgical characteristics of these implants to avoid those effects and optimize their performance.

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.

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.

Are There Long-term Benefits to Cementing the Metaphyseal Stem in Hip Resurfacing?

BACKGROUND

Cementing the metaphyseal stem during hip resurfacing surgery improves the initial fixation of the femoral component. However, there may be long-term detrimental effects such as stress shielding or an increased risk of thermal necrosis associated with this technique.

QUESTIONS/PURPOSES

We compared (1) long-term survivorship free from radiographic femoral failure, (2) validated pain scores, and (3) radiographic evidence of component fixation between hips resurfaced with a cemented metaphyseal stem and hips resurfaced with the metaphyseal stem left uncemented.

METHODS

We retrospectively selected all the patients who had undergone bilateral hip resurfacing with an uncemented metaphyseal stem on one side, a cemented metaphyseal stem on the other side, and had both surgeries performed between July 1998 and February 2005. Forty-three patients matched these inclusion criteria. During that period, the indications for cementing the stem evolved in the practice of the senior author (HCA), passing through four phases; initially, only hips with large femoral defects had a cemented stem, then all stems were cemented, then all stems were left uncemented. Finally, stems were cemented for patients receiving small femoral components (< 48 mm) or having large femoral defects (or both). Of the 43 cemented stems, two, 13, 0, and 28 came from each of those four periods. All 43 patients had complete followup at a minimum of 9 years (mean, 143 ± 21 months for the uncemented stems; and 135 ± 22 months for the cemented stems; p = 0.088). Survivorship analyses were performed with Kaplan-Meier and Cox proportional hazards ratios using radiographic failure of the femoral component as the endpoint. Pain was assessed with University of California Los Angeles (UCLA) pain scores, and radiographic femoral failure was defined as complete radiolucency around the metaphyseal stem or gross migration of the femoral component.

RESULTS

There were four failures of the femoral component in the press-fit stem group while the cemented stem group had no femoral failures (p = 0.0471). With the numbers available, we found no differences between the two groups regarding pain relief or radiographic appearance other than in patients whose components developed loosening.

CONCLUSIONS

Cementing the metaphyseal stem improves long-term implant survival and does not alter long-term pain relief or the radiographic appearance of the proximal femur as had been a concern based on the results of finite element studies. We believe that patients with small component sizes and large femoral head defects have more to gain from the use of this technique which adds surface area for fixation, and there is no clinical downside to cementing the stem in patients with large component sizes.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Usefulness of ultrasonography for detection of pseudotumors after metal-on-metal total hip arthroplasty

We retrospectively analyzed 83 metal-on-metal total hip arthroplasties in 74 patients. Ultrasonography and magnetic resonance imaging (MRI) of each hip were performed to detect abnormal patterns and pseudotumors. We examined the reliability of ultrasonography for detecting pseudotumors in comparison with MRI. We also compared the acetabular component inclination between patients with and without pseudotumors. The mean positive and negative predictive values for pseudotumor detection by ultrasonography were 65% and 91%, respectively. The mean positive and negative likelihood ratios were 5.78 and 0.32, respectively. There was no clear association between pseudotumor presence and acetabular component inclination. We concluded that ultrasonography is a suitable technique to screen for the presence of pseudotumors. We also need to distinguish between bearing-related and taper junction corrosion-related complications.

Metal-on-metal hip resurfacing: correlation between clinical and radiological assessment, metal ions and ultrasound findings

PURPOSE

We report the clinical, radiological and wear analysis of 52 consecutive MoM hip resurfacings (performed on 49 younger patients) to a mean follow-up of 9.2 years.

METHODS

Every patient underwent X-ray and clinical evaluation (HHS). Ultrasonography of the hip was performed in all patients in order to identify possible cystic or solid mass in periprosthetic tissue. In case of mass >20 mm, further MRI was performed to better analyse the characteristics of lesion.

RESULTS

Five patients (five hips) had a revision. The overall survival rate was 90.38 %. The average HHS at follow-up examination was 95.5 points. No progressive radiolucent areas and no sclerosis or osteolysis around the implants were found. The US and RMI imaging showed a pseudotumour formation in two patients (correlated with high metal ion levels in blood and urine), both asymptomatic.

CONCLUSION

A significant positive correlation between inclination of the acetabular component and serum metal ion levels was found (r = 0.64 and r = 0.62 for cobalt and chromium, respectively).

Our midterm results of the Birmingham hip resurfacing with and without navigation

We reviewed 148 consecutive hip resurfacings in order to assess the clinical outcomes of the BHR at midterm follow-up and to compare the accuracy of the navigation in the positioning of femoral component. We retrospectively analyzed 85 hips using the conventional jig to implant the femoral component and we prospectively followed 63 hips operated on by navigation. At a mean follow-up of 50.54 months, the Harris hip score improved significantly from 44.66 preoperatively to 98.45 postoperatively without any differences between the groups. Radiologically, we classic navigated group. Our clinical outcomes are excellent at midterm follow-up and the navigation definitely improves the implant position in both planes.

Hip resurfacing arthroplasty at a non-specialist centre

INTRODUCTION

Few studies have reported the outcome of hip resurfacing arthroplasty (HRA) with respect to implant characteristics from non-specialist centres. We report the survival, clinical and radiological outcomes of a single surgeon series of HRA with an average follow-up duration of five years.

METHODS

All consecutive HRAs performed by a single surgeon between 2003 and 2011 at a district general hospital were retrospectively examined clinically and radiologically.

RESULTS

A total of 85 patients underwent 109 HRAs (58 male [53.2%] and 51 female patients [46.8%]) with a mean follow-up period of 62 months (range: 12-102 months). The median age was 57 years (range: 25-75 years). The mean acetabular and femoral head component sizes were 54 mm (range: 48-64 mm) and 48 mm (range: 42-58 mm) respectively with a mean acetabular inclination angle of 42.9° (range: 20-75°). The survival rate was 95% with five revisions due to aseptic loosening (n=3) and fracture (n=2): these were predominantly for female patients (n=4), with significantly smaller mean acetabular (51 mm, p=0.04) and femoral (44 mm, p=0.02) implant sizes. Furthermore, they had a higher mean acetabular inclination angle of 48.1° (p=0.74). The mean Oxford hip score was 43.8 (range: 25-48) and the mean University of California Los Angeles (UCLA) activity score was 6.8 (range: 3-10). Radiological findings included heterotopic ossification in 13 (11.9%), radiolucent lines in 6 (5.5%), femoral neck thinning in 2 (1.8%) and femoral neck notching in 5 patients (4.6%).

CONCLUSIONS

We have shown that HRA at a non-specialist centre has short to medium-term outcomes comparable with those at specialist centres. HRA therefore remains a viable option although vigilance is required in case selection and follow-up according to national guidance.

Effects of positioning on radiographic measurements of ankle morphology: a computerized tomography-based simulation study

Background

Measurements of the morphology of the ankle joint, performed mostly for surgical planning of total ankle arthroplasty and for collecting data for total ankle prosthesis design, are often made on planar radiographs, and therefore can be very sensitive to the positioning of the joint during imaging. The current study aimed to compare ankle morphological measurements using CT-generated 2D images with gold standard values obtained from 3D CT data; to determine the sensitivity of the 2D measurements to mal-positioning of the ankle during imaging; and to quantify the repeatability of the 2D measurements under simulated positioning conditions involving random errors.

Method

Fifty-eight cadaveric ankles fixed in the neutral joint position (standard pose) were CT scanned, and the data were used to simulate lateral and frontal radiographs under various positioning conditions using digitally reconstructed radiographs (DRR).

Results and discussion

In the standard pose for imaging, most ankle morphometric parameters measured using 2D images were highly correlated (R > 0.8) to the gold standard values defined by the 3D CT data. For measurements made on the lateral views, the only parameters sensitive to rotational pose errors were longitudinal distances between the most anterior and the most posterior points of the tibial mortise and the tibial profile, which have important implications for determining the optimal cutting level of the bone during arthroplasty. Measurements of the trochlea tali width on the frontal views underestimated the standard values by up to 31.2%, with only a moderate reliability, suggesting that pre-surgical evaluations based on the trochlea tali width should be made with caution in order to avoid inappropriate selection of prosthesis sizes.

Conclusions

While highly correlated with 3D morphological measurements, some 2D measurements were affected by the bone poses in space during imaging, which may affect surgical decision-making in total ankle arthroplasty, including the amount of bone resection and the selection of the implant sizes. The linear regression equations for the relationship between 2D and 3D measurements will be helpful for correcting the errors in 2D morphometric measurements for clinical applications.

Impact of implant size on cement filling in hip resurfacing arthroplasty

Larger proportions of cement within femoral resurfacing implants might result in thermal bone necrosis. We postulate that smaller components are filled with proportionally more cement, causing an elevated failure rate. A total of 19 femoral heads were fitted with polymeric replicas of ReCap (Biomet) resurfacing components fixed with low-viscosity cement. Two specimens were used for each even size between 40 and 56 mm and one for size 58 mm. All specimens were imaged with computed tomography, and the cement thickness and bone density were analyzed. The average cement mantle thickness was 2.63 mm and was not correlated with the implant size. However, specimen with low bone density had thicker cement mantles regardless of size. The average filling index was 36.65% and was correlated to both implant size and bone density. Smaller implants and specimens with lower bone density contained proportionally more cement than larger implants. According to a linear regression model, bone density but not implant size influenced cement thickness. However, both implant size and bone density had a significant impact on the filling index. Large proportions of cement within the resurfacing head have the potential to generate thermal bone necrosis and implant failure. When considering hip resurfacing in patients with a small femoral head and/or osteoporotic bone, extra care should be taken to avoid thermal bone necrosis, and alternative cementing techniques or even cementless implants should be considered. This study should help delimiting the indications for hip resurfacing and to choose an optimal cementing technique taking implant size into account.

Patterns of changes in femoral bone mineral density up to five years after hip resurfacing

This is a prospective study of 26 patients (29 hips) on the patterns of change in the Bone Mineral Density (BMD) in various zones of the femoral neck and proximal femur five years after hip resurfacing. We have found that BMD continues to positively change up to five years after hip resurfacing. This was observed primarily in the trochanteric and superior neck regions. In both these regions BMD had decreased by up to 10% at six-weeks and three-months after surgery and then had recovered to preoperative level by one year. A regression analysis to assess the influence of age, gender, BMI, preoperative BMD, component size and orientation revealed that the best predictor of change in BMD at five years in the trochanteric area was acetabular component inclination.

The role of biomechanics and engineering in total hip replacement. Why surgeons need technical help

Implanting the acetabular cup of hard-on-hard bearings, like metal-on-metal or ceramic-on-ceramic, requires considerable surgeon skill to avoid the complications associated with edge loading. Successful cup positioning instruments have been designed in the past by pioneering surgeons, like Peter Ring and Michael Freeman, and these are re-visited in this article. An advantage of these instruments is that they could position the acetabular cup without defining a reference pelvic plane. Computer-assisted cup orientation is able to reduce outliers in cup orientation, but the technology has not been widely adopted. There may be an opportunity to improve the uptake of computer-assisted surgery by incorporating some of the concepts from historically successful manual instruments.

Durom hip resurfacing system: retrospective study of 644 cases with an average follow-up of 34 months

INTRODUCTION

The performance of second-generation metal-on-metal bearings has led to the reintroduction of hip resurfacing. The goal of this multicentre study was to evaluate the short-term radiological and clinical outcomes with the Durom hip resurfacing system.

HYPOTHESIS

The Durom hip-resurfacing system will have similar results to other hip resurfacing systems and traditional hip arthroplasty implants.

MATERIALS AND METHODS

In the four participating centers, 580 patients (406 men, 174 women) and 644 hips were included. The average patient age was 48 years (range 16-77). A posterolateral surgical approach was used in 357 cases; a Hardinge-type approach was used in 182 cases and a Rottinger-type approach in 105.

RESULTS

After an average follow-up of 34 months, 31 hips (4.8%) had been revised. The reasons for revision were the following: 10 (1.6%) neck fracture (seven with Rottinger operative approach, one with Hardinge approach and one with posterolateral approach); 12 (1.9%) femoral loosening (four with lateral approach and eight with posterolateral approach); four (0.6%) acetabular cup migration; three (0.5%) unexplained pain; one (0.2%) adverse reaction to metal debris; one (0.2%) infection. Four hips (0.6%) dislocated but without recurrence - all were operated using the Hardinge approach. The 613 hips that were not operated on again had satisfactory clinical results; the Merle d'Aubigné score was 17.2 (range 12-18) and the WOMAC score was 91 (range 20-100). The five-year survival rate was 91% (95% CI: 87-94%). Based on radiographs, the average cup inclination was 44.4° (range 30 to 70°). The femoral offset was reduced by an average of 2.4mm (-31 to 23 mm) and the leg length had increased by an average of 0.8mm (-15 to 19 mm) relative to the other side, which was prosthesis-free. None of the non-revised implants showed any signs of loosening.

DISCUSSION

This multicentre evaluation revealed that the Durom revision rate was slightly higher than the rate with other hip resurfacing systems and traditional total hip arthroplasty. Although the Durom system displayed excellent tribological performance, the differences relative to other implants may be attributed to the challenges associated with impaction, related to the geometry and design of the cup, and to precarious primary fixation. The choice of surgical exposure and implantation technique was an important factor in the survival of the implant.

LEVEL OF PROOF

Level IV - Retrospective study.

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

The use of large diameter metal bearing total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) increased in popularity in the last decade. More recent literature has highlighted the effect of head size in patient outcomes. Data was obtained from the Australian Orthopaedic Association National Joint Replacement Registry (AOA-NJRR) to evaluate the Birmingham (MoM) bearing surface when used with THA and HRA. There is no difference in the overall rate of revision between the THA and HRA but head size has a significant effect on revision rate. The data show that small diameter metal bearings in HRA (below 50mm) have a higher rate of revision than large diameter metal bearings in HRA (equal to and above 50mm) (P<.001). Conversely the large diameter metal bearings in THA have a higher rate of revision than the small diameter metal bearings in THA (P=.027). The revision rate for large diameter HRA compared to small diameter THA is not significantly different P=.670. We recommend caution when choosing either a large diameter (≥50mm) metal on metal THA or small diameter (<50mm) HRA.

Results of metal-on-metal hip resurfacing in patients 40 years old and younger

The prevalence of total hip arthroplasty in young patients is small but increasing. We analyzed the results of metal-on-metal hip resurfacing (MMHR) in patients aged 40 years or less. In total 74 operations were performed on 64 patients. Mean age at operation was 33.2 years. HHS averaged 92.3 points at latest follow-up, mean UCLA activity was 8.2. Patients with comorbidity evinced lower scores in HHS, in UCLA activity and in quality of life than patients without comorbidities. Eight revisions (10.8 %) were performed, of which seven due to adverse reaction to metal debris. Seven-year survival was 90.5 %. The functional outcome of hip resurfacing in this cohort was excellent, but overall survival was unsatisfactory. Further analysis is required to verify the role of hip resurfacing among young and active patients.

Hip resurfacing in a district general hospital: 6-year clinical results using the ReCap hip resurfacing system

BACKGROUND

The purpose of our study was to prospectively report the clinical results of 280 consecutive hips (240 patients) who received a ReCap Hip Resurfacing System implant (Biomet Inc., Warsaw, USA) in a single district general hospital. Literature reports a large variation in clinical results between different resurfacing designs and published results using this particular design are scarce.

METHODS

Mean follow up was 3.3 years (1.0 to 6.3) and four patients were lost to follow-up. All patients were diagnosed with end-stage hip osteoarthritis, their mean age was 54 years and 76.4% of all patients were male.

RESULTS

There were 16 revisions and four patients reported a Harris Hip Score <70 points at their latest follow up. There were no pending revisions. Kaplan-Meier implant survival probability, with revision for any reason as endpoint, was 93.5% at six years follow-up (95%-CI: 88.8-95.3). There were no revisions for Adverse Reactions to Metal Debris (ARMD) and no indications of ARMD in symptomatic non-revised patients, although diagnostics were limited to ultrasound scans.

CONCLUSIONS

This independent series confirms that hip resurfacing is a demanding procedure, and that implant survival of the ReCap hip resurfacing system is on a critical level in our series. In non-revised patients, reported outcomes are generally excellent.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00603395.

Failure rates of metal-on-metal hip resurfacings: analysis of data from the National Joint Registry for England and Wales

BACKGROUND

Implant survival after conventional total hip replacement (THR) is often poor in younger patients, so alternatives such as hip resurfacing, with various sizes to fit over the femoral head, have been explored. We assessed the survival of different sizes of metal-on-metal resurfacing in men and women, and compared this survival with those for conventional stemmed THRs.

METHODS

We analysed the National Joint Registry for England and Wales (NJR) for primary THRs undertaken between 2003 and 2011. Our analysis involved multivariable flexible parametric survival models to estimate the covariate-adjusted cumulative incidence of revision adjusting for the competing risk of death.

FINDINGS

The registry included 434,560 primary THRs, of which 31,932 were resurfacings. In women, resurfacing resulted in worse implant survival than did conventional THR irrespective of head size. Predicted 5-year revision rates in 55-year-old women were 8·3% (95% CI 7·2-9·7) with a 42 mm resurfacing head, 6·1% (5·3-7·0) with a 46 mm resurfacing head, and 1·5% (0·8-2·6) with a 28 mm cemented metal-on-polyethylene stemmed THR. In men with smaller femoral heads, resurfacing resulted in poor implant survival. Predicted 5-year revision rates in 55-year-old men were 4·1% (3·3-4·9) with a 46 mm resurfacing head, 2·6% (2·2-3·1) with a 54 mm resurfacing head, and 1·9% (1·5-2·4) with a 28 mm cemented metal-on-polyethylene stemmed THR. Of male resurfacing patients, only 23% (5085 of 22076) had head sizes of 54 mm or above.

INTERPRETATION

Hip resurfacing only resulted in similar implant survivorship to other surgical options in men with large femoral heads, and inferior implant survivorship in other patients, particularly women. We recommend that resurfacing is not undertaken in women and that preoperative measurement is used to assess suitability in men. Before further new implant technology is introduced we need to learn the lessons from resurfacing and metal-on-metal bearings.

FUNDING

National Joint Registry for England and Wales.

Corrosion at the cone/taper interface leads to failure of large-diameter metal-on-metal total hip arthroplasties

BACKGROUND

Metal-on-metal (MoM) THAs have reduced wear rates compared with metal-on-polyethylene. However, elevated serum metal ion levels and pseudotumors have been reported in large MoM articulations.

QUESTIONS/PURPOSES

We therefore determined (1) if corrosion occurred at the cone/taper interface leading to instability in patients with large-diameter THAs; (2) how patients presented clinically and radiographically; (3) if adverse periprosthetic tissue reactions occurred; (4) whether metal was released from the implants into the periprosthetic tissues; and (5) if head size correlated with metal release.

METHODS

We reviewed 114 patients who had revisions of large-diameter head MoM articulations. Mean time of implantation was 46 months. To identify adverse reactions and particle load, tissues were stained by hematoxylin and eosin and CD3/CD20/CD68 antibodies. Periprosthetic tissues were analyzed for metal content and distribution in different regions. Electrochemical reactions between the stem and adapter were investigated by a minicell electrode.

RESULTS

Electrochemical studies on the stem and the head adapter showed a risk for galvanic corrosion. Ninety-four percent of patients had instability at the cone/taper interface. All patients presented with early clinical symptoms; 59 patients had radiographic signs of loosening. One hundred four patients had foreign body reactions and necrosis. The largest amounts of metal released were titanium or iron. We found no correlation between head size and metal ion release.

CONCLUSIONS

These findings suggest that in modular cone/taper connections, friction of the MoM articulations may cause failure of the cone/taper interface leading to galvanic corrosion and loosening. It is unclear whether the design of this MoM system provides sufficient stability at the taper.

Bearing surfaces for total disc arthroplasty: metal-on-metal versus metal-on-polyethylene and other biomaterials

BACKGROUND CONTEXT

Concerns about the effect of metallic wear debris from metal-on-metal bearing surfaces in total hip arthroplasty have increased. Some spinal arthroplasty devices include metal-on-metal bearing surfaces.

PURPOSE

To review the literature for clinical reports of complications because of wear debris from metal-on-metal spinal arthroplasty devices. To review the biology of wear debris from metal-on-metal bearing surfaces drawn from the hip arthroplasty literature and place it in the context of global regulatory actions and clinical and laboratory studies.

STUDY DESIGN

Literature review.

METHODS

To identify clinical reports, the PubMed database from the United States National Library of Medicine was queried using Medical Subject Headings terms and additional keyword terms. In addition, experts from academia and regulatory agencies were questioned regarding their knowledge of reports, including experts who attended the US Food and Drug Administration roundtable in September 2010.

RESULTS

Three case reports and one case series including seven total cases were identified in which abnormal inflammatory reactions and soft-tissue masses after metal-on-metal disc replacements were consistent with pseudotumor and metal hypersensitivity. Spinal cases are present as pain and neurologic symptoms. On plain radiography, there is no clear periprosthetic osteolysis or loosening. On magnetic resonance imaging, there is increased magnetic susceptibility artifact because of metallic debris that renders images inadequate. Computed tomography myelography demonstrates a soft-tissue mass, which exhibits epidural extension surgically. Histologically, large areas of necrotic debris and exudates are interspersed with chronic inflammatory cells. Lymphocyte or macrophage predominance is determined by the rate of wear and the presence of gross, microscopic, or submicron metallic wear debris. The metallurgy of the involved devices is cobalt-chromium-molybdenum (CoCrMo) alloy, and the bearing surface is CoCrMo-on-CoCrMo.

CONCLUSIONS

Metal-on-metal spinal arthroplasty devices are subject to postoperative complications because of metallic wear debris with similar clinical, radiographic, histologic, gross anatomic, and device-related features to those found in metal-on-metal bearing surfaces in total hip arthroplasty.

Ultrasound screening of periarticular soft tissue abnormality around metal-on-metal bearings

Although metal hypersensitivity or pseudotumors are concerns for metal-on-metal (MoM) bearings, detailed pathologies of patterns, severity, and incidence of periprosthetic soft tissue lesions are incompletely understood. We examined the potential of ultrasound for screening of periarticular soft tissue lesions around MoM bearings. Ultrasound examinations were conducted in 88 hips (79 patients) with MoM hip resurfacings or MoM total hip arthroplasties with a large femoral head. Four qualitative ultrasound patterns were shown, including normal pattern in 69 hips, joint-expansion pattern in 11 hips, cystic pattern in 5 hips, and mass pattern in 3 hips. Hips with the latter 3 abnormal patterns showed significantly higher frequency of clinical symptoms, without significant differences of sex, duration of implantation, head sizes, and cup abduction/anteversion angles, compared with hips with normal pattern. Ultrasound examination provides sensitive screening of soft tissue reactions around MoM bearings and may be useful in monitoring progression and defining treatment for periarticular soft tissue abnormalities.

Birmingham hip resurfacing at a mean of ten years: results from an independent centre

We report the findings of an independent review of 230 consecutive Birmingham hip resurfacings (BHRs) in 213 patients (230 hips) at a mean follow-up of 10.4 years (9.6 to 11.7). A total of 11 hips underwent revision; six patients (six hips) died from unrelated causes; and 13 patients (16 hips) were lost to follow-up. The survival rate for the whole cohort was 94.5% (95% confidence interval (CI) 90.1 to 96.9). The survival rate in women was 89.1% (95% CI 79.2 to 94.4) and in men was 97.5% (95% CI 92.4 to 99.2). Women were 1.4 times more likely to suffer failure than men. For each millimetre increase in component size there was a 19% lower chance of a failure. The mean Oxford hip score was 45.0 (median 47.0, 28 to 48); mean University of California, Los Angeles activity score was 7.4 (median 8.0, 3 to 9); mean patient satisfaction score was 1.4 (median 1.0, 0 to 9). A total of eight hips had lysis in the femoral neck and two hips had acetabular lysis. One hip had progressive radiological changes around the peg of the femoral component. There was no evidence of progressive neck narrowing between five and ten years. Our results confirm that BHR provides good functional outcome and durability for men, at a mean follow-up of ten years. We are now reluctant to undertake hip resurfacing in women with this implant.

Metal ion levels in large-diameter total hip and resurfacing hip arthroplasty--preliminary results of a prospective five year study after two years of follow-up

Background

Metal-on-metal hip resurfacing is an alternative to metal-on-metal total hip arthroplasty, especially for young and physically active patients. However, wear which might be detected by increased serum ion levels is a matter of concern.

Methods

The aims of this preliminary study were to determine the raise of metal ion levels at 2-years follow-up in a prospective setting and to evaluate differences between patients with either resurfacing or total hip arthroplasty. Furthermore we investigated if the inclination of the acetabular component and the arc of cover would influence these findings. Therefore, 36 patients were followed prospectively.

Results

The results showed increments for Co and Cr in both implant groups. Patients treated with large-diameter total hip arthroplasty showed fourfold and threefold, respectively, higher levels for Co and Cr compared to the resurfacing group (Co: p < 0,001 and Cr: p = 0,005). Nevertheless, we observed no significant correlation between serum ion levels, inclination and arc of cover.

Discussion

In order to clarify the biologic effects of ion dissemination and to identify risks concerning long-term toxicity of metals, the exposure should be monitored carefully. Therefore, long-term studies have to be done to determine adverse effects of Co and Cr following metal-on-metal hip replacement.

Ten-year clinical, radiological and metal ion analysis of the Birmingham Hip Resurfacing

We present the clinical results and survivorship of consecutive 100 Birmingham Hip Resurfacings in 90 patients at a minimum follow-up of ten years. All procedures were carried out by an independent surgeon who commenced a prospective study in 1998. Patients were assessed clinically using the Western Ontario and McMaster Universities osteoarthritis index, Short-Form 36, Harris hip score and University of California, Los Angeles activity score. Radiological analysis was performed by an independent observer and blood metal ion levels concentrations were measured at ten years post-operatively in 62 patients. The median acetabular component inclination was 46.2° (34° to 59°) and anteversion 11.0° (0° to 30°). The median chromium concentration in the unilateral group was 1.74 (0.41 to 15.23) and for the bilateral group was 2.98 (1.57 to 18.01). The equivalent values for cobalt were 1.67 (0.54 to 20.4) and 1.88 (1.38 to 19.32).

In total there were eight failures giving an overall survival at ten years of 92% (95% confidence interval (CI) 86.7 to 97.3). BHR in male patients had an improved survivorship of 94.6% (95% CI 89.4 to 100) compared with females at 84.6% (95% CI 70.7 to 98.5), but this did not reach statistical significance (p = 0.119). Four of the nine BHRs with a bearing diameter of 42 mm failed.

The overall results were consistent with data produced from other centres in that the clinical outcome of large male patients was extremely encouraging, whereas the survival of the smaller joints was less satisfactory.

What advantage is there to be gained using large modular metal-on-metal bearings in routine primary hip replacement?

The aim of this study was to investigate the possible benefit of large-head metal-on-metal bearing on a stem for primary hip replacement compared with a 28 mm diameter conventional metal-on-polyethylene bearing in a prospective randomised controlled trial. We investigated cemented stem behaviour between these two different bearings using Einzel-Bild-Röntgen-Analyse, clinical and patient reported measures (Harris hip score, Western Ontario and McMaster Universities osteoarthritis index, Short Form-36 and satisfaction) and whole blood metal ion levels at two years. A power study indicated that 50 hips were needed in each group to detect subsidence of > 5 mm at two years with a p-value of < 0.05.

Significant improvement (p < 0.001) was found in the mean clinical and patient reported outcomes at two years for both groups. Comparison of outcomes between the groups at two years showed no statistically significant difference for mean stem migration, clinical and patient reported outcomes; except overall patient satisfaction which was higher for metal-on-metal group (p = 0.05). Metal ion levels were raised above the Medicines and Healthcare products Regulatory Agency advised safety level (7 µg per litre) in 20% of the metal-on-metal group and in one patient in metal-on-polyethylene group (who had a metal-on-metal implant on the contralateral side). Two patients in the metal-on-metal group were revised, one for pseudotumour and one for peri-prosthetic fracture.

Use of large modular heads is associated with a risk of raised whole blood metal ion levels despite using a proven bearing from resurfacing. The head-neck junction or excess stem micromotion are possibly the weak links warranting further research.

Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement

Blood metal ions have been widely used to investigate metal-on-metal hip replacements, but their ability to discriminate between well-functioning and failed hips is not known. The Medicines and Healthcare products Regulatory Agency (MHRA) has suggested a cut-off level of 7 parts per billion (ppb). We performed a pair-matched, case-control study to investigate the sensitivity and specificity of blood metal ion levels for diagnosing failure in 176 patients with a unilateral metal-on-metal hip replacement. We recruited 88 cases with a pre-revision, unexplained failed hip and an equal number of matching controls with a well-functioning hip. We investigated the 7 ppb cut-off level for the maximum of cobalt or chromium and determined optimal mathematical cut-off levels from receiver-operating characteristic curves. The 7 ppb cut-off level for the maximum of cobalt or chromium had a specificity of 89% and sensitivity 52% for detecting a pre-operative unexplained failed metal on metal hip replacement. The optimal cut-off level for the maximum of cobalt or chromium was 4.97 ppb and had sensitivity 63% and specificity 86%. Blood metal ions had good discriminant ability to separate failed from well-functioning hip replacements. The MHRA cut-off level of 7 ppb provides a specific test but has poor sensitivity.

A comparison of explanted Articular Surface Replacement and Birmingham Hip Resurfacing components

The Articular Surface Replacement (ASR) hip resurfacing arthroplasty has a failure rate of 12.0% at five years, compared with 4.3% for the Birmingham Hip Resurfacing (BHR). We analysed 66 ASR and 64 BHR explanted metal-on-metal hip replacements with the aim of understanding their mechanisms of failure. We measured the linear wear rates of the acetabular and femoral components and analysed the clinical cause of failure, pre-revision blood metal ion levels and orientation of the acetabular component.

There was no significant difference in metal ion levels (chromium, p = 0.82; cobalt, p = 0.40) or head wear rate (p = 0.14) between the two groups. The ASR had a significantly increased rate of wear of the acetabular component (p = 0.03) and a significantly increased occurrence of edge loading (p < 0.005), which can be attributed to differences in design between the ASR and BHR. The effects of differences in design on the in vivo wear rates are discussed: these may provide an explanation as to why the ASR is more sensitive to suboptimal positioning than the BHR.

Insufficient acetabular version increases blood metal ion levels after metal-on-metal hip resurfacing

BACKGROUND

Many factors affect the blood metal ion levels after metal-on-metal (MOM) hip arthroplasty. The main surgically adjustable variable is the amount of coverage of the head provided by the cup which is a function of the inclination and version angles. However, most studies have used plain radiographs which have questionable precision and accuracy, particularly for version and large diameter metal heads; further, these studies do not simultaneously assess version and inclination. Thus the relationship between version and blood metal ions levels has not been resolved.

QUESTIONS/PURPOSES

We determined whether cup inclination and version influence blood metal ion levels while adjusting for age at assessment, gender, body mass index, horizontal femoral offset, head size, manufacturer hip type, and Oxford hip score.

PATIENTS AND METHODS

We prospectively followed 100 individuals (51 females, 49 males) with unilateral MOM hip resurfacing who underwent clinical assessment, CT scanning, and blood metal ion measurement. Multiple regression analysis was used to determine which variables were predictors of blood metal ion levels and to model the effect of these variables.

RESULTS

Only cup inclination, version angles, and gender influenced blood cobalt or chromium levels. Cobalt and chromium levels positively correlated with inclination angle and negatively correlated with version angle. The effect of changes in version angle was less than for inclination angle. Based on our observations, we developed a formula to predict the effect of these parameters on metal ion levels.

CONCLUSIONS

Our data suggest insufficient cup version can cause high blood metal ions after MOM hip arthroplasty. We were unable to show that excessive version caused high levels.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

High revision rate at 5 years after hip resurfacing with the Durom implant

BACKGROUND/RATIONALE

There is growing evidence that different resurfacing implants are associated with variable survival and revision rates. A registry analysis indicated the Durom resurfacing implant had high revision rates at 5 years, whereas three original studies reported low revision rates at short-term followups. Thus, the revision rates appear controversial.

QUESTIONS/PURPOSES

We therefore assessed (1) the survivorship including differences between women and men at a mean of 5 years after resurfacing with the Durom implant, and (2) clinical scores and radiographic parameters.

PATIENTS AND METHODS

We prospectively followed all 100 Durom hip resurfacings implanted in 91 patients (25 women and 66 men; mean age, 52 years) between 2003 and 2004. Survivorship analysis was performed with pending revision or revision for any reason as the endpoint. The minimum followup was 47 months (mean, 60 months; range, 47-72 months).

RESULTS

At a mean of 5 years, 11 hips were revised for various reasons. Cumulative survival was 88.2% for all patients and 81.5% for women. The mean Oxford (OHS) and Harris hip (HHS) scores were 14.6 and 94.7, respectively. The mean UCLA activity level was 7.9. Sclerotic changes around the short femoral stem (pedestal sign) were detected in 40% of the hips. We observed considerable femoral neck thinning with component-to-neck ratios of 0.85 preoperatively and 0.82 at 5 years.

CONCLUSIONS

Our study highlights a high revision rate 5 years after hip resurfacing with the Durom implant. This observation underlines previous findings from registry data and suggests that revision rates increase with time.

LEVEL OF EVIDENCE

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

Assessment of inter- and intra-observer reliability in the determination of radiographic version and inclination of the cup in metal-on-metal hip resurfacing

PURPOSE

Determination of the cup orientation after metal-on-metal hip resurfacing may provide important information in the postoperative follow-up. We present a mathematical method based on a previously described approach to assess the version and inclination of the cup in the metal-on-metal bearing without a separate software computation from plain radiographs. The aim of the study was to assess the intra- and inter-observer reliability of this method.

METHODS

Calculation of version and inclination were done twice for 20 hip resurfacings by four observers. Intra-observer reliability was estimated by mean error and correlation of the two sets of measurement for version and inclination. Bland-Altman plots, intra-class coefficient and mean error were used to assess the inter-observer reliability of the measurements.

RESULTS

Intra-observer correlation for version measurement ranged from 0.74 to 0.94. Correlation for inclination varied between 0.94 and 0.97. Upper and lower limits of agreement in Bland-Altman plots for version measurements between observers ranged from 4.1 to 7.2 degrees and from -3.2 to -8.3 degrees, respectively. For inclination measurements the upper and lower limits ranged from 3.1 to 5.3 degrees and from -2.7 to -6.0 degrees.

CONCLUSIONS

Mean errors, correlation coefficients and 95% limits of agreement were on an acceptable level. We believe that this method is applicable for clinical use.

Metal-on-metal bearings: the evidence so far

Lately, concerns have arisen following the use of large metal-on-metal bearings in hip replacements owing to reports of catastrophic soft-tissue reactions resulting in implant failure and associated complications. This review examines the literature and contemporary presentations on current clinical dilemmas in metal-on-metal hip replacement.

[Approach to painful hip resurfacing]

Hip resurfacing in young patients has been increasingly performed within the last decade. In comparison to standard total hip arthroplasty the failure rate remains high. Age and implant size have a significant effect on the risk of revision for primary total resurfacing and the risk of revision increases with increasing age. At 7 years the cumulative revision rate for patients is 5% and females have more than twice the cumulative revision rate as males. Even in hip resurfacing arthroplasty which has been performed in a perfect manner, a certain percentage of patients suffer from persistent pain for various reasons, such as neck fracture, iliopsoas tendinopathy, metal hypersensitivity, such as aseptic lymphocytic vasculitis associated lesions (ALVAL) and aseptic loosening. Diagnostic work-up of the painful hip resurfacing is challenging even for experienced surgeons. Recommendations for the diagnostic procedure are described.

Survival of metal-on-metal hip resurfacing arthroplasty: a systematic review of the literature

We systematically reviewed the peer-reviewed literature to relate the survival of hybrid metal-on-metal hip resurfacing arthroplasty devices to a National Institute of Clinical Excellence (NICE) benchmark for choosing a primary total hip replacement, which is a survival rate of 90% at a follow-up of ten years. A total of 29 articles (10 621 resurfaced hips) met the inclusion criteria. The mean follow-up ranged from 0.6 to 10.5 years and the survival of the implant ranged from 84% to 100%. Of the 10 621 hips, 370 were revised (3.5%), with aseptic loosening as the most frequent mode of failure. None of the hip resurfacing arthroplasty implants used to date met the full ten-year NICE benchmark of survival. A total of 13 studies showed satisfactory survival compared with the three-year NICE benchmark.

The relationship between the angle of version and rate of wear of retrieved metal-on-metal resurfacings: a prospective, CT-based study

We measured the orientation of the acetabular and femoral components in 45 patients (33 men, 12 women) with a mean age of 53.4 years (30 to 74) who had undergone revision of metal-on-metal hip resurfacings. Three-dimensional CT was used to measure the inclination and version of the acetabular component, femoral version and the horizontal femoral offset, and the linear wear of the removed acetabular components was measured using a roundness machine. We found that acetabular version and combined version of the acetabular and femoral components were weakly positively correlated with the rate of wear. The acetabular inclination angle was strongly positively correlated with the rate of wear. Femoral version was weakly negatively correlated with the rate of wear. Application of a threshold of > 5 μm/year for the rate of wear in order to separate the revisions into low or high wearing groups showed that more high wearing components were implanted outside Lewinnek's safe zone, but that this was mainly due to the inclination of the acetabular component, which was the only parameter that significantly differed between the groups. We were unable to show that excess version of the acetabular component alone or combined with femoral version was associated with an increase in the rate of wear based on our assessment of version using CT.

Failure modes of 433 metal-on-metal hip implants: how, why, and wear

Metal-on-metal total hip replacements (THRs) and hip resurfacings are coming under increasing scrutiny in light of concerns that they fail because of high wear and elevated metal ions. The aim of this study was to investigate the modes of failure in a collection of 433 metal-on-metal THRs and hip resurfacings and to examine the correlations between the reasons for revision and a range of patient and implant variables considered relevant to implant wear.

Retrieval analysis of 240 metal-on-metal hip components, comparing modular total hip replacement with hip resurfacing

This study compared component wear rates and pre-revision blood metal ions levels in two groups of failed metal-on-metal hip arthroplasties: hip resurfacing and modular total hip replacement (THR).

There was no significant difference in the median rate of linear wear between the groups for both acetabular (p = 0.4633) and femoral (p = 0.0872) components. There was also no significant difference in the median linear wear rates when failed hip resurfacing and modular THR hips of the same type (ASR and Birmingham hip resurfacing (BHR)) were compared.

Unlike other studies of well-functioning hips, there was no significant difference in pre-revision blood metal ion levels between hip resurfacing and modular THR.

Edge loading was common in both groups, but more common in the resurfacing group (67%) than in the modular group (57%). However, this was not significant (p = 0.3479). We attribute this difference to retention of the neck in resurfacing of the hip, leading to impingement-type edge loading. This was supported by visual evidence of impingement on the femur.

These findings show that failed metal-on-metal hip resurfacing and modular THRs have similar component wear rates and are both associated with raised pre-revision blood levels of metal ions.

Metal-on-metal hip resurfacing: a critical review

In this article, a concise review of the current literature on metal-on-metal hip resurfacing (MoMHR) is given. In contrast to conventional total hip arthroplasty, older age, female sex and small femoral head sizes predispose to failure. Neck fracture and metal wear-related complications account for the most frequent reasons for re-operations. Although the long-term consequences of metal ion release remain unknown, the increasing prevalence of soft tissue related problems with potentially devastating functional consequences in this younger patient group are of concern. Outcome after revision for metal wear related failure of MoMHR is poor. In our opinion, patients with this device should be managed in dedicated centers with facilities for data collection and monitoring. The majority of proposed advantages of MoMHR cannot be supported by the published evidence.

Birmingham hip resurfacing: the prevalence of failure

Despite the increasing interest and subsequent published literature on hip resurfacing arthroplasty, little is known about the prevalence of its complications and in particular the less common modes of failure. The aim of this study was to identify the prevalence of failure of hip resurfacing arthroplasty and to analyse the reasons for it. From a multi-surgeon series (141 surgeons) of 5000 Birmingham hip resurfacings we have analysed the modes, prevalence, gender differences and times to failure of any hip requiring revision. To date 182 hips have been revised (3.6%). The most common cause for revision was a fracture of the neck of the femur (54 hips, prevalence 1.1%), followed by loosening of the acetabular component (32 hips, 0.6%), collapse of the femoral head/avascular necrosis (30 hips, 0.6%), loosening of the femoral component (19 hips, 0.4%), infection (17 hips, 0.3%), pain with aseptic lymphocytic vascular and associated lesions (ALVAL)/metallosis (15 hips, 0.3%), loosening of both components (five hips, 0.1%), dislocation (five hips, 0.1%) and malposition of the acetabular component (three hips, 0.1%). In two cases the cause of failure was unknown. Comparing men with women, we found the prevalence of revision to be significantly higher in women (women = 5.7%; men = 2.6%, p < 0.001). When analysing the individual modes of failure women had significantly more revisions for loosening of the acetabular component, dislocation, infection and pain/ALVAL/metallosis (p < 0.001, p = 0.004, p = 0.008, p = 0.01 respectively). The mean time to failure was 2.9 years (0.003 to 11.0) for all causes, with revision for fracture of the neck of the femur occurring earlier than other causes (mean 1.5 years, 0.02 to 11.0). There was a significantly shorter time to failure in men (mean 2.1 years, 0.4 to 8.7) compared with women (mean 3.6 years, 0.003 to 11.0) (p < 0.001).