Aims. Head-taper corrosion is a cause of failure in total hip arthroplasty (THA). Recent reports have described an increasing number of V40 taper failures with adverse local tissue reaction (ALTR). However, the real incidence of V40 taper damage and its cause remain unknown. The aim of this study was to evaluate the long-term incidence of ALTR in a consecutive series of THAs using a V40 taper and identify potentially related factors. Methods. Between January 2006 and June 2007, a total of 121 patients underwent THA using either an uncemented (Accolade I, made of Ti. 12. Mo. 6. Zr. 2. Fe; Stryker, USA) or a cemented (ABG II, made of cobalt-chrome-molybdenum (CoCrMo); Stryker) femoral component, both with a V40 taper (Stryker). Uncemented acetabular components (Trident; Stryker) with crosslinked polyethylene liners and CoCr femoral heads of 36 mm diameter were used in all patients. At a mean folllow-up of 10.8 years (SD 1.1), 94 patients (79%) were eligible for follow-up (six patients had already undergone a revision, 15 had died, and six were lost to follow-up). A total of 85 THAs in 80 patients (mean age 61 years (24 to 75); 47 (56%) were female) underwent clinical and radiological evaluation, including the measurement of whole blood levels of cobalt and chrome. Metal artifact reduction sequence MRI scans of the hip were performed in 71 patients. Results. A total of 20 ALTRs were identified on MRI, with an incidence of 26%. Patients with ALTR had significantly higher median Co levels compared with those without ALTR (2.96 μg/l (interquartile range (IQR) 1.35 to 4.98) vs 1.44 μg/l (IQR 0.79 to 2.5); p = 0.019). Radiological evidence of osteolysis was also significantly associated with ALTR (p = 0.014). Median Cr levels were not significantly higher in those with ALTR compared with those without one (0.97 μg/l (IQR 0.72 to 1.9) v 0.67 μg/l (IQR 0.5 to 1.19; p = 0.080). BMI, sex, age, type of femoral component, head length, the inclination of the acetabular component, and heterotopic ossification formation showed no significant relationship with ALTR. Conclusion. Due to the high incidence of local ALTR in our cohort after more than ten years postoperatively, we recommend regular follow-up investigation even in asymptomatic patients with V40 taper and metal heads. As cobalt levels correlate with ALTR occurrence, routine metal ion screening and consecutive MRI investigation upon elevation could be discussed. Cite this article: Bone Joint J 2022;104-B(7):852–858

Aims. Modular dual-mobility constructs reduce the risk of dislocation after revision total hip arthroplasty (THA). However, questions about metal ions from the cobalt-chromium (CoCr) liner persist, and are particularly germane to patients being revised for adverse local tissue reactions (ALTR) to metal. We determined the early- to mid-term serum Co and Cr levels after modular dual-mobility components were used in revision and complex primary THAs, and specifically included patients revised for ALTR. Patients and Methods. Serum Co and Cr levels were measured prospectively in 24 patients with a modular dual-mobility construct and a ceramic femoral head. Patients with CoCr heads or contralateral THAs with CoCr heads were excluded. The mean age was 63 years (35 to 83), with 13 patients (54%) being female. The mean follow-up was four years (2 to 7). Indications for modular dual-mobility were prosthetic joint infection treated with two-stage exchange and subsequent reimplantation (n = 8), ALTR revision (n = 7), complex primary THA (n = 7), recurrent instability (n = 1), and periprosthetic femoral fracture (n = 1). The mean preoperative Co and Cr in patients revised for an ALTR were 29.7 μg/l (2 to 146) and 21.5 μg/l (1 to 113), respectively. Results. Mean Co and Cr levels were 0.30 μg/l and 0.76 μg/l, respectively, at the most recent follow-up. No patient had a Co level ≥ 1 μg/l. Only one patient had a Cr level ≥ 1 μg/l. That patient’s Cr level was 12 μg/l at 57 months after revision THA for ALTR (and decreased ten-fold from a preoperative Cr of 113 μg/l). Conclusion. At a mean of four years, no patient with a modular dual-mobility construct and ceramic femoral head had elevated Co levels, including seven patients revised specifically for ALTR. While further studies are required, we support the selective use of a modular dual-mobility construct in revision and complex primary THAs for patients at high risk for instability. Cite this article: Bone Joint J 2019;101-B(6 Supple B):57–61

Background. Adverse local tissue reactions (ALTR) in metal-on-polyethylene (MoP) total hip arthroplasty (THA) with head-neck taper corrosion is likely to be multifactorial involving implant and patient factors. However, there is a paucity of clinical data on implant parameters as predisposing factors in MoP head-neck taper corrosion. The aim of this study was to identify any potential implant factors associated with failed MoP THA due to head-neck taper corrosion. Methods. A total of 67 MoP THA patients in two groups was investigated: 1) ALTR (n=38) on MARS MRI and 2) non-ALTR (n=29) on MARS MRI. All patients had highly cross-linked polyethylene liners with cobalt-chromium femoral heads with a single head-neck modularity. Parameters compared between groups included: acetabular component orientation, femoral neck shaft angle, radiographic measurement of medial and vertical femoral offsets, limb length discrepancy, component size, femoral head offset, implant type, femoral stem alloy and taper design. Results. The occurrence of ALTR was associated with increased femoral head offset (non-ALTR vs. ALTR, 0.5 ± 3.7 vs. 4.1 ± 3.6, p = 0.008), increased radiographic femoral stem offset (35.9 ± 7.4 mm vs 40.7 ± 7.1mm, p = 0.018), and the use of TMZF alloy stems (p = 0.051). The presence of ALTR was significantly associated with higher cobalt (9.1 µg/L vs. 0.4µg/L, p=0.001) and chromium (2.6µg/L vs. 0.4µg/L). A significant correlation was identified between the serum cobalt level and the femoral stem offset (R=0.375, p=0.009). Conclusions. Although the occurrence of head-neck taper corrosion in MoP THA is likely to be an interplay between implant and patient factors, the results of this study identified increased femoral head and stem offset and the use of TMZF alloy stems as risk factors associated with clinically relevant ALTR due to head-neck taper corrosion in MoP THA patients. The study provides evidenced-based information in risk stratification of symptomatic MoP THA patients for head-neck taper corrosion. For any tables or figures, please contact the authors directly

Introduction. Modular dual-mobility constructs reduce the risk of dislocation after total hip arthroplasty (THA). However, questions about metal ions from the cobalt-chrome (CoCr) liner persist, and are particularly germane to patients being revised for adverse local tissue reactions (ALTR) to metal. We determined the mid-term serum Co and Cr levels after modular dual-mobilities used in revision and complex primary THAs, and specifically included patients revised for ALTR. Methods. Serum Co and Cr levels were measured prospectively in 22 patients with a modular dual-mobility construct and a ceramic femoral head. Patients with CoCr heads or contralateral THAs with CoCr heads were excluded. Mean age 64 years with 50% female. The mean follow-up was 4 years. Indications for modular dual-mobility were: periprosthetic joint infection treated with 2-stage exchange and subsequent reimplantation (n=8), ALTR revision (n=7), complex primary THA (n=6), and periprosthetic femoral fracture (n=1). Mean preoperative Co and Cr in patients revised for an ALTR were 29.7 µg/L and 21.5 µg/L, respectively. Results. Mean Co and Cr levels were 0.26 µg/L and 0.82 µg/L, respectively, at most recent follow-up. No patients had a cobalt level ≥1 µg/L. Only one patient had a chromium level ≥1 µg/L. That patient's chromium level was 12 µg/L at 57 months after revision THA for ALTR (and decreased 10-fold from a preoperative Cr of 113 µg/L). Conclusion. At a mean of 4 years, no patient with a modular dual-mobility construct and ceramic femoral head had elevated cobalt levels, including seven patients revised specifically for ALTR. While further studies are required, we support selective use of a modular dual-mobility construct in revision and complex primary THAs for patients at high risk for instability. Summary. At a mean of 4 years after revision or complex primary THAs with a modular dual-mobility construct and a ceramic head, none of 22 patients had serum cobalt levels that measured ≥1 µg/L

Introduction. Failure of metal on metal (MOM) total hip arthroplasty (THA) and resurfacing arthroplasty (HRA) due to development of adverse local tissue reaction (ALTRs) is a significant problem. The prevalence of ALTRs in asymptomatic MOM arthroplasty patients is highly variable. The purpose of this prospective, longitudinal study was to: 1) determine MRI ALTR prevalence in patients with HRA; 2) determine if patients with HRA have a greater rate of MRI ALTRs compared to control patients with ceramic on poly (COP) THA; and 3) evaluate changes in patient reported outcomes between these implant designs. Methods. Following IRB approval with informed consent, self-reported asymptomatic primary COP and HRA patients greater than one year post arthroplasty were evaluated with 4 annual (TP1–4) MRIs using a standardized protocol and serum ion level testing. Morphologic and susceptibility reduced images were acquired for each hip and evaluated for synovial thickness, volume, capsule dehiscence and the presence of ALTR. Patient reported outcomes were evaluated by Hip Disability and Osteoarthritis Outcome Scores (HOOS). Analyses were performed to detect differences of synovial thickness and volume, and HOOS subgroups between and within bearing surfaces at each time point and over time, and to compare the time to and the risk of developing MRI ALTR. Analyses were adjusted for age, gender, and length of implantation. Results. 86 hips were evaluated at the initial time point (TP1): HRA, n=41, age=58±8 y.o., 34/7 (M/F); COP, n=45, age=65±9 y.o., 22/23 (M/F). The mean synovial volume of the subjects was similar at TP1, and the synovial volume in HRA subjects increased significantly from TP1 to TP4 (mean volume difference=9 cm3, p=0.031) while COP subjects displayed a minimal increase from TP1 to TP4 (mean volume difference =0.3 cm3, p=0.9). The synovial volume in HRA subjects tended to be larger and with greater variability than COP subjects at TP4 (HRA=15±58 cm3; COP=6 ±10 cm3, p=0.3). By TP4, MRI ALTRs developed in 13/41 HRA subjects (mean time to ALTR=1.5 yr) compared to 2/25 COP subjects (mean time to ALTR=2.0 yr), p=0.001. While risk of MRI ALTRs in HRA subjects was 9.9 times the risk in COP subjects (p=0.07), 68% of HRA subjects did not have an MRI ALTR present. Significant differences of [Co] and [Cr] in HRA subjects with MRI ALTR present were not detected at 2/4 time points and 1/4 time points, respectively, and there were no significant differences in ion levels in the COP group. The HOOS sub-scores of Pain and Activity of Daily Living scores of HRA subjects were similar to COP subjects, and HRA subjects had better Sporting Ability than COP subjects at all time points. HRA subjects had higher Symptoms at TP1 (p=0.016) but both cohorts had high scores (HRA=92.3/100; COP=87.7/100). Initially dehiscent posterior capsules of HRA subjects (9%) tended not to resolve (10/11, 91%), while dehiscent COP subjects (15%) had greater resolution (6/22, 27%). The presence of osteolysis was limited (HRA: 6/41; COP: 3/45; p=0.101). Conclusion. A greater synovial volume and higher rate of MRI ALTRs was found in HRA subjects, while the patient symptomatology via HOOS remained slightly better in HRA subjects than COP subjects, suggesting a poor association between MRI ALTRs and symptoms. The presence of posterior decompression of the posterior capsule into the bursa alone was not necessarily indicative of an ALTR, and is likely a normal postoperative finding. The inconsistent findings of the serum ion level testing further supports MRI as a non-invasive imaging modality capable of assessing peri-prosthetic soft tissue complications, and should be considered as part of the routine patient follow up to allow early detection and monitoring of ALTRs

The differential diagnosis of the painful total hip arthroplasty (resurfacing or total hip) includes infection, failure of fixation (loosening), tendinitis, bursitis, synovitis, adverse local tissue reaction (ALTR) to cobalt-chromium alloys, and non-hip issues, such as spinal disorders, hernia, gynecologic, and other pelvic pain. Assuming that the hip is the source of pain, the first level question is prosthetic or non-prosthetic pain generator? The second level prosthetic question is septic or aseptic? The third level question (aseptic hips) is well-fixed or loose? ALTR is best diagnosed by cross-sectional imaging. Successful treatment is dependent on correct identification and elimination of the pain generator. Treatment recommendations for ALTR and taper corrosion are evolving

Recently, corrosion at the head-neck junction in metal-on-polyethylene bearing total hip arthroplasty (THA) has been recognized as a cause of adverse local tissue reactions (ALTR). Serum metal levels have been advocated as a tool for the diagnosis of ALTR, however no prior studies have specifically examined their utility. The purpose of this study was to determine the optimal cut-off values for serum cobalt and chromium in diagnosing ALTR after metal-on-polyethylene bearing THA. We reviewed 447 consecutive patients with serum metal levels tested at our institution and identified 62 with a metal-on-polyethylene bearing who had axial imaging or underwent reoperation to confirm the presence or absence of ALTR. Receiver operating characteristic curves were produced to identify cut-off thresholds to optimize sensitivity and diagnostic test performance was characterized. 42 Of the 62 patients (66%) were positive for an ALTR. The best test for the diagnosis of ALTR was the serum cobalt level (area under the curve [AUC]=99%). A threshold cut-off of ≥ 1.0 ng/ml had a sensitivity of 100%, specificity of 90%, positive predictive value (PPV) of 96%, and negative predictive value (NPV) of 100%. Serum chromium levels were also diagnostic (AUC=87%). A threshold cut-off of ≥ 0.15 ng/ml had a sensitivity of 100%, specificity of 50%, PPV of 81%, and NPV of 100%. Finally, serum cobalt to chromium ratio was also helpful for diagnosis (AUC=90%). A threshold cut-off of 1.4 for the cobalt to chromium ratio offered a sensitivity of 93%, specificity of 70%, PPV of 87%, and NPV of 82%. Measurement of serum cobalt with a threshold value of 1.0 ng/ml in our experience is the best test for identifying the presence of ALTR in patients with a metal-on-polyethylene THA. Measurement of chromium and the ratio of cobalt to chromium are also of value

Aims. Advances in surgical technique and implant design may influence the incidence and mechanism of failure resulting in revision total hip arthroplasty (rTHA). The purpose of the current study was to characterize aetiologies requiring rTHA, and to determine whether temporal changes existed in these aetiologies over a ten-year period. Methods. All rTHAs performed at a single institution from 2009 to 2019 were identified. Demographic information and mode of implant failure was obtained for all patients. Data for rTHA were stratified into two time periods to assess for temporal changes: 2009 to 2013, and 2014 to 2019. Operative reports, radiological imaging, and current procedural terminology (CPT) codes were cross-checked to ensure the accurate classification of revision aetiology for each patient. Results. In all, 2,924 patients with a mean age of 64.6 years (17 to 96) were identified. There were 1,563 (53.5%) female patients, and the majority of patients were Caucasian (n = 2,362, 80.8%). The three most frequent rTHA aetiologies were infection (27.2%), aseptic loosening (25.2%), and wear (15.2%). The frequency of rTHA for adverse local tissue reaction (ALTR) was significantly greater from 2014 to 2019 (4.7% vs 10.0%; p < 0.001), while the frequency of aseptic loosening was significantly greater from 2009 to 2013 (28.6% vs 21.9%; p < 0.001). Conclusion. Periprosthetic joint infection was the most common cause for rTHA in the current cohort of patients. Complications associated with ALTR necessitating rTHA was more frequent between 2014 to 2019, while aseptic loosening necessitating rTHA was significantly more frequent between 2009 to 2013. Optimizing protocols for prevention and management of infection and ALTR after THA may help to avoid additional financial burden to institutions and healthcare systems. Cite this article: Bone Joint Open 2020;2(1):16–21

Introduction. Modular neck (MN) components in total hip arthroplasty (THA) offer intraoperative flexibility, but adverse local tissue reactions (ALTR) due to tribocorrosion at modular junctions are a potential complication of such designs. Serum ion levels and metal artifact reduction sequence (MARS) MRI are used to assess ALTR following modular THA. This study investigates serum ion levels and MARS MRI findings in a series of hips with MN components and differing articulating surfaces. Methods. We retrospectively evaluated a cohort of 184 primary THAs in 159 patients implanted with a dual modular femoral stem by one surgeon from 2005–2013. 121 THAs had a cobalt-chromium neck component and non-metal-on-metal articulation, while 63 THAs had a titanium neck component and metal-on-metal (MoM) articulation. Serum ion levels were recorded for all patients. MARS MRI scans were read by musculoskeletal-trained radiologists. Pseudotumor grade and location were measured. Results. Serum cobalt levels as a function of time post-operatively demonstrated no correlation. In THAs with non-MoM articulation, pseudotumors were visualized in 13 of 54 (24.1%) initial MARS MRIs performed 1–40 months post-operatively compared to 5 of 67 (7.5%) performed 41–120 months post-operatively (p=0.02), and findings typically remained consistent across multiple MARS MRI scans. Pseudotumors were generally located lateral to the hip joint in hips with non-MoM articulation compared to anteromedial following MoM arthroplasty. In the cobalt-chrome MN group, cobalt levels were elevated in 11 of 20 (55%) of patients with pseudotumor compared to 15 of 19 (79%) in the MoM group. Conclusion. Generation of ALTR leading to pseudotumor formation is a concern with cobalt-chrome MN designs. Psuedotumor characteristics differ between patients with cobalt-chrome designs versus MoM articulation. Normal serum ion levels did not exclude the presence of a pseudotumor and routine MARS MRI should be included in follow-up of patients with cobalt-chromium MN prostheses

Introduction. Adverse local tissue reactions (ALTR) can result in devastating soft tissue and osseous destruction, while potentially increasing the risk of concomitant periprosthetic joint infection (PJI). The aims of this study were to evaluate cobalt (Co) and chromium (Cr) levels generated in simulators from metal-on-polyethylene (MoP) and ceramic-on-polyethylene (CoP) constructs, and determine their impact on native tissues and PJI risk through evaluation of human adipose-derived mesenchymal stem cells (AMSCs) and Staphylococcus epidermidis isolates. Methods. Ten hip simulator constructs were assembled with 36-mm high-offset femoral heads, highly cross-linked polyethylene liners, and titanium stems. Five constructs used CoCr femoral heads and five used ceramic. Constructs were submerged in bovine serum (BS) and run for 1,000,000 cycles. Samples of BS were collected and evaluated for CoCr concentration. Various concentrations of CoCr were chosen for further assessment of cytotoxicity and growth impact on AMSCs and S. epidermidis and compared to inert SiO2. Results. After 1,000,000 cycles, mean MoP and CoP Co concentration was 2264 ng/mL and 0.6 ng/mL, respectively (p<0.001). Mean MoP and CoP Cr concentration was 217 ng/mL and 4.3 ng/mL, respectively (p<0.001). Mean MoP Co:Cr ratio was 10. Co nanoparticles were significantly more toxic to human AMSCs than control SiO2 in a dose-response manner (p<0.001). S. epidermidis growth was not significantly impacted by Co concentrations derived from the simulators. Conclusions. MoP constructs built in ideal conditions generated substantial CoCr debris, highlighting a baseline risk with these implants that may be exacerbated by host factors or imperfect surgical technique. Evaluation of impact on AMSCs suggests that debris levels produced under ideal conditions can be cytotoxic. Additionally, these concentrations did not potentiate or inhibit S. epidermidis growth, suggesting elevated PJI rates with ALTR may be related to other factors potentially associated with tissue necrosis. For any tables or figures, please contact the authors directly

Aims

The aims of this study were to determine if an increasing serum cobalt (Co) and/or chromium (Cr) concentration is correlated with a decreasing Harris Hip Score (HHS) and Hip disability and Osteoarthritis Outcome Score (HOOS) in patients who received the Articular Surface Replacement (ASR) hip resurfacing arthroplasty (HRA), and to evaluate the ten-year revision rate and show if sex, inclination angle, and Co level influenced the revision rate.

Aims

Modular dual mobility (MDM) acetabular components are often used with the aim of reducing the risk of dislocation in revision total hip arthroplasty (THA). There is, however, little information in the literature about its use in this context. The aim of this study, therefore, was to evaluate the outcomes in a cohort of patients in whom MDM components were used at revision THA, with a mean follow-up of more than five years.

Serum and blood cobalt (Co) and chromium (Cr) ion levels are used to monitor patients at risk for adverse reaction to metal debris (ARMD) following metal-on-metal (MoM) total hip arthroplasty (THA). However, these levels often do not correlate with the degree of local soft-tissue reaction and damage observed at the time of revision. The purpose of this study was to analyze synovial fluid metal ion concentrations in patients with a failed THA in the setting of an ARMD and determine if these levels can be more predictive of soft-tissue destruction than serum or whole blood levels. Synovial, blood and serum samples were prospectively collected from patients undergoing revision THA with ARMD (n=29) and those undergoing aseptic revision without ARMD (n=29). There was no difference in mean age (P=0.50), BMI (P=0.18), sex distribution (P=0.18), serum creatinine (P=0.74), or time to revision THA (P=0.13) between the cohorts. In the AMRD cohort, the components included MoM THA (n=18), hip resurfacing (n=5), dual-modular taper THA (n=4) and MoM and dual-modular taper THA (n=2). At the time of revision THA, 26 (90%) patients in the metal reaction cohort had gross evidence of metallosis in the soft-tissues, the remaining 3 (10%) had evidence of corrosion of the dual taper neck or MoM bearing. In the non ARMD cohort the bearing surfaces included metal-on-polyethylene (n=19) and ceramic-on-polyethylene (n=10). The indications for revision included isolated acetabular loosening (n=11), isolated femoral component loosening (n=11), polyethylene wear (n=5), recurrent dislocation (n=1) and combined femoral and acetabular component loosening (n=1). None had a clinical diagnosis or gross evidence of taper corrosion. Pre-revision, 21 (72%) patients in the metal reaction group had periarticular fluid collections or a mass on MRI. Mean cyst size was 202.9±71.6 cm3 and masses were grouped into Type I (cyst wall <3 mm, n=10), Type II (cyst wall ≥3 mm, n=8) and Type III (mainly solid, n=3). At the time of revision THA, the mean Co levels were elevated in patients with ARMD compared to those without in synovial fluid (1,833 ppb vs. 12.3 ppb, P=0.008), whole blood (22.6 ppb vs 0.5 ppb, P=0.005)) and serum (19.6 vs. 0.6, P=0.001). Likewise, mean Cr levels were significantly elevated in patients with an ARMD compared to those undergoing revision without in synovial fluid (3,128 ppb vs. 10.3 ppb, P=0.01), whole blood (8.9 ppb vs. 0.5 ppb, P=0.009) and serum (14.1 ppb vs. 0.5 ppb, P=0.005). The synovial fluid Co levels were the most accurate test for detecting pseudotumor (AUC 0.951) and adverse local tissue reaction (AUC 0.826). At a synovial fluid Cr level of 110 ppb, the synovial fluid metal ion analysis was 94% sensitive and 86% specific for pseudotumor formation. In this prospective study, synovial fluid analysis of metal ion levels was more accurate in predicting the presence and extent of pseudo-tumor or ALTR compared to blood or serum analysis. The addition of synovial aspiration with metal ion analysis may provide another helpful data point when risk stratifying these patients for need for revision THA

Aims

This study aims to assess the relationship between history of pseudotumour formation secondary to metal-on-metal (MoM) implants and periprosthetic joint infection (PJI) rate, as well as establish ESR and CRP thresholds that are suggestive of infection in these patients. We hypothesized that patients with a pseudotumour were at increased risk of infection.

Aims

Dual mobility (DM) implants have been shown to reduce the dislocation rate after total hip arthroplasty (THA), but there remain concerns about the use of cobalt chrome liners inserted into titanium shells. The aim of this study was to assess the clinical outcomes, metal ion levels, and periprosthetic femoral bone mineral density (BMD) at mid-term follow-up in young, active patients receiving a modular DM THA.

Aims

The purpose of this study is to examine six types of bearing surfaces implanted at a single institution over three decades to determine whether the reasons for revision vary among the groups and how long it takes to identify differences in survival.

Aims

This study aimed to determine if macrophages can attach and directly affect the oxide layers of 316L stainless steel, titanium alloy (Ti6Al4V), and cobalt-chromium-molybdenum alloy (CoCrMo) by releasing components of these alloys.

Aims

Leucocyte esterase (LE) has been shown to be an accurate marker of prosthetic joint infection (PJI), and has been proposed as an alternative to frozen section (FS) histology for intraoperative diagnosis. In this study, the intraoperative assessment of LE was compared with FS histology for the diagnosis of prosthetic hip infection.

Aims

Dual mobility (DM) bearings are an attractive treatment option to obtain hip stability during challenging primary and revision total hip arthroplasty (THA) cases. The purpose of this study was to analyze data submitted to the American Joint Replacement Registry (AJRR) to characterize utilization trends of DM bearings in the USA.

Aims

This study presents the long-term survivorship, risk factors for prosthesis survival, and an assessment of the long-term effects of changes in surgical technique in a large series of patients treated by metal-on-metal (MoM) hip resurfacing arthroplasty (HRA).