Background. Second-generation high-carbon CoCrMo-alloy metal-on-metal total hip arthroplasty (THA) was introduced in the late 1980s following reports of early loosening, impingement, pronounced wear, and hypersensitivity in the first-generation metal-on-metal articulations. There has been inconsistent data that specifically addresses the clinical performance and longevity of second-generation metal-on-metal THA. The purpose of this study was to evaluate the survival of second-generation metal-on-metal primary THA and to assess the influence of demographic factors on implant survival in a large patient cohort. Methods. One thousand two hundred and seventy second-generation 28 mm metal-on-metal primary THA in 1121 patients were performed at one institution from 1994 to 2004. According to the International Documentation and Evaluation System patients were followed routinely at one year, two years and every five years thereafter. Clinical and radiographic outcome data was prospectively recorded using a hospital joint registry. At a mean follow-up of 6.8 years postoperatively, the probability of survival of THA was estimated using the method of Kaplan and Meier. Relative risk factors for implant failure that included age, gender, BMI, type of implant fixation and size of implant components were calculated using the Cox proportional-hazards model. Results. Sixty three (5%) hips were revised because of aseptic loosening (28 hips), infection (8 hips), periprosthetic fracture (8 hips), recurrent dislocation (8 hips), pain without implant loosening (7 hips) and breakage of the cup (4 hips). The probability of survival at ten years, with revision for any reason as the endpoint, for the THA as a whole was 0.90 (95% confidence interval, 0.87 to 0.94). The probability of survival for the cup was 0.90 (95% confidence interval, 0.86 to 0.93) and for the stem 0.94 (95% confidence interval, 0.91 to 0.97). No demographic factors or covariates were found to significantly affect survivorship. Conclusion. Second-generation metal-on-metal primary THA did not demonstrate a superior probability of survival at ten years compared with previous reports on other weight-bearing surfaces. Based on these findings and with consideration of concerns that relate to putative local and systemic toxicity of metal debris, the use of second-generation metal-on-metal articulations for primary THA remains moot

Introduction. A recent review of the literature on metal-on-metal total hip arthroplasties (THA) revealed the lack of comparative clinical studies with a sufficient sample size and the inclusion of patient-reported outcomes as well as patient activity levels. Methods. We conducted a prospective cohort study including all metal-on-metal and conventional polyethylene (PE)-ceramic THAs with an uncemented cup (Morscher press-fit cup), a 28mm head and operated upon via a lateral approach at our University hospital between 1/1999 and 12/2008. Only THAs for primary osteoarthritis were included. The study population is part of the Geneva Hip Arthroplasty Registry, a prospective cohort followed since 1996. The following outcomes were compared between the two groups (metal-on-metal=group 1 vs. PE-ceramic bearing=group 2): (1) Complication rates with respect to infection, dislocation and revision, (2) Radiographic outcomes (presence of linear or focal femoral osteolysis, loosening), and (3) Clinical outcomes (Harris Hip score increase, SF-12, activity and patient satisfaction evaluation, presence of groin pain). Patients operated between 1/1999 and 12/2004 were evaluated five years postoperatively by an independent assessor. Cox regression analysis was used to compare incidence rates while adjusting for differences in baseline characteristics. Results. 1988 THAs were included, 544 with a metal-on-metal and 1444 with a PE-ceramic bearing. The two groups differed significantly with respect to gender distribution (men 56% vs. 41%), mean age (66 vs. 73 years), co-morbidities and type of stem (uncemented 16% vs. 2%). Crude incidence rates for complications were: 0.16 vs. 0.11 cases/100 person-years for infection; 0.37 vs. 0.35 cases/100 person-years for dislocation; and 0.29 vs. 0.16 cases/100 person-years for all-cause revision (incidence rate ratio 1.8, 95% CI 0.7; 4.6). After adjusting for baseline differences the slightly higher risks for infection and revision in group 1 were attenuated. Osteolytic lesions were found in 3.7% of metal-on-metal vs. 4.7% of PE-ceramic THAs. After adjustment for age, gender and activity the OR was 0.6 (95% CI 0.2;2.1). Five years postoperative, 176 THAs of group 1 and 695 THAs of group 2 were seen at follow-up. Clinical outcomes were similar among the two groups with a mean Harris Hip score increase of 39.2 vs. 40.9 points. SF-12 mental and physical health, patient satisfaction (9.3 vs. 8.9 on visual analogue scale) as well as the incidence of groin pain (1.7% vs. 1.2%) was also similar among the two groups. The activity level was significantly higher in group 1 (6.4 vs. 5.4, p<0.001). Conclusion. Mid-term results with respect to complications, revision rates, presence of osteolysis and clinical outcomes were similar among patients with metal-on-metal and PE-ceramic total hip arthroplasties

Background. Hip resurfacing arthroplasty (HRA) has seen a recent revival with third generation Metal-on-Metal prostheses and is now widely in use. However, safety and effectiveness of hip resurfacing are still questioned. We systematically reviewed peer-reviewed literature on hip resurfacing arthroplasty to address these issues. Objective. To evaluate implant survival and functional outcomes of hybrid Metal-on-Metal hip resurfacing arthroplasty (HRA). Method. Electronic databases and reference lists were searched from 1988 to May 2010. Identified abstracts were checked for inclusion or exclusion by two independent reviewers. Data were extracted and summarized by one reviewer and verified by a second reviewer. Main study endpoint was implant survival, which we compared with the National Institute of Clinical Excellence (NICE) benchmark. We also evaluated radiological and functional outcomes, failure modes and other adverse events. The quality of evidence was judged using the Grading of Recommendations Assessment, Development and Evaluation system (GRADE). Results. We identified 539 articles, of which 29 met the inclusion criteria. The studies included one randomised clinical trial, 27 prospective case series and one retrospective case series. Data were extracted from these 29 articles, totalling 10621 resurfaced hips, providing details on five out of 11 resurfacing devices on the market. Mean follow up ranged from 0.6 to 10.5 years and implant survival ranged from 84% to 100%. Of the 10621 hips, 370 were revised (3.5%), with aseptic loosening as most frequent failure mode. None of the HRA implants used to date met the full 10 year NICE benchmark. Thirteen studies showed satisfactory implant survival percentages compared to the three year NICE entry-benchmark. These 13 studies used the BHR implant (eight studies), the Conserve plus (two studies), the Durom implant (one study), the Cormet 2000 implant (one study) or both the McMinn and the BHR implant (one study)

Introduction. Hip wear simulation is a widely used technique for the pre-clinical evaluation of new bearing designs. However, wear rates seen in vitro can often be significantly different to those seen clinically. This can be attributed to the difference between the optimal conditions in a simulator and wide ranging conditions in real patients. This study aimed to develop more clinically relevant simulator tests, looking specifically at the effects of cup inclination angle (in vivo) and stop-dwell-start (SDS) protocols on a clinically available product. Method. Five tests using a Paul type walking cycle (ISO 14242) were carried out on two ProSim hip simulators: . 28mm MoM, standard walking, cup inclination 45°, (n = 5). 36mm MoM, standard walking, cup 45°, (n = 4). 36mm MOM, SDS: 10 walking cycles and pause of 5s with stance load of 1250N cup 45°, (n = 5). 36mm MOM, SDS: 10 walking cycles and pause of 30s with stance load of 1250N, (n = 5) cup 45°. 36mm MOM, standard walking, cup 55°(n = 5), and 65°(n = 5). All samples had matched clearances, measured using a CMM (Prismo Navigator, Zeiss, Germany). Wear was measured gravimetrically (Sartorius ME235S: 0.01mg). Results and Discussion. Metal-on-metal hip bearings are known to exhibit a bi-phasic wear pattern in-vitro (1), with the majority of wear occurring over the first 1–1.5mc, followed by lower steady state wear as the components conform to each other. Therefore bedding in wear over the first 1 million cycles was compared for each of the sample groups in this study. Bedding in wear for 36mm bearings under standard angle (45 inclination) and walking conditions was 0.16±0.15mm3/mc, while for 28mm bearings, wear was 2.67±2.06mm3/mc. Positioning the acetabular cup at an increased angle led to increased wear. At 55bedding in wear was .25±0.29mm3/mc, while at 65wear was 0.65±0.32mm3/mc. When SDS conditions were applied, no significant increase in wear was observed under either the 5s or 30s pause conditions, with bedding in wear of 0.19±0.31mm3/mc and 0.14±0.13mm3/mc respectively. Conclusion. This study illustrates the robust performance of the 36mm MoM bearing under extreme test conditions when compared with 28mm MoM. No effect was observed with the application of stop-dwell-start conditions, and only a small increase in wear was observed when the cup was inclined to a greater angle. Despite the application of extreme test conditions, the 36mm MoM still demonstrates lower wear than 28mm under all conditions. In all but the 65 inclination conditions, this difference is statistically significant. This study replicates some of the more frequently observed extreme conditions measured in real patients with THRs (2,3). Even under these more aggressive scenarios, wear of the 36mm bearing is still relatively low when compared with a commercially available 28mm THR

Early failure of metal-on-metal (MoM) total hip replacements (THR) is now well established. We review 93 consecutive patients with CPT¯ stems MoM THR. Our series demonstrates a new mechanism of failure, which may be implant combination specific. Between January 2005 and June 2009, 93 consecutive MoM total hip replacements were preformed using CPT stems by 3 surgeons at our unit. 73 CPT¯ stems, Metasul¯ Large Diameter Heads (LDH) with Durom¯ acetabulae and 20 CPT¯ stems, Metasul¯ 28mm diameter heads in Allofit¯ shells (zimmer). Clinical outcomes were collected prospectively before surgery, at 3 months, 1 year, 2 years, 3 years, and at 5 years post surgery. Revision for any cause was taken as the primary endpoint and the roentgenograms and explanted prostheses were analyzed for failure patterns. In the LDH/Durom¯ group a total of 13 (18%) patients required revision (figs. 1) at a median of 35 months (range 6-44). 6 (8%) for periprosthetic fracture. All 6 periprostethic fractures were associated with minimal or no trauma and all had ALVAL identified histologically. To date there have been no failures in the CPT¯/28mm head Allofit¯ group. Several failures demonstrated bone loss in Gruen zones 8 ± 9 ± 10 (fig. 2). We demonstrate an unacceptably high rate of failure in CPT¯ MoM LDH hip replacements, with a high failure secondary to periprosthetic fracture and postulate a mechanism associated with local toxicity to metal ions. We strongly advise against this combination of prosthesis

MHRA guidance for patients with metal on metal hip replacements (MOM) was provided in 2012 and updated in 2017 to assist in the early detection of soft tissue reactions due to metal wear debris. A large number of metal on metal hip replacements were undertaken at our trust. A program of recall for all patients with metal on metal hip replacements was undertaken and MHRA guidelines implemented.

Identification and recall of all patients from 2001 with MOM hip replacements using theatre logs, patient records and consultant log books. Two consultant review of X-rays and patient records. Postal questionnaires and GP requests for cobalt & chromium blood tests. Two consultant led MOM review clinics undertaken with metal artefact reduction scans (MARS) performed following consultation in 2017.

674 patients, 297 available for review. 59 refused follow up. 87 moved out of area, 36 untraceable, 26 not MOM, 147 RIP, 22 already revised. From 297 patients 126 female, 171 male, age range 39 – 95 yrs. 126 resurfacing, 171 MOM THR. 26 patients with elevated metal ions, MARS performed of which 17 positive, 9 negative. Of 17 positive scans 10 patients asymptomatic, 7 waiting revision.

A time consuming effort and additional resource was needed and supported by the trust. From 297 hips 17 positive MARs were identified (5.7%). A new database registry has been developed to track MOM patients, clinics set up for ongoing follow up with radiological protocols for imaging. An arthroplasty advanced nurse practitioner (ANP) is now trained reviewing patients independently.

Introduction

Metal-on-metal hip resurfacing (MOMHR) is a good surgical indication for young active patients. However, it cannot be used in patients with an excessively short femoral head/neck. To address these cases, a new surgical technique has been developed comprising femoral head augmentation using impacted morcellized bone grafts.

INTRODUCTION

Hip wear simulator test results could be affected by many non-bearing related factors such as fixation surface conditions, equipment calibration and component set-up. In an effort to improve the accuracy, reliability and repeatability of hip simulator test, a quality management system has been established at the IDC hip tribology laboratory, which has been accredited by UKAS (United Kingdom Accreditation Service) in accordance with the recognised international standard ISO17025. This study demonstrates that under well-controlled laboratory and testing conditions, satisfactory repeatability can be achieved during hip simulator studies.

Introduction. Alternative bearings – metal-on-metal and ceramic-on-ceramic bearings have been introduced in the last decade with the aim to diminish wear and, subsequently, aseptic loosening and osteolysis. These bearings were aimed for younger, more active patients. Clinical results which would compare the performance of various alternative and traditional bearings are scarce. Methods. Between January 2000 and December 2002, we performed 487 total hip replacements in 474 patients using three types of bearings: metal-on-metal (MOM), metal-on-polyethylene (MOP), and ceramic-on-ceramic (COC). All patients received the same type of acetabular cup (Bicon-Plus, Plus Orthopedics) and same type of femoral component (SL-Plus, Plus Orthopedics). We used the hospital computer database for the evaluation of patient data and data on revision operations. Results. At a mean follow-up of 8.5 years (range, 6.8 to 9.9 years), eighteen hips were revised. Seventeen revisions were aseptic, and one was septic. The percentage of revision in the whole group was 3.7%. The percentage of revisions for individual groups of bearings varied and ranged from 1.5% in the MOP group, 4.1% in the COC group to 8.7% in the MOM group. Reasons for revisions were analyzed in details. We noticed that the percentage of aseptic loosening differed among the groups, with the MOM group having the highest percentage of revisions due to aseptic loosening. Conclusions. The results obtained for this large series of THRs with the same type of acetabular and femoral components, and differing only in the type of bearing, indicate that the combination of material of acetabular cup and femoral head affect the performance of the hip prosthesis

INTRODUCTION. Ceramic-on-metal hip replacements (COM, where the head is a Biolox Delta ceramic and liner is Co Cr alloy), have demonstrated reduced wear under standard conditions in vitro compared to metal-on-metal (MOM) [1]. Early clinical results are also encouraging [2]. Recently concerns have been raised regarding the poor clinical performance of MOM hip resurfacings [3], particularly when cups are steeply inclined. Laboratory hip simulator testing has been used to replicate edge loading, also demonstrating elevated wear [4]. Therefore, a range of conditions to replicate sub-optimal use clinically to better predict in vivo performance should be used. The aim of this study was to compare the wear rates of MOM and COM under adverse edge loading conditions in an in vitro hip simulator test. METHODS. Ceramic-on-metal (n=3) and metal-on-metal (n=3) 36mm hip prostheses (supplied by DePuy International Ltd, UK) were tested in the Leeds Physiological Anatomical Hip Joint Simulator. Liners were mounted to provide a clinical angle of 45o, and stems positioned anatomically. A simplified gait cycle and microseparation was applied as previously described [5] for two million cycles in 25% new born calf serum. Gravimetric analysis was completed every million cycles and wear volumes calculated. RESULTS. The overall mean volumetric wear rate of COM bearings was 0.36 ± 0.55mm3 per million cycles, this was significantly less than the MOM bearing wear (1.32 ± 0.91mm3 per million cycles). For both COM and MOM bearings wear under these edge loading conditions was significantly greater if compared to previously reported wear under standard conditions [1]. DISCUSSION. The reduced wear of COM has been attributed to the differential hardness decreasing adhesive wear and reduced corrosive wear [6]. Wear under the harsh edge-loading conditions in this study is also reported to be significantly less in COM bearings compared to MOM. In MOM bearings in edge contact conditions, the wear zone becomes starved of lubrication, this elevates wear and increases damage at the edge of the cup. In COM bearings the harder head does not become damaged when there is lubricant starvation and hence wear does not accelerate in the same way. In conclusion, COM bearings show reduced wear compared to MOM bearings under standard and adverse conditions and there is some early evidence to support this finding clinically. ACKNOWLEDGEMENTS. Supported by DePuy International Ltd. SW is supported by a Royal Academy of Engineering/EPSRC (UK) fellowship

Introduction. Large diameter metal on metal cups have been used in total hip arthroplasty advocating superior results with respect to dislocation rates, range of motion and long term survival. The Durom cup used as part of the Durom hip resurfacing system has been incriminated with poor short term results sometimes correlated to incorrect positioning of either the femoral or acetabular component. Our objective was to evaluate short term results of the Durom cup used in conjunction with standard stems. Methods. We prospectively followed all patients with a large diameter metal-on-metal articulation (Durom) and a standard stem operated upon between 9/2004 and 9/2008. Patients were seen at follow-up for a clinical (Harris hip score=HHS, UCLA scale and patient satisfaction), radiographic and questionnaire assessment. Results. 89 primary THAs in 80 patients (74% men) with a mean age of 52 (±12) years were included. Main diagnoses were primary osteoarthritis in 47% and aseptic necrosis in 35%. An uncemented stem was used in 79%. Overall, 80 THAs were controlled at a mean follow-up of 39 months (range 16–67 months), 4 patients were lost to follow-up and 5 patients refused or were unable to attend the visit. However, none of the 5 underwent revision. Overall, 8 THAs (8/85, 9.4%) were revised in mean 28 months (range 8–60) after the operation. One additional patient was awaiting revision for aseptic loosening of both cup and stem. The reasons for revision were aseptic loosening in three cases, presence of a granuloma (histological diagnosis of ALVAL) in three, deep infection in one and impingement in one case. Radiographic analysis revealed linear (n=2) and focal (n=3) osteolysis as well as early cup migration (n=2). In 5 revised patients no radiographic changes were found. 56 (70%) of the 80 patients with follow-up had a HHS between 80 and 100. Among those who were not revised, the mean HHS improved from 55.2 to 88.4 (mean increase 33.2, 95% CI 27.7; 38.7). The mean activity level (UCLA scale) at follow-up was 6.4 (±1.8). Overall, mild to severe pain was reported in 14 cases and occasional pain in 22. Groin pain was present in 18 patients (22.5%), 7 of them belonged to the revised group. 61 (76.3%) of the 80 patients with follow-up were satisfied. Mean patient satisfaction on the VAS scale among those who were not revised was 9.0 (±1.3). Conclusion. This study confirms the increased short-term revision rate of the large diameter metal-on-metal couple (Durom) reported by others. In all revision cases the retrieved cups showed no osteo-integration and were removed easily. The operative indication for revision was based upon groin pain and patient dissatisfaction. Radiographic signs of implant loosening were not always present even though in all revised cases except for one the cup was found loose

Background. An increased incidence of periprosthetic osteolysis, resulting in loss of biologic fixation, has been recently reported in contemporary THAs with low-carbide metal-on-metal compared to metal-on-polyethylene couple bearings. A hypersensitivity reaction due to Co and Cr debris is reported as a potential cause for failure of THAs with high-carbide bearings, but there are no evidence-based data for this reaction in low-carbide metal-on-metal bearings. Questions/purposes. We investigated whether there were differences in immunologic hypersensitivity reactions in retrievals from revised THAs with COP versus MOM bearing couples. Patients and Methods. We compared newly formed capsule and periprosthetic interface membranes retrieved from revision surgery due to aseptic failure in 20 patients with low-carbide bearings and 13 patients with ceramic-on-polyethylene bearings. For control tissue we obtained samples from the hip capsule during the primary THA implantation in 13 patients with low-carbide bearings and seven with ceramic-on-polyethylene. We examined the tissues with conventional histologic and immunohistochemical methods. Results. Compared to the controls and the tissue from patients with ceramic-on-polyethylene bearings, the tissues from patients with low-carbide metal-on-metal bearings were associated with (1) extensive necrosis and fibrin exudation in the newly formed hip capsule and (2) diffuse and perivascular lymphocytic infiltration of a higher degree than in the ceramic-on-polyethylene hips in conventional histologic examination and (3) more T than B cells. Conclusions. The conventional histologic and immunohistochemical findings in tissues retrieved from failed THAs with low-carbide metal-on-metal bearings are consistent with a link between hypersensitivity and osteolysis with low-carbide bearing couple THA

Background. Pseudotumours have been associated with metal-on-metal (MoM) hip replacements. We define it as a solid mass which may have cystic components that is neither neoplastic nor infectious in aetiology. The cause of a pseudotumour is not fully understood but could be due to excessive wear, metal hypersensitivity or due to an as-yet unknown cause. Aim. We present the retrieval analysis of early failure MoM hips revised for pain, loosening or a symptomatic mass. Tissues and implants were examined for the possible causes of failure and pseudotumour formation. Corrosion as a potential new cause for pseudotumour formation will be presented. Methods. A group of 16 MoM hip replacements were collected for retrieval analysis. Six of which had a pseudotumour. An Artificial Hip Profiler (Redlux Ltd) was used to measure wear. Edge loading was determined using the 3D wear data. Tissues were histologically evaluated using a 10-point ALVAL scoring system, which strongly suggests hypersensitivity (1). Cases were assigned to one of three categories: high wear (rates >5m/yr), hypersensitivity or corrosion. Results. Of the 6 pseudotumours, 3 had edge loading, 2 had high ALVAL scores and one had corrosion at the head taper junction. The high wear group, (3 cases) all demonstrated edge loading. Histology revealed more metal wear particles and macrophages, with a low ALVAL score in these cases. Two cases were found to have hypersensitivity with a high ALVAL score, more lymphocytes with less visible wear debris and macrophages. The wear rates were also lower, <4m/yr. One total hip replacement had corrosion at the junction between the head and adaptor taper for the stem. The bearings had low wear and the tissue had extensive necrosis as well as products of corrosion enclosed in fibrin (2). There was no suggestion of hypersensitivity (low ALVAL score). Conclusion. Pseudotumours can be caused by high wear, but if this is ruled out, a hypersensitivity or corrosion product reaction should be considered

In a randomized study of 60 patients allergic reactions are evaluated in three joint prosthesis groups, a resurfacing arthroplasty (ReCap), a non-cemented, large metal-on-metal head (Bimetric Magnum) and a non-cemented, alumina ceramic-on-ceramic bearing in a titanium shell (Bimetric C2a). The inclusion criteria were osteoarthritis, ASA I–II, MRI-scan without caput necrosis, DXA-scan without osteoporosis. The exclusion criteria were short neck (<2cm.), large cysts (>1cm.), medical treatment affecting the bone metabolism, severe deformity of the femoral head, impaired kidney function and inability to co-operate. Blood samples were drawn prior to and 6 weeks, 6 months, 1 year, and 3 years after surgery; two tubes from which plasma was prepared, and two tubes for serum. From the last included 20 patients in each group was also taken blood one and three years after surgery for an in vitro lymphocyte assay for scoring of possible hypersensitivity to prosthesis metals. The isolated lymphocytes were subjected to measurement of proliferation and expression of CD69 by flow cytometry and measurement of the Migration Inhibitory Factor (MIF) by ELISA. Plasma concentrations of the cytokines IL-1, IL-4, IL-6, IL-8, IL-12p70, IL-15, interferon-and osteoprotegerin were determined by multiplex-immunoassay. Serum concentrations of chromium and cobalt were determined by graphite furnace atomic absorption spectrometry. The serum concentrations of chromium and cobalt were lowest in patients with the C2a implant and highest with Magnum, some of these differences were significant at 6 weeks, 6 months, and 1 year after surgery. No patient had a very high serum metal concentration. The values of the variables measured in the in vitro lymphocyte assay mainly changed in the expected direction depending on the concentration of the same metal in the serum sample drawn at the same time, but no significant correlation was seen. One patient had uncertain symptoms of metal hypersensitivity and relatively high serum metal concentrations 3 years after arthroplasty with a Magnum prosthesis and was assessed extraordinarily, and elicited the marginally highest MIF responses in the lymphocyte assay. A strong correlation was found between the plasma concentrations of most cytokines, but the cytokine concentrations were not correlated to contemporary metal concentrations

Introduction. Due to the commercial launch of newly developed ceramic-on-metal (COM) bearings, we compared the deformation and stresses in the liner with ceramic-on-ceramic (COC), metal-on-metal (MOM) as well as ceramic-on-polyethylene (COP) bearings using a finite-element (FE)-model, analyzing a variety of head size and implant position. Liner deformation in terms of change in inner diameter as well as peak stresses were evaluated. Methods. The FE-model consisting of a commercial THR, the proximal femur and a section of the hemipelvis was created based on our previously published approach. Static load and muscle forces were applied according to the maximum load during gait. Polyethylene was modelled using a nonlinear definition with isotropic hardening, cobalt-chromium was modelled elastic-plastic and ceramic was modelled linear-elastic. Validity of the model was checked using an experimental setup with artificial bone and strain gauges located at the rim of the liner. Implant material (COM vs. COC vs. MOM vs. COP), head size (28 mm vs. 36 mm) and cup position (45° inclination/15° anteversion vs. 60° incl./0° antev.) were varied. Results. The experimental validation showed high correlation between strain measurements and FE-results. Liner deformation was evaluated by change in diameter at different levels. Change in head size had a high influence on cup deformation in COM, COC and MOM bearings, most possibly due to decreased liner thickness using bigger heads. Differences in MOM, COC and COM liner deformation were only in sub-micrometer range and not further evaluated. Evaluation of von Mises stress and minimum principal stress showed high differences between the bearing couples, implant positions and head sizes. COM liner stress was less sensitive to the steep cup position, but principal stress amounts were about ten times higher than in polyethylene liners. Thereby, MOM liners developed about 13 % less peak stress than COM. COC liners showed 11 % to 16 % higher stresses than COM. In accordance with published results, bigger head size correlated with lower principal stresses in the liner. Also, bigger heads were less sensitive to steep cup positions. Discussion. Deformation of the liner in total hip replacement has an important influence on lubrication, wear and clinical long-term success. The deformation occurring during intraoperative impaction and press-fit of the metal shell was not included in this study, hence the results are only valid considering the late postoperative phase when the implant is fully integrated in the bone. The FE-analysis showed no significant difference in liner deformation between COM, COC and MOM bearings. However, principal stresses were slightly higher in COM under the same conditions, but lower than COC

INTRODUCTION. Although simulation studies have shown superior wear properties of metal-on-metal articulations, increased concern exists regarding the excess in-vivo wear of a small number of Metal-on-Metal-Hip-Resurfacing (MoMHRA) implants. Serum ion levels of Chromium (Cr) and Cobalt (Co) are surrogate markers of wear. Risk factors associated with increased wear include female gender, small components, dysplasia, cup orientation outside safe zone and femoral head downsize during surgery with an associated decrease in Head-Neck-Ratio (HNR). However, these factors are interlinked. This study aims to identify the factors that are most important for subsequent wear of MoMHRA, by performing a multivariate analysis. METHODS. 206 patients (124M: 82F) with unilateral MoMHRA were included in this study. The average follow up was 3.3 years. All patients had Cr/Co levels measured at follow up. Inclination and anteversion of each cup were measured using EBRA. Cups were analysed as being within or outside the previously defined optimum-zone. HNR measurements were made from pre-operative (HNRpre) and post-operative (HNRpost) radiographs. The immediate changes in HNR (downsize/upsize of femoral head) as a result of the operation were expressed as:. HNRprepost=HNRpost–HNRpre. Multivariate linear regression modelling was used to explore the association between measures of ions with the following predictor variables (gender, age, diagnosis, femoral component size, orientation of the acetabular component, head/neck ratio and position of femoral stem). Analyses were carried out separately for each outcome (Cr and Co). Classification and Regression Tree (CART) models were fitted as a complimentary approach to regression modelling. RESULTS. Articular surface downsize followed by cup orientation within/outside optimum zone, followed by cup anteversion followed by gender were the strongest predictors of ion levels. A percentage decrease in HNRartpost, predicted an increase in Cr ion level by 5% (and 6% for Co). If the cup was within the optimum zone this was associated with decreased levels of Cr and Co ions. As acetabular component anteversion increased, levels of ions increased. Gender had a strong effect on ion levels. Adjusting for other variables, the effect of gender was attenuated due to a confounding effect of component size and the amount of femoral head downsize. Predictors identified as important in regression analyses were similar to those produced in the CART model, where the highest levels of ions were seen in patients with a percentage decrease in pre-operative HNR −11.3. DISCUSSION. This analysis shows that (surgical) factors, such as amount of femoral head downsize at operation and whether the cup was orientated within the optimum zone, explained the majority of the variability in ion levels in MoMHRA

Introduction. Metal-on-metal (MoM) articulations in total hip replacement (THR) have become an attractive option for young, active patients. Short-term reports have demonstrated elevated systemic metal ion levels in the blood and urine. Disseminated concentrations of cobalt and chromium have raised concern regarding cellular toxicity, chromosomal damage and adverse local soft tissue reactions. Long-term studies are required to support the increased use of MoM bearings in younger patients given their potential deleterious effects. The purpose of the current study was to report the 7–13 year clinical, radiographic, and metal ion results in patients following MoM THR. Methods. We prospectively followed 165 patients (196 hips) after second-generation MoM THR between July 1997 and November 2003. Functional outcome was measured using the Harris Hip Score (HHS) and the University of California Los Angeles (UCLA) Activity Score. Radiographic analysis was performed using Einzel-Bild-Roentgen-Analyse (EBRA) by two of the authors blinded to the study. Cobalt and chromium metal ions were measured from whole blood and analyzed using inductively coupled plasma-mass spectrometry. Results. 163 prostheses were analyzed. The mean age at surgery was 50.8 years (range, 17 to 66). There were 80 females and 83 males. The mean follow-up was 8.87 years (range, 7–13 years). Four hips (2.5%) were revised: 2 for infection at 0.2 and 7 years; 1 for a loose stem at 1.3 years; and 1 for a loose cup at 9 years. One patient received wound debridement for a superficial infection and did not have any components revised. The mean HHS and UCLA scores at the last follow-up were 91 and 6.8, respectively. The mean acetabular inclination and anteversion was 40 degrees (range, 24 to 57), and 19 degrees (range, 3 to 39), respectively. Median cobalt levels peaked at a value of 2.87 μg/L at 4 years (p<0.0001 vs. pre-operative) and subsequently decreased to 2.0 μg/L after 9 years (p=0.002 vs. 4-years). Median chromium levels maximally increased up to 0.75 μg/L after 5 years (p<0.0001 vs. pre-operative) and tended to decrease thereafter to values of 0.56 μg/L after 7 years. The Kaplan-Meier survivorship was 91.3% for revision for all causes, and 97.5% when excluding the hips revised for a manufacturer's defect at a mean of 8.87 years (range, 7–13 years). Conclusion. The present 7–13 years follow-up study of MoM THRs indicates that the clinical and radiological results are satisfactory with low revision rates. Furthermore, our study demonstrates the trend of metal ion levels in whole blood over a long-term. Both cobalt and chromium ion levels peaked at 4 and 5 years, respectively, and gradually decreased thereafter

INTRODUCTION. Femoral neck narrowing (NN) following Metal-on-Metal Hip Resurfacing Arthroplasty (MoMHRA) is a well-recognised clinical phenomenon. The incidence of resurfaced hips with NN > 10% is reported to be up to 27%. Its pathogenesis is thought to be multi-factorial secondary to stress shielding, impingement, osteolysis secondary to wear/ion particles and as a result of reduced vascularity and pressure effect on cancellous bone secondary to the presence of a soft-tissue mass around the resurfaced hip. Recognised risk factors for its development include: female gender and the presence of a pseudotumour. Serum Chromium (Cr) and Cobalt (Co) are recognised surrogate markers of in-vivo wear of MoMHRA. The aims of this study were to establish whether NN is associated with increased wear. METHODS. A cohort of 214 patients with unilateral MoMHRA (139M: 75F) was included in this study. Primary osteoarthritis was the diagnosis leading to surgery for the majority of patients (208). The average age at surgery was 54.1 years old (13–73). Six different implants were used; BHR (116), Conserve plus (92), Recap (2), ASR (2), Adept (1) and Cormet (1). The average femoral component size was 49.2mm (range: 38–59). The average follow up was 4.3 years (range: 2–10). Patients were subdivided into 3 groups as per implant size. Small size component group had implants <45mm, average size group had components 45–51mm and large component size group had components >51mm. All patients had Prosthesis-Junction-Ratio (PJR) measured from postoperative (PJRpost) and at latest follow up (PJRfollow) radiographs. Measurements were made using the method described by Lilikakis1. Metal ion levels (Cr/Co) were measured at last follow-up for all patients. Cr level >5.1g/ml and Co levels >4.4 g/ml were considered high2 and patients with such levels formed the high ion group. RESULTS. For the whole cohort, mean NN was 3.2% (range: 0–32%, SD:4.3). Females (4.7%, range: 0–32%, SD: 5.8) had significantly greater NN than males (2.4%, range: 0–23%, SD: 2.9) (p=0.001). Patients in the large component group had less NN (2.1%, SD: 2.3) in comparison to the average (3.2%, SD: 3.7%) (p=0.046) and the small (5.9%, SD: 7.9) (p=0.007) component size groups. There was no difference in NN between small and average sized components (p=0.1). Patients in the high ion group (25 patients) had significantly greater NN than patients with low ions (10.1%, range: 1%–32%, SD: 8.3 Vs 2.3%, range: 0–11, SD 2.3) (p<0.0001). NN >10% was seen in 16 hips (7.5%). The odds ratio of having high ions if NN >10% was 125 (p<0.001). DISCUSSION. The findings of this study showed that greater NN occurs in females and patients with small components and in patients with high ions. Furthermore, hips with NN >10% should be investigated further as they are more likely to have increased wear

Endoprosthetic replacement of the proximal femur may be required to treat primary bone tumours or destructive metastases either with impending or established pathological fracture. Modular prostheses are available off the shelf and can be adapted to most reconstructive situations for this purpose. We have assessed the clinical and functional outcome of using the METS (Stanmore Implants Worldwide) modular tumour prosthesis to reconstruct the proximal femur in 100 consecutive patients between 2001 and 2006. We compared the results with the published series for patients managed with modular and custom-made endoprosthetic replacements for the same conditions.

There were 52 males and 48 females with a mean age of 56.3 years (16 to 84) and a mean follow-up of 24.6 months (0 to 60). In 65 patients the procedure was undertaken for metastases, in 25 for a primary bone tumour, and in ten for other malignant conditions. A total of 46 patients presented with a pathological fracture, and 19 presented with failed fixation of a previous pathological fracture. The overall patient survival was 63.6% at one year and 23.1% at five years, and was significantly better for patients with a primary bone tumour than for those with metastatic tumour (82.3% vs 53.3%, respectively at one year (p = 0.003)). There were six early dislocations of which five could be treated by closed reduction. No patient needed revision surgery for dislocation. Revision surgery was required by six (6%) patients, five for pain caused by acetabular wear and one for tumour progression. Amputation was needed in four patients for local recurrence or infection.

The estimated five-year implant survival with revision as the endpoint was 90.7%. The mean Toronto Extremity Salvage score was 61% (51% to 95%). The implant survival and complications resulting from the use of the modular system were comparable to the published series of both custom-made and other modular proximal femoral implants.

We conclude that at intermediate follow-up the modular tumour prosthesis for proximal femur replacement provides versatility, a low incidence of implant-related complications and acceptable function for patients with metastatic tumours, pathological fractures and failed fixation of the proximal femur. It also functions as well as a custom-made endoprosthetic replacement.