INTRODUCTION

Whilst there is a great deal of research on hip implants, few studies have looked at implant orientation and the subsequent effect upon the wear performance of a hip resurfacing. This study aimed to measure implantation angles through radiographic analysis and linear wear for retrieved acetabular cups in order to investigate possible causal links between wear and implant orientation.

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

Cemented total hip arthroplasty yields reliable results in short to medium term studies, but aseptic loosening remains a problem in long-term follow up, especially in young and active patients. Aseptic loosening has been related to wear, and in order to minimize wear various alternatives to the traditional metal on polyethylene have been proposed. Both ceramic on polyethylene (COP) and metal on metal (MOM) have been shown to produce less wear than metal on polyethylene (MOP). In order to study the effect of the bearing, we have utilized identical stems and cups while comparing the different bearings. Methods and material. 396 hips were randomized to MOP, COP or MOM using a cemented triple tapered polished stem (MS-30; Sulzer Orthopedics) with a cemented polyethylene cup (Weber; Sulzer, Orthopedics) and a 28 millimeter head. For the MOP and COP articulations, a all-polyethylene cup was used with a Protasul™ metal head or a Sulox™ alumina head, whereas a polyethylene cup with metal insert was used for the MOM articulations (Weber Polyethylene Cup with Metasul™ Insert) with a Metasul™ metal head. Harris Hip Score (HHS) and radiological evaluation was performed after two, five and seven years. Ethical approval was obtained. Results. HHS was available for 338 hips after seven years. The HHS in the MOP group (116 hips) was 93.7 (SD 9.0), 93.5 in the COP group (112 hips) (SD 8.8), and 91.0 (SD 13.4) in the MOM group (110 hips). Radiographic evaluation was available for 335 hips. Radiolucencies around the stem larger than one millimeter were found in five of 115 MOP hips, seven of 111 COP hips and in seven of 110 MOM hips. Periacetabular radiolucencies identified as larger than one millimeter were found in none of the 116 MOP hips, five of the 112 COP hips and in 19 of the 110 MOM hips. Ten revisions were performed. In the MOP group there were three revisions (infection, dislocation, pain); one in the COM group (infection), and six in the MOM group (three infections, two aseptic loosening and one septic loosening). Discussion. Clinically, the three bearing types perform equally well at seven years, and there are few signs of impending failure for the stem. However, there are an alarmingly high proportion of cups showing signs of loosening. Two hips have been revised in the MOM group for aseptic loosening as opposed to none in the two other groups, which adds to the concern. The MOM articulation used in this study should be monitored closely for signs of aseptic loosening

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

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. The advantages of metal on metal (MOM) hip replacement are decreased wear rate, preservation of bone stock, anatomical restoration and enhanced stability. Large amounts of metal wear particles and metal ions are released which may induce adverse reactions including local soft tissue toxicity, hypersensitivity reactions, bone loss and risk of carcinogenesis. Aseptic loosening can be the result of a peri prosthetic osteolysis generated as a result of a biological response to particulate wear debris. Our aim in this study was to determine whether a steeply inclined acetabular component would give rise to a higher concentration of metal ions. Patients and methods. Between April 2003 and June 2006, 22 patients had MOM hip replacement for osteoarthritis by a single Surgeon. There were 12 male and 10 female patients. The average age at the time of surgery was 56 years (Range: 44–69 years). We divided the 22 patients into 2 groups, one group (A) of 11 patients with the acetabular inclination angle more than 50 degrees and the other group (B) of 11 patients with the angle less than 50 degrees. The inclination of the acetabular cup was measured using a standard AP radiograph of the pelvis. The patients had metal ion levels (blood chromium and serum cobalt) measured at an average follow up of 3.2 years (Range 2.4 to 5 years). Results. Mean blood chromium level in the group A (146 nM/L) was significantly higher (p=0.005) than in Group B (92 nM/L). Mean serum cobalt level in the group A (245 nM/L) was significantly higher (p=0.002) than in Group B (110 nM/L). Discussion. The early to mid term published results of MOM hip replacements have been encouraging. There are, however, a number of concerns about the MOM bearing. Although its wear rate is low, it still releases metal ions into the body particularly cobalt and chromium since most metal on metal bearings are made of a cobalt chromium alloy. The long-term consequences of increased levels of these ions in the body are not known. High concentrations of Co and Cr are toxic and are known to interfere with a number of biological functions. There also have been recent reports of soft tissue reactions with MOM hip replacement. In the light of these concerns, it is important to examine factors which may influence the release of metal ions after MOM hip replacement. It has been reported in the recent literature that the position of the acetabular component will influence the bearing wear inturn leading to the release of metal ions after MOM hip replacement. Our findings indicate that steeply inclined acetabular components with an inclination angle greater than 50 degrees gives rise to higher concentration of metal ions

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. 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

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

INTRODUCTION. The advantages of large diameter metal on metal total hip arthroplasty (MoM THA) and hip resurfacing arthroplasty are decreased wear rate, preservation of bone stock, anatomical restoration and enhanced stability. Large amounts of metal wear particles and metal ions are released which may induce adverse reactions including local soft tissue toxicity, hypersensitivity reactions, bone loss and risk of carcinogenesis. Aseptic loosening can be the result of a peri-prosthetic osteolysis generated as a result of a biological response to particulate wear debris. No reports in the literature exist as to whether circulating levels of Chromium (Cr) and Cobalt (Co) decrease upon removal of a symptomatic large diameter MoM implant or whether levels remain high due to the effect of metal ions debris left behind in the soft tissues after revision surgery. PATIENTS AND METHODS. Between June 2006 and June 2009 we undertook 44 revision surgeries of both large head MoM THAs (femoral head diameter 38mm) and metal-on-metal hip resurfacings for suspected metallosis. Mean time from original implant to revision was 4 years, 8 months (1yr 4mo–7yr 9mo). The mean follow up evaluation was 2 years and 2 months (1yr 2mo–4 years). Blood samples were taken for whole blood Cr and serum Co according to a recognised protocol and compared with reference levels indicated by the Medicines and Healthcare Regulatory Agency recommendation of less than 7ppb for Cr (130nM/L) and Co (119nM/L). RESULTS. 42 patients were found to have histological evidence of either metal allergy, metal toxicity or foreign body reaction. 2 patients had evidence of infection with no features of metal reaction. 3 patients suffered early dislocation requiring closed reduction. 1 patient had infective complications necessitating Girdlestones. 11 patients were lost to follow up, 8 patients were diagnosed pre operatively on Co and Cr levels in urine or synovial fluid aspirate alone. 23 patients had pre revision blood or serum metal ion level results available for direct comparison. Median serum Co level pre revision was 176.6nM/L, falling post revision to 5.1nM/L (p=<0.001∗). The median whole blood Cr level pre revision was 117nM/L and 19nm/L post revision (p=<0.001∗). Mean Oxford Hip Score was 23.7. DISCUSSION. This study demonstrates that at greater than one year post removal of a large diameter MoM hip implant for the indication of symptomatic metallosis or metal hypersensitivity, metal ion levels fall to almost normal levels and that outcome of revision surgery in terms of patient satisfaction is not adversely affected

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. A detailed clinical examination and investigations are required to evaluate the cause of persisting groin pain following a metal on metal (MoM) hip replacement. Adverse reaction to metallic debris (ARMD) is an emerging problem with MoM hip replacements. It is an umbrella term encompassing metallosis, pseudo-tumors and aseptic lymphocytic vasculitis associated lesions (ALVAL). The role of imaging in the diagnosis of this complex problem is still unclear. A study was undertaken to evaluate the efficacy of ultrasound in diagnosis of ARMD following a MoM hip replacement. METHODS. The study group included 35 patients with a clinical and histological diagnosis of ARMD, who had a preoperative ultrasound. All ultrasound procedures were performed on the anterior and lateral aspects of the painful hip with a high frequency probe of 9–13 MHz (Sonoline Antares – Siemens). RESULTS. All patients diagnosed with ARMD had abnormalities identified on ultrasound. Fluid inside the joint was noted in 30 out of 35 procedures (85.7 %). Fluid outside the joint was noted in 33 procedures (94.3 %). Amongst the patients with fluid outside the joint, 32 had iliopsoas and 30 had trochanteric bursitis. Echogenic reflections were noted in 31 out of 35 procedures (88.6 %). Considerable attenuation or absence of iliopsoas and gluteus tendon reflection was seen in many patients with echogenic fluid collections on the anterior and trochanteric aspects of hip. Progression of such changes was noted on further 5 patients, who had a repeat ultrasound within an interval of 3–6 months. 1 patient had a progression from anechogenic to echogenic joint effusion. DISCUSSION. Different radiological investigations including MRI scan have been used for evaluation of painful MoM hip arthroplasty. To our knowledge, this is the first study to demonstrate the efficacy of ultrasound in diagnosis of ARMD. Floating echogenic reflections and fluid collections around iliopsoas and gluteus medius/minimus tendons is highly suggestive of ARMD. Ultrasound is a cheap, non-invasive and dynamic investigation and has been shown to be reliable in diagnosis of ARMD

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

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. METHODS. Between 2008 to 2010, ten 50 mm Birmingham Hip Resurfacing (BHR) devices were tested by the IDC tribology laboratory using two ProSim hip wear simulators in three different tests (T1, T2 and T3). All tests were performed following the same IDC testing protocols at 1 Hz frequency for 5 million cycles (Mc) or until after a steady state was reached. Paul type stance phase loadings with a maximum load of 3 kN and a swing phase load of 0.3 kN was used. The flexion and extension angles were 30 and 15 degree. The internal/external rotation angel was ±10 degree. Wear was measured gravimetrically using an analytical balance (Mettler, Toledo xp504) with an accuracy of 0.1 mg. RESULTS. Results showed that wear of all the components tested followed the typical biphasic trend of wear for MoM hip joint device with a high “running-in” wear during the initial stage followed by a low “steady state” wear in the later stage. The data points scattered in a narrow range following the same trend line throughout the tests. The maximum difference in accumulated volume loss between any two tests at any given cycle was less in 0.2 mm3. The average running-in wear rates (±SD) were 0.72 ±0.17, 0.86 ±0.01 and 0.71 ±0.19 mm3/Mc respectively for test T1, T2 and T3. The running-in wear rates for test T1 and T3 were identical, whilst that for T2 was slightly higher. In spite of this, the wear rates for the bearings tested in T2 were still in the same range as those tested in T1 and T3 during the running-in stage. The steady state (>1.0Mc) wear rate of three different tests was practically the same, being 0.18 ±0.02, 0.18 ±0.06 and 0.16 ±0.04 mm3/Mc respectively for test T1, T2 and T3. Overall, the mean running-in wear rate was 0.74 ±0.16 mm3/Mc, and the steady state wear rate was 0.17 ±0.04 mm3/Mc for the 10 BHR devices tested in three different studies. DISCUSSIONS. This study shows that satisfactory repeatability can be achieved during hip simulator test of metal on metal hip joint devices. Well controlled test procedures including calibration of testing and measurement equipment, correct and consistence test set-up and attention to non-bearing surfaces are some of the most important prerequisites for reliable and accurate hip simulator test results