Summary. The M2a-38. tm. metal on metal total hip arthroplasty showed a high incidence of pseudotumors and an unexpected high revision rate in our thoroughly screened cross sectional cohort. Introduction. After the revival of the metal on metal (MoM) bearing in total hip arthroplasty (THA) at the beginning of this century, there are now serious questions about this type of bearing. The advantage of large head MoM bearing is the increase in range of motion and stability. In our institution the choice was made for 38 mm heads. During the last few years concerns have been raised about the relationship of MoM bearing and elevated serum cobalt and chromium ion levels, their local and systemic toxicological effects and the incidence of local tumorous masses (pseudotumors). Are these findings applicable for all MoM bearings or are there also product specific issues. We present the outcome of a cementless MoM THA using a 38mm head in a unique consecutive series of 377 THA who were performed in our institution. Patients and Methods. All 351 patients (377 THA) with a cementless MoM THA (M2a-38. tm. , Biomet Inc, Warsaw, IN, USA, and Taperloc® stem, Biomet UK, Bridgend) between 2008 and 2011 were evaluated. All patients were analyzed by a physical exam, serum levels of cobalt and chromium and an interview to determine if there were any complaints. An MRI of the hip was made if patients reported pain during physical activity, allergies to metals, serum cobalt or chromium ion levels ≥ 5 ppb or if the inclination of the acetabular component was more than 50 degrees. Nine patients deceased, three were lost to follow up and four already underwent a revision before the screening. We analyzed 361 hips with an average follow up of 30 (range 2–58) months. The average preoperative age was 63 years (41–88). Results. 219 patients with 235 THA (65%) reported no complaints. Median cobalt level in patients with complaints was 6.6 (0.2–173) ppb and in the group without complaints 3.7 (0.2–27.3) ppb. Median chromium level in patients with complaints was 5.0 (0.1–134) ppb and in the group without complaints 3.7 (0.2–27) ppb. On the 226 performed MRI scans, 56 pseudotumors were diagnosed and described using the Anderson classification (9 C1, 41 C2 and 5 C3). 71 hips had been revised after a mean follow of 30 months (range 0.2–50 months). Reasons for revision were because of pain, raised metal ions and a pseudotumor in 28; pain and raised metal ion levels in 15; aseptic loosening of the acetabular or femoral component in 11; raised metal ions and a pseudotumor in 7; combination of luxations, luxation feelings and fractures in 5; infections in 3 and for other reasons in 2. Conclusion. The short-term results of the THA with a 38mm head metal on metal articulation are higher compared with other MoM bearings. They show a revision rate of 7% and 10% in the Australian and England register. In other peer reviewed literature we find a revision rate between 0–13% after five years. We also observed a high incidence of elevated serum levels of metal ions, pseudotumors and an unexpected high early revision rate

Metal on metal press-fit acetabular cups are the worst performing acetabular cup type with severe failure consequences compared to cups made from more inert materials such as polyethylene or ceramic. The cause of failure of these cup types is widely acknowledged to be multi-factorial, therefore creating a complex scenario for analysis through clinical studies. A factorial analysis has been carried out using an experimentally validated finite element analysis to investigate the relative influence of four input factors associated with acetabular cup implantation on output parameters indicating potential failure of the implantation. These input factors were: cup material stiffness; cup inclination; cup version; cup seating; and level of press-fit. The output parameter failure indicators were: wear; tensile strains in the underlying bone; bone remodelling; and cup-bone micromotions. The factorial analysis concluded that the most significant influence was that of cup inclination on wear, and the second most significant was the influence of the level of press-fit on bone remodelling at the acetabular rim. Significant influence was also observed between version angle and wear, and cup-seating and micro-motion. The results demonstrated the clear multi-factorial nature of implant failure and highlighted the importance of correct implant positioning and fit

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal articulating surface wear has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as quantitative assessment of wear volume. This study aimed to assess and compare qualitatively tapers from small and large diameter MOMTHR's. Tapers from 3 retrieval groups were analysed. Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Gp 3 (control): 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. RedLux profiling of tapers produced a taper angle and 3D surface maps. The taper angles were compared to those obtained using CMM measurements. There was no difference between groups in mean 12/14 taper angles or bearing surface volumetric and linear wear. Only LHMOMs showed transfer of pattern from stem trunnion to head taper, with clear demarcation of contact and damaged areas.3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure

This study reports the mid-term results of a large bearing hybrid metal on metal total hip replacement (MOMHTHR) in 199 hips (185 patients) with mean follow up of 62 months. Clinical, radiological outcome, metal ion levels and retrieval analysis were performed. Seventeen patients (8.6%) had undergone revision, and a further fourteen are awaiting surgery (defined in combination as failures). Twenty one (68%) failures were females. All revisions and ten (71%) of those awaiting revision were symptomatic. Twenty four failures (86%) showed progressive radiological changes. Fourteen revision cases showed evidence of adverse reactions to metal debris (ARMD). The failure cohort had significantly higher whole blood cobalt ion levels (p=0.001), but no significant difference in cup size (p=0.77), inclination (p=0.38) or cup version (p=0.12) in comparison to the non revised cohort. Female gender was associated with an increased risk of failure (chi squared p=0.04). Multifactorial analysis demonstrated isolated raised Co levels in the absence of either symptoms or XR changes was not predictive of failure (p=0.675). However both the presence of pain (p<0.001) and XR changes (p<0.001) in isolation were both significant predictors of failure. Wear analysis (n=5) demonstrated increased wear at the trunnion/head interface (mean out of roundness measurements of 34.5 microns +/−13.3 (+/−2SD, normal range 8-10 microns) with normal levels of wear at the articulating surfaces. There was evidence of corrosion at the proximal and distal stem surfaces. The cumulative survival rate, with revision for any reason was 92.4% (95%CI: 87.4-95.4) at 5 years. Including those awaiting surgery, the revision rate would be 15.1% with cumulative survival at 5 years of 89.6% (95% CI: 83.9-93.4). This MOMHTHR series has demonstrated unacceptable high failure rates with evidence of high wear at the head/trunnion interface and passive corrosion to the stem surface. This raises concern with the use of large heads on conventional 12/14 tapers. Female gender was an independent risk factor of failure. Metal ion levels remain a useful aspect of the investigation work up but in isolation are not predictive of failure

INTRODUCTION

There is increasing worldwide interest in the assessment of wear in explanted hip components. This is due is part to high profile failures of orthopaedic components in the US, whilst in the UK hip resurfacings have been experiencing a higher than expected failure rate. The reasons for these failures are not well understood, with data from the NJR suggesting the 43% of MoM resurfacing failures are unexplained.

Wear analysis is a vital tool in determining failure mechanisms and ultimately improving the longevity of joint replacements through improved design and manufacturing control. There are currently no relevant measurement standards for the evaluation of retrieved orthopaedic components. This paper will assess two of the most commonly used techniques namely roundness measurement and co-ordinate measurement. The advantages and disadvantages of both techniques are considered in this paper.

In vitro the introduction of microseparation and edge loading to hip simulator gait cycle has replicated clinically relevant wear rates and wear mechanisms in ceramic-on-ceramic bearings^[1], and elevated the wear rates of MoM surface replacements (SR) to levels similar to those observed in retrievals^[2]. The aim was to assess the wear of two different sized MoM total hip replacement bearings under steep cup inclination angles and adverse microseparation and edge loading conditions.

Two tests were performed on the Leeds II hip joint simulator using two different size bearings (28mm and 36mm). Cups were mounted to provide inclination angles of 45 degrees (n=3) and 65 degrees (n=3). The first three million cycles were under standard gait conditions. Microseparation and edge loading conditions as described by Nevelos et al^[1] were introduced to the gait cycle for the subsequent three million cycles. The lubricant was 25% new born calf serum. The mean wear rates and 95% confidence limits were determined and statistical analysis was performed using One Way ANOVA.

Under standard gait conditions, when the cup inclination angle increased from 45 degrees to 65 degrees, the wear of size 28mm bearing significantly (p=0.004) increased by 2.7-fold, however, the larger bearings did not show any increase in wear (p=0.9). The introduction of microseparation conditions resulted in a significant (p=0.0001) increase in wear rates for both bearing sizes under both cup inclination angle conditions. Under microseparation conditions, the increase in cup inclination angle had no influence on the wear rate for both bearing sizes (Figure 1).

With larger bearings, head-rim contact occurs at a steeper cup inclination angle providing an advantage over smaller bearings. The introduction of edge loading and microseparation conditions resulted in a significant increase in wear rates for both bearing sizes. The wear rates obtained in this study under combined increased cup inclination angle and microseparation were half of those obtained when SR MoM bearings were tested under similar adverse conditions^[2]. This study shows the importance of prosthesis design and accurate surgical positioning of the head and acetabular cup in MoM THRs.

The implantation of endoprosthesis is a routine procedure in orthopaedics. Endoprosthesis are mainly manufactured from ceramics, polymers, metals or metal alloys. To ensure longevity of the implants they should be as biocompatible as possible and ideally have antibacterial properties, to avoid periprosthetic joint infections (PJI). Various antibacterial implant materials have been proposed, but have so far only been used sporadically in patients. PJI is one of the main risk factors for revision surgeries. The aim of the study was to identify novel implant coatings that both exhibit antibacterial properties whilst having optimal biocompatibility. Six different novel implant coatings and surface modifications (EBM TiAl6V4, strontium, TiCuN, TiNbN, gentamicin phosphate (GP), gentamicin phosphate+cationic polymer (GP+CP)) were compared to standard CoCrMo-alloy. The coatings were further characterized with regard to the surface roughness. E. coli and S. capitis were cultured on the modified surfaces to investigate the antibacterial properties. To quantify bacterial proliferation the optical density (OD) was measured and viability was determined using colony forming units (CFU). Murine bone marrow derived macrophages (BMMs) were cultured on the surfaces and differentiated into osteoblasts to quantify the mineralisation using the alizarin red assay. All novel coatings showed reduced bacterial proliferation and viability compared to standard CoCrMo-alloy. A significant reduction was observed for GP and GP+CP coated samples compared to CoCrMo (OD. GP,E.coli. = 0.18±0.4; OD. GP+CP,E.coli. = 0.13±0.3; p≤0.0002; N≥7-8). An increase in osteoblast-mediated mineralisation was observed on all surfaces tested compared to CoCrMo. Furthermore, GP and GP+CP coated samples showed a statistically significant increase (M. GP. = 0.21±0.1; M. GP+CP. = 0.25±0.2; p<0.0001; N≥3-6). The preliminary data indicates that the gentamicin containing surfaces have the most effective antibacterial property and the highest osseointegrative capacity. The use of antibiotic coatings on prostheses could reduce the risk of PJI while being applied on osseointegrative implant surfaces

An increase in metal ion levels is seen after implantation of all MoM hip prosthesis due to release from the surface directly, more so during articulation and corrosion of the bearing surfaces. The bearing surfaces in MoM prosthesis consist of cobalt, chromium and molybdenum. Several case-reports of cobalt toxicity due to a MoM prosthesis have been published in the last decade. Cobalt intoxication may lead to a variety of symptoms: neuro-ocular toxicity (tinnitus, vertigo, deafness, blindness, convulsions, headaches and peripheral neuropathy), cardiotoxicity and thyroid toxicity. Nausea, anorexia and unexplained weight loss have been described. Systemic effects from metal ions even with well functioning implants or with ion concentrations lower than those associated with known adverse effects may exist and warrant investigation. The aim of this study is to investigate self-reported systemic complaints in association with cobalt ion concentrations in patients with any type of MoM hip prosthesis. A cohort study was conducted. Patients with both unilateral and bilateral, resurfacing and large head metal on metal total hip arthroplasties were included for the current study. Blood metal ion concentrations (cobalt and chromium) were measured by inductively coupled plasma mass spectrometry (ICP-MS). Based on the known cobalt toxicity symptoms of case-reports and toxicology reports a new non-validated questionnaire was developed. questions were subdivided in general questions/symptoms, vestibular symptoms, neurological symptoms, emotional health and cardio- and thyroid toxicity symptoms. Independent samples T test, Fishers Exact Test and Pearsons (R) correlation were used. Analysis was performed on two groups; a low cobalt ion concentration group and a high cobalt ion concentration group A total of 62 patients, 36 (58%) men and 26 (42%) women, were included with a mean age at surgery of 60.8 ± 9.3 years (41.6 – 78.1) and a mean follow up of 6.3 ± 1.4years (3.7 – 9.6). In these patients a total of 71 prosthesis were implanted: 53 unilateral and 9 bilateral. Of these, 44 were resurfacing and 27 large head metal on metal (LHMoM) total hip arthroplasties. Mean cobalt and chromium ion concentrations were 104 ± 141 nmol/L (9 – 833) and 95 ± 130nmol/L (6 – 592), respectively. Based on the different thresholds (120 – 170 or 220 nmol/L) the low cobalt ion concentration group consisted of 44 (71%), 51 (82%) or 55 (89%) subjects respectively. No differences were found in general characteristics, independently of the threshold. The composite score of vestibular symptoms (vision, hearing, tinnitus, dizziness) was significantly higher (p < .050) in all high cobalt ion concentrations groups, independent of the threshold value This study aimed to detect a trend in self-reported systemic complaints in patients with metal-on-metal hip arthroplasty due to raised cobalt ion concentrations. Vestibular symptoms were more common in high cobalt ion concentration groups independent of the three threshold levels tested. The upper limit of acceptable cobalt ion concentrations remains uncertain. With regards to proactively inquired, self-reported symptoms the threshold where effects may be present could be lower than values currently applied in clinical follow-up. It is unknown what exposure to elevated metal ion concentrations for a longer period of time causes with aging subjects. Further research with a larger cohort and a more standardized questionnaire is necessary to detect previously undiscovered or under-reported effects

The biological reaction in metallosis and pseudotumor generation after metal on metal total hip arthroplasty or corroding metal implants remains unsettled. Clinically, still lethal cases appear with massive bone loss and metal ions are suspected to be responsible for this inflammatory reaction, solid metal wear particles instead are usually not observed in the common literature. The aim of this study was to compare the biological reactions of metal ions and metal wear particles in a murine in vivo model. Metal ions (CoCr), metal particles (CoCr), polyethylene particles (UHMWPE) and phosphate buffered saline (PBS) were injected into the left knee joint of female BALB/c mice. 7 days after injection, the microcirculation was observed using intravital fluorescence microscopy, followed by euthanasia of the animals. After the assessment of the knee diameter, the knees underwent histological evaluations of the synovial layer. Throughout all recorded data, CoCr particles caused higher inflammatory reactions compared to metal ions and UHMWPE particles. The mice treated with the solid particles showed enlarged knee diameters, more intensive leukocyte–endothelial cell interactions and an elevated functional capillary density. Pseudotumor-like tissue formations in the synovial layer of the mice were only seen after the exposition to solid CoCr particles. Even if the focus of several national guidelines concerning metallosis and pseudotumor generation is on metal ions, the present data reveal that solid CoCr particles have the strongest inflammatory activity compared with metal ions and UHMWPE particles in vivo

Summary. Management of metal on metal hip replacements can be accomplished with a simple algorithm including easily available metal ion levels and hip MRI with metal artifact reducing software. After revision serum metal ion levels can be expected to fall rapidly. Introduction. Metallic ion release may be related to bearing surface wear and thus serves as an indicator of the in-vivo performance of metal on metal articulations. The purpose of this prospective, controlled study was to compare new large head metal on metal hip components with established modular metal on metal and metal on polyethylene and to determine their effects on serum metal levels before and after revision. Patients & Methods. We performed a multi-surgeon, prospective, controlled trial to compare clinical, radiographic, and metal ion concentration in serum (cobalt and chrome) results across multiple devices including the Large Head ASR XL System (MoM-1), the Ultamet Advanced Modularity System (MoM-2), and as the control the Pinacle Acetabular Cup System with polyethylene liner (MoP). One hundred and fifty-one consecutive patients undergoing THA were enrolled in the study: MoM-1 n=97; MoM-2 n=22; MoP n=32. Clinical, radiographic, and venous blood assessments were performed pre-operatively, and post-operatively at 6 months, 1 year and 2 years, and after revision (1,3,6,12 months). All serum ion concentrations are reported in nmol/L. We are following metal ion levels after revision and have developed an algorithm to diagnose and manage patients with MoM THA. Results. MoM-1 patients had significantly increased average cobalt and chromium levels. Clinical scores improved after surgery in all groups and continued to improve in MoM-2 and MoP patients after 2 years but decreased slightly in the MoM-1 patients at 2 years. Average cup inclination angle did not differ significantly between the groups: MoM-1 50.2, MoM-2 47.8, and MoP 51.7. In the MoM-1 group 11 patients (11%) had significantly elevated ion levels (MoM-1 Outliers). Nine hips (9.3%) in 8 MoM-1 outlier patients required revision. Metal ion levels were not significantly different between MoM-2 and MoP groups. Metal ion levels after revision in the MoM-1 group decreased rapidly but at one year post-operatively have still not returned to an equivalent baseline comparable to the MoM-2 and MoP groups. All revisions were in the MoM-1 group. Chromium levels decreased more slowly than Cobalt levels. Discussion. To our knowledge this is the only data in the literature prospectively comparing ion levels among groups and reporting post revision ion levels. Average serum ion levels were elevated at all post-operative samples in the MoM-1 group but this was due to significantly elevated levels in a subset of outliers who required revision. Excluding the outliers there is not a significant difference in post-operative ion levels between the groups. There was no radiographic evidence of component malposition or aseptic loosening in any of the groups. Control groups (MoM-2, MoP) performed comparatively across all variables. We present an algorithm to diagnose and manage patients with metal on metal THA and offer evidence that metal ion levels do decrease after revision but still remain abnormally elevated at one-year post revision compared to the control group. A significant portion of MoM-1 performs comparatively to the controls in terms of ions

Metal on metal hip replacements have been one of worst failures in recent years in terms of orthopaedic implants. Some of these devices have had catastrophic failure rates, with reports of 48% failure at 6 years. The failure of these devices has led to considerable suffering, pain and reduction in quality of life; consequently, they have given rise to high costs and multi-million-dollar legal cases. This talk will describe the history of the current metal on metal failure and discuss some of the reasons why might have occurred. It will also consider the reasons that wear debris arising from the trunnion is worse in terms of biological activity then that arising from the bearing surfaces

Adverse reaction to metal debris (ARMD) is well recognised as a complication of large head metal on metal total hip replacement (THR) leading to pain, bone and tissue loss and the need for revision surgery. An emerging problem of trunnionosis in metal on polyethylene total hip replacements leading to ARMD has been reported in a few cases. Increased metal ion levels have been reported in THR's with a titanium stem and a cobalt chrome head such as the Accolade-Trident THR (Stryker). We present 3 cases of ARMD with Accloade-Trident THR's with 36mm cobalt chrome head and a polyethylene liner. Metal ion levels were elevated in all three patients (cobalt 10.3 – 161nmol/l). Intraoperative tissue samples were negative for infection and inflammatory markers were normal. Abnormal fluid collections were seen in all three cases and bone loss was severe in one patient leading to a proximal femoral replacement. Histology demonstrated either a non-specific inflammatory reaction in a case which presented early or a granulomatous reaction in a more advanced case suggesting a local foreign body reaction. All patients had improved symptoms post-operatively. 1 patient who had staged bilateral Accolade-Trident THR's required revision of both THR's. ARMD in metal on polyethylene THR's with a titanium stem represents a potential emerging problem. Further studies are required to assess whether these occurrences are rare or represent the tip of an iceberg

Summary. 162 patient cohort with serial Metal Artefact Reduction Sequence MRI scans. Patients with normal initial scans can be followed up at 1 year. Those with abnormal scans should be followed up at a shorter interval of 6 months. Introduction. Cross-sectional imaging is a key investigation in the assessment and surveillance of patients with metal-on-metal (MoM) hip arthroplasty. We present our experience of Metal Artefact Reduction Sequence (MARS) MRI scanning in metal on metal hip arthroplasty. We aimed to investigate the natural history and radiological disease progression from Adverse Reactions to Metallic Debris. Methods. A total cohort of 626 patients who had metal on metal arthroplasty underwent MARS MRI scanning with 162 patients having more than one MRI scan. A musculoskeletal radiologist reviewed and reported on all MRI scans. The findings were described as either normal or classified according to Hart et al. We then considered the patient's progression between groups on serial scans and the time intervals between them. Results. 65 patients had a normal first MRI, 38 (54%) remained normal on follow-up scan with a mean scanning interval of 14.6 months. The remaining 27 patients who progressed form normal to either Type 1/2/3 did so over a mean scan interval of 14 months. Of those 56 patients with a Type 1 (thin walled fluid collection) 28.5% of these progressed during interval scanning and 8.9% of Type 1 reactions returned to normal. Over half the patients with an abnormal initial MARS MRI scan 46/85 (54%), with either Type 1 or 2 abnormal soft tissue reaction, had progressed to more severe types following a mean interval scan time of 12.2 months. Discussion. A safe interval for a follow-up MARS MRI scanning in a patient who has normal initial findings appears to be 12 months. We consider a 6-month scan appropriate for patients under surveillance who have initial abnormal cross-sectional imaging

Background. Hip resurfacing has resurged in the last decade due to a renewed interest in metal on metal bearing. One of the proposed advantages is ease of revision of the femoral component. Short term functional results after femoral revision are similar to those after conventional total hip replacement. Survival and function after revision of the acetabular component only or of both components have not been reported. We aimed to assess hip function and implant survival after revision of the acetabular component for failed Birmingham hip resurfacing (BHR). Methods. The Oswestry Outcome Centre collected data prospectively on 5000 patients who underwent hip resurfacing between 1997 and 2002. Of these, 182 hips were revised: 42% had revision of the femoral component only, 8% revision of the acetabular component only, and 50% revision of both components. This study analyzed patients who had revision of the acetabular component, either in isolation or in combination with the femoral component. Results. In the isolated acetabular revision group the median Harris Hip Score was 74 at a mean of 4.5 years post-revision. In the both components revision group the median Harris hip score was 85 at a mean of 4 years. There was no significant difference in function between the groups. Kaplan-Meier survivor ship analysis after revision showed an average survival of 91% at 10 years. There was a significant difference between survival of isolated acetabular revision (75%) and both component revision (96%). Conclusions. Revision total hip replacement subsequent to failure of hip resurfacing has good outcome and good midterm survival. Isolated acetabular revision and revision of both components had similar function but survival was significantly worse in the isolated acetabular revision group

Metal on metal (MoM) bearings in hip surgery may result in increased blood levels of metal ions. The nature of the relationship between ion levels and failure is still not fully understood. We compared three cohorts of resurfacing patients, grouped for brand and diameter of femoral component. We measured the blood level of Cobalt and Chromium ions at an average of 4 years postoperatively. The results were grouped as follows: Birmingham Hip Resurfacing ≥50 mm diameter, Durom resurfacing ≥50 mm diameter and Durom resurfacing <50 mm diameter. 120 patients were included in each group. There were significant differences in Cobalt levels between the groups. The median cobalt level for the BHR group was 8 nmol/L higher than the Durom ≥50 mm group (P<0.005). The Durom <50 mm group recorded cobalt levels 8.5 nmol/L higher than the Durom ≥50 mm group (P=0.0004). Revision rates were equal in the Large BHR's and Large Durom HRA (both 3.3%) however the small Durom HRA had a revision rate of 8.3%. Elevated blood ion levels can indicate a failing MoM bearing. When similar ion levels were reported for BHR and small Durom the latter had significantly higher revision rates. The large BHR and large Durom HRA have similar revision rates yet the large Durom HRA had significantly lower metal ion levels. Only one of the patients having revision surgery (n=18) had metal ion levels above the MHRA threshold. This suggests ion levels do not absolutely predict the rate of HRA failure. Given similar revision rates with different ion levels between the large BHR and large Durom hips, mechanisms of failure leading to revision must be isolated from the release of metal ions. Therefore clinical and image based follow up are recommended in addition to ion level monitoring

SUMMARY. We report a prospective study of clinical data collected pre, intra and post operation to remove both cup and head components of 118 failed, current generation metal on metal (MOM) hips. Whilst component position was important, the majority were unexplained failures and of these the majority (63%) had cup inclination angles of less than 55 degrees. Poor biocompatibility of the wear debris may explain many of the failures. BACKGROUND. Morlock et al reported a retrospective analysis of 267 MOM hips but only 34 head and cup couples (ie most were femoral neck fractures) and without data necessary to define cause of failure. The commonest cause of failure in the National Joint Registry (NJR) is unexplained. METHODS. We categorised the cause of failure, as defined by the NJR, of all MOM hips received over an 18 month period that had a full set of pre, intra and post op data. A group of 40 patients with unilateral well functioning MOM hips was used for comparison. RESULTS. In the retrieval group, the median age was 61 years (25 to 87) and there were 80 females and 38 males. The median time between primary and revision operation was 35 months (4 to 121). Femoral head size was <50mm in 89 and >=50mm in 29. The causes of failure were: unexplained in 75; aseptic loosening (acetabular) in 12; aseptic loosening (femoral) in 7; dislocation/subluxation in 1; infection in 11; periprosthetic femoral fracture in 2; malalignment in 6; size mismatch in 3; other in 1. 47 (63%) of unexplained failures had cup inclination angles of less than 55 degrees. The unexplained failures had increased blood metal ions (p <0.0001) and cup inclination angle (p <0.005) but a decreased femoral head size (p <0.0001) when compared to well functioning MOM hip patients. CONCLUSION. The commonest cause of failed MOM hips was unexplained. Comparison to well functioning hips revealed that the mechanism may involve high blood metal ions but high cup inclination angle was not found in the majority of cases. Further biological and mechanical investigation into the underlying mechanism of failure is required

Summary. Despite high revision rates, the mean two year migration of the ASR. TM. cup is within an acceptable threshold. Slightly higher migration rates found for the M2a- Magnum™ Porous Coated Acetabular Component but longer follow up is needed to establish if this implant is at risk. Introduction. RSA can detect the migration of an implant, and continuous migration is a predictor for failure (1). The ASR. TM. resurfacing implant was withdrawn from the marked due to excessive failure rate but showed initial femoral component stability. The aim of this study was to investigate the initial implant stability for the ASR cup as a possible explanation for the high revision rate, and to compare it to another metal on metal (MoM) cup. Patients and Methods. 36 patients with primary osteoarthritis from a RCT received either an ASR. TM. (n=19) or an M2a-Magnum Cup. TM. (n=17) without markers. Ten 0.8mm tantalum markers were injected in the periacetabular bone. Using a UmRSA® 43Calibration Cage™ (RSA Biomedical, Sweden), supine RSA images were obtained within 3 days of surgery, at 8 w, 6 m, 1 and 2 years. A model based RSA system using an EGS Hemi-sphere model (Medis specials, Leiden) calculated migration. For the 2 year analysis 16 and 15 sets of images were available. ANOVA with repeated measurements analysed movement over time for each type of implant as well as difference between implants. Results. Mean translations in the medial –lateral (X), proximal-distal (Y) and anterior-posterior (Z) direction are depicted. Initial movement was noted, especially for the M2a-Magnum cup, where the 2 year mean (sd) X translation was −0.307 (0.53)mm (p = 0.01), Y translation was 0.282 (0.36)mm (p < 0.001) and Z translation was −0.343 (0.63)mm p = (0.03). After 2 years the ASR cup displayed a mean X translation of −0.115 (0.60) mm (p = 0.82), Y translation of 0.075 (0.14)mm (p = 0.01) and Z translation of 0.438 (0.88)mm (p = 0.04). The implants had a similar pattern for X and Y with slightly more movement for M2a-Magnum in the X translations (p < 0.01) On the Z axis the implants displayed movement in opposite directions (p=<0.001). At two years 4 ASR and 5 M2aMagnum displayed movement above 1 mm in one axis . Discussion/Conclusion. The early migration of both cups were low. The ASR implant is slightly higher than a competing implant with better survival rates on the Z axis, but low at particularly the Y axis, where the mean 0.075 mm is well below the limit of 0.2mm recently suggested as an acceptable threshold. The M2a-Magnum cup has migration rates just above that, but longer clinical follow up is needed to establish if this cup has greater risk of revision. We will continue to monitor our patients to establish if the individual patient with excess migration is at risk. Continuous migration is not likely to explain failure of neither the cup nor the femoral side of the ASR hip

The renewed interest in the clinically proven low wear of the metal-on-metal bearing combined with the capacity of inserting a thin walled cementless acetabular component has fostered the reintroduction of hip resurfacing. As in other forms of conservative hip surgery, i.e. pelvic osteotomies and impingement surgery, patient selection will help minimize complications and the need for early reoperation. Patient Selection and Hip Resurfacing. Although hip resurfacing was initially plagued with high failure rates, the introduction of metal on metal bearings as well as hybrid fixation has shown excellent survivorships of 97 to 99% at 4 to 5 years follow-up. However, it is important to critically look at the initial published results. In all of these series there was some form of patient selection. For example, in the Daniel and associates publications, only patients with osteoarthritis with an age less than 55 were included with 79% of patients being male. Treacy and associates stated that: “the operation was offered to men under the age of 65 years and women under the age of 60 years, with normal bone stock judged by plain radiographs and an expectation that they would return to an active lifestyle, including some sports”. However in the materials and methods, although the mean age is 52 years, the range is from 17 to 76 years including some patients with rheumatoid arthritis as well as osteonecrosis. Obviously, some form of patient selection is needed; but how one integrates them is where the Surface Arthroplasty Risk Index (SARI) is useful. With a maximum score of 6, points are assigned accordingly: femoral head cyst >1cm: 2 points; patient weight <82kg: 2 points; previous hip surgery: 1 point; UCLA Activity level >6: 1 point. A SARI score >3 represented a 4 fold increase risk in early failure or adverse radiological changes and with a survivorship of 89% at four years. The SARI index also proved to be relevant in assessing the outcome of the all cemented McMinn resurfacing implant (Corin¯, Circentester, England) at a mean follow-up of 8.7 years. Hips which had failed or with evidence of radiographic failure on the femoral side had a significantly higher SARI score than the remaining hips, 3.9 versus 1.9. Finally, one must consider the underlying diagnosis when evaluating a patient for hip resurfacing. In cases of dysplasia, acetabular deficiencies combined with the inability of inserting screws through the acetabular component may make initial implant stability unpredictable. This deformity in combination with a significant leg length discrepancy or valgus femoral neck could compromise the functional results of surface arthroplasty, and in those situations a stem type total hip replacement may provide a superior functional outcome. In respect to other diagnoses (osteonecrosis, inflammatory arthritis), initial analyses have not demonstrated any particular diagnostic group at greater risk of earlier failure. The only reservation we have is in patients with compromised renal function since metal ions generated from the metal-on-metal bearing are excreted through the urine and the lack of clearance of these ions may lead to excessive levels in the blood. Surgical Technique. Because resurfacing has not been within the training curriculum of orthopaedic surgeons for the last 2 decades, there will most likely be a learning curve in the integration of this implant within clinical practice. This data was confirmed for hip resurfacing when looking at the Canadian Academic Experience where in the first 50 cases of five arthroplasty surgeons only a 3.2% failure rate was noted of which 1.6% were due to neck fracture. Femoral neck fracture can occur because of significant varus positioning as well as osteonecrosis of the femoral head due to either disruption of the blood supply or over cement penetration. Finally, abnormal wear patterns leading to severe soft tissue reactions are being increasingly recognized and are related to either impingement or vertically placed acetabular components. Although impingement has long been recognized after total hip arthroplasty to limit range of motion and in extreme cases to hip instability, the risk after hip resurfacing may be greater since the femoral head-neck unit is preserved. Beaulé and associates have reported that 56% of hips treated by hip resurfacing have an abnormal offset ratio pre-operatively, with the two main diagnostic groups presenting deficient head-neck offset being osteonecrosis and osteoarthritis both of which have been associated with femoroacetabular impingement in the pre arthritic state. Conclusion. Although patients with a high activity level are likely to put their hip arthroplasties at risk for earlier failure, limiting a patient's activity because of fear of revision with a stem type hip arthroplasty has been shown to negatively impact the quality of life at long term follow-up. Thus hip resurfacing arthroplasty plays a significant role in the treatment of hip arthritis by permitting a return to full activities or what the patient perceives as his/her full capacities to do so, permitting them to enjoy a better quality of life without fearing a major hip revision

Metal-on-metal (MOM) hip arthroplasty, including resurfacing, has become the subject of recent research and debate. There is the perceived benefit of improved wear rates of bearing surfaces leading to superior durability and performance of these types of implant. An associated feature of MOM bearing surfaces is the generation of metal ions. These can have local and systemic cytotoxic effects. An immunoloigical response has been suggested, however, metal wear debris may cause direct damage to cellular DNA. Studies have shown that release of these ions is related to bearing diameter and component alignment. However, little is known about the relationship between metal ion levels and implant survivorship. The MHRA has published guidelines on the follow-up of patients with MOM implants including measurement of serum ion levels and cross sectional imaging. Between February 2001 and November 2009, 135 patients (164 hips) had MOM resurfacing arthroplasty at our institution. We report a retrospective analysis of the data generated by review of these patients. Of the 135 patients, 91 were identified for clinical review. Each patient had serum metal ion levels measured, plain AP radiographs of the pelvis examined and, in the presence of raised metal ions, a Metal Artefact Reduction Sequence (MARS) MRI performed. 27 patients (35 hips) had raised metal ion levels (Cobalt and Chromium). Patients with raised metal ion levels had a mean acetabular cup inclination of 52.7 degrees compared with a mean inclination of 48.6 degrees in patients with normal ion levels (p<0.05). MARS MRI in the raised ion group revealed 9 patients with appearances suggestive of ALVAL. A number of these patients had hip revision surgery with the remainder awaiting potential revision. These findings reflect current evidence suggesting a relationship between sub-optimal component position and raised metal ion levels and an increased rate of ALVAL

Objectives. We sought to determine if a durable bilayer implant composed of trabecular metal with autologous periosteum on top would be suitable to reconstitute large osteochondral defects. This design would allow for secure implant fixation, subsequent integration and remodeling. Materials and Methods. Adult sheep were randomly assigned to one of three groups (n = 8/group): 1. trabecular metal/periosteal graft (TMPG), 2. trabecular metal (TM), 3. empty defect (ED). Cartilage and bone healing were assessed macroscopically, biochemically (type II collagen, sulfated glycosaminoglycan (sGAG) and double-stranded DNA (dsDNA) content) and histologically. Results. At 16 weeks post-operatively, histological scores amongst treatment groups were not statistically different (TMPG: overall 12.7, cartilage 8.6, bone 4.1; TM: overall 14.2, cartilage 9.5, bone 4.9; ED: overall 13.6, cartilage 9.1, bone 4.5). Metal scaffolds were incorporated into the surrounding bone, both in TM and TMPG. The sGAG yield was lower in the neo-cartilage regions compared with the articular cartilage (AC) controls (TMPG 20.8/AC 39.5, TM 25.6/AC 33.3, ED 32.2/AC 40.2 µg sGAG/1 mg respectively), with statistical significance being achieved for the TMPG group (p < 0.05). Hypercellularity of the neo-cartilage was found in TM and ED, as the dsDNA content was significantly higher (p < 0.05) compared with contralateral AC controls (TM 126.7/AC 71.1, ED 99.3/AC 62.8 ng dsDNA/1 mg). The highest type II collagen content was found in neo-cartilage after TM compared with TMPG and ED (TM 60%/TMPG 40%/ED 39%). Inter-treatment differences were not significant. Conclusions. TM is a highly suitable material for the reconstitution of osseous defects. TM enables excellent bony ingrowth and fast integration. However, combined with autologous periosteum, such a biocomposite failed to promote satisfactory neo-cartilage formation. Cite this article: E. H. Mrosek, H-W. Chung, J. S. Fitzsimmons, S. W. O’Driscoll, G. G. Reinholz, J. C. Schagemann. Porous tantalum biocomposites for osteochondral defect repair: A follow-up study in a sheep model. Bone Joint J 2016;5:403–411. DOI: 10.1302/2046-3758.59.BJR-2016-0070.R1