There are several component position and design variables that increase the risk of edge loading and high wear in metal-on-metal hip resurfacing (MOM-HR). In this study we combined all of these variables to calculate the ‘contact patch to rim distance’ (CPRD) in patients undergoing revision of their MOM-HR. We then determined whether CPRD was more strongly correlated with component wear and blood metal ion levels, when compared to any other commonly reported clinical variable. This was a retrospective study of 168 consecutively collected MOM-HR retrieval cases. All relevant clinical data was documented, including pre-revision whole blood cobalt and chromium ion levels. Wear of the bearing surfaces was then measured using a roundness-measuring machine. We found four variables to be significantly (p < 0.05) correlated with component wear and blood metal ion levels: (1) cup inclination angle, (2) cup version angle, (3) arc of cover, and (4) CPRD. The correlations between CPRD and both wear and ion levels were significantly stronger than those seen with any other variable (all p < 0.0001). Our study has shown that CPRD is the best predictor of component wear and blood metal ion levels, and may therefore be a useful parameter to help determine those patients who are at risk of high wear and require more frequent clinical surveillance

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

Introduction. Metal-on-metal (MoM) hip resurfacing arthroplasty is a popular choice for young and active patients. However, there are concerns recently regarding soft tissue masses or pseudotumours. The appearance of these complications is thought to be related blood metal ion levels. The level of metal ions in blood is thought to be the result of MoM wear. In the present study the contribution of acetabulum orientation to stress distribution was investigated. Methods. Four subjects with MoM resurfacings and with known blood metal ion levels underwent motion analysis followed by CT scans. The positions of the acetabular (cup) and femoral components were determined the CT data relative to local coordinate systems in the pelvis (PCS) and the femur (FCS). Transformations, calculated from the motion analysis data, between the PCS and FCS gave the position of the cup relative to the femoral component for each frame of captured motion data. Hip reaction forces were taken from published data1. The intersection of hip reaction force with each subject's cup and the increase in inclination required to move the force to the edge of the cup was calculated for 2% intervals during the stance phase of gait. Finite element models representing each subject's cup and femoral components were created and contact stresses were determined for the native cup inclination angle. For each model, the effect of increasing the inclination of the cup, by up to 10°, in 1° increments, was determined. Results and Discussion. The two subjects with high metal ion levels had inclination angles of 60.2° and 53.7° whereas the two with low metal ion levels had inclination angles of 45.6° and 46.5°. The subjects with high metal ion levels required very little increase to their inclination angle to cause the hip reaction force vector to intersect at the edge. The contact stress on the cup increased dramatically when the inclination angle was such that the hip reaction force intersected with the edge. The average increase in contact stress under edge-loading conditions was 57% for the two subjects with high metal ions. In contrast, the subjects with low metal ions exhibited no change in contact stress when the inclination angle of their cups was increased by 10°. The inter-subject variability in the measured hip reaction forces was greater than the amount of increase in cup inclination required to induce edge-loading for the subjects with high metal ion levels. These results suggest that poor positioning of the cup during surgery may result in edge-loading, a greater rate of wear and adverse biological reactions associated with metal ion release

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 aim of this study is to investigate whether MoM implants result in more chromosome aberrations and increased blood metal ions postoperatively whe compared to MoP implants. MoM arthroplasties are being inserted in increasing numbers of younger patients due to the increased durability and reduced requirements for revision in these implants. Recent studies have raised many concerns over possible genotoxicity of MoM implants. This is a prospective study of patients who have undergone elective total hip replacement, they were selected and then randomised into two groups. Group A received a MoP implant and group B received a MoM implant. Patients are reviewed pre-operatively (control group), at 3 months, 6 months, 1 year and 2 years post-operatively. On each occasion blood tests are taken to quantify metal ion levels (chromium, cobalt, titanium, nickel and vanadium) using HR-ICPMS method and chromosome aberrations in T lymphocytes using 24 colour fluorescent in situ hydridisation (FISH). 51 patients have been recruited to date, 23 of whom had MoP prosthesis and 28 a MoM. 47 of these had their 1 year follow-up with blood analysis and 38 have had 2 year follow up. There appeared to be a bedding period for both MoM and MoP groups, with an increase in metal ion release. The blood concentration of chromium, cobalt and titanium rise significantly in the MoM group at the 2 year stage. Chromosome aberrations occurred in both groups. Both the MoM and MoP groups showed increase frequency of aneuploidy aberrations and structural damage. The greatest increase in metal ion levels occurred at the 1 to 2 year interval corresponding to significant rise in chromosome aberrations. Preliminary results of this study show that the levels of chromium, cobalt and titanium are significantly higher in the MoM group compared to the MoP group. This corresponds to increases in chromosome aberrations in the groups with increases in structural chromosome damage after two years

Introduction. Total hip prostheses which use a ceramic head within a metal liner are a relatively recent introduction. As such, survivorship rates from independent centres alongside explant analysis are rare. The early experience with this novel ceramic-on-metal (CoM) bearing couple is reported. Methods and Materials. All CoM hips implanted between 2008 and 2009 at a single hospital by a single surgeon were reviewed. Radiographs were analysed using EBRA software to determine acetabular cup inclination and anteversion angles. Blood metal ion concentrations were measured using inductively coupled plasma mass spectroscopy (ICPMS). Explants were measured for bearing surface and taper wear using a high precision co-ordinate measuring machine. The roughness of the articulating surfaces was measured with a non-contact profilometer. Results. In 54 patients 56 CoM hips were implanted. Mean (range) age was 64 years (34-87). There were 41 females and 15 males. Patients were followed-up for a mean of 1.5 years. Three hips were revised at mean of 1.2 years (2 female, 1 male) with a further 3 listed for revision under 1.5 years giving an overall failure rate of 10.7%. All these patients reported with pain. X-rays of failed devices showed a characteristic pattern of femoral stem loosening. Serum cobalt and chromium were less than 2 micrograms/L. Explant analysis of the three revised hips showed wear at the liner rim in each case. In two of these cases the wear extended completely around the circumference. The wear volumes were 4.1, 2.0 and 2.3mm3 respectively. The ceramic heads were unworn but some transfer of metal could be seen visually. There was no significant wear or deformation at the taper junctions. Typical ceramic head roughness values were 3nm Ra and so most of the surface area of the heads remained in a pristine condition. Discussion. The very high early failure rate using COM is concerning. Explant analysis suggests equatorial contacts with propagation of high frictional forces distally. These forces may have caused early loosening of the femoral stems. Orthopaedic surgeons need to be aware of this new mechanism of failure which is associated with low metal ions

Summary. Particulate wear debris with different chemical composition induced similar periprosthetic tissue reactions in patients with loosened uncemented and cemented titanium hip implants, which suggests that osteolysis can develop independent of particle composition. Introduction. Periprosthetic osteolysis is a serious long-term complication in total hip replacements (THR). Wear debris-induced inflammation is thought to be the main cause for periprosthetic bone loss and implant loosening. The aim of the present study was to compare the tissue reactions and wear debris characteristics in periprosthetic tissues from patients with failed uncemented (UC) and cemented (C) titanium alloy hip prostheses. We hypothesised that implant wear products around two different hip designs induced periprosthetic inflammation leading to osteolysis. Patients & Methods. Thirty THR-patients undergoing revision surgery were included: Fifteen patients had loose cemented titanium stems (Titan. ®. , DePuy) and 15 had well-fixed uncemented titanium stems (Profile, DePuy), but loose or worn uncemented metal-backed cups with conventional UHMWPE liners (Gemini, Tropic and Tri-Lock Plus, DePuy; Harris/Galante and Trilogy, Zimmer). A semi-quantitative histological evaluation was performed in 59 sections of periprosthetic tissues using light microscopy. Wear particles were counted by polarised light and high resolution dark-field microscopy. Additionally, particle composition was determined by SEM-EDXA following particle isolation using an enzymatic digestion method. Blood metal ions were determined with high resolution-ICP-MS. Results. The implants in the uncemented group were revised after a median of 15.7 years (range: 7.25–19.3) due to osteolysis and high wear of the polyethylene liner and metal backing resulting in gross metallosis, and/or cup loosening. The average lifetime of implants in the cemented group was only 6.5 years (range: 1.5–11.75) due to early stem loosening with large osteolysis pockets in the femur close to the cement mantle. Tissue examination revealed similar results for both groups: numerous mononuclear histiocytes and chronic inflammatory cells, a few neutrophils and multinucleated giant cells, and to some extent necrosis. The amount of metal particles per histiocyte positively correlated with the tissue reactions in the cemented, but not in the uncemented group. A higher particle load (medians: C: 14727 vs. UC: 1382 particles/mm. 2. , p<0.0001) was found in tissues adjacent to cemented stems, which contained mainly submicron ZrO. 2. particles. Particles containing pure Ti or Ti alloy elements (size range: 0.21 to 6.46 µm) were most abundant in tissues from the uncemented group. Here, also PE was more frequent, but accounted only for a small portion of total particles (2.8 PE/mm. 2. ). The blood concentrations of titanium (range: 3.8–138.5 microgram/L) and zirconium (cemented cases, range: 0.6–3.5 microgram/L) were highly elevated in cases with high abrasive wear and metallosis. Discussion/Conclusion. Phagocytosis of different wear particles by histiocytes induced a similar chronic inflammatory reaction in the periprosthetic tissues in both groups. ZrO. 2. particles, originating from bone cement degradation, dominated in the cemented group, while in the uncemented group the high abundance of pure Ti and Ti alloy particles of various sizes indicates wear of the metal-backed cups. The low density of polyethylene particles in the tissues suggests that they are not solely responsible for the tissue reactions and accompanying osteolysis. Our findings suggest that the chemical composition of wear particles plays a minor role in the mechanism of osteolysis. Particle size, load and ionic exposure might be more important

Aims

Second-generation metal-on-metal (MoM) articulations in total hip arthroplasty (THA) were introduced in order to reduce wear-related complications. The current study reports on the serum cobalt levels and the clinical outcome at a minimum of 20 years following THA with a MoM (Metasul) or a ceramic-on-polyethylene (CoP) bearing.