Background. Published simulator studies for metal/UHMWPE bearings couples showed that increasing the femoral head diameter by 1 mm increases wear by approximately 10% due to increased contact area. Therefore, there are concerns about increased wear with dual mobility hip bearings. Purpose of the study. The purpose of the study was to compare wear from dual mobility hip bearings to that with traditional fixed bearings. In addition, for the dual mobility bearings, the effect of femoral head material type on the liner wear was also evaluated. Methods. The bearings selected for the study are listed in Table 1. Prior to the start of the test all liners were soaked in lubricant for 48 hours. Hip testing was performed on a Shore Western Orbital Bearing machine in the anatomically oriented position. A simulated gait profile (synchronized at +/-23° biaxial rocking motion) with a minimum/maximum 200/2000N force was applied to the bearings at frequency of 1Hz. The lubricant used for the testing was 25% bovine serum with 0.2 % sodium azide, 20 mMol EDTA and distilled water. The test was interrupted at regular intervals for gravimetric assessment of wear amount. Findings of Study. Figure 1 shows total wear at 3 Mc and wear rates (determined from the slope of the linear regression) for all the groups. At 3 Mc, dual mobility bearings with stainless steel femoral head demonstrated 5% lower wear rate than those articulated against CoCrMo femoral heads. However, there was no statistically significant difference in the observed wear rate due to the femoral head material type. The results from the study also exhibited lower wear and wear rate for dual mobility bearings compared to fixed bearings. Dual mobility bearings with CoCrMo femoral head and stainless steel femoral head demonstrated 17% and 21% lower wear rate when compared to fixed bearings. Although dual mobility bearings possess greater contact area (due to the contact between head-liner and liner-shell compared to only head-liner in fixed bearings), no such increased trend in wear was observed. Conclusions. Dual mobility hip bearings are designed to reduce the risk of dislocation and allow for increased range of motion thus improving joint function and stability. The results from the study demonstrate that dual mobility bearings have comparable wear properties when compared to fixed bearings. For figure/table, please contact authors directly

Expectations for ceramic-on-metal (COM) bearings included (i) optimal lubrication due to smoother ceramic heads (ii), reduction of metal ions due to elimination of CoCr heads, and (iii) ‘differential hardness’ reducing adhesive wear and squeaking (Firkins 2001, Williams 2007). Additional benefits included (iv) use of heads larger than for ceramic-on-ceramic (COC), (v) reduction in taper corrosion and (vi) simulator studies clearly demonstrated metal ions and wear both reduced compared to MOM (Firkins 2001, Williams 2007, Ishida 2007). However, contemporary ‘3rd body wear’ paradigms focused only on metal debris size range 0.025–0.035um (Firkins 2001). Thus, neglected was the effect of hip impingement, provoking release of large metal particles sized 20–200um (Clarke 2013). In this study, we compared COM retrievals using hypotheses that adverse COM cases would demonstrate a combination of (a) steeply inclined cups, (b) liner “edge-loading”, (c) Ti6Al4V contamination on ceramic, and (d) evidence of 3rd-body CoCr wear by large particles. As a case example, this 51-year old female had her metal-polyethylene (MPE) bearing revised to COM in June 2011. She reported no symptoms 1-year post-op, but scans revealed a palpable mass in the inguinal region of left hip. By March 2013 the patient reported mild pain in her hip, which progressed to severe by April 2014. Scans showed a solid and cystic iliopsoas bursitis while cup position had changed from 43o to 73o inclination. Revision was performed in June 2014, her joint tissues were found extensively stained due to metal contamination, and histology described formation of a large pseudotumor. Analysis of retrieved components was by interferometry, SEM and EDS. Detailed maps were made of wear areas in heads and cups and volumetric wear was determined by CMM techniques. This adverse COM example revealed large diametral mismatch (595um) compared to COM controls (75–115um). The ceramic head had a broad polar stripe of CoCr contamination, roughness 0.1–0.3um high. Equatorial ceramic areas showed arrays of thin metal smears that demonstrated elemental Ti and Al. The CoCr liner revealed wear area into cup rim, as “edge loading”, and also featured a focal rim-defect over 18o circumferential arc. Liner scratches were 20um wide and larger, and wear-rate of CoCr liner averaged approximately 50mm3 per year. In contrast, ceramic head had minimal wear. Our study highlights the underappreciated risk of impingement by metallic prosthetic components. Prior studies of ceramic heads showed black metallic smears. With COM we can anticipate that the broad polar smear will be CoCr alloy (wear of liner on head). However, Ti6Al4V smearing on ceramic heads is a notable signpost indicating impingement by the Ti6Al4V acetabular shell. The femoral neck (Ti6Al4V: CoCr), may also be damaged. Release of large metal particles, 1500-times larger than prior predictions, provoke a particularly adverse ‘3rd body wear’ (Halim, 2015). Such cases confirm our four hypotheses, that COM bearings will then fail in a way similar to MOM. In contrast, COC bearings are immune to such impingement and 3rd-body metal damage

Introduction. Previous registry studies of ceramic-on-polyethylene (C-PE) and ceramic-on-ceramic (COC) have focused on revision outcomes following primary surgery. Less is known about the effect of ceramic bearings on infection, dislocation, and mortality as outcomes following primary total hip arthroplasty (THA) for the Medicare population. We asked (1) does the use of C-PE bearings influence outcomes following THA as compared with metal-on-polyethylene (M-PE); and (2) does the use of COC bearings influence outcomes following THA as compared with M-PE?. Methods. A total of 315,784 elderly Medicare patients (65+) who underwent primary THA between 2005 and 2014 with known bearing types were identified from the Medicare 100% inpatient sample administrative database. Outcomes of interest included relative risk of 90-day readmission, infection, dislocation, revision, or mortality at any time point after primary surgery. Propensity scores were developed to adjust for selection bias in the choice of bearing type at index primary surgery. Cox regression incorporating propensity score stratification (10 levels) was then used to evaluate the impact of bearing surface selection on outcomes, after adjusting for patient-, hospital-, and surgeon-related factors. Results. For primary THA patients treated with C-PE bearings and COC bearings, there was significantly reduced risk of infection relative to M-PE bearings (C-PE Hazard Ratio, HR: 0.86, p=0.001; COC Hazard Ratio, HR: 0.74, p=0.01). For the C-PE cohort, we also observed reduced risk of 90-day readmission (HR: 0.94, p<0.001); dislocation (HR: 0.81, p<0.001); and mortality (HR: 0.92, p<0.001). There was no significant difference in risk of revision for either the C-PE or COC bearing cohorts when compared with M-PE. For the COC cohort, there was no significant difference in readmission, dislocation, or mortality risk. Conclusions. The results indicate that, after adjusting for selection bias and various confounding patient-, surgeon-, and hospital-related factors, Medicare patients treated with primary THA with ceramic bearings exhibit lower risk of infection than those treated with M-PE bearings. In addition, C-PE bearings were associated with lower risk of dislocation and mortality. As in previous registry studies, we found that ceramic bearings have similar revision risk as M-PE bearings in primary THA at between 8 and 9 years of follow-up. The findings of this study support further research into the long-term association between ceramic bearings in primary THA and clinical outcomes

Introduction and Aims. There are many surgical, implant design and patient factors that should be considered in preclinical testing of hip replacement which are not being considered in current standards. The aim of this study was to develop a preclinical testing method that consider surgical positioning, implant design and patient factors and predict the occurrence and severity of edge loading under the combination of such conditions. Then, assess the safety and reliability of the implant by predicting the wear, deformation and damage of the implant bearings under worst case conditions. Methods. Ceramic-on-ceramic (CoC, 36mm, BIOLOX. ®. delta, Pinnacle. ®. , DePuy Synthes, UK) and metal-on polyethylene (MoP, 36mm, Marathon®, Pinnacle. ®. , DePuy Synthes, UK) bearings were used for this study on multi-station multi-axis hip joint simulators. Two factors were varied, cup inclination angles (45° and 65°) and translational mismatch between the femoral head and acetabular cup (0, 2, 3 and 4 (mm)). Under each condition for both CoC and MoP bearings, three million cycles of gait cycle testing were completed with wear, deformation and/or damage measurements completed at one million cycle intervals. Other outputs of the study were the level of dynamic separation between the femoral head and acetabular cup during gait, the maximum force at the rim during edge loading when the head was sliding back to the cup confinement. Means and 95% confidence limits were determined and statistical analysis were done using one way ANOVA with significance taken at p<0.05. Results. As the level of mismatch and the cup inclination angle increased, the magnitude of dynamic separation and the force at the rim increased. The level of dynamic separation and the force on the rim correlated with the wear of CoC bearings (R= 0.96). For polyethylene, steeper inclination angle did not significantly increase the wear (p>0.05) however, edge loading under 4mm translational mismatch and steep cup inclination angle did (p<0.01). The combined wear and deformation of the polyethylene liners at the rim increased under larger levels of dynamic separation. Conclusions. The magnitude of dynamic separation and force at the rim were predictive of the severity of edge loading. These parameters can be measured using short term testing (500 cycles). This will determine the effect of variations in surgical positioning, implant design and patient factors on the occurrence and severity of edge loading. Then, the wear, deformation and/or damage on hip replacement bearings can be determined using longer term simulator testing under selected conditions. The short term tests do not only help identify worst case scenarios but may identify the boundary of surgical position under which the implants performance may be considered acceptable. A new approach for preclinical testing of hip replacement was developed:. Stage 1: Short biomechanical tests. : assess the occurrence and severity of edge loading conditions where the outputs are:. Magnitude of medial-lateral dynamic separation. Maximum force under edge loading. Stage 2: Wear assessment. : assess the tribological performance of hip replacement under selected conditions where the outputs are:. Wear rates. Deformation and/or damage on the bearing surface

Introduction. Previous studies of ceramic-on-polyethylene (C-PE) and ceramic-on-ceramic (COC) hip bearings have focused on outcomes following primary surgery. Less is known about the utilization or outcomes of ceramic bearings in revision total hip arthroplasty (R-THA) for the Medicare population in the US. We asked (1) what is the utilization of ceramic bearings for R-THA in the Medicare population and how has it evolved over time; (2) does the use of C-PE bearings influence outcomes following R-THA as compared with metal-on-polyethylene (M-PE); and (3) does the use of COC bearings influence outcomes following R-THA as compared with M-PE?. Methods. A total of 31,809 Medicare patients (aged > 65y) who underwent R-THA between 2005 and 2013 with known bearing types were identified from the Medicare 100% inpatient sample administrative database. Outcomes of interest included relative risk of readmission (90 days) or infection, dislocation, rerevision, or mortality at any time point after revision. Propensity scores were developed to adjust for selection bias in the choice of bearing type at revision surgery. Cox regression incorporating propensity score stratification (10 levels) was then used to evaluate the impact of bearing surface selection on outcomes, after adjusting for patient-, hospital-, and surgeon-related factors. Results. The utilization of C-PE and COC bearings in RHA increased from 5.3% to 26.6% and from 1.8% to 2.5% between 2005 and 2013, respectively. For R-THA patients treated with C-PE bearings, there was reduced risk of 90-day readmission (Hazard Ratio, HR: 0.90, 95% CI: 0.84–0.96, p=0.007). We also observed a trend for reduced risk of infection with C-PE (HR: 0.88, 95% CI: 0.74–1.04) that did not reach statistical significance (p = 0.14). For R-THA patients treated with COC, there was reduced risk of dislocation (Hazard Ratio, HR: 0.76, 95% CI: 0.58–0.99, p=0.04). There was no significant difference in risk of rerevision or mortality for either the C-PE or COC bearing cohorts when compared with M-PE. Discussion. The results indicate that, after adjusting for selection bias and various confounding patient-, surgeon-, and hospital-related factors, Medicare patients treated in a revision scenario with ceramic bearings exhibit similar risk of rerevision, infection, or mortality as those treated with M-PE bearings. Conversely, we found an association between the use of specific ceramic bearings in R-THA and reduced risk of readmission (C-PE) and dislocation (COC). The findings of this study support further research into the association between ceramic bearings in R-THA and lower risk of hospital readmission, dislocation, and, potentially, infection

Introduction. Looking for optimal solutions to wear risks evident in total hip arthroplasty (THA), silicon nitride ceramic bearings (Si. 3. N. 4. ) are noted for demanding high-temperature applications such as diesel engines and aerospace bearings. As high-strength ceramic for orthopedic applications, Si. 3. N. 4. offers improved fracture toughness and fracture strength over contemporary aluminas (Al. 2. O. 3. ). Our pilot studies of Si. 3. N. 4. in 28mm diameter THA showed promising results at ISTA meeting of 2007. 1. In this simulator study, we compared the wear resistance of 40mm to 28mm diameter Si. 3. N. 4. bearings. The 28mm and 40mm bearings (Fig. 1) were fabricated from Si. 3. N. 4. powder (Amedica Inc, Salt Lake City, UT). 1. Wear tests run were run at 3kN peak load in an orbital hip simulator (SWM, Monrovia, CA) and. The lubricant was standard bovine serum (Hyclone: diluted to 17 mg/ml protein concentration). Wear was measured by gravimetric method and wear-rates calculated by linear regression. SEM and interferometic microscopic was performed at 3.5-million cycles (3.5Mc) to 12Mc. The simulator was run to 3.5Mc duration with no consistent weight-loss trends. The bearings could show either small positive or negative weight fluctuations in an unpredictable manner (Fig. 2). Surface analysis showed protein layers up to 3μm thick, furrowed due to abrasion by small particles (Fig. 3). The low ceramic wear was camouflaged by protein contaminants alternatively forming and shedding. From 3.5 to 12.8Mc duration we experimented with various detergents and wash-procedures, all to no avail. Protein coatings were also more prevalent on 44 mm heads, likely due to frictional heating by the larger diameter effect. Selected heads were washed with a mild acid solution - the cumulative effect appeared to be removal of some protein layers, but not in a predictable manner. The Si. 3. N. 4. ceramic is used in demanding industrial applications and it is therefore unfortunate that we are yet not able to quantify the actual wear performance of Si. 3. N. 4. / Si. 3. N. 4. bearings (COC). The contaminating protein layers combined with low-wearing silicon nitride obscured the actual wear data. This has also been a problem in prior studies with alumina and zirconia bearings. Considerable challenges still stand in the way of the optimal biomaterials choices that will result in reduced risk of failure while providing extended lifetimes. Thus important issues remain unsolved and call for innovative solutions. Searching for a more effective ‘wear-measurement’ remedy, we noted that abrasive slurries of bone cement (PMMA) used in contemporary simulator studies were effective in promoting adverse wear in polyethylene bearings. These investigations also revealed that PMMA debris did not damage CoCr heads. 2,3. , alumina heads. 4,5. or diffusion-hardened zirconia heads (ZrDH). 6. We can therefore speculate at this ISTA meeting of 2014 that future ceramic wear tests should incorporate PMMA slurries. Here a new hypothesis can be formulated, that PMMA particulates will provide a continual and beneficial removal of contaminating proteins from the ceramic surfaces (see Fig. 3) and thereby aid definition of low-wearing COC bearings such as Si. 3. N. 4. . The application of non-oxide ceramics such as silicon nitride presented here may become a viable alternative for THA designs of next decade

Introduction. Are there really ‘conventional’ bearings, offering more security and less risk than the ‘alternative’ bearings that feature in the programme?. Alternative, when used as an adjective has 2 meanings:. offering or expressing a choice, as in several alternative plans. different from or functioning outside the usual or conventional:. eg alternative newspaper, alternative rock music, alternative medicine. This paper reviews the elements that make up the bearing couples available today in the developed world, and tests each bearing against these meanings. Materials. what are the alternatives?. The materials available today fall into the following broad families:. Metals. Stainless Steel and Cobalt-Chromium Alloy, are the dominant metals available. There is no variation in the Steel, but the characterisation of the Co-Cr does vary. Several manufacturers use different carbide content for the femoral and acetabular components, and different processes. One has been withdrawn from the market, and others may be at risk of this, although it is not the material itself that seems to be the main issue. Ceramics include alumina and zirconia ceramics. Alumina has been available unchanged for over 40 years, although delta ceramic (a zirconia toughened alumina) has only been available unchanged since 2001, making in available for 10 years. Polymers. a huge range of polyethylenes are now available, with different individual claims. All claim superior wear resistance, and oxidation resistance. More than 20 unique products are available in the EU, each with a proprietary formula giving individual characteristics. Coatings and surface treatments. these are now available today from many companies, who either ceramicise the surface of cobalt chrome or titanium with titanium nitride, or use oxinium (a proprietary product from a single company). Bearing couples. what are the alternatives Symmetric and Asymmetric bearings are currently offered. Symmetric bearings are available for Ceramic on Ceramic and Metal on Metal bearings only. Asymmetric bearings are available with metals, including metal on poly, and metal on peek. Ceramics can couple with metal or polymers. Bearing Sizes. Larger than 32mm should be considered ‘alternative’. The larger metal bearings have seen the start of crevice corrosion at the taper between titanium and Co-Cr, and even between different Co-Cr alloys. This new class of complication seems to be unique to metal femoral heads. Bearing-stem compatibility. Larger metal on metal head bearings have brought an entirely new world of complications. The choices of trunion are mainly twofold: the 12/14 tapers which differ significantly between products, and the V40 taper still used by one manufacturer. Neither was designed for use with a larger diameter head. Conclusions. The use of the word ‘alternative’ implies a ‘standard’ or conventional bearing. Ceramic bearings have changed least, have been immune from the metallosis and crevice corrosion seen with large ball Metal head whether bearing on metal or polyethylene. They also have reassuring long term results. In 2011 they should be considered the standard bearing for the young and active patient. The large diameter metal on highly cross-linked poly bearings should now be considered ‘alternative’

Introduction. Dislocation is one of the major factors for revision surgery. Current literature states that the usage of larger bearing couples (> 36 mm) have the potential of reducing the risk of dislocation. Smaller ceramic-on-ceramic bearing couples (< 36 mm) have demonstrated very low wear rates. But does the wear behaviour change with increasing diameter? Therefore, the aim of this study was to compare wear rates of larger ceramic-on-ceramic bearing couples for total hip arthroplasty. Materials and Methods. Wear tests according to ISO 14242 with 36, 40 and 44 mm zirconia platelet toughened alumina (ZPTA) bearings were performed in a servo-hydraulic hip simulator. In total, the specimens were loaded up to 5 million cycles. Wear was measured gravimetrically every million cycles. For each diameter three different combinations regarding clearance and roundness were chosen. One combination represented in tolerance parts (70 μm clearance, < 5 μm roundness). The other two combinations represented parts at the lower end and at twice the upper end of the tolerance band regarding clearance and out of specification parts regarding the roundness. Results. In general, ball heads showed higher wear than liners. 44 mm bearings showed highest and 36 mm bearings showed lowest run-in wear rates (Table 1). Except for the 36 mm bearing negligible influence on wear rates caused by the different clearance and roundness was found. The highest linear wear rate was found for the 36 mm bearing having a clearance of 20 μm and a roundness of 15 μm. The smallest linear wear rate was also found for the 36 mm bearing. Here, in tolerance parts were tested. Discussion and Conclusion. Generally, the current study shows extremely low wear rates for ZPTA/ZPTA even for larger diameter bearings. Except for the 36 mm bearing different machining tolerances in the investigated range seem to have only minor effects on the wear rates of larger diameter bearings under ISO 14242 test conditions. The wear rates determined in the current study might be lower in reality due to metal transfer from the tapers and the cups to the ball heads and liners occurring while assembling and disassembling procedures throughout testing. Larger diameter bearings increase range of motion, stability and reduce the risk of impingement. Thus, larger diameter ZPTA bearings have the potential to minimize the dislocation risk while at the same time having maintained the extremely low wear rates of small diameter ceramic articulations

Introduction and Aims. The 21. st. Century has seen ceramic bearings become an increasingly popular choice in total hip arthroplasty due to their high wear resistance and inert wear debris without osteolysis promising a long term bearing solution. Early ceramic bearings were hindered by fracture but improved manufacturing processes and materials subsequently produced stronger ceramics. These third generation ceramics showed greatly reduced fracture rates but there is limited evidence in the literature reporting their long term survival and wear characteristics. The purpose of this study was to determine osteolysis and survival rates of Alumina ceramic bearings in cementless total hip arthroplasties with a minimum follow-up of 15 years. Methods. We analyzed a series of 301 third-generation alumina-on-alumina cementless primary total hip replacements in 283 patients. The average age of the patients at the time of the arthroplasty was fifty-eight years, 51% were in women and 54% were right sided. All procedures were performed using the same surgical technique and the same implant at a single centre. Patients were followed up at six weeks, one, two, five, ten and 15 years. At 15 years postoperatively 46 patients (17%) had died of unrelated causes and 31 (10.2%) were lost to follow-up. Patients were assessed clinically and radiographically. Retrieved bearings were analyzed for wear. Results. At the time of the latest follow-up the mean Harris Hip Score was 94 points and 97% of the patients scored an excellent or good result with less than 4% having moderate residual pain. Radiographically, all patients assessed had evidence of stable bony ingrowth. Minor osteolysis was seen adjacent to 4% of cups and in none of the stems. There were eleven revisions in all, four stem revisions due to periprosthetic fracture, one secondary to aseptic loosening and one to facilitate a femoral shortening osteotomy. One cup was revised for aseptic loosening and one cup was revised for soft tissue impingement. One cup underwent revision due to acetabular osteolysis due to metallosis with some ceramic wear caused by neck impingement. There were two revisions for ceramic fracture, one liner and one femoral head. Overall, the survival rate of the implants for any cause revision was 96% at 15 years, with. The rate of survival of both components, with revision because of aseptic loosening or osteolysis as the end point, was 99% at 15 years. Analysis of retrieved femoral heads identified a median wear rate of 0.2mm3/year. Conclusion. Ceramic bearings were designed to overcome the problem of osteolysis due to wear from polyethylene bearings. This study has shown that Alumina bearings in cementless primary total hip arthroplasty have an excellent survival rate at 15 years with good function, low wear rate and no adverse radiographic changes typical of osteolysis. The fracture rate was low in our study. These findings strongly supporting the use of Ceramic as a bearing choice for the 21. st. Century

Due to issues related to osteolysis which became increasingly evident in the 1990's, approaches to combat wear focused upon either improving ultra-high molecular grade polyethylene or to abandon it and employ alternative bearings: metal upon metal or ceramic upon ceramic (COC). Ceramics have played a role in hip bearings for decades with much of the experience coming from Europe. While there is consistent evidence of low wear rates in this bearing couple due to its surface hardness, wettability and resultant low friction, problems unique to this bearing couple were noted: a small but real incidence of fracture, surface damage due to metal transfer and stripe wear as well as the unique issue of squeaking. What we have learned is that these hard bearings (either COC or Metal on Metal) despite being able to use larger diameter heads, are exquisitely sensitive to component position and orientation. With the tremendous improvements in 2nd and now 3rd generation crosslinked polyethylenes demonstrating vastly reduced wear rates and having none of the issues of fracture, stripe wear, or squeaking, it remains unclear what role ceramic bearings have in modern use. Until the aforementioned issues are resolved, ceramic on ceramic bearings in the young patient should be used with caution. Ceramic-on-ceramic total hip arthroplasty: incidence of instability and noise

Purpose. Metal-on-Metal (MoM) hip bearings are being implanted in ever-increasing numbers and into ever-younger patients. The consequence of chronic exposure to metal ions is a cause for concern. Therefore, using cytogenetic biomarkers, we investigated a group of patients who have had MoM bearings in situ for in excess of 30 years. Method. Whole blood specimens were obtained from an historical group of patients who have had MoM bearings in situ for in excess of 30 years. Blood was also obtained from an age and sex matched control group and from patients with Metal-on-Polyethylene (MoP) components of the same era. The whole blood was cultured with Pb-Max karyotyping medium and harvested for cytogenetics after 72 hrs. The 24 colour FISH (Fluorescent In Situ Hybridisation) chromosome painting technique was performed on the freshly prepared slides, allowing chromosomal mapping. Each slide was evaluated for chromosomal aberrations (deletions, fragments and translocations) against the normal 46 (22 pairs and two sex) chromosomes. At least 20 metaphases per sample were scored and the number of aberrations per cell calculated. Results. Chromosomal aberrations, including deletions, fragments and translocations were only detected in the peripheral blood lymphocytes isolated from the group that had MoM bearings. These changes were not present in the age and sex matched control group. The chromosomal aberrations were also detected in the patients previously exposed to MoM bearings who have been revised to a MoP articulation. Conclusion. We have detected dramatic chromosomal aberrations in peripheral blood lymphocytes in a group of patients chronically exposed (over 30 years) to elevated metal ions. It is not known whether these aberrations have clinical consequences or whether they are reproduced in other cells in the body. The results emphasise the need for further investigations into the effect of chronic exposure to elevated metal ions produced by orthopaedic implants

Purpose. There are concerns of soft-tissue reactions such as metal hypersensitivity or pseudotumors for metal-on-metal (MoM) bearings in hip arthroplasty, however, such reactions around ceramic or polyethylene bearings are incompletely understood. The present study was conducted to examine the capabilities of ultrasound screening and to compare the prevalence of periarticular soft-tissue lesions among various types of bearings. Methods. Ultrasound examinations were conducted in 163 hips (153 patients) with arthroplasty after mean a follow-up of 8.1 years (range, 1–22 years). This included 39 MoM hip resurfacings (M-HR) including 30 Birmingham hip resurfacings (BHR) and 9 ADEPT resurfacings; 36 MoM total hip arthroplasties (M-THA) with a large femoral head including 26 BHR and 10 ADEPT bearings; 21 ceramic-on-ceramic THAs (C-THA) of Biolox forte alumina bearings; 24 THAs with a conventional polyethylene liner (cPE-THA) including 19 Lubeck and 5 Omnifit systems; and 43 THAs with a highly cross-linked polyethylene liner (hxPE-THA) including 28 Crossfire and 15 Longevity liners. All procedures were performed in the lateral position through the posterior approach without trochanteric osteotomy. The M-HR group had a significantly higher frequency of male patients than the C-THA, cPE-THA, and hxPE-THA groups, and the patients in the M-HR group were younger than those in the other four groups. Ultrasound images were acquired as a still picture and in video format as the hip moved in flexion and rotation, and 4 qualitative classifications for periarticular soft-tissue reactions were determined as normal pattern, joint-expansion pattern (marked hypoechoic space between the anterior capsule and the anterior surface of the femoral component), cystic pattern (irregularly shaped hypoechoic lesions), and mass pattern (a large mass extending anterior to the femoral component). Magnetic resonance imaging (MRI) was subsequently performed in 45 hips with high-frequency encoding bandwidths. For the reliability of ultrasound screening, positive predictive value, negative predictive value, and the accuracy of the presence of abnormal patterns on ultrasound were calculated using the abnormal lesions on MRI as a reference. Results. Among the 45 hips that underwent MRI, periarticular abnormal lesions were detected in 26 hips (58%). Using MRI findings as reference, positive predictive value, negative predictive value, and the accuracy of ultrasound examination for the detection of soft-tissue lesions were 83%, 71%, and 78%, respectively. Abnormal ultrasound lesions with joint expansion, cystic, or mass patterns were most frequently observed in the cPE-THA group (50%), followed by the M-THA (25%), hxPE-THA (23%), M-HR (18%), and C-THA groups (14%). Compared to the hxPE-THA group, the frequency of abnormal patterns did not differ significantly in the two MoM groups. A mass pattern was detected in 3 hips of the M-THA group and 1 hip of the C-THA group (Figure 1). Abnormal ultrasound lesions were significantly associated with the presence of symptoms. Conclusion: Various soft-tissue reactions could be observed other than those for MoM bearings, and pseudotumors may not be a specific feature of MoM bearings. Ultrasound examination may be a suitable screening tool for further large prospective investigations of soft-tissue reactions around various types of bearings

Purpose. The fourth generation ceramic, in which zirconia is incorporated into the alumina matrix, was developed to reduce the risk of ceramic fractures. The purpose of this study was to evaluate the survivorship, clinical and radiographic results, and bearing-related failures associated with total hip arthroplasty using zirconia-toughened alumina ceramic-on-ceramic bearings over a minimum follow-up of 5 years. Materials and methods. We retrospectively analysed 135 patients (151 hips) who underwent cementless total hip arthroplasty using zirconia-toughened alumina ceramic-on-ceramic bearings. There were 58 men and 77 women with mean age of 55.9 years (range, 20 to 82 years) at index surgery. Acetabular and femoral components were cementless in all hips. A 36 mm head was used in 81 of 151 hips and a 32 mm head was used in 70 hips with smaller acetabular shells. The mean duration of follow-up was 6.1 years (range, 5 to 6.8 years). Results. Kaplan-Meier survival analysis with an end point of revision for any reason was 100% at 6.8 years. All acetabular and femoral components showed bony ingrowth. No radiographic evidence of osteolysis was identified. No ceramic fracture occurred. There were 4 (2.6%) noisy hips (1 squeaking and 3 clickings), but no patient could reproduce the noise and required revision. Other complications included one iliopsoas tendonitis and one dislocation. Conclusions. The minimum 5-year results of total hip arthroplasties performed using 32 mm or 36 mm zirconia-toughened alumina ceramic-on-ceramic bearings were encouraging with excellent survivorship. However, it was also found that the risk of noise development remains even for the newest generation of ceramics

Dislocation and instability remain leading cause of failure following THA. We present a single-surgeon 10-year experience with use of Dual Mobility (DM) bearings in Primary and Revision THA using posterior approach. 127 DM bearings were implanted between September 2006 – September 2016; 102 in high-risk primary THA's and 25 revision THA's for either treatment or prevention of instability. Selection for DM bearing followed individual patient risk assessment. Criteria for use of DM bearing were presence of multiple risk factors. Mean age was 72.9 years. 100 Mono-block DM implants, 22 Modular DM implants and 5 custom-made DM devices were implanted. Revision cohort included those used in conjunction with a cage or porous metal augments. 2 dislocations (1.6%) were observed, both in the Revision group, 1 was recurrent requiring revision to constrained liner. Primary group had 2 revisions; 1 peri-prosthetic fracture and 1 deep infection. No DM bearing specific complications were observed. A constructed life table calculated survival function with endpoint set as revision for any reason demonstrated a cumulative survival of 94% at 7.4 years. In high-risk patients, DM bearings are successful at preventing and treating dislocation in THA. Primary cohort in this study all had multiple risk factors for instability but no dislocations or bearing specific complications were observed. Dislocations observed in Revision group were associated with major soft tissue deficiency. This study adds to the promising results already reported with DM THA articulations and should be considered for patients at risk of dislocation or instability. Runner Up – Best Paper Award

Introduction and Aims. Clinically many factors such as variations in surgical positioning, and patients' anatomy and biomechanics can affect the occurrence and severity of edge loading which may have detrimental effect on the wear and durability of the implant. Assessing wear of hundreds of combinations of conditions would be impractical, so a preclinical testing approach was followed where the occurrence and severity of edge loading can be determined using short biomechanical tests. Then, selected conditions can be chosen under which the wear can be determined. If a wear correlation with the magnitude of dynamic separation or the severity of edge loading can be shown, then an informed decision can be made based upon the biomechanical results to only select important variables under which the tribological performance of the implant can be assessed. The aim of this study was to determine the relationship between the wear of ceramic-on-ceramic bearings and the (1) magnitude of dynamic separation, (2) the maximum force reached during edge loading and (3) the severity of edge loading resulting from component translational mismatch between the head and cup centres. Methods. The Leeds II hip joint simulator with a standard walking cycle and 36mm diameter ceramic-on-ceramic bearings (BIOLOX. ®. delta, DePuy Synthes Joint Reconstruction, Leeds, UK.) were used. The study was in two parts. Part one: a biomechanical study where the dynamic separation, the maximum load during edge loading, and the duration of edge loading alongside the magnitude of forces under edge loading (severity of edge loading) were assessed. Part two; a wear study where the wear rates of the bearing surfaces were assessed under a series of input conditions. These input testing conditions included inclining the acetabular cups at 45° and 65° cup inclination angle (in-vivo equivalent), with 2, 3, and 4mm medial-lateral component mismatch between the centres of the head and the cup. This equated to six conditions being assessed, each with three repeats for the biomechanical test, and six repeats completed for the wear study. The severity of edge loading was assessed as described in Equation 1. Severity of Edge Loading = ∫. t. t0. F(x) dx + ∫. t. t0. F(y) dy … Equation 1,. where F(x) is the axial load, F(y) is the medial-lateral load and t-t0 is the duration of edge loading. The wear of the ceramic bearings were determined using gravimetric analysis (XP205, Mettler Toledo, UK). Results. The wear rates of ceramic-on-ceramic bearings increased as the magnitude of dynamic separation (Figure 1), the maximum load at the rim during edge loading (Figure 2), and the severity of edge loading (Figure 3) increased. The magnitude of dynamic separation was found to have the highest correlation to the wear rate under the conditions tested in this study (R. 2. =0.94). Conclusions. A preclinical testing approach has been developed to understand the occurrence and severity of edge loading associated with variation of component positioning. A good correlation was found between the wear rates obtained for ceramic-on-ceramic bearings and the magnitude of parameters obtained under edge loading during a short-term biomechanical study. For figures/tables, please contact authors directly.

Hip simulator studies on MOM bearings have historically involved ‘custom’ cetabular cups. I.e. having neither beaded layers nor biological coatings. The aim of this study was to investigate wear using such MOM bearings and evaluate the potential wear and evaluate the potential for error in the gravimetric assessment. Six x 38 mm HC Co-Cr bearings were supplied (Global and IO International Orthopaedics). The cups were received in ‘off-the-shelf’ condition with a cast Co-Cr beaded/HA-coated backing. To remove the HA-coating, the cups were pre-soaked in lemon juice for 4 days (articular surfaces shielded). Custom plastic fixtures were machined to fit the beaded contours of the cups. Test duration was 5Mc inorbital hip simulator (Shore-Western). MOM wear was estimated from serum ion contamination. Serum samples were digested and assessed using ICP/MS (Weck Labs Inc, CA). The majority of the HA-coating was removed from the cups after four days of soaking inlemon juice after 21 days of soaking all cup weights appeared atable (within 1 mg). Reflected-light microscopy (RLM) showed no descernible signs of HA and the total weight loss due to HA remval averaged∼400mg. During hip simulator there was no visual evidence of lost or broken beads, 3rd body abrasion etc (Sa<30nm). Both gravimetric and metal ion analysis showed consistent wear trends for all MOM cups. The MOM with the highest wear (predicted by ion analysis) demonstrated 1.2 mm (3)/Mc)OWR) at 5Mc. In comparsion, gravimetric analysis predicted an OWR of 1.3 mm (3)Mc for the same MOM, a difference of only 8%. Soaking beaded-HA cups in lemon juice and BCS proved effective in removing the coating. The beaded cups remained stable in weight during the wear study and caused little discrepancy in gravimetric analysis (8%). The method described did not lead to breaking of beads, elevated 3rd-body abrasion, cup damage or distorted wear scars

Introduction. Hip simulators proved to be valuable, pre-clinical tests for assessing wear. Preferred implant positioning has been with cup mounted above head, i.e. ‘Anatomical’ (Figs. 1a-c) . 1,2. while the ‘Inverted’ test (cup below head) was typically preferred in debris studies (Figs. 1d-f). 3,4. In an Anatomical study, wear patterns on cups and heads averaged 442 and 1668 mm² area, respectively, representing 8% and 30% of available hemi-surface (Table 1), i.e. the head pattern was ×3.8 times larger than cup. This concept of wear patterns is illustrated well in the ‘pin-on-disk’ test (Fig. 1) in which the oscillating pin has the ‘contained’ wear area (CWP) and the large wear track on the disk is the ‘distributed’ pattern (DWP). Hip simulators also create CWP and DWP patterns, site dependant on whether Anatomical (Fig. 1a-c) or ‘Inverted’ (Fig. 1d-f) test. However there is scant foundation as to clinical merits of either test mode. Retrieval studies of MOM bearings have indicated that cups have the larger wear patterns, i.e. contrary to simulator tests running Anatomical cups (Table 1). 5. Therefore we compared Anatomical and Inverted cup modes using 38mm and 40mm MOM in two 5-million cycle simulator studies. Methods. 38mm and 40mm MOM bearings were run in Anatomical mode (study-1) and Inverted (study-2) mode, respectively, in a hip simulator. Lubricant was bovine serum diluted to provide protein concentration 17 mg/ml. Wear was measured gravimetrically and wear-rates calculated by linear regression. Wear patterns were assessed by stereomicroscopy and compared to algorithms using standard spherical equations. Results. MOM wear-rates ranged 0.3 to 6 mm³/Mc by 5-million cycles duration. Contained wear patterns (CWP) averaged 410 mm² for cups in study-1 (Anatomical) and 397 mm² for heads in study-2 (Fig. 3: Inverted). Distributed wear patterns (DWP) averaged 945mm² in study-1 (heads, Anatomical) and 846mm² in study-2 (cups, Inverted). Cup Hemi-ratios averaged 18% and 38% in studies 1 and 2 respectively (Table 2). Discussion. While vendor, implant and experimental differences were clearly present, study-1 (Anatomical) and study-2 (Inverted) produced almost identical CWP and DWP wear patterns, only reversed on heads versus cups. This unequivocal evidence demonstrated that there was no difference in wear mechanics for spherical CoCr bearings run in either test mode. In addition, wear patterns observed in MOM cup retrievals. 5. (1000–2700 mm²) were much larger than produced in Anatomical simulator tests (Fig. 2h: 400–500 mm²). Such large discrepancies in cup wear patterns between Anatomical simulator tests and retrieved MOM cups indicated that the Inverted cup mode (Fig. 2g) may be more clinically relevant

Metal Bearings in Hip Arthroplasty – What Have We Learned?. Large metal on metal bearings have come back to hip arthroplasty the past five to ten years with great promise to minimize wear debris, eliminate osteolysis, reduce dislocations and improve range of motion. While some of these claims have proven to be true, new problems have surfaced that threaten the success of these devices. Metalosis, “pseudotumours” and ALVAL (aseptic lymphocytic vasculitis associated lesions) are appearing. These lesions produce pain that is difficult to confirm on routine exam and xray but eventually lead to early revision surgery. This paper will examine the advantages and complications of this hard bearing surface with a special look at complications, their prevention and management

INTRODUCTION. Ceramic-on-ceramic hip replacements have generated great interest in recent years due to substantial improvements in manufacturing techniques and material properties. 1. Microseparation conditions that could occur due to several clinical factors such as head offset deficiency, medialised cup combined with laxity of soft tissue resulting in a translation malalignment, have been shown to cause edge loading, replicate clinically relevant wear mechanisms. 2,3. and increase the wear of ceramic-on-ceramic bearings. 3,4. The aim of this study was to investigate the influence of increasing the femoral head size on the wear of ceramic-on-ceramic bearings under several clinically relevant simulator conditions. MATERIALS AND METHODS. The wear of size 28mm and 36mm ceramic-on-ceramic bearings (BIOLOX® Delta, CeramTec, Germany) was determined under different in vitro conditions using the Leeds II hip simulator. For each size bearing, two clinical cup inclination angles were considered, 55° (n=3) and 65° (n=3) for the 28mm bearing and 45° (n=3) and 65° (n=3) for the 36mm bearing. The first two (28mm study) or three (36mm study) million cycles ran under standard gait conditions and a subsequent three million cycles ran under microseparation conditions. A standard gait cycle included a twin peak load (300N–3000N), extension/flexion (−15°/+30°) and internal/external rotation (±10°). Microseparation. 3. was achieved by applying a 0.4–0.5mm medial displacement to the cup relative to the head during the swing phase of the standard gait cycle resulting in edge loading at heel strike. The lubricant was 25% (v/v) new-born calf serum which was changed approximately every 333,000 cycles. The wear volume was ascertained through gravimetric analysis every million cycles. One way ANOVA was performed (significance: p<0.05), and 95% confidence limits were calculated. RESULTS AND DISCUSSION. The mean wear rate under standard gait conditions was 0.05mm. 3. / million cycles for the 28mm bearings and significantly lower (p=0.003) for the 36mm bearings (Figure 1) which could be due to improved lubrication regime. The wear of ceramic-on-ceramic bearings was not influenced by the increase in cup inclination angle for either bearing size (Figure 1). The introduction of microseparation into the gait cycle resulted in stripe wear on the femoral head with a corresponding wear area at the rim of the acetabular cup and significantly higher wear rates of the ceramic-on-ceramic bearings (Figure 2). The wear rate of BIOLOX® Delta bearings under microseparation conditions was still low (<0.25mm. 3. /million cycles) compared to the third generation alumina ceramic-on-ceramic bearings (1.84mm. 3. /million cycles). 4. under the same adverse conditions. Under microseparation conditions, the wear rate of size 36mm bearings was significantly higher (p=0.004) than that for size 28mm bearings. This was thought to be due to the larger contact area for the larger bearings and deprived lubrication under edge loading conditions. For both bearing sizes, the combination of both steep cup inclination angles and microseparation conditions did not increase the wear rates any further compared to microseparation conditions alone (Figure 3). This study shows the importance of surgical positioning of the femoral head and acetabular cup and the importance of testing new bearing materials and designs using these adverse simulator methods. ACKNOWLEDGEMENT. This study was supported by the Furlong Research Charitable Foundation (FRCF) and the National Institute of Health Research (NIHR) as part of a collaboration with the Leeds Musculoskeletal Biomedical Research Unit (LMBRU)

Metal ion levels are used to track the performance of metal containing bearings in hip replacement patients. Changes in whole blood metal ion levels are indicators of wear rates in these bearings. Normal metal ion levels are variable, and range widely. Changes in these “non-bearing” levels over a period of time may influence the monitoring of these bearings. Methods. As part of a prospective randomised trial of different bearing surfaces, whole blood metal ion levels were monitored. This included four cohorts of patients, namely ceramic-on-ceramic (CoC), ceramic-on-polyethylene (CoP), ceramic-on-ceramic (CoC) and ceramic-on-metal (CoM). Serial whole blood metal ion levels in the non-metal bearings, namely CoC and CoP, were analyzed. Results. There was no consistency in these whole blood metal ion levels. Intra-patient variations in these levels over a period of time could not be due to bearing-produced metal ions as these were all metal free, and thus not the source of any endogenous ions. These intra-patient variations may reflect changes in exogenous exposure to these metal ions, fluctuations in these patient's metabolic functions or production of metal ions from non-bearing prosthetic sources. Conclusion. This finding of variations of “normal” intra-patient whole blood metal ions highlights the importance of determining a patient's average baseline levels, particularly when these are used to determine changes in these levels when part of a protocol to monitor the performance of metal containing hip replacement bearings