Two types of ceramic materials currently used in total hip replacements are third generation hot isostatic pressed (HIPed) alumina ceramic (commercially known as BIOLOX®forte, CeramTec) and an alumina matrix composite material consisting of 75% alumina, 24% zirconia, and 1% mixed oxides (BIOLOX®delta, CeramTec). The aim of this study is to compare BIOLOX delta femoral heads to BIOLOX forte femoral heads revised within 2 years in vivo.

Ceramic bearings revised at one center from 1998 to 2010 were collected (61 bearings). BIOLOX delta heads (n=11) revised between 1–33 months were compared to BIOLOX forte femoral heads with less than 24 months in vivo (n=20). The surface topography of the femoral heads was measured using a chromatically encoded confocal measurement machine (Artificial Hip Profiler, RedLux Ltd.).

The median time to revision for BIOLOX delta femoral heads was 12 months, compared to 13 months for BIOLOX forte femoral heads. Sixteen out of 20 BIOLOX forte femoral heads and 6 out of 11 BIOLOX delta femoral heads had edge loading wear. The average volumetric wear rate for BIOLOX forte was 0.96 mm3/yr (median 0.13 mm3/yr), and 0.06 mm3/yr (median 0.01 mm3/yr) for BIOLOX delta (p=0.03). There was no significant difference (p>0.05) in age, gender, time to revision or femoral head diameter between the two groups.

Early results suggest less volumetric wear with BIOLOX delta femoral heads in comparison to BIOLOX forte femoral heads.

Introduction

Edge loading commonly occurs in all bearings in hip arthroplasty. Edge loading wear can occur in these bearings when the biomechanical loading axis reaches the edge and the femoral head loads the edge of the cup producing wear damage on both the head and cup edge. When the biomechanical loading axis passes through the polished articulating surface of the acetabular component and does not reach the edge, the center of the head and the center of the cup are concentric. The resulting wear known as concentric wear is low in metal-on-metal (MOM) bearings, and is negligible in ceramic-on-ceramic (COC) bearings. Edge loading is well defined in COC hip bearings. However, edge loading is difficult to identify in MOM bearings, since the metal bearing surfaces do not show wear patterns macroscopically. The aims of this study are to compare edge loading wear rates in COC and MOM bearings, and to relate edge loading to clinical complications.

Ceramic-on-ceramic alumina bearings (ALX) have demonstrated low wear with minimal biological consequences for almost four decades. An alumina-zirconia composite (BIOLOX-DELTATM) was introduced in 2000 as an alternative ceramic. This contains well-distributed zirconia grains that can undergo some surface phase transformations from tetragonal to monoclinic. We analyzed 5 cases revised at 1–7 years to compare to our simulator wear studies. For the retrieved DELTA bearings, two important questions were. how much tetragonal to monoclinic transformation was there in the zirconia phase and. how much did the articular surfaces roughen, either as a result of this transformation or from formation of stripe wear zones?. The retrieval cases were photographed and logged with respect to clinical and revision details. The DELTA balls varied from 22mm to 36mm diameters. These had been mated with liner inserts varying by UHMWPE, BIOLOX-FORTE and BIOLOX-DELTA materials. Bearing features were analyzed for roughness by white-light interferometry, for wear by SEM, for dimensions by CMM and for transfer layers by EDS technique. Surface transformations on DELTA retrievals were mapped by XRD. The four combinations of 36mm diameter BIOLOX-FORTE and BIOLOX-DELTA were studied in a hip simulator, which was run in ‘severe’ micro-separation test mode to 5 million cycles. Wear rates, wear stripes, bearing roughness and wear debris were compared to the retrieval data. In two DELTA ball cases, there were conspicuous impingement signs, stripe wear and black metallic smears. It is to be noted that the metal transfer sites (EDS) appeared to be from the revision procedures. The retrieved balls run with alumina liners showed monoclinic phase peaking at 32% on the particular surface and internal bore. On the fracture surface of case 1, the monoclinic content had increased to 40%. Various surface roughness indices were assessed on the bearings. The polished articular surfaces averaged roughness (Sa) of the order 3 nm, representing extremely smooth surfaces. The main wear zone was only marginally rougher (5 nm). In contrast the stripe wear zones had roughness of the order 55–140 nm. In the laboratory, the DELTA bearings provided a 3–6 fold wear reduction compared to FORTE controls. Roughness of stripes increased to maximum 113nm on controls. Roughness of wear stripes showed FORTE with the highest and DELTA with the lowest values. DELTA bearings also revealed much milder wear by SEM imaging. Phase transformations showed peaks at < 30% for both main wear zone and stripe wear sites. It is hypothesized that the concentration of monoclinic phase reached a certain level due to compression contraint imposed by the alumina matrix. With implant wear, additional tetragonal grains of zirconia are exposed and these will also transform to tetragonal. This consistency between laboratory and retrieval studies confirmed the stable nature of the bearings. The BIOLOX-DELTA combination provides optimal potential for a clinically relevant reduction in stripe wear

INTRODUCTION. Ceramic-on-ceramic hip resurfacing offers a bone conserving treatment for more active patients without the potential metal ion risks associated with resurfacing devices. The Biolox Delta ceramic material has over 15 years of clinical history with low wear and good biocompatibility but has been limited previously in total hip replacement to 48mm diameter bearings [1]. Further increasing the diameter for resurfacing bearings and removing the metal shell to allow for direct fixation of the ceramic cup may increase the wear of this material and increase the risk of fracture. METHODS. Eighteen implants (ReCerf™, MatOrtho, UK; Figure1) were wear tested; six were ⊘40mm (small) and twelve ⊘64mm (large). All small and six large implants were tested under ISO 14242 standard conditions for 5 million cycles (mc) at 30° inclination (45° clinically). The six remaining large implants were tested under microseparation conditions in which rim contact was initiated during heel strike of the gait cycle for 5mc. Cups were orientated at 45° inclination (60° clinically) to allow for separation of the head and cup with a reduced 50N swing phase load and a spring load applied to induce a 0.5mm medial-superior translation of the cup. Wear was determined gravimetrically at 0.5mc, 1mc and every mc after. RESULTS. Wear was low in both standard and microseparation tests, less than 1mm. 3. cumulatively over 5mc (Figure 2). Standard conditions showed a run-in wear phase over the first mc followed by negligible wear in both diameters. The run-in wear significantly increased from 0.2mm. 3. /mc in the 40mm diameter bearings to 0.5mm. 3. /mc with the larger diameter implants. Under microseparation conditions, there was low wear over the first mc, increasing to 0.28mm. 3. /mc between 1–3mc. The wear rate reduced to 0.11mm. 3. /mc from 3=5mc. Stripe wear was evidenced on the microseparated components. There were no incidences of fracture or squeaking. DISCUSSION. Biolox Delta is known for its low wear rates but published results have only reported testing up to ⊘36mm [2]. Increasing the diameter to 64mm showed increased wear compared to smaller diameters but this was only significant over the first mc suggesting similar performance long term. Microseparation testing of these large sized bearings doubled the cumulative wear produced over 5mc but wear measured was still much lower than other bearing combinations. Wear of metal-on-metal resurfacing implants under these high angle, microseparation conditions has been reported up to 10.5mm. 3. /mc [3], significantly higher than any wear rate reported in the current study. Despite the 3mm wall thickness, no fracture of the cup occurred but stripe wear was observed in the ceramic components. SIGNIFICANCE. Biolox Delta ceramic is appropriate for use in larger diameters without excessive wear or damage to the bearings. The improved biocompatibility of the material may allow for hip resurfacing to be offered to more patients than currently available. For any figures or tables, please contact the authors directly

Young and active patients require bearing materials that can last up to 200 million walking steps, ten fold greater than conventional polyethylene bearings. Cross linked polyethylene provides reduced wear rate compared to conventional polyethylene, and further advantage is gained from using ceramic femoral heads. However in polyethylene bearings wear increases with the head diameter, and there is currently little opportunity to use head sizes greater then 36mm diameter. There is evidence of polyethylene fracture with steeply positioned cups. Ceramic on ceramic bearings provide substantially lower wear rates than polyethylene bearings. Steep cups, lateralised heads or neck impingement can lead to head contact on superior rim of the cup and stripe wear, but this still results in very low wear rates. Recently developed ceramic matrix composites Biolox Delta provide greater resistance to stripe wear. In a few patients stripe wear may lead to squeaking. Metal on metal bearings also provide substantially lower wear than polyethylene bearings. However there remains concern about elevated metal ion levels in a few patients and resultant risk of hypersensitivity reactions. In metal on metal bearings larger head sizes and reduced diametrical clearance can lead to reduced wear. Increased wear is associated with steep cups and lateralised heads resulting in rim wear. Ceramic on metal bearings have been introduced recently as the first differential hard on hard bearings. These bearings show substantial reduction in wear, corrosive wear mechanisms, metal ion levels in laboratory simulators and initial clinical studies have shown a reduction in metal ion levels in vivo compared to metal on metal bearings

Retrieved alumina-on-alumina hip joints frequently exhibit a localised region of high wear, commonly called ‘stripe wear’. This ‘stripe wear’ can be replicated in vitro by the introduction of micro-separation, where the joint contact shifts laterally reproducing edge loading during the simulated walking cycle. While the origin of stripe wear is clearly associated with the micro-scale impact resulting from micro-separation, the wear processes leading to its formation and the wear mechanisms elsewhere on the joint are not so well understood. The purpose of this study was to compare the surface microstructure of in vivo and in vitro alumina hip prostheses, and investigate the origins of the damage accumulation mechanisms that lead to prosthetic failure. The in vivo alumina hip prosthesis was Biolox (Ceram-Tec, AG, Plochingen, Gemany) implanted for 11 years [. 1. ]. The in vitro alumina hip prosthesis was Biolox-forte (CeramTec, AG, Plochingen, Gemany), which had been tested in a hip joint simulator under micro-separation at Leeds University using the procedures given in [2]. The worn surfaces of the alumina hip prostheses were investigated using a Scanning Electron Microscopy (SEM). Similar worn surfaces were seen for both in vivo and in vitro samples. Focused ion beam (FIB) microscopy was used to determine the sub-surface damage across the stripe wear. Samples were subsequently removed for Transmission Electron Microscopy (TEM). Sub-surface damage was found to be limited to a few μm beneath the surface; ~ 2μm for in vivo samples and ~1μm for in vitro samples. The transition from mild wear to more severe (stripe) wear was entirely triggered by intergranular fracture. The first stages of fracture lead to the liberation of surface grains which act as 3rd body abrasives. The TEM showed that abrasive grooves are associated with extensive surface dislocation activity, which leads to further grain boundary fracture. This allows the cycle to be repeated and accelerated, thus yielding the stripe wear region. The conclusions are: 1. In vitro hip simulation with micro-separation can produce similar microstructure to in vivo alumina hip prostheses; 2. To extend the life of the joint through the avoidance of severe wear, material and design solutions can be investigated using ceramic materials that have an increased surface inter-granular fracture toughness and component designs with reduced contact stress under edge loading

FDA approval of metal-on-metal (MOM: 28, 32mm) bearings has provided 10 years of clinical experiences in USA. However there has been no detailed mapping of wear phenomena in retrieval cases. We present an analysis of 28 cases, MOM retrievals with 1 to 10 years follow-up, radiographic reviews and metal ion studies. Ball diameters ranged from 28mm to 42mm. Two balls were the early design with skirts. Main indicators for revision were the progressive radiographic changes indicative of osteolysis, with associated hip pain. Approximately 54% of patients were males and ages ranged from 36 to 76 years of age. Only 7 femoral stems were recovered but all had impingement marks. Only three cases lacked any evidence of stripe wear and these were in very elderly patients. Approximately 85% of these cases showed some evidence of stripe wear and multiple stripes were clearly visible on 50% of the femoral balls. The medial ball stripes were twice as common as lateral. Stripe wear was identified in 25% of CoCr liners. In the hip simulator studies generally show ‘run-in’ wear rates of 1–7mm3 per million cycles (Mc). We noted that above the 5mm3/Mc threshold, the serum generally appeared black. In contrast, the ‘steady-state’ wear rates of 0.1–1.6 mm3/Mc showed the true potential of MOM bearings. However there were often examples of higher wear (7–20 mm3/Mc), which gave confounding trends in published studies. Our studies of metal ions in the simulator lubricant provided a very accurate representation of MOM wear. There are many limitations in comparing in-vitro to in-vivo wear performance. Our retrieval data are biased to cases that failed due to hip pain, had radiographic signs of progressive osteolysis and some showed high levels of metal ions. There was also the bias of having predominantly a CoCr sandwich design (polyethylene adaptor). Use of the small ball added the well-known risks of impingement, subluxation and dislocation with rigid cups. Using the ‘damage modes’ from McKellop, we found only normal Mode-1 wear to be rare in these cases, whereas Modes# 2–4 had an incidence approaching 30% each. Signs of impingement were evident in 85% of our cases. Thus summarizing these MOM wear phenomena in retrieved 28mm sandwich cups, the evidence implicated impingement and 3rd-body wear modes (#2–4) as the clinical risk for adverse wear effects at 10 years follow-up. The in-vitro wear studies have not yet simulated such adverse clinical effects

INTRODUCTION. Analysis of retrieved ceramic components have shown areas of localized ‘stripe wear’, which have been attributed to joint laxity and/or impingement resulting in subluxation of the head, causing wear on the edge of the cup. Studies have been conducted into the effects of mild subluxation, however few in vitro tests have looked at severe subluxation. The aim of this study was to develop a more clinically relevant subluxation protocol. MATERIALS & METHODS. Seven (Subluxation n=4; standard test n=3) of 36mm Biolox Forte (R3, Smith & Nephew) ceramic devices were tested for 0.5m cycles (mc). Two of the subluxed joints were further tested to 1 Mc. The devices were subjected to subluxation under standard testing conditions. The flex/ext was 30° and 15° respectively, with internal/external rotation of ±10°. The force was Paul type stance phase loading with a maximum load of 3 kN, and a standard ISO swing phase load of 0.3 kN at 1 Hz. The test was conducted on a ProSim hip joint wear simulator (SimSol, UK). The simulator is equipped with a novel mechanism to achieve translation of the head, to achieve subluxation. During the ISO swing phase load of 0.3kN, a controlled lateral force required for the translation of the head is applied by a cam mechanism, head retraction then occurs during heel strike. The lubricant used was new born calf serum diluted with de-ionised water to achieve average protein concentration of 20 g/l, with 0.2 wt % concentration NaN3, and changed every 250k cycles. Measurements have been taken at 0.5 & 1 mc stages. RESULTS. Linear wear measurements conducted on the subluxed joints resulted in stripe wear similar to that reported in vivo. Average length, width and depth dimensions were 25.34±1.96 mm, 8±1.60 mm and 16.95±3.87 μm (± 95% CL) respectively. Linear wear at 0.5 Mc for standard joints, were undistinguishable from the original profile. Gravimetrically, weight loss was undetectable for joints tested under standard conditions. The volume loss of the joints under subluxation was 1.9± 0.7 mm3 at 0.5 mc. Two joints tested to 1mc generated an average volume loss of 3.1±2.3 mm3. The stripe wear length, width and depth at 1 Mc were 25.30±3.33mm, 8±3.92mm and 35±17.07 μm respectiveley. DISCUSSION. The current study presents test results of a hip joint simulator with a novel subluxation mechanism to simulate severe and clinically relevant hip joint. Past techniques have had to reduce the swing phase load to achieve stripe wear patches of varying size and depth. The subluxed joints produced significantly higher volumetric wear than the standard joints. Dimensional measurements in terms of length, width and depth of wear patches of subluxed joints generated similar results to that which have been observed following retrieval analysis. Tests that can simulate different types of activity in hip joint simulators will help to improve the design and understanding of implant behaviour in vivo

While there are many variation laboratory and clinical studies using metal-on-metal (MOM) bearings after introduction of the 28mm MOM THR in 1988, the mapping of wear phenomena in such retrieval cases has been mimimal. In laboratory study, 28mm MOM bearing’s wear-rate was low with “run-in” and “steady-state” than large diameter MOM without theory of fluid-filum lubrication. In clinical results were not superior to the same way of laboratory study. We present a detailed analysis of 33 retrieved MOM hip bearings with 1–11 years follow-up,. We compiled 33 retrieval cases (MetasulTM: Zimmer/CenterPulse Inc., Austin, TX) including clinical information, ion concentrations from ball diameters, cup designs and stripe wear damage. The bearing surfaces were mapped using reflected light microscope (RLM), white light interferometer (Zygo Newview 600, Zygo.) and SEM(XL-30 FEG). Wear maps were constructed according to types of surface wear identified. Patients ranged from 36 to 76 years of age (Means: 56.9 years); 54% were males. Main causes for revision were progressive radiographic lines around the cups, osteolysis and pain. The 28mm ball diameter was used in 86% of cases (largest = 52mm ball). The CoCr liner incorporated a polyethylene adaptor in 75% of cases. Cup diameter > 50mm was present in 75% of cases. Eight femoral stems were recovered and all showed major impingement marks around the neck and five also had a metallosis (Mode-4A). Stripe wear was evident on 71% of CoCr balls with medial stripes twice as common as lateral. Stripe wear was identified in 25% of CoCr liners and extended 25–160° circumference around the liners. Clear liner rim damage was present in 10 (30%) and 3 demostrated severe damage of polyethelene adaptors. There are many limitations to such retrieval studies. These data are biased to cases that failed due to hip pain, radiographic signs of progressive osteolysis and some with high levels of metal ions. There was also the bias of having predominantly a CoCr sandwich design (polyethylene adaptor in 75% of cases). In early 1980s, the thin walled UHMWPE cup was introduced and used larger diameter balls for decreased risk of dislocation. However, unfortunally these big-ball cups produced significant PE wear debris, and diameter trends were returned to the Chanley’s small-ball paradigm again. In the same time (late of 1980’s), these second-generation MOM (28,32mm) was introduced for low wear characteristics alternate THR bearings, with sacrificing of joint stability and motion range. However, use of the small ball added well-known risks of impingement, subluxation and dislocation with rigid cups. In this study, using the ‘damage modes’ from McKellop, normal mode-1 wear occurred in only 14% of cases whereas modes 2–4 had an incidence approaching 30% each and signs of cup impingement were evident in 64% of cases. Thus summarizing MOM wear phenomena in “small” 28mm sandwich cup designs, there was retrieval evidence showing that damage modes 2–4 likely placed these patients at risk for adverse wear effects

The recent introduction of modern ceramic-on-ceramic total hip arthroplasties have demonstrated excellent clinical and radiographic results without catastrophic failure such as implant fracture associated with earlier designs. In laboratory wear testing, ceramicon-ceramic provides the least volumetric wear among all bearing surfaces. In recent years, with modern ceramic-on-ceramic bearing surfaces, clinical results with 5-to 7-year follow up have been good to excellent in 95–97% of cases. In spite of excellent results, certain limitations still exist including occasional fracture, stripe wear, squeaking, and neck-socket impingement producing metallic third body. Future improvement in ceramics (and other hard-bearing surfaces) and its coupling with other hard bearing surfaces appears to have significant advantages in reducing dislocation, impingement, stripe wear and squeaking

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

From 1985 metal-on-metal (MOM) designs of resurfacing (RSA) and total hip arthroplasties (THR) have been available over a large diameter range (28–60mm). In-vitro studies indicated satisfactory low wear performance for all designs and diameters tested (wear = 0.1 to 7 mm3). While reports from many centers have been encouraging, some have reported adverse effects. We reviewed clinical and metal ion studies in large diameter retrievals and compared these to 28mm MOM cases. Patients with the latter THR ranged 36–76 years of age and were followed 9–11 years. Main finding in our revisions was osteolysis and pain. The 28mm ball was represented 86% of cases; 71% balls had stripe wear. For liners, 25% had circumferential stripe wear and impingement was evident in 64% cases. Seven cemented stems were recovered with impingement marks; 26 stems were undamaged and therefore not revised. Using the concept of ‘damage modes’ from McKellop, normal wear mode #1 was evident in only 14% of 28mm retrievals whereas incidence of ‘abnormal’ modes #2-4 approached 30% each. Thus the 28mm MOM appeared susceptible to impingement risks with CoCr liners. Summarizing MOM retrievals, damage modes 2–4 were most likely implicated in revisions. The performance of such ‘small diameter’ THRs will be contrasted to our large diameter THR and RSA experience. The questions to be reviewed include, how much of the reported MOM adversity was predictable and how much risk was due to. wear of small diameter MOM,. adverse cup positioning and hip instability,. cup-stem impingement issues or. design conformity issues?

Introduction. Translational surgical mismatch in the centres of rotation of the femoral head and acetabular cup in hip joint replacements can lead to dynamic microseparation resulting in edge loading contact [1]. Increased wear in retrieved ceramic-on-ceramic bearings has been associated with edge loading [2]. Hip joint simulators were used to replicate increased wear rate, stripe wear and bimodal wear debris size distribution, as seen clinically [3,4]. Recently developed electromechanical simulators are able to comply with the latest international standards, which include three axes of rotation conditions [5]. Previous simulators had applied two axes of rotation under microseparation conditions [6]. Therefore, the aim of this study was to compare the wear of ceramic-on-ceramic bearings obtained under edge loading due to microseparation conditions during gait using the same electromechanical hip joint simulator with two axes of rotation and three axes of rotation conditions. Materials and Methods. A six-station electromechanical hip joint simulator (ProSim EM13, Simulation Solutions, UK) was set up with 36mm diameter ceramic-on-ceramic (BIOLOX® delta, PINNACLE®, DePuy Synthes, UK) hip replacements. The wear was determined for two million cycles under standard conditions with two axes of rotation conditions (n=6), two million cycles under microseparation conditions with two axes of rotation conditions (n=6) (Figure 1a), and two million cycles under microseparation conditions with three axes of rotation conditions (n=6) (Figure 1b). The loading profiles [5,7] comprised of 3kN twin peak loads and 300N swing phase load under standard conditions. The swing phase load was reduced to approximately 70N under microseparation conditions. Approximately 0.5mm of dynamic microseparation between the head and the cup was applied in the medial/lateral direction. The components were lubricated with 25% new-born calf serum supplemented with 0.03% sodium azide to minimise bacterial growth. The gravimetric wear rates were compared over two million cycles for each test (XP205, Mettler Toledo, UK). The mean wear rates of the head and cup were calculated with 95% confidence limits and statistical analysis was carried out (t-test) with significance levels taken at p<0.05. A coordinate-measurement machine (Legex 322, Mitutoyo, UK) was used to construct a three-dimensional map of the femoral head surface wear. Results. Under standard conditions, the mean wear rate of BIOLOX® delta ceramic-on-ceramic bearings was 0.03±0.01 mm3/million cycles. The mean wear rates under microseparation conditions for two axes and three axes of rotation conditions were 0.14±0.01 mm3/million cycles and 0.14±0.03 mm3/million cycles respectively. There was no statistically significant difference between the wear rates using two axes and three axes of rotation conditions under microseparation conditions (p=0.86). Stripe wear was observed and wear depth measured on the femoral heads under microseparation conditions using two axes (Figure 2a) and three axes (Figure 2b) of rotation. Conclusion. Higher wear rates were observed under microseparation compared with standard conditions, as reported in a previous study [6]. Similar wear rates were obtained under microseparation conditions with two axes and three axes of rotation conditions using the same simulator

Dislocation remains one of the most common complications after total hip arthroplasty. Precise cup position appears to be a main factor as significant variations occur for frontal and sagittal acetabular tilt and anteversion according to sitting or standing positions. An innovative dual mobility ceramic-on-ceramic joint has been developed to solve these problems. The dual mobility ceramic-on-ceramic joint allows to move the rotation center much deeper inside the insert in order to increase the joint stability without negative impact on the ROM. This device revealed higher torques against subluxation in comparison to the classical Al-Al systems, even with 36mm head diameters, or 41 mm metal on metal bearings. The additional outer-bearing surface motion creates a second “adjustable acetabulum” due to the eccentration between the rotation center of the ball head and the rotation center of the bipolar head. This offset creates a resultant force that rotates the bipolar component. Using two bearing ceramic surfaces, the intermediate component acts as a “self adjusting cup”, dealing with the variations of pelvic orientation and acetabulum anteversion. The use of the dual mobility ceramic-on-ceramic joint seems an interesting alternative when facing difficult or unexpected situations for cup adjustment and cases with hip instability In a hip simulator in micro separation condition, the wear of the dual mobility ceramic-on-ceramic was less than 0.01 mm3/million cycles, the detection limit for wear measurement. There was no change in the surface roughness of the inserts. The design of the joint with the mobile ceramic head prevented edge loading of the head on the edge of the cup. No stripe wear was observed. Since 2006 more than 2000 dual mobility ceramic-on-ceramic systems have been implanted in Europe and clinical studies are conducted. The aim is to demonstrate the resistance to dislocation in primary total hip arthroplasty. Previous results over 125 patients in a prospective multicentric study show a Harris and Womac score equivalent to a standard hip prosthesis. No dislocations have been reported. No ceramic breakage or “squeaking” phenomenon appears. Dislocation and microseparation are major causes of failure for ceramic-ceramic hip prosthesis. When no ideal solution has been found for acetabular implantation, the dual mobility ceramic-on-ceramic device is a real alternative. The exclusive design of the bipolar head give the high resistance to wear and stripe wear to the dual mobility ceramic-on-ceramic joint. Reducing the risk of dislocation and reducing wear drastically are two advantages that can place the dual mobility ceramic-on-ceramic joint as the best choice in primary Total Hip Arthroplasty. Obviously this choice applies to recurrent dislocation also

Background: Recently, the new phenomenon of “squeaking” noises emitted from THAs with ceramic-onceramic bearings has spared international interest. It shows a frequency of 0,7–19,5% in literature, but infrequently requires revision surgery. However, an even higher incidence of various other noises from those THAs audible to the human ear have become popular in the process: this noise can resemble clicking, grinding or creaking and can be caused by distinct movements, during longer periods of walking, or can be constant with movement. The incidence of those noises can reach up to 30% of THAs. However, memory has faded that other bearings like metal-on-metal and PE/ceramic have been associated with noises in the past. Therefore we aimed to investigate the occurence of acoustic emissions in patients, who had all received the same implant but with alternate bearings, to investigate the nature of noise, duration and clinical consequence for all 3 bearings (polyethylene/ceramic, metalon-metal, ceramic-on-ceramic). Method: Between 1999–2001, 360 patients were matched in a prospective randomised trial. All of them received a cementless Zimmer© Alloclassic Variall™ implant at the Orthopaedic Hospital Vienna – Speising, Austria with either a ceramic-on-ceramic bearing, a metal-on-metal bearing or a polyethylene/ceramic bearing. A questionnaire was sent via mail, including questions on first occurence of hip noise, information on the kind and duration of the phenomenon and possible adverse evaluation on behalf of the patient. In case of a positive report, the patient was invited to a clinical examination and radiographic analysis. In addition, a specialised audiography was conducted in patients with audible sensations. Finally, the SF-36 and WOMAC were analysed. A number of patients received further examination with methods of gait analysis in order to detect the distinct point of occurence of the noise during the gait cycle. Results: 33 patients reported an audible phenomenon from their THA, 14 received a ceramic-onceramic bearing (Cerasul), 13 a polyethylene/ceramic bearing (Durasul) and 6 a metal-onmetal bearing (Metasul). The most common noise was a distinct clicking, followed by a creaking noise. Only 1 patient reported a squeaking sensation, he received a polyethylene/ceramic bearing. Conclusion: The emission of specific noises from THAs of all bearings has been well documented in recent trials and could be verified in this survey of cementless THAs. No trend towards an increased incidence of noise from THAs with ceramic-on-ceramic bearings could be detected. Interestingly, the single case of „squeaking” was reported from a patient with polyethylene/ceramic bearing. Microseparation and subluxation of the femoral head with resulting edge loading and formation of stripe wear has recently been suspected as the main cause for “noisy hips.” So far 2 ceramic-on-ceramic hips of this study group population have been revised. Both articulations showed areas of stripe wear due to subluxation of the joint

Introduction. Stripe wear, observed on retrieved ceramic hip replacements, has only been replicated in vitro under translational mal-positioning conditions where the centres of rotation of the head and the cup are mismatched. 1,2. ; an in vitro condition termed “microseparation”. The aim of this study was to compare the edge loading mechanisms observed under microseparation conditions due to translational mal-positioning conditions simulated on two different hip joint simulators. Materials and Methods. The components used in this study were zirconia-toughened-alumina ceramic-on-ceramic bearings (36 mm) inserted into titanium alloy acetabular cups (BIOLOX® delta and Pinnacle® respectively, DePuy Synthes Joint Reconstruction, Leeds, UK). Six couples were tested for two million cycles under 0.5 mm dynamic microseparation conditions on the Leeds II hip joint simulator as described by Nevelos et al. 2. and Stewart et al. 3. (Figure 1). Ten bearing couples were tested for two million cycles under microseparation conditions achieved in two different ways on the ProSim pneumatic hip joint simulator (SimSol, Stockport, UK). Two conditions were tested; condition (1)- the femoral head was left to completely separate (the vertical motion was controlled at 1 mm) causing it to contact the inferior rim of the acetabular cup before edge loading on the superior rim at heel strike (n = 5) and condition (2)- springs were placed below the plate holding the femoral head to control the tilt of the head laterally towards the rim of the acetabular cup as the negative pressure was applied (n = 5; Figure 1). Wear was assessed gravimetrically every million cycles using a microbalance (Mettler AT201, UK). Three-dimensional reconstructions of the wear area on the heads were obtained using a coordinate measuring machine (Legex 322, Mitutoyo, UK) and SR3D software (Tribosol, UK). Results. The wear rates of the 36 mm ceramic-on-ceramic bearings obtained under microseparation conditions on the ProSim, where the medial-lateral displacement was controlled (condition 2), and under microseparation conditions on the Leeds II simulator were 0.22 mm. 3. and 0.13 mm. 3. /million cycles respectively, however, the difference was not statistically significant (p = 0.092). The wear rates obtained under microseparation conditions on the Leeds II and the ProSim (condition 2) were both significantly higher (p = 0.006 and p = 0.009 respectively) than the wear rate obtained under microseparation conditions on the ProSim where full distraction of the head was provided (condition 1, 0.05 mm. 3. /million cycles). The wear stripe areas formed on the femoral head under the three simulator set-ups are shown in Figure 2. Discussion and Conclusion. Edge loading due to translational mal-positioning with 0.5 mm dynamic medial-lateral displacement on the Leeds II simulator has been validated against retrievals and shown to replicate stripe wear mechanisms, wear rates and bimodal wear debris distribution as that observed in vivo. 1,2,4,5. The edge loading due to translational mal-positioning simulated on different machines can result in different wear rates and wear mechanisms. One microseparation technique (condition 2) achieved on the ProSim simulator has demonstrated similar results to the validated Leeds II simulator

Introduction: Increasing numbers and incidence rates of noisy (squeaking, scratching, clicking) ceramic-on-ceramic (CoC) total hip arthroplasties (THA) are being reported. The etiology seems to always involve stripe wear producing a stick-slip effect in the bearing which excites vibrations. As stripe wear is also found in silent CoC bearings, a theory has been developed that the vibrations become audible only via amplification through the vibrating stem (bell-clapper theory). This was supported by showing that the excitation frequency and the resonance frequency of the plain stem are similar. However, stem resonance in-vivo would be influenced by the periprosthetic bone damping and transmitting stem vibrations. Thus, if the bell-clapper theory were true, noisy CoC hips should show periprosthetic bone different to silent hips. This study compares stem fit& fill and periprosthetic bone between noisy and silent CoC hips. Methods: In a consecutive series of 186 primary CoC hips with identical stems, cups (Stryker ABG-II) and femoral heads (Alumina V40, 28mm) a survey identified 38 noisy hips (incidence rate: 20.4%, squeakers: n=23). Stem fit& fill and cortical wall thickness (CWT, medial and lateral) were measured on post-op AP x-rays according to the method of Kim & Kim. Measurements were repeated by a single blinded observer in a control group of silent hips matched for gender, age, stem size and follow-up time (4.6yrs). Fit& fill and CWT were compared between the noisy and silent group at proximal, mid-stem and distal level and on the medial and lateral side. Results: The endosteal canal width was equal in noisy (N) and silent hips (S) at all levels (e.g. proximal: N=39.7+/−5.5mm, S=41.3+/−5.7mm). On the lateral side also cortical wall thickness (CWT) was the same at all levels (e.g. proximal: N=2.0+/−0.8mm, S=1.9+/−0.9mm). However, on the medial side, noisy hips had higher CWT at proximal (N=4.9+/−2.8mm, S=3.0+/−2.1mm, p< 0.01) and mid-stem level (N=6.2+/−2.1mm, N=4.6+/−1.7mm, p< 0.001). Also Fit& fill was slightly higher (proximal: N=66%, S=62%; mid-stem: N=63%, S=59%, p< 0.05). Differences and significance levels increased when only squeakers were considered. Discussion: Despite equal endosteal canal widths and lateral cortical wall thickness for noisy and silent hips, noisy hips had sign. thicker medial walls at proximal (+63%) and mid-stem level (+35%) where also fit& fill was higher. This gives evidence that periprosthetic bone (PPB) may play a role in the development of audible noise in CoC hips by providing particular conditions of support, damping and transmission for an oscillating stem which influences noise frequency and intensity. Comparing PPB at different time points indicated that the differences are less due to post-op remodeling but more to pre-op conditions, surgical canal preparation and possibly stem design. The findings shall be verified by a DEXA study

Introduction. Increasing numbers and incidence rates of noisy (squeaking, scratching or clicking) ceramic-on-ceramic (CoC) total hip arthroplasties (THA) are being reported. The etiology seems to always involve stripe wear producing a stick-slip effect in the bearing which excites vibrations. As stripe wear is also found in silent CoC bearings, a theory has been developed that the vibrations become audible only via amplification through the vibrating stem. This was supported by showing that the excitation frequency and the resonance frequency of the plain stem are similar [1]. However, stem resonance in-vivo would be influenced by the periprosthetic bone damping and transmitting stem vibrations. Thus, if stem resonance is conditional for noisy COC hips, these should show periprosthetic bone different to silent hips. This study compares stem fit&fill and periprosthetic bone between noisy and silent CoC hips. Methods. In a consecutive series of 186 primary CoC hips with identical stems, cups (Stryker ABG-II) and femoral heads (Alumina V40, 28mm) a dedicated patient questionnaire [2] identified 38 noisy hips (incidence rate: 20.4%, squeakers: n=23). Stem fit&fill and cortical wall thickness (CWT, medial and lateral) were measured on post-op AP x-rays according to an established method [3, Fig 1]. Measurements were repeated by a single blinded observer in a control group of silent hips matched for gender, age, stem size and follow-up time (4.6yrs). Fit&fill and CWT were compared between the noisy and silent group at proximal, mid-stem and distal level and on the medial and lateral side. Results. The endosteal canal width was equal in noisy (N) and silent hips (S) at all levels (e.g. proximal: N=39.7±5.5mm, S=41.3±5.7mm, Fig 2). On the lateral side also cortical wall thickness (CWT) was the same at all levels (e.g. proximal: N=2.0±0.8mm, S=1.9±0.9mm). However, on the medial side, noisy hips had higher CWT at proximal (N=4.9±2.8mm, S=3.0±2.1mm, p<0.01) and mid-stem level (N=6.2±2.1mm, N=4.6±1.7mm, p<0.001). Also Fit&fill was slightly higher (proximal: N=66%, S=62%; mid-stem: N=63%, S=59%, p<0.05). Differences and significance levels increased when in the noise group only squeakers were considered. The mid-stem line, assumed to sit distal to LT, actually cut through LT significantly more often in the noisy (18/38) than in the silent group (9/38, p=0.02) indicating a tendency of noisy stems to sit more proximally. Discussion. Despite equal endosteal canal widths and lateral cortical wall thickness for noisy and silent hips, noisy hips had significantly thicker medial walls at proximal (+63%) and mid-stem level (+35%) where also fit&fill was higher. Noisy stems also sat more proximal (Fig. 3). This gives evidence that periprosthetic bone (PPB) may play a role in the development of audible noise in CoC hips by providing particular conditions of support, damping and transmission for an oscillating stem which influences noise frequency and intensity. Comparing PPB at different time points indicated that the differences are less due to post-op remodeling but more to pre-op conditions o

In an effort to understand the role of metal ion analysis and how it relates to revision surgery and implant wear, four revised MOM cases were reviewed. The first case was revised for acute infection and is representative of the low bearing wear predicted by MOM simulator studies. Two of the four cases had apparent anterior subluxation as a result of hip hyperextension occurring with long stride gaits. The last case is a true hypersensitivity response to CoCr ions. All four MOM prostheses were implanted by one surgeon and revised by the same surgeon approximately 6–8 years postoperatively. The implants had been positioned satisfactorily with inclination angles 45°–55° and anteversion angles 28°–42°. Patient A (76 y/o female) with bilateral MOM hip replacements, was revised at approximately 8 years due to infection and had moderately elevated ions at the time of revision surgery (Co = 5, Cr = 2.3, Ti = 4). Only the femoral head was retrieved in this case. Retrieval analysis identified a well defined main-wear zone and one polar stripe. The CMM indicated there was minimal wear overall (form factor = 11 μm). Patient B (33 y/o male) with bilateral MOM hip replacements, was revised at approximately 8 years due to pain, popping/catching sensations, and elevated ions (Co = 33, Cr = 17, Ti = 90). Intraoperatively, the implant was observed subluxing superiorly from the acetabular cup with anterior rotation of the leg. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and multi-directional polar stripe formations similar to those reported on dislocated implants (Figure 1)[McPherson 2012, 2013]. The CMM indicated that overall wear was significant (form factor > 100 μm). Patient C (77 y/o female) was revised at approximately 6 years due to pain, suspected implant loosening, osteolytic cysts determined by CT, and highly elevated ions (co = 164, Cr = 45, Ti = 33). Intraoperatively, there was evidence of wear including darkly stained tissue and osteolytic cysts. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. CMM indicated considerable wear (head form factor > 200, cup form factor >300). Patient D (45 y/o female) was revised at approximately 6 years due to pain, apparent reactive response joint effusion, and moderately elevated ions (Co = 5, Cr = 6, Ti = 71). Only the femoral head was retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. Minimal wear was indicated by CMM (form factor = 21). These four cases demonstrate distinct failure models of MOM hips and their respective metal ion results. Due to the diversity of patient location, a variety of clinical labs were utilized for this patient population. Caution should be used in interpreting metal ion analysis, as there are still no standards. Figure 1: Retrieval analysis of stripe wear identified on femoral head from patient B. Figure 2: Femoral head from patient C showing broader polar stripe associated with anterior subluxation in comparison to narrow polar stripe found on femoral head from patient A

Ceramic-on-ceramic total hip replacements (THRs) have shown low wear volumes in standard gait hip simulator studies. 1. However clinical reports have indicated a variation in wear rates and formation of stripe wear on the ceramic femoral heads. 2. The aim of this study was to investigate the influence of different clinical conditions such as cup inclination angle and microseparation (head offset deficiency) on the wear of ceramic-on-ceramic THRs. The six station Leeds II hip joint simulator was used to investigate the wear of size 28mm ceramic-on-ceramic bearing couples. The alumina matrix composite ceramic material (AMC, Biolox Delta, CeramTec AG, Germany) was used in this study. The lubricant used was 25% bovine serum. The study was carried out for a total of five million cycles; the first two million cycles under standard gait conditions and a further three million cycles under microseparation conditions. During microseparation, a lateral movement of 0.5mm was applied to the cup relative to the head during the swing phase of the gait cycle. 3. Three of the cups were mounted to provide a clinical angle of 55°, which is referred to as the ‘standard’ condition; and the other three cups were mounted to provide a clinical angle of 65°, which is referred to as the ‘steep angle’ condition. These combinations provided four different testing conditions: standard, steep cup angle, microseparation, and combination of steep cup angle and microseparation conditions. Volumetric wear was determined gravimetrically and statistical analysis was performed using One Way ANOVA (significance at p< 0.05). Increasing the cup inclination angle from 55° to 65° had no significant effect on the wear rate in Biolox Delta ceramic-on-ceramic THRs under both standard (p> 0.42) and microseparation (p> 0.55) conditions. Under standard gait conditions, the mean wear rate for both cup inclination angles was very low at 0.05 mm3/million cycles. The introduction of microseparation to the standard gait cycle significantly increased the mean wear rates (p< 0.01) to 0.13 mm3/ million cycles for the ‘standard’ cup inclination angle of 55° and 0.11 mm3/million cycles for the ‘steep’ cup inclination angle of 65°. A stripe of wear on the head also formed, with corresponding superior rim wear on the cup. For comparison, the steady state wear rate of HIPed third generation alumina ceramic (Biolox Forte) under microseparation conditions was 1.3 mm3/million cycles [. 4. ]. In conclusion, increasing the cup inclination angle by 10° had no influence on the wear rate of Biolox Delta ceramic-on-ceramic bearings. The introduction of microseparation conditions significantly increased the wear rate and resulted in stripe-like wear on the femoral head, which has previously been observed on retrieved ceramic prosthesis. However, these wear rates were still low, and were ten times lower than those previously reported for Biolox Forte