Introduction: Patients’ demands from hip arthroplasty are changing. Bigger bearings with alternative bearing surfaces are marketed to meet these demands. The aim of this study is to investigate the level of function achieved by patients with the larger hard-on-hard hip replacements in the short term.

Methods: Three groups of patients were identified from the arthroplasty register. The two study groups were those who received a 36mm ceramic-on-ceramic hip replacement (28 patients) and those who received larger metal-on-metal hip replacements (56 patients). The control group (25 patients) was age matched patients receiving 28mm hip replacements with a polyethylene acetabular component.

All patients received postal questionnaires comprising the Oxford Hip Score, the HOOS score and a satisfaction score. Routine yearly radiological examination was also undertaken. Demographic data are shown in Table 1.

Results: All three groups showed significant improvement in the oxford hip score after hip arthroplasty. Those with the larger head sizes had significantly lower scores than those with 28mm.

Activity scores in the HOOS hip survey were not significantly different in the three groups.

There was no difference in satisfaction scores and whether patients would have the same operation again.

Discussion: Our findings suggest that in the short term, functional levels achieved following hip replacement are not influenced by the size of bearing. Should these results be reproduced in larger and longer term studies use of these costly implants may have to be questioned.

Hip simulator studies have shown reduced hip offset can cause microseparation and increased wear in hard-on-hard hip bearings. However this has not been analysed yet in vivo. We studied the effect of reduced hip offset on serum metal ion levels in patients with metal-on-metal (MoM) hip arthroplasty. From all patients who underwent unilateral MoM bearing hip arthroplasty between 2005 and 2009, 63 patients had complete clinical evaluation, measurement of serum chromium and cobalt ion levels as well as biomechanical measurements on pre- and post operative radiographs (cup inclination, head inclination, change in hip offset and change in hip length.). Ten arthroplasties were revised due to adverse metal reaction and six patients awaiting revision. 55% of ASR hips showed higher metal ions (>7 ppb) whereas only 15% of non-ASR hips had higher ion levels. Patients with reduced postoperative hip offset by more than 5 mm had significantly higher mean metal ion levels compared to the the rest of the hips (31.8 ppb vs. 7.4 ppb, p=0.002). On subgroup analysis this effect was present in non-ASR hips (18.7 ppb vs. 4.7 ppb, p=0.025) but was not significant in ASR hips (29.6 ppb vs. 16.3 ppb, p=0.347). Our study demonstrated significantly higher serum metal ion levels in patients who lost more than 5 mm hip offset after arthroplasty. Reduced soft tissue tension leading to microseparation of the articulation and edge loading is a theoretical explanation for this effect. This may be relevant in other hard bearings such as ceramic-on-ceramic as well

Aims. The Corail stem has good long-term results. After four years of using this stem, we have detected a small group of patients who have presented with symptomatic metaphyseal debonding. The aim of this study was to quantify the incidence of this complication, to delineate the characteristics of patients presenting with this complication and to compare these patients with asymptomatic controls to determine any important predisposing factors. Patients and Methods. Of 855 Corail collarless cementless stems implanted for osteoarthritis, 18 presented with symptomatic metaphyseal debonding. A control group of 74 randomly selected patients was assembled. Clinical and radiological parameters were measured and a logistic regression model was created to evaluate factors associated with metaphyseal debonding. Results. The prevalence of this complication was 2.1% in our series. In the multivariable model, the presence of a Dorr B-type proximal femur was associated with metaphyseal debonding (odds ratio (OR) 10.73, 95% confidence interval (CI) 2.31 to 49.97, p = 0.002), as was a body mass index > 25 kg/m. 2. (OR 6.85, 95% CI 1.06 to 44.28, p = 0.04). Smaller stems and the use of a polyethylene acetabular liner appeared to be protective when compared with metal and ceramic setting hard-on-hard bearings. Conclusion. We have described an uncommon but important mode of failure of the Corail stem. Surgeons should be aware of this phenomenon; overweight patients with Dorr B-type femurs and in whom hard bearings are used appear to be particularly at risk. Cite this article: Bone Joint J 2017;99-B:1435–41

Design of hard-on-hard bearing couples has traditionally been characterized by the material of the bearing couple, clearance between the bearing surfaces, sphericity of the components, surface roughness, and the radii of the components. All of these factors play a role in the lambda ratio and fluid film thickness calculations. However, the fluid film for hard on hard bearings can be interrupted by issues like the presence of 3rd body particles, intermittent walking, jogging, and subluxation. Only recently have researcher begun to simulate some of these disruptions in the fluid film for hard on hard bearings. Recent laboratory testing has looked at the effects of utilizing different materials and methodologies to evaluate hard-on-hard bearings. Ceramic-on-metal is a unique combination of components that is currently available. Several authors have shown that this combination can reduce the amount of metal wear generated during the test by a factor of 4–100. However, an occasional anomaly has shown up in some of these tests where a wear couple in a steady state wear mode will have a several-fold increase in wear for a short duration. For bearing couples that have a metal component, ion analysis of the serum lubricant can be utilized to monitor the amount of wear. This technique can provide real-time data on the amount of wear seen in simulator testing without removing the specimens from the machine. Further, there are some designs of metal cups that cannot be removed from the simulator without causing damage to the component. Data from a ceramic-on-metal simulator test confirmed that the short-term anomaly in gravimetric wear correlated with an increase in metal ion levels. Distraction testing evaluates the change in wear due to the unintended subluxation of the hip. This may occur during a standard walking gait if the hip is loose, during impingement, or during deep-knee bends, squatting, or rising from a chair. Distraction testing has various effects on wear depending on the material of the bearing couple. UHMWPE is insensitive to this additional mode of simulator testing. Metal-on-metal and ceramic-on-ceramic can increase in wear by up to an order of magnitude. The utilization of Biolox-delta rather than Biolox-forte can reduce the amount of wear seen during distraction testing. Diamond-on-diamond is insensitive to this wear mode and showed immeasurable wear. Other issues during testing of hard-on-hard bearings are still being explored. It is well known that 3rd body particles will disrupt fluid films and can increase wear. But the results from adding particles is variable. Metal-on-metal tests can have one specimen with very little increase while another specimen has an order of magnitude increase. Deformation of the shell caused by insertion during surgery has been shown to occur. Currently, this deformation has not been able to be replicated in a simulator, therefore, its effects are unknown. The design and laboratory testing of hard-on-hard bearings has improved significantly over the past decade. Further research is still needed to evaluate designs that may potentially increase resistance to failure modes other than standard walking gait cycles

Introduction. Modularity is being increasingly used throughout the world for both primary and revision total hip arthroplasty. Recently there have been concerns of increased corrosion and fretting at the modular junctions. In the SROM® modular hip system, two modular junctions are the head-neck taper junction and the stem-sleeve taper junction. The aim of this study was to investigate corrosion at these junctions with the use of different bearing materials. Methods. Between 1994 and 2012, fourty-two patients were revised with SROM® stems. Reasons for revision included aseptic loosening of the cup or stem (11), periprosthetic fracture (2), osteolysis (8), dislocation (13) and other reasons (7). One was revised for stem breakage, and this was excluded from this study. We examined 41 retrieved S-ROM® comprised of 6 metal-on-metal (MOM), 12 metal-on-polyethylene (MOP), 7 ceramic-on-polyethylene (COP) and 16 ceramic-on-ceramic (COC). The orientation for all components was marked at the time of revision surgery. Both the proximal sleeve/stem and the femoral head-neck modular junctions were examined under 10X magnification, and graded by two independent observers. The head tapers were divided into 4 regions, and graded using a previously published 3 point scoring system for fretting and corrosion damage (Goldberg et al, Kop et al), for a total corrosion damage score of 12. The SROM stems were also assessed at the sleeve/stem taper junction. Each stem was divided into 8 quadrants, and graded for corrosion and fretting using the same system as the taper. In addition to severity, we also quantified area of corrosion damage of the stem at the sleeve-stem junction from 0–3, which was multiplied by the severity of damage, to give a score out of 9 for each quadrant (maximum total score of 72 for the stem). The bearing type was unknown to the investigators, so the grading was done in a blinded fashion. Corrosion scores were divided by time to account for differences in time to revision. Results. Corrosion at the head-neck taper junction was higher for 17 stems with metal heads compared to 23 stems with ceramic heads (p=0.008). The average corrosion rate at the stem-sleeve taper junction in hips with hard-on-hard bearings (COC and MOM) was higher than polyethylene (MOP and COP) bearings, but this was not significant (p=0.07). Conclusions. Corrosion at the head-neck modular junction of hips with metal heads was greater than ceramic heads, likely due to galvanic corrosion in a mixed-metal system. Greater corrosion was found at the stem-sleeve taper junction in stems with hard-on-hard bearings. This may be related to friction in the bearings

In hip joint simulator studies, wear measurement is usually performed gravimetrically. This procedure is reliable for metal-on-polyethylene or ceramic-on-polyethylene bearings, in which relatively high amounts of abrasive wear particles are produced. With modern hard-on-hard bearings, volumetric wear decreases significantly up to 100 to 200-fold. The gravimetric method reaches its detection limit with metal-on-metal bearings and even more so with ceramic-on-ceramic bearings. This study establishes a new method of determining wear in hard-on-hard bearings by measuring the amount of worn particles/ions in the serum of hip simulators. A wear study on three resurfacing hip implants (BHR. ®. , Smith& Nephew) was conducted using a hip joint simulator. Prior to the wear study, tests were performed to validate the detection power for high resolution-inductively coupled plasma-mass spectrometry (HR-ICP-MS). More importantly the system’s accuracy was compared to the gravimetric method, which is described in ISO 14243-2. The simulator was altered to run completely metal ion free. The ion concentration in the serum was measured every 100 000 cycles up to 1 500 000 cycles and subsequently in intervals of 500 000 cycles using HR-ICP-MS. The implants were neither removed from the simulator nor excessively cleaned during the course of the simulation. Serum was refreshed every 500 000 cycles. The serum samples were digested with purified nitric acid and hydrogen peroxide using a high pressure microwave autoclave in order to measure wear particles as well as dissolved ions. All steps were carried out under clean room conditions. Wear was calculated using the ion concentration and measured serum volume. Wear rates and transition from running-in to steady-state wear phases were calculated. A detection power better than 0.028 μg/l for Co (cobalt), 0.017 μg/l for Cr (chromium) and 0.040 μg/l for Mo (molybdenum) was found for HR-ICP-MS. The validation of HR-ICP-MS showed good agreement between gravimetric data and measured ion concentrations. The tested implants showed similar wear behaviour. Implant wear resulted in high ion concentrations during the first 380 000 to 920 000 cycles. During this period, a mean wear rate of 6.96 mm3/10E6 cycles was determined. Subsequently, the wear rate significantly decreased to a mean wear rate of 0.37 mm3/10E6 cycles. Thus, a mean ratio between running-in and steady-state wear of 18.8 was found. The mean overall wear volume at the end of the simulation was 4.42 mm3. This study showed that measuring the ion concentrations in the serum of hip simulators can be used to determine wear in metal-on-metal bearings. The main advantages of this new method are the ability to detect ultra-low wear rates and to precisely specify the duration of different wear phases. Because the implants do not have to be removed from the simulator and aggressive cleaning processes may be skipped, fluctuations in wear detection are extremely low. This in turn leads to a shorter duration of the simulation. Wear rates of the tested implants are low compared to polyethylene. Transferring the results to patient activity, wear would be the same during the first four to six months after implantation as in the next ten years. Minimizing the duration of running-in would be most effective in further reducing wear of metal-on-metal bearings

Intentionally crosslinked polyethylene has improved the survivorship of total hip replacement and is the current standard bearing material for total hip arthroplasty. Regardless of the manufacturing method and counter-surface, the wear rates have been reduced on the order of 90% compared to historical materials, with a substantial reduction in the occurrence of osteolysis. Squeaking is not an issue. The wear of crosslinked polyethylene bearings has not shown the position sensitivity of hard-on-hard bearings. Liner fracture and dissociation have been reported, most commonly in association with malposition, and their occurrence has been decreased by improved modularity. Further, the consequences of a fractured polymeric bearing are substantially less than those of a fractured ceramic bearing. In most markets, there is a cost-differential favoring crosslinked polyethylene. A clinical advantage of ceramic-ceramic must be demonstrated, not theorised, before declaring it to be the new standard

INTRODUCTION. There is great potential for the use of computational tools within the design and test cycle for joint replacement devices. The increasing need for stratified treatments that are more relevant to specific patients, and implant testing under more realistic, less idealised, conditions, will progressively increase the pre-clinical experimental testing work load. If the outcomes of experimental tests can be predicted using low cost computational tools, then these tools can be embedded early in the design cycle, e.g. benchmarking various design concepts, optimising component geometrical features and virtually predicting factors affecting the implant performance. Rapid, predictive tools could also allow population-stratified scenario testing at an early design stage, resulting in devices which are better suited to a patient-specific approach to treatment. The aim of the current study was to demonstrate the ability of a rapid computational analysis tool to predict the behaviour of a total hip replacement (THR) device, specifically the risk of edge loading due to separation under experimental conditions. METHODS. A series of models of a 36mm BIOLOX. ®. Delta THR bearing (DePuy Synthes, Leeds, UK) were generated to match an experimental simulator study which included a mediolateral spring to cause lateral head separation due to a simulated mediolateral component misalignment of 4mm. A static, rigid, frictionless model was implemented in Python (PyEL, runtime: ∼1m), and results were compared against 1) a critically damped dynamic, rigid, FE model (runtime: ∼10h), 2) a critically damped dynamic, rigid, FE model with friction (µ = 0.05) (runtime: ∼10h), and 3) kinematic experimental test data from a hip simulator (ProSim EM13) under matching settings (runtime: ∼6h). Outputs recorded were the variation of mediolateral separation and force with time. RESULTS/DISCUSSION. The low cost PyEL model successfully replicated experimental trends in maximum separation with changing swing phase load. PyEL provided a good estimate of the high separation values which resulted from lower swing phase loads, but overestimated the separation resulting from higher swing phase loads. The separation verses time curve of the dynamic rigid FE (with and without friction) closely matched that of the PyEL model. Inertia caused a small delay when moving into and out of the cup (peak delay ∼0.025s). Therefore there was no substantial advantage to the more costly dynamic finite element models as a predictive design tool for hard-on-hard bearings

Traditional polyethylene oxidizes, wears and generates particles over time, which most probably contributes to increased risk of periprosthetic osteolysis. Even contemporary sterilization methods such as radiation and package in oxygen reduced or oxygen substituted environment do not eliminate oxidation over time. Thus, there is a need for alternative bearing in total hip replacement surgery and especially in patients with high activity and long life expectancy. All three major alternate bearings, ceramic-on-ceramic, metal-on-metal and highly crosslinked polyethylene produce major reductions in volumetric wear. The electron beam, melted highly cross-linked polyethylene has an in vivo penetration rate after the bedding in period, which is less than 8 microns per year. This is not substantially different from ceramic on ceramic or metal on metal. Therefore, the inherent risk of periprosthetic osteolysis with these alternate bearings is probably smaller than observed with conventional polyethylene. In the competition between different articulations highly cross-linked polyethylene has some advantages. The polyethylene is more adaptable than the hard bearing surfaces. This means that extended lip liners, offset liners, constrained liners and further special designs may be used. These options are not possible with any of the hard bearings. Another advantage with polyethylene is forgiveness. Impingement in hard-on-hard bearings may lead to serious complications such as chipping of the ceramics or metallosis in a metal on metal articulation. Impingement should also be avoided with use of polyethylene, but if it occurs, the consequences are often more benign at least in the short term perspective. Micro-separation results in less material damage with use of polyethylene than with the 2 other types of articulations. A few degrees of additional abduction above the geometrical limits for a particular socket is far less harmful if it is made of polyethylene compared to the situation in ceramic-on-ceramic or metal-on-metal bearings. Polyethylene is also more familiar to the majority of orthopaedic surgeons. In the operating room the cross-linked polyethylene is identical to those types of polyethylene, which have been used fore 3 to 4 decades. Finally the cost is a major factor (Harris 2004). The hard-on-hard bearings are substantially more expensive. The fracture incidence of ceramics components has decreased with improved manufacturing technology, but the risk of polyethylene fracture appears to be still smaller. On the other hand using highly cross-link polyethylene carries some risks. Particles generated from this new material are smaller with higher inflammatory response. Compared with joints including conventionally sterilised polyethylene the total particle production is, however, reduced with more than 85%, which has implications for the magnitude of the inflammatory response. The significance and importance of the irradiation and melting induced changes of the mechanical properties of the polyethylene is not known. Long term follow-up is needed to evaluate this issue. Charnley preferred small head sizes in total hip replacement because they resulted in transmittance of low frictional torque to the acetabular implant. Mueller advocated larger head sizes with improved joint stability and lower contact pressure. Large heads do, however, imply increased volumetric wear. Therefore, 32 mm heads were abandoned in the early 90ties in favour of 28 mm heads. Another consequence of using larger heads is that polyethylene liners are relatively thin. The highly cross-link polyethylene and the hard bearings can be used with bigger femoral heads, which increases the range of motion and the hip joint stability. Amorphous diamond coatings has been studied as an alternative bearing surface in the laboratory (Santavirta 2003). Such coatings may provide wear rates 104 to 105 times lower than conventional THR articulations, because of their extremely hard surface and low coefficient of friction without any corrosion paths (Santavirta et al. 1999 Lappalainen et al. 2003). Oxidized Zirconium (OxZr) is another material, which has similar advantages. Oxinium materials are the results of a process that allows thermally–driven oxygen to diffuse and transform the metallic zirconium alloy surface into a durable low-friction oxide. The Oxinium material is harder than commonly used cobalt chrome, and with only the surface changing during the manufacturing process, the rest of the implant remains metal to maintain its overall strength. OxZr provides superior abrasion resistance without the risk of brittle fracture, thereby combining the benefits of metal and ceramics. Knee simulator tests have shown that OxZr can reduce polyethylene wear substantially (Ries et al. 2002). Although promising, these two coatings still lack clinical documentation. During the last decade it has become evident that many designs of total hip arthroplasty can in patients with normal bone quality be fixed to the bone with a high degree of reproducibility. This has had the effect that younger patients have been operated on in increasing numbers. Wear and periprosthetic bone loss have remained a serious and comparatively frequent complications. The introduction of more wear resistant articulations has the potential to solve these problems making the procedure safer also among these patients. So far there is no or very scarce evidence that these articulations can be used safely during decades without complications causing progressive and often silent bone destruction resulting in difficult revisions with high morbidity. In the case of metal on metal articulations release and accumulation of ions remains a long term concern and especially if the patients will suffer from a temporary or permanent disease associated with impaired renal function. Because evidence of long term superiority of these new articulations is lacking it is of utmost importance that these new implants and materials are introduced into clinical practice in a controlled way. Careful surveillance of preclinical and gradually enlarged randomised studies followed by multicenter trials is necessary to avoid disastrous mistakes so common in the past

Background. Hard-on-hard bearings showed advantages of reduction of wear rates, osteolysis and aseptic loosening in total hip arthroplasty (THA). A new combination of ceramic-on-metal (COM) was developed to compensate the disadvantages of MOM and COC. COM showed good short-term results in vitro and in vivo studies. There was no report of stripe wear and metal ion level elevation. Our study was designed to evaluate the wear pattern of this bearing in early loosening THA. Methods. During January 2009 to December 2010, 121 primary THAs were performed at our institution by single-surgeon, using the same acetabular component and same uncemented femoral stem with a 32-mm modular head. All patients received the information of the bearing couples and made their own decision to choose one of the following bearings: COM, MOP and MOM. The functional outcomes (Harris Hip Score), Serum Co and Cr levels and survival rates were compared between groups at 5 years. The retrievals were tested by optical microscopy and Raman spectroscopy to evaluate the wear pattern in the cases those need revision. Results. At the follow-up 5 years ago, 2 in 10 patients of the COM group received revision due to bearing related complications and loosening although MOP and MOM groups have good clinical follow-up without revision. Metal ion levels were higher in the revision cases. The retrieval analyses revealed metal transfer at weight-bearing area of ceramic femoral head and large wear located on the center of acetabular liner. Spectral shift and broadening of Raman bands demonstrated incorporation of metal ions into the ceramic lattices. Conclusion. Wear pattern in COM was the same as MOM. Severe metal contamination at the ceramic surface might be affected from frictional heating. While the actual causes and contributing factors of high failure rate in COM were not clearly identified, it is important to take precautions in using COM THA

Introduction:. Hard-on-hard bearings and surface replacement (SR) have been used in young and active patients due to the reduced wear and lower rates of osteolysis. However, neither of these options resulted in survivorship higher than 90%–95% in this group of patients. The purpose of this prospective study was to compare minimum 10-year survivorship of non-cemented total hip arthroplasty (THA) using 28 mm metal head against highly-cross linked polyethylene (HXLPE) in our cohort as compared to published reports of other bearings, including surface replacements, in young-active patients. Matierial and Methods:. From 1999 to 2003, 91 consecutive patients (112 hips; 57 males and 34 females) with average UCLA score of 8 and mean age 53 years (range 24–65 years), who received metal on HXLP (Crossfire), were included. At minimum 10-years follow-up, patients' clinical data was assessed. All level I, II studies, registry data, and prospective cohorts published in the literature with minimum 10 years of surface replacement (SR) and ceramic on ceramic (CoC) in young patients were included. Results:. There were no revisions for fracture, osteolysis or loosening. There were 2 revisions: one periprosthetic infection and one chronic dislocation. Kaplan-Meier survivorship was 97% for all cause failures and 100% for wear-related failures. In review of the literature, the 10-year results of metal on HCLPE in young patients as well as the registry data were similar or better than SR and CoC. Discussion and Conclusion:. This study demonstrates that 28 mm metal head on HXLPE has lower revision rates as compared to other bearings and surface replacement in the published literature at a minimum 10-year follow-up in young-active patients, without the limitations of heard-on-heard bearings. This bearing should be considered as the gold standard for young and middle age patients. Oxidation of Crossfire is an overly stated limitation

Total hip arthroplasty (THA) performed in patients aged 60 years and younger requires several decades of implant use under increased activity demands. Implant longevity and stable fixation are necessary for 30 or more years. The search for the optimal bearing combination for use in younger, high demand patients presents a challenge for orthopaedic surgeons as they consider the pros and cons of each material and interaction. A recent U.S. study of implant utilization trends that included 174 hospitals and 105,000 THA between 2001 and 2012 found that in 2012 93% of THA were cementless and 35% of THA bearings were ceramic-on-highly crosslinked polyethylene (HXLPE). Another recent article used the Nationwide Inpatient Sample from 2009 to 2012 to study bearing usage trends in 9265 primary THA in patients 30 years old or younger. The researchers observed ceramic-on-polyethylene as the most commonly bearing surface, used in 36% of patients, and which represented an increase from an earlier study of extremely young patients undergoing primary THA between 2006 to 2009, use of so-called hard-on-hard bearings decreased. Benefits of ceramic-on-HXLPE bearings are that unlike metal-on-polyethylene and metal-on-metal combinations, taperosis and adverse reactions to metal debris are non-existent. Ceramic-on-polyethylene is forgiving, it is an extremely low wear couple, it is the current presenter's bearing of choice in high demand patients, and it is a good option in the scenario of revision of failed metal-on-metal or for taperosis. Advantages to bulk ceramics are: extremely hard and scratch resistant to third body wear, not damaged by instruments and repositioning, excellent wettability, extreme low wear against itself with no known pathogenic reaction to ceramic particles, inherently stable with no oxidation or aging effect, no corrosion, safe in terms of metal ion release, no known risk of hypersensitivity or allergy, and no concerns about biological reaction. Biolox® (Ceramtec AG; Plochingen, Germany) ceramics have been available since 1974, with fourth generation Biolox® Delta introduced in 2003. Extensive clinical experience includes over 1630 published studies with over 12 million Biolox® components implanted with almost every available hip system. Two recent meta-analyses studies of randomised controlled trials comparing ceramic-on-ceramic to ceramic-on-polyethylene found significantly higher linear wear in ceramic-on-polyethylene but higher incidences of noise and fracture in ceramic-on-ceramic THA. There were no differences in revision, function, dislocation, osteolysis or loosening. A recent meta-analysis review of randomised controlled trials reporting survivorship of ceramic-on-ceramic, ceramic-on-HXLPE, and metal-on-HXLPE found no difference among bearing surfaces in risk of revision after primary THA in patients younger than 65. Risk ratio for revision was 0.65 (p=0.50) between ceramic-on-ceramic and ceramic-on-HXLPE, and 0.40 (p=0.34) between ceramic-on-ceramic and metal-on-HXLPE. A recent study of ceramic-on-HXLPE bearings for 130 cementless THA in 119 patients younger than 50 years at mean follow-up of 8.3 years (range, 7–9) reported a mean post-operative Harris hip score of 94, UCLA activity score of 8.1, no acetabular revisions, no osteolysis, no head or liner fracture, and 0.022 ± 0.003 mean annual penetration rate of the femoral head. While longer follow-up is necessary, ceramic-on-HXLPE bearings are an attractive option in younger, high demand patients undergoing primary THA

The inability to consistently position components is associated with the major complications of hip replacement including instability, wear, liner breakage, limb length discrepancy, and limited function. This was a major catalyst for the demise of hard-on-hard bearings. The greatest challenge is accurate, reproducible positioning of acetabular component which is obtained in a surprisingly low percentage of cases. Other major issues include consistently obtaining proper limb length, offset, component sizing, and complete seating without fracture of either the acetabulum or the femur. There are two approaches to this issue; to either use virtual reality which applies technology that provides surrogates to direct visualization of components. The major issues with computer assisted techniques include questions of accuracy and increased time and cost. The other approach is to utilise intraoperative imaging which has been the gold standard traditionally, however, previously it has been a challenge to utilise intraoperative imaging without adding substantial time and cost. Historically intraoperative imaging has not been adopted because it disrupts work flow, the quality of images has been inadequate, and it has added too much additional time to allow for a series of repeat radiographs to be obtained. Modifications of existing portable imaging that utilise direct radiography (DR plate technology) allow for intraoperative images that display within seconds. Imbedded software allows measurement of all parameters of interest. Three or 4 systems are currently in use, and this is not virtual reality but it is the gold standard. Advantages include higher quality images, faster service speed, minimal impact on OR work flow, eventual reduction in operating costs, elimination of processing of chemicals and film room/storage room, and most importantly the elimination of outliers and return to the operating room due to unexpected findings on recovery room radiographs. Intraoperative imaging has been utilised at a number of centers in recent years and has led to numerous intraoperative changes to optimise component implantation in a surprisingly high percentage of cases. Advances in technology have made intraoperative digital imaging a practical feasible strategy to avoid outliers that increase complications and compromise results. The rapidly evolving technology makes this a very attractive option for optimising total hip component placement. In addition it is an excellent teaching tool that is rapidly embraced by residents and fellows and is an extremely effective in eliminating outliers

Wear testing of THR has chaperoned generations of improved UHMWPE bearings into wide clinical use. However, previous in vitro testing failed to screen many metal-on-metal hips which failed. This talk tours hip wear testing and associated standards, giving an assortment of THR wear test results from the author's laboratory as examples. Two international hip wear-simulator standards are used: ISO-14242-1 (anatomic configuration) and ISO-14242-3 (orbital-bearing). Both prescribe 5 million (MC) force-motion cycles involving cross-shear synchronized with compression simulating walking gate of ideally aligned THRs. ISO-14242-1 imposes flexion (flex), abduction-adduction (ad-ab) and internal-external (IE) rotations independently and simultaneously. An orbital-bearing simulator more simply rotates either a tilted femoral head or acetabular component, switching from flexion-dominated to ad-ab-dominated phases in each cycle with some IE. In the latter, the acetabular component is typically placed below the femoral head to accentuate abrasive conditions, trapping third-body-wear debris. Wear is measured (ISO-14242-2) gravimetrically (or volumetrically in some hard-on-hard bearings). Wear-rate ranges from negligible to >80mg/MC beyond what causes osteolysis. This mode-1 adhesive wear can therefore “discriminate” to screen hip designs-materials in average conditions. Stair-climbing, sitting, squatting and other activities may cause THR edge-loading and even impingement with smaller head-to-neck ratios or coverage angle, naturally worse in metal-on metal hips. Deformation of thin acetabular components during surgical impaction may cause elevated friction or metal-metal contact, shedding more metal-ions and accelerating failure. Surgical misalignments in inclination angle, version and tilt can make this worse, even during modest activities in hard-on-hard bearings. Abrasive particulate debris from bone or bone-cement, hydroxyapatite, neck-impingement, normal wear, or corrosion can compound the above. Such debris can scratch the femoral head surface, or embed in the UHMWPE liner compromising the wear of even metal-on-plastic hips. Much of the belated standardization activity for higher demand hip testing is in response to the metal-metal failures. ASTM F3047M is a recent non-prescriptive guide for what more rigorous testing can generally be done. Third-body particulate can be intentionally introduced or random scratching of the femoral component surface in extra abrasion testing. Also, the compressive load can be increased, more frequent start-stops to disrupt lubrication, and steepening acetabular shell-liner angles to reduce contact area and cause edge-loading, made harsher when combined with version misalignment. Transient separation can occur between head and liner during the swing phase in a lax THR joint with low coverage angle and misalignments; the separated head impacts the liner rim when reseating. An edge-loading ISO test is currently being discussed where (so-called) “microseparation” to a known distance is directly imposed by a lateral spring force in a hip simulator. Friction testing of a THR in a pendulum-like setup undergoing flexion or abduction swings is being discussed in the ASTM, and so have multi-dimensional THR friction measurements during a long-term wear test simultaneously measuring and separating friction of three rotational (flex, ad-ab, and IE) axes. THR wear test methods continue to evolve to address more challenges such as novel duo-mobility THR designs, where UHMWPE bearings cannot be removed for gravimetric wear measurements

Introduction. Concerns regarding UHMWPE wear particle induced osteolysis in total hip replacement (THR, [1]) have led to alternative materials to be sought. Carbon-fibre reinforced poly-ether-ether-ketone (CFR-PEEK) has shown reduced wear in hip and knee configurations compared with conventional polyethylene [2-4]. The aim of this study was to investigate the wear performance of a ceramic-on-CFR PEEK THR through a simulator study. Methodology. Five 36mm diameter Biolox Delta heads were paired with extruded CFR-PEEK cups and tested in a hip wear simulator (Simulator Solutions, UK) for 10 million cycles (Mc). Tests were performed in a Prosim hip simulator, which applied a twin peak loading cycle, with a peak load of 3kN. Flexion-extension of −15 to +30 degrees was applied to the head and internal-external rotation of +/− 10 degrees was applied to the cup, components were mounted anatomically. The lubricant was 25% (v/v) calf serum supplemented with 0.03% (w/v) sodium azide. Wear was assessed gravimetrically at several intervals adjusted for moisture uptake using loaded and unloaded soak controls. Results. The volumetric wear of the CFR-PEEK cups was calculated from weight loss, corrected for fluid uptake by a mean value of the loaded and unloaded soak controls. The CFR-PEEK bearings exhibited step-like wear behaviour throughout the study (Figure 1), with periods of ‘higher’ wear rate (between 0.4mm–1.4mm. 3. /Mc) and periods of a ‘lower’ wear rate (less than 0.4mm. 3. /Mc), a phenomenon that has previously been observed with this material [3]]). Discussion. The wear of a novel ram-extruded CFR-PEEK cup, articulating with a Biolox Delta ceramic head was assessed through a 10Mc experimental wear study. The mean wear rate over the period of the study was very low, with less than 1mm. 3. /Mc measured. The wear rates observed in this study are comparable with reported wear rates for 36mm diameter hard-on-hard bearings [5], and lower than wear rates measured for a highly cross-linked polyethylene bearing [6]. The wear rates reported in this study are lower than those previously reported [3], however, as CFR-PEEK operates within a boundary lubrication regime, the reduced head diameter in the present study would result in reduced sliding distance and lower surface wear

A multitude of different bearing combinations exist to recreate the artificial hip joint. To date, there is no particular ‘gold-standard’ total hip arthroplasty (THA) couple since none is faultless. Strategies to improve performance are aimed either at modifying the shape and design of components or their material properties. Wear particle generation is now well recognised as a cause of aseptic loosening which consistently features amongst the most common indication for revision THA and thus minimising wear lies at the cornerstone of developing bearing couples. However, history has shown the use of supposed newer and improved materials have not been without occasional catastrophic failure. Hard-on-hard bearings are theoretically more resistant to wear but component fracture and squeaking has been witnessed with ceramic-on-ceramic articulations whilst metal-on-metal articulations have been plagued by reports of pseudotumor and ALVAL formation. This has all led to resurgence in the hard-on-soft couple. More recently, corrosion at taper junctions has been identified as a significant factor in hip arthroplasty failure. Femoral head materials, surface changes or coatings may therefore have an increasing role to play. In 2005, a multi-center, prospective, assessor and patient-blinded, randomised control trial was initiated. This was designed as a three armed study with either cobalt-chrome or oxidized zirconium femoral heads articulating against highly cross-linked polyethylene (XLPE) liners and oxidized zirconium articulating against ultra-high molecular weight polyethylene (UHMWPE). Early reports that XLPE was significantly superior to UHMWPE when coupled with cobalt-chrome meant no patient involved in the study was approved to receive a couple of cobalt-chrome and UHMWPE since it was deemed to be a high wear group. We hypothesised that oxidized zirconium femoral heads would produce less linear wear than cobalt- chrome femoral heads at mid-term evaluation, whilst maintain similar outcomes when recording WOMAC, SF-36 and pain scores, and complication rates. All three groups were statistically comparable preoperatively and at five years when measuring normalised WOMAC, SF-36 and pain scale scores; all groups showed a statistically significant improvement in scores from baseline compared to at five years (p<0.001). There was no significant difference in mean femoral head penetration when either oxidized zirconium or cobalt-chrome where articulated with XLPE (p=0.1533) but a significant difference in mean femoral head penetration was observed between the group that had used UHMWPE and both the other groups which had used XLPE (p<0.001). There were no hips in which either acetabular or femoral osteolysis was observed. We have demonstrated that oxidized zirconium femoral heads are safe with low rates of wear when coupled with XLPE. However at five year follow-up, it appears that the choice of material of the acetabular bearing is more important than the choice of femoral head bearing. Further follow-up is needed in order to see if femoral head choice leads to a difference in outcome beyond 5 years as laboratory data suggests. Moreover the potential reduction of corrosion with ceramic or oxidized zirconium heads may yet also prove to be significant. It is likely that current and future data will lead us away from the use cobalt chrome heads towards alternatives that are less likely to be associated with corrosion or wear and osteolysis

The use of hard-on-hard bearings, including ceramics peaked in the mid 2000's and has seen rapid decline since that time. Ceramics are not new to the market place but have had a 40 year history outside the U.S. The basis for renewed enthusiasm for ceramics included improved manufacturing, improved taper tolerances, higher strength, and lower wear. In spite of the major improvements concerns have been expressed with new generation ceramics by the experts and thought leaders in the field. The major concerns included complications related to modularity, continued problems with fracture and consequences of fracture, limited surgical options, and squeaking and impingement. The conclusion of one review article was that “although ceramics show promise as a lower wear articulation, manufacturing and design modifications and improvements will continue in an attempt to address the substantial concerns that persist”. Modifications have indeed occurred. The question is rather all of these concerns have been addressed and the answer is no. One proposed solution was a hybrid material of Alumina and Zirconia (Delta Ceramic). The advantages included higher strength, lower wear, more options and possibly less squeaking. Unfortunately the modest material improvements did not begin to overcome the obstacles to adopting this technology. High on this list is the problem with cost with the current health care environment unwilling to pay for expensive new technology that does not have proven value. A 2nd major issue is new technology must account for variability in surgeon performance in maximising margin for error. The medical legal environment is unforgiving of failure of new unproven options. Most of the old issues with ceramics have not been completely resolved. Delta Ceramic in particular, has increased cost with no demonstrated benefit. A major problem is there is no known problem with metal or ceramic against cross-linked polyethylene bearing in terms of wear or osteolysis in the 10–15 year time frame. Among all the bearing articulations, metal-on-cross-linked performs the best. The persistent vexing problems with ceramics include impingement, liner breakage, and squeaking. Ceramic components do not tolerate component malposition which increases wear and squeaking. The problem is that a substantial percentage of hip replacements are put in outside of the ideal radiographic zone even at specialty centers. Breakage continues to be a problem especially with liners. There is also a need for complete rim exposure for concentric placement with impaction of liners which makes ceramics less compatible with small incision surgery. The problem of squeaking has not been solved by Delta Ceramic. Originally a case report appeared in the literature of squeaking with Delta Ceramic. Since that time a large scale study has showed that only 69% of Delta Ceramic hips were silent with up to 13% being associated with reproducible squeaking. While a new generation of ceramics are better than the earlier generation and have lowered the fracture risk and increased intraoperative options, the current generation ceramics still provide far fewer options than a standard metal-on-cross-linked total hip. The current generation metal-on-cross-linked total hips have 10–15 year results that cannot be improved upon in terms of wear and osteolysis. Other unsolved problems include breaking, chipping and squeaking. Ceramic-on-ceramic is less tolerant of suboptimal position which leads to impingement, edge loading, and an increased incidence of squeaking. Until all of these problems are successfully addressed, ceramic-on-ceramic cannot be advocated for widespread use

INTRODUCTION. The introduction of hard-on-hard bearings and the consequences of increased wear due to edge-loading have renewed interest in the importance of acetabular component orientation for implant survival and functional outcome following hip arthroplasty. Some studies have shown increased dislocation risk when the cup is mal-oriented which has led to the identification of a safe-zone1. The aims of this prospective, multi-centered study of primary total hip arthroplasty (THA) were to: 1. Identify factors that influence cup orientation and 2. Describe the effect of cup orientation on clinical outcome. METHODS. In a prospective study involving seven UK centers, patients undergoing primary THA between January 1999 and January 2002 were recruited. All patients underwent detailed assessment pre-operatively as well as post-op. Assessment included data on patient demographics, clinical outcome, complications and further surgery/revision. 681 primary THAs had adequate radiographs for inclusion. 590 hips received cemented cups. The primary functional outcome measure of the study was the change between pre-operative and at latest follow up OHS (OHS). Secondary outcome measures included dislocation rate and revision surgery. EBRA was used to determine acetabular inclination and version. The influence of patient's gender, BMI, surgeon's grade and approach on cup orientation was examined. Four different zones tested as possibly ± (Lewinnek Zone, Callanan's described zone and zones ± 5 and ±10 about the study's mean inclination and anteversion) for a reduced dislocation risk and an optimal functional outcome. RESULTS. There were 21 dislocations (3.1%) and 8 (1.2%) patients required revision at a mean follow up of 7 years. Experienced surgeons (2=0.047) and those operating with the patient in the lateral decubitus position (p=0.04) were more likely to achieve a cup orientation within any of the tested zones. Surgical approach (2=0.14) and patient's BMI (2=0.93) had no influence on whether a cup was within or outside any zone. There was no difference in dislocation rate between the posterior and anterio-lateral approaches (2=0.88). None of the zones tested had a significantly reduced dislocation risk (2=0.13), nor revision risk (2=0.55). OHS was not different for patients with cups within or outside any of the zones tested (p=0.523). DISCUSSION. There was a wide variation in cup orientation. Despite the wide scatter in cup orientation, no safe zone could be identified that would reduce dislocation and revision rate, nor improve patient reported outcome (OHS). Hence, these data suggest that acetabular component orientation should not be considered predictive of patients' early/mid-term complication/revision rate and outcome following THA

Introduction: The tribiological properties of bearing surfaces are one of the main topics in discussion in the orthopaedic research. Hard-on-hard bearings are one of the ways to reduce wear rates. Modern hard-on-hard bearing low wear rates depend on the correct pairing of bearing surfaces and strict manufacturing tolerances in surface roughness, clearance, and roundness. There have been some concerns in using ceramic bearings, particularly regarding the fracture rate and their subsequent management. Hence, we present here 2 similar cases that highlight the catastrophic failure of metal head when used subsequently to treat the complication of ceramic fractures in Total Hip Arthroplasty (THA). Case Details: Two patients underwent primary THA at different centres with ceramic-on-ceramic bearing. After an initial asymptomatic period of 2 years, ceramic fracture occurred in both the cases, which were subsequently replaced by metal-on-polyethylene bearings by the primary surgeons. One year after the revision of bearings, both the patients developed severe pain and discomfort, which on further investigation revealed massive metallosis, wear of the metal head and aseptic loosening of the acetabular components with cavitation in acetabulum. Both the patients underwent revision THA under the senior author at our tertiary centre-Wrightington Hospital. Intraoperatively near total erosion of the metal head was noted with more than one litre of black, dense material collection in and around the hip joint revealing extensive metallosis. The acetabular cup was grossly loose and significant loss of bone stock was noted due to metallosis. Single stage revision surgery was performed with impaction bone grafting for deficient acetabulum and cemented components were used. At one-year follow-up none of the cases have shown any further wear or complications. Conclusion: One of the main objectives of successful THA is to improve implant longevity. To achieve this understanding the mechanisms of wear between the interacting surfaces is extremely important. The use of ceramic head is good, but there is always a risk of fracture. We do not recommend using metal heads in cases with prior ceramic fractures, as the wear of metal is most likely to occur as it is an ongoing process due to the residual ceramic debris. Hence in these difficult scenarios we recommend usage of ceramic-on-polyethylene as a safe option to prevent catastrophic erosion of metal head and improve implant longevity

The extension of THR to younger and more demanding patients implies the need of bearings enhancing the implants survival, raising the interest on hard-on-hard bearings (metal-on-metal and ceramic-on-ceramic). The standard bearing diameters in THR range from 7/8in (22,225 mm) to 32 mm. Larger diameter bearings were used by McKee-Farrar and Ring THR a solution that was abandoned after the success of Charnley Low Friction Arthroplasty that offered the advantage of much lower torques at the implant-bone interface, due also to the state-of-the-art of the cementation in the early 1960s. Increasing the diameter of THR bearings offers several advantages in terms of increased stability of the joint, as a larger displacement is necessary to produce the joint subluxation, and for a given neck diameter the risk of impingement is reduced while the prosthesis range of motion is increased. The reduced wear of metal-on-metal and ceramic-on-ceramic bearings has led recently to revitalise the design concept of the early THR designs, and large diameter joints today are available in sizes ranging from 36 to 52 mm. Large metal-on-metal bearings are used mostly in resurfacing prostheses. This surgery, which requires a specific surgical training, is indicated for patients performing physical activity, as those patients are relatively young, and have a long life expectation. This raises-some concerns, as increased cobalt and chromium concentrations were measured in the blood and urine of patients having Metal on Metal bearings and the effect of such high metal concentration in the long time is still unknown, as it is controversial if the metal ions are originated by wear debris of by the corrosion of the implant. Recently 36 mm ceramic on ceramic bearings were introduced in THR as a solutions to overcome many of the problems of metal-on-metal joints. Ceramic-on-ceramic bearings have a 35-year clinical history in THR. The extremely low wear of these joints is well assessed , as well as the extreme biocompatibil-ity of the material and the absence of local and systemic negative reaction to ceramic debris. Besides the enhanced safety of the design of the 36 mm heads, the development of thin ceramic inserts allowed to limit the overall diameter of the cup. It is expected that the use of the new alumina matrix composites will allow to further enhance the performances of large diameter ceramic THR bearings