Introduction. Ceramic femoral heads have superior scratch resistant with better wettability and improved wear characteristics compared to metal heads in the laboratory setting. The objective of this study was to compare long-term in vivo wear rates of ceramic and metal femoral heads against conventional polyethylene articulation with cementless stems in young, active patients. Materials and Methods. Thirty-one matched pair of alumina and metal (Cr-Co) femoral heads against conventional polyethylene in young patients (between 45 and 65 years old) were analyzed for wear and failures for mechanical reasons. The match was based on gender and age at the time of surgery. All procedures were performed between June 1989 and May 1992 by a single surgeon via posterolateral approach, using cementless RB (Ranawat-Bernstein) stems, HG II (Harris-Galante) cups, 4150 conventional polyethylene and 28 mm femoral heads. Hospital for Special Surgery (HSS) hip score was used for clinical analysis. Wear measurements were performed between the initial anteroposterior standing pelvis radiographs, at a minimum of one year after the index procedure to eliminate the effect of bedding-in period, and the latest follow-up. Two independent observers analyzed polyethylene wear rates using the computer-assisted Roman 1.70 software. In revision cases, the wear rates were calculated from radiographs prior to revision surgery. A pair student t test was performed to analyze the statistical difference. Two-tailed ρ values less than 0.05 were considered statistically significant. Results. The mean age was 54.5 ± 8.5 at the time of surgery (range 23.3–65). Average clinical and radiographic follow-up were 17 ± 2.1 (range 12.8–20) and 14.1±2.6 years (range 10–19.1) respectively. The mean HSS score in ceramic and metal groups were 30.4 ± 8 (range 24–56) and 36.6 ± 4.7 (range 20–40) respectively. The mean wear rate for the ceramic group and the metal group were 0.086 ± 0.046 mm/year and 0.137 ± 0.052 mm/year, respectively which was statistically significant (p < 0.001). There were no revisions in the ceramic group for osteolysis or loosening, however one patient required a strut graft for femoral osteolysis that was distal to the tip of the implant due to non-circumferential porous coating of the stem. There were 3 cup revisions in the metal group, all for acetabular osteolysis, and no stem lysis or loosening. Discussion and Conclusion. The low mean wear rate of ceramic compared to metal in this study is consistent with previously published laboratory reports. There was no revision for loosening or osteolysis in the ceramic group, which demonstrates superior durability compared to metal femoral heads. The strength of this study is that this is the first long-term report comparing ceramic and metal femoral heads against conventional polyethylene with cementless stems using a matched pair analysis in young patients

Introduction. Ceramic femoral heads have proven to be more scratch resistant with better wettability and improved wear characteristics compared to metal heads in the laboratory setting. The objective of this study was to compare long-term survivorship and in vivo wear rates of ceramic and metal femoral heads against conventional polyethylene articulation in young patients. Materials and Methods. Thirty-one matched pair of alumina and metal femoral heads against conventional polyethylene in young patients (≤ 65 years) were analyzed for wear and failures for mechanical reasons. The match was based on gender and age at the time of surgery. All procedures were performed between June 1989 and May 1992 by a single surgeon via posterolateral approach, using non-cemented RB (Ranawat-Bernstein) stems, HG II (Harris-Galante) cups, 4150 conventional polyethylene and 28mm femoral heads. Hospital for Special Surgery (HSS) hip score was used for clinical analysis. Wear measurements were performed between the initial anteroposterior standing pelvis radiographs, at a minimum of one year after the index procedure to eliminate the effect of bedding-in period, and the latest follow-up. Two independent observers analyzed polyethylene wear rates using the computer-assisted Roman 1.70 software. In revision cases, the wear rates were calculated from radiographs prior to revision surgery. A pair student t test was performed to analyze the statistical difference. Two-tailed ρ values less than 0.05 were considered statistically significant. Results. The mean age was 54.5 ± 8.5 at the time of surgery (range 23.3–65). Average clinical and radiographic follow-up were 17 ± 2.1 (range 12.8–20) and 14.1 ± 2.6 years (range 10–19.1) respectively. The mean HSS score in ceramic and metal groups were 30.4 ± 8 (range 24–56) and 36.6 ± 4.7 (range 20–40) respectively. The mean wear rate for the ceramic group and the metal group were 0.086 ± 0.046 mm/year and 0.137 ± 0.052 mm/year, respectively which was statistically significant (p < 0.001). There were no revisions in the ceramic group for osteolysis or loosening, however one patient required a strut graft for femoral osteolysis that was distal to the tip of the implant due to non-circumferential porous coating of the stem. There were 3 cup revisions in the metal group, all for acetabular osteolysis, and no stem lysis or loosening. The Kaplan-Meier survivorship for revision for mechanical failure in the ceramic and metal group was 100% and 90.3% respectively. Discussion. The low mean wear rate of ceramic compared to metal in this study is consistent with previously published laboratory reports. There was no revision for loosening or osteolysis in the ceramic group, with 100% survivorship for revision due to mechanical failures, which demonstrates superior durability of this material compared to metal femoral heads. The strength of this study is that this the first long-term report comparing ceramic and metal femoral heads against conventional polyethylene using a matched pair analysis in young patients

Purpose of Study:. To look at the difference in metal ion levels using Ceramic on Metal (COM) and Metal on Metal (MOM) bearings in Total Hip Replacements, comparing the results between well placed and poorly placed cups. Methods:. Metal ion levels using the ICP-MS method of assay have been studied as part of a prospective randomised trial between 4 different bearing combinations. The ion levels have been raised in the COM and MOM bearings. Metal ions are not raised in the Ceramic on Ceramic (COC) and Ceramic on X linked Poly(COP) bearings, showing that no other material in the study prosthesis aside from the bearing surfaces contribute to raised ion levels. Cup inclination and cup anteversion has been measured in all patients. Results:. At 3 year follow-up the Cobalt and Chrome levels are significantly lower with the COM bearing than the MOM bearing when both well and poorly placed cups are included, and seem to be returning to normal pre-operative levels. Taking cups put in in Lewinnik's safe zones, then the Chrome levels are similar between the two bearings, but the Cobalt levels remain raised in the MOM bearing. Conclusion:. Cobalt and Chrome levels are significantly lower in COM bearings than MOM bearings when cups are not placed in the ideal position. This represents an added advantage in the use of COM bearings as compared to MOM bearings

This study presents an unusual recurrent case of pigmented villonodular synovitis (PVNS) around a ceramic-on-metal (COM) hip retrieved at 9-years. PVNS literature relates to metal-polyethylene and ceramic-ceramic bearings. Amstutz reported 2 cases with MOM resurfacing and Xiaomei reported PVNS recurring at 14 years with metal-on-polyethylene THA. Friedman reported on PVNS recurrence in a ceramic THA. Ours may be the first reported case of recurrent PVNS of a ceramic-on-metal articulation.

This young female patient (now 38-years of age) had a total hip replacement in 2006 for PVNS in her left hip. In her initial work-up, this case was presumed to be a pseudotumor problem, typical of those related to CoCr debris with high metal-ion concentrations. She had an CoCr stem (AML), 36mm Biolox-delta head (Ceramtec), and a Pinnacle acetabular cup with CoCr liner (Ultramet, Depuy J&J). This patient had no concerns regarding subluxation, dislocation or squeaking. Three years ago she complained of mild to moderate groin and thigh pain in her left hip. This worsened in the past year. She noticed increased swelling now with an asymmetry to her right hip. She went to the emergency room in Dec-2014 and was referred to a plastic surgeon. In our consult we reviewed MARS-MRI and CT-scans that demonstrated multiple mass lesions surrounding the hip. Laboratory results presented Co=0.7, Cr=0.3 ESR=38 and Crp=0.3.

At revision surgery, the joint fluid was hemorrhagic/bloody with hemosiderin staining the soft tissues. Multiple large 4–5×5cm nodules were present in anterior aspect of the hip as well as multiple nodules surrounding posterior capsule and sciatic nerve. Pathology demonstrated a very cellular matrix with hemosiderin-stained tissue and multiple giant cells, which was judged consistent with PVNS. The trunnion showed no fretting, no contamination and no discoloration. The superior neck showed impingement due to low-inclination cup. There was minimal evidence of metal-debris staining the tissues. There was a large metallic-like stripe across the ceramic head.

This is a particularly interesting case and may be the first reported recurrent PVNS around a ceramic-on-metal bearing (COM). Data is scant regarding clinical results of COM bearings and here we have a nine-year result in a young and active female patient. She was believed to have a metalosis-related pseudotumor yet her metal-ion levels were not alarmingly high and there was no particular evidence of implant damage or gross wear products. In addition, the CoCr trunnion appeared pristine. Our work-up continues with analyses of wear and histopath-evidence. This case may demonstrate the need for a broadening of the differential diagnosis when dealing with hip failures.

Introduction

Hip replacements are falling short of matching the life expectancy of coxarthritis patients, due to implanting THR in younger patients and due to increasingly active patients. The most frequently implanted hip prostheses use cross linked (XL) polyethylene (PE) on metal bearings in the USA and most of the Western world. Concerns remain in the long term around the potential of wear debris-induced aseptic loosening. Thus exploring lower-wearing alternative bearings remains a major research goal.

PEEK (poly-ether-ether-ketone) is a thermoplastic polymer with enhanced mechanical properties. This study compared the wear of PEEK to the wear of cross linked polyethylene, when sliding against cobalt chrome (CoCr) metallic counterfaces, and compared the wear of carbon-fibre reinforced (CFR)-PEEK to cross linked polyethylene when sliding against metallic and ceramic counterfaces under different contact stresses within the hip joint.

Introduction

The process of wear and corrosion at the head-neck junction of a total hip replacement is initiated when the femoral head and stem are joined together during surgery. To date, the effects of the surface topography of the femoral head and metal stem on the contact mechanics during assembly and thus on tribology and fretting corrosion during service life of the implant are not well understood. Therefore, the objective of this study was to investigate the influence of the surface topography of the metal stem taper on contact mechanics and wear during assembly of the head-neck junction using Finite Element models.

Background

The main reasons for hip prosthesis failure are aseptic loosening and periprosthetic joint infection (PJI). The real frequency of PJI is probably largely underestimated because of non-standardized definition criteria, diagnostic procedure, treatment algorithm and other confounders. Therefore, data from joint registries are not reflecting the frequency of PJI and can be misleading; particularly low-grade PJI can be frequently misdiagnosed as aseptic failure. Therefore, prospective clinical studies with standardized protocol, comprehensive diagnostic procedure and sufficient follow-up should be performed. Sonication of explanted prosthesis is highly sensitive for detection of biofilms on prosthetic surface and allows quantitative analysis of biofilm formation. We hypothesize that by using sonication, ceramic components (BIOLOX®delta, BIOLOX®forte) will show higher resistance against biofilm adhesion compared to polyethylene (PE) and metal (CoCrMo).

Introduction. Significant reduction in the wear of current orthopaedic bearing materials has made it challenging to isolate wear debris from simulator lubricants. Ceramics such as silicon nitride (SiN), as well as ceramic-like surface coatings on metal substrates have been explored as potential alternatives to conventional implant materials. Current isolation methods were designed for isolating conventional metal, UHMWPE and ceramic wear debris. The objective of this study was to develop methodology for isolation and characterisation of modern ceramic or ceramic-like coating particles and metal wear particles from serum lubricants under ultra-low wearing conditions. Sodium polytungstate (SPT) was used as a novel density gradient medium due to its properties, such as high water solubility, the fact that it is non-toxic and acts as a protein denaturant, coupled with a large density range of 1.1–3.0 g/cm3 in water. Methods. SiN nanoparticles (<50nm nanopowder, Sigma-Aldrich) and clinically relevant cobalt-chromium wear debris were added to 25% (v/v) bovine serum lubricant at concentrations of 0.03 and 0.3 mm3/ million cycles. The particles were isolated by a newly developed method using SPT gradients. The sample volume was reduced by centrifuging the lubricant at 160,000 g for 3 h at 20°C. Then, re-suspended pellet was digested twice with 0.5 mg/ml proteinse K for 18 hours at 50°C in the presence of 0.5% (w/v) SDS. Particles were then isolated from partially hydrolysed proteins by density gradient ultracentrifugation at 270,000 g for 4 h using SPT gradients [Figure 1]. At the end of centrifugation, particles were pelleted at the bottom of the centrifuge tube, leaving protein fragments and other impurities suspended higher up the tube. Isolated particles were then washed with pyrogen free water, dispersed by sonication and filtered through 15 nm polycarbonate membrane filters for SEM and EDX analysis. Results and Discussion. The morphology and size distribution of the SiN and cobalt-chromium particles was not altered after isolation [Figure 2] [Figure 3]. The mode size of the SiN particles was 30–40 nm, while the mode size of cobalt-chromium particles was 10–20 nm [Figure 3]. Unlike current isolation methods, the present study developed a highly sensitive method which uses cost effective commercially available reagents and components. Furthermore, the particles are recovered in solution and can be readily analysed using commercial size analysers, prior to use in cell studies. This study also confirmed the aggregation characteristics of silicon nitride particles in aqueous medium as observed in previous studies. The above method may also be used to isolate wear debris of materials that have density higher than 1.6 g/cm3. This includes the majority of ceramics, metals and ceramic-like coatings used in TJR components such as alumina, zirconia toughened alumina, titanium, chromium nitride coating, titanium nitride coating and chromium carbon nitride coating. Conclusions. The new isolation method successfully isolated silicon nitride nanoparticles and cobalt-chromium wear debris from serum lubricant at ultra-low concentrations of 0.03 mm3/million cycles. Acknowledgements. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. GA-310477 LifeLongJoints

Osteolysis is one of a major cause of failure that affect long term survival rate in THA. Hard-on-hard bearing surface were developed to reduce wear and osteolysis, such as ceramic-on-ceramic which is the lowest wear rate was introduced but it still has squeaking and ceramic fracture. Metal-on-metal bearing surface significantly reduce wear rate but it still release metal ion which affect local tissue reaction. Then ceramic-on-metal is another choice of bearing with combine the advantage of reduce wear rate, metal ion release, no stripe wear, no squeaking and no ceramic fracture. However after clinical use ALTRs may occur and disturb the longevity of THA. During January 2009 to December 2009 we performed 98 THR with the same femoral stem and acetabular cup with difference bearing which were 87 cases of metal on cross-linked PE, 8 cases of ceramic on metal and 5 cases of metal on metal. Routinely postoperative care were done with clinical evaluation, plain x-rays and Harris hip score. After 5 years follow up there are clinical problems in ceramic on metal THA with decrease clinical score and progressive osteolysis in radiographic finding in 2 cases then we investigated to find the cause of this problem and revise the components. We preformed magnetic resonance imaging and collect blood sample for ESR, CRP and Cobalt and Chromium level. We revised 2 cases of ceramic on metal THA, during surgery we collected tissue for bacterial and AFB and histopathology. All retrieval components were studied for wear pattern. First patient have thigh pain and progressive osteolysis after year 4. th. of follow up. She had normal ESR and CRP with high level of cobalt and chromium level. We revised both components and tissue histopathology showed metallosis with chronic inflammation. Another patient had failure due to ALTRs with mixed solid-cystic mass at trochanteric bursa but component is stable then only bearing surface were change. Wear pattern at femoral head was in weight bearing area with corresponding to apical center wear of metal liner. Our study showed that only in group of ceramic-on-metal THA that have 5 years follow up have early reoperation due to osteolysis and tissue reaction. We routinely stop to use this bearing since 2010. But we have small number of cases in our study to conclude that is bearing are not suitable for clinical usage

In 1998, lysis / wear were the biggest concerns in THR. 3 distinct tacks emerged: Alternatives to polyethylene: Ceramic / Ceramic; Metal / Metal; Make a better polyethylene. MOM story is well known: bad ending!!. Large adoption of Ceramic / Ceramic: positives: low wear, benign MR findings, even low dislocation rates !! negatives: fractures still occurred, noise generation, liner malseating, metal transfer (edge effects). Crosslinked Polyethylene: Update: 13–15 year follow-up of 1st generation XLPE with remelted product: Annual wear rates of 0.004 (metal heads) 0.002 (ceramic heads)!. No lysis!! Wear rates for “standard” heads and large heads both low approaching the lower limits of detection!!. CONCLUSION: Crosslinked Polyethylene with Ceramic Heads: The Winner and Still Champion!

Background. Wear and osteolysis are major contributors, which limit the durability of total hip Arthroplasty (THA) and ultimately cause it to fail. Efforts were made to decrease wear by highly cross-linked polyethylene (HXLPE) and using ceramic bearings. Questions/Purposes. The purpose of this study is to analyze and compare the five year performance of large sized (32mm and 36mm) ceramic and metal heads on X3 HXLPE (Stryker, Mahwah, NJ, USA). Materials and Methods. One hundred and twenty near-consecutive patients that underwent primary THA between January 2006 and December 2009 for osteoarthritis with five-year radiographic and clinical follow-up were identified from our institutional review board-approved prospective database. All patients received a non-cemented THA with larger femoral head (32 or larger) on X3 HXLPE, either a ceramic (n=60) or metal (n=60). Linear and volumetric wear was measured using the computer-assisted Roman software. Results. At final follow up, the mean wear rates were not significantly different (p=0.63): 0.018 ± 0.06 mm/yr and 0.021 ± 0.06 mm/yr for ceramic-on-X3 and metal-on-X3, respectively. When negative values were considered zero as worst-case scenario, wear rates for ceramic-on-X3 and metal-on-X3 HXLPE groups were 0.032 ± 0.04 mm/yr and 0.041 ± 0.05 mm/yr, respectively (P=0.55). Mean volumetric wear rates were also statistically similar: 68.56 mm3/y and 79.96 mm3/y for the ceramic-on-X3 and metal-on-X3 HXLPE groups respectively (p=0.78); when negatives were considered zeroes, they were 121.42 mm3/y and 164.63 mm3/y, respectively (p=0.20). Patients with ceramic heads were significantly younger (p <0.01), more active (p<0.01) and had better clinical scores than those with metal heads. Conclusions. Large ceramic and metal heads on HXLPE have excellent durability at minimum 5 years followup without any statistical significant difference in linear or volumetric wear rates

Introduction. Wear and osteolysis are major contributors which limit the durability of total hip arthroplasty (THA) and ultimately cause it to fail. Efforts were made to decrease the wear by highly cross-linked polyethylene (HXLPE) and using ceramic bearings. The purpose of this study is to analyze the five year performance of large sized (32mm and 36mm) ceramic and metal heads on X3 HXLPE (Stryker, Mahwah, NJ). Materials and Method. From Jan 2006 to June 2008, 81 consecutive patients with minimum 5 year radiographic and clinical followup were identified from out institutional prospective database. 51 non-cemented THA (45 patients) had ceramic on HXLPE (CoX3) group and 30 hips (29 patients) had metal on HXLPE (MoX3) group. Mean age was 36 ± 8 years (36–76) and 50 ± 9 years (51–86) in ceramic and metal group, respectively. Wear rates were measured on an anteroposterior weight-bearing pelvis radiographs using the computer-assisted Roman software. Results. The mean WOMAC, PAQ, HSS and UCLA scores for CoX3 and MoX3 groups at final follow-up were 13.2 ± 17.3, 10.1 ± 14.4, 36.4 ± 5.3 and 5.9 ± 1.8 and 16.5 ± 17.8, 17.1 ± 17.2, 31.6 ± 10.5 and 5.3 ± 1.6, respectively. At the final follow up, the mean wear rates were 0.022 ± 0.06 mm/yr and 0.022 ± 0.05 mm/yr for CoX3 and MoX3 groups, respectively. This was not statistically significant (p=0.8). When negative values were considered zero, wear rates for CoX3 and MoX3 groups were 0.037 ± 0.04 mm/yr and 0.033 ± 0.04 mm/yr, respectively (p=0.6). Radiographic analysis does not reveal any incidence of osteolysis or loosening in both groups. Discussion and Conclusion. The five year wear rate of large diameter metal and ceramic femoral heads on HXLPE bearing demonstrated excellent similar wear rates. Longer follow-ups are required to assess superiority of one bearing over another

Age is often used as a surrogate for activity. However, it has been demonstrated that BMI has a stronger correlation to post-operative activity than age. The fundamental exercise in choosing a bearing is maximizing the benefit-to-risk ratio. The following question should be addressed on a patient by patient basis: what available bearing is most likely to meet the needs of this patient, with an acceptable risk of revision surgery during their lifetime, is accepted in my community, and with a justifiable cost?. The risk of ceramic fracture is very low with Biolox® Delta, and that risk decreases with increasing head size. However, concerns of taper corrosion, not wear and osteolysis, have driven the increase in utilization of ceramic heads. More research is needed into the etiology of taper corrosion, especially surgeon variability in taper assembly. Crosslinked polyethylene has substantially reduced wear, osteolysis, and revision rates compared to non-crosslinked polyethylene, regardless of the countersurface. In the AOA National Joint Replacement Registry, ceramic/ceramic, metal/XLPE, ceramic/XLPE, and ceramicised metal/XLPE are the most commonly used bearing surfaces. With 12–15 year follow-up, there is no difference in the cumulative percent revision of these four bearings in patients aged <55. Ceramic heads are variably more expensive. The ability to recoup the increased cost of ceramic heads through a diminished lifetime revision cost is dependent on the price premium for ceramic and the age of the patient. A wholesale switch to ceramic bearings regardless of age or cost differential could result in an economic burden to the health system. One measure of “standard” is simply “the most frequently used”. In this regard, market data alone makes the determination of “standard” without regard to clinical or economic outcomes. However, longer follow-up, including financial data, is necessary to better assess the relative value (benefit-to- risk ratio) of all the available bearing couples

Revision is a key negative outcome of joint replacements. The purpose of this abstract is to present revision risk curves for hip and knee replacements based on the most recently available national data sources. Having a better understanding of determinants of revision risk can help inform clinical and health care system improvements. We explored revision risk of primary joint replacement stratified by key clinical, prosthesis, and surgeon-level factors using data from three databases managed by CIHI: the Canadian Joint Replacement Registry (CJRR), the Discharge Abstract Database, and the National Ambulatory Care Reporting System. To investigate early revisions, we used Kaplan-Meier analysis stratified by demographic factors to determine the risk of revision within up to five years of primary surgery. This analysis identified the primary cohort from the CJRR from April 1, 2012 to March 31, 2017 and was limited to mandatory reporting provinces (British Columbia, Manitoba and Ontario) to ensure maximal coverage of prosthesis information. Bearing surface was obtained from the International Prosthesis Library maintained by the International Consortium of Orthopaedic Registries (ICOR) and the International Society of Arthroplasty Registers (ISAR). The total revision risk cohort contained 283,620 primary surgeries, of which 5,765 (2%) had at least one revision. For total hip arthroplasties, revision risk at the end of the follow-up period did not differ by age, by sex or across bearing surface (metal on cross-linked polyethylene [XLPE], ceramic on XLPE, ceramic on ceramic, metal on non-cross-linked polyethylene). For hemiarthroplasties in hip fracture patients, cement fixation was significantly associated with decreased revision risk. Surgeon volume had a positive effect on survivorship with cementless fixation (2.7% at one year [95% CI 2.3%, 3.1%] for high-volume vs 3.2% [2.7%, 3.7%] for low-volume). However, surgeon volume did not have an effect on survivorship with cemented fixation (2% at one year [95% CI 1.3%, 2.6%] for high-volume vs. 2% [1.4%, 2.6%] for low-volume). For total knee replacements, revision risk increased with decreasing age and male sex. For patients aged 75 and older, four-year revision risks were 1.5% (95% CI 1.3%, 1.7%) for women and 2.0% (1.7%, 2.3%) for men, but for patients under 55 years old, they were 4.3% (3.7%, 5%) for women and 5.9% (4.9%, 6.9%) for men. Additional results from the upcoming 2019 CJRR annual report, including data up to March 31, 2018, will be presented. Revisions represent a key failure of the primary replacement, they are costly to the health care system and negatively affect patients' quality of life. CJRR's coverage is currently 72%, increased coverage and follow-up time will allow increasingly comprehensive reporting on hip and knee prostheses in Canada. Future work in this area involves exploring additional prosthesis attributes for stratification of revision risk curves and calculation of hazards ratios adjusted by age and sex

1. Do large heads result in better stability in practice?. –. Prospective Randomized Studies showing increased stability. 2. How much of a risk is ceramic head fracture with current generation materials?. –. Minimal (0.004%). 3. How much of an actual risk is liner fracture with thin polyethylene liners?. –. Minimal (only in isolated case reports with component malposition/impingement). 4. What wear advantage is gained by using ceramic over metal heads?. –. Simulator studies (clear advantage). –. Clinical studies – Small difference in linear wear rate (with Zirconia). –. Larger difference in wear rate with newer materials (BIOLOX). 5. What other advantage is gained by using ceramic heads over metal heads?. –. No CoCr in system – less corrosion. –. Corrosion at head-neck junction can be a big problem – pseudotumours. –. Meftah/Rodriguez COP. –. Ceramic heads cause less fretting and corrosion than metal heads in in vitro study

Introduction. Bearing surfaces used for total hip arthroplasty must have characteristics including bio-compatibility, low friction and low wear rate. Bearing combinations are generally characterised as Soft on Hard/Hard. In general, all newer bearing combinations have reduced wear but may present with other issues that impact on patient outcomes. Materials. The Australian Orthopaedic Association – National Joint Replacement Registry classifies bearing surfaces into six categories. These are metal on polyethylene, ceramic on polyethylene, metal on metal, ceramic on ceramic, ceramic on metal and a sixth category relating to a small number of procedures where the bearing surface is yet to be classified. 147,422 conventional total hip arthroplasty procedures have been recorded by the Registry between 1 September 1999 and 31 December 2008 and analysis has been performed of the cumulative percentage revision in relation to bearing surface. Results. In general, metal on polyethylene has the lowest risk of revision compared to all other bearing surfaces and metal on metal has the highest revision rate. The risk of revision, however, does vary depending on head size, with larger head sizes having a lower risk of revision with the exception of metal on metal. Conclusion. When deciding which bearing surface is suitable for patients it must be emphasised that wear reduction is only one of several considerations when choosing the most appropriate combination

Introduction. Metallic resurfacing systems have been widely used until pseudotumors and ALTR have been clinically found and related to excessive wear of these metal-on-metal hip systems. Hence, surgeons widely abandoned the use of resurfacing systems. Meanwhile, there is a ceramic on ceramic (CoC) resurfacing system (Embody, London, UK) made of zirconia toughened alumina (BIOLOX. ®. delta, CeramTec, Plochingen, Germany) in a clinical safety study. Even though conventional CoC hip systems are known for their excellent wear behavior, it has to be ensured that intraoperative and in-vivo deformations of the ceramic acetabular cup do not infringe the proper functionality of the system. The method of determining the minimum clearance of such a system will be presented here. Materials and Methods. Combined experimental and numerical results were used to determine the deformation of the ceramic shell. In a cadaver lab, the resulting deformations after impaction of generic metal shells have been measured, see e.g. [1] for the method of measurement. The maximum deformation has been chosen for further calculation. Additionally, the stiffness of both generic metal and ceramic shells has been measured using ISO 7206–12. The deformation of the ceramic shells were then calculated by the equation. where u. c. and u. m. are the deformations of the ceramic and the metal shell, respectively, and K. m. and K. c. are the respective stiffnesses. Additionally, in a finite element simulation, the resulting deformation of the ceramic shell under in-vivo conditions was calculated and superposed with u. c. The resulting deformation was used as the minimum value of the clearance for the ceramic resurfacing system. Results. The average value of the maximum deformation of the 8 generic metal shells was 177 µm (StD. 68 µm). Using the stiffness values for the ceramic and the metal shells, a maximum deformation for the ceramic shells (with the smallest and the largest outer diameter) were calculated to 56 µm and 74 µm, respectively. The superposition with the results from the FE studies led to deformation values of 69 µm (smallest shell) and 87 µm (largest shell), respectively. These values were chosen as the minimum values for the realization of the minimum clearance. Discussion. The above described minimum clearance results from a worst-case scenario for the long-term deformation of the ceramic shells. The values from the experimental measurements were taken ten minutes after impaction in the cadaveric hips, when first relaxation already took place. Any other bone remodeling in the long-term, leading to further relaxation of the ceramic shell, has not been taken into account. The maximum deformations resulting from the numerical investigations have been superposed to the experimental values, assuming that both maximum deformations are acting in the same direction. In reality, this is most likely not the case because the line-of-action of the in-vivo forces acting on the hip are not collinear with the direction where the maximum deformation during intra-operative impaction takes place. Additionally, the experimentally chosen underreaming (1 mm) can also be considered as a worst-case. Hence, the calculated minimum clearances are representing the maximal deformation that in the long-term may take place in-vivo

Ceramic-on-ceramic bearings provide a solution to the osteolysis seen with traditional metal-on-polyethylene bearings. Sporadic reports of ceramic breakage and squeaking concern some surgeons and this bearing combination can show in vivo signs of edge loading wear which was not predicted from in vitro studies. Taper damage or debris in the taper between the ceramic and metal may lead to breakage of either a ceramic head or insert. Fastidious surgical technique may help to minimise the risk of ceramic breakage. Squeaking is usually a benign complication, most frequently occurring when the hip is fully flexed. Rarely, it can occur with each step of walking when it can be sufficiently troublesome to require revision surgery. The etiology of squeaking is multifactorial in origin. Taller, heavier and younger patients with higher activity levels are more prone to hips that squeak. Cup version and inclination are also relevant factors. Osteolysis following metal-on-UHMW polyethylene Total Hip Arthroplasty (THA) is well reported. Earlier generation ceramic-on-ceramic bearings did produce some osteolysis, but in flawed implants. As third and now fourth generation ceramic THAs come into mid- and long-term service, the orthopaedic community has begun to see reports of high survival rates and very low incidence of osteolysis in these bearings. The technique used by radiologists for identifying the nature of lesions on Computed Tomography (CT) scan is the Hounsfield score which will identify the density of the tissue within the lucent area. Commonly the radiologist will have no access to previous imaging, especially pre-operative imaging if a long time has elapsed. With such a low incidence of osteolysis in this patient group, what, then, should a surgeon do on receiving a CT report on a ceramic-on-ceramic THA, which states there is osteolysis? This retrospective review aims to determine the accuracy of CT in identifying true osteolysis in a cohort of long-term third generation ceramic-on-ceramic uncemented hip arthroplasties in our department. Pelvic CT scans were performed on the first 27 patients from a cohort of 301 patients undergoing 15-year review with third generation alumina-alumina cementless THAs. The average follow-up was 15 years (15–17). The CT scans were reviewed against pre-operative and post-operative radiographs and reviewed by a second musculoskeletal specialist radiologist. Eleven of the CT scans were reported to show acetabular osteolysis, two reported osteolysis or a possible pre-existing cyst and one reported a definitive pre-existing cyst. After review of previous imaging including pre-operative radiographs, eleven of the thirteen patients initially reported to have osteolysis were found to have pre-existing cysts or geodes in the same size and position as the reported osteolysis, and a further patient had spot-welds with stress-shielding. One patient with evidence of true osteolysis awaits aspiration or biopsy to determine if he has evidence of ceramic wear or metallosis. Reports of osteolysis on CT should be interpreted with care in modern ceramic-on-ceramic THA to prevent unnecessary revision. Further imaging and investigations may be necessary to exclude other conditions such as geodes, or stress shielding which are frequently confused with osteolysis on CT scans

The advantages of modularity in both primary and revision hip surgery are well documented, and have been at the heart of innovation in hip implant design over the last two decades. Modularity allows us to address version, length and offset issues and to restore optimal hip biomechanics. There are, however, increasing clinical concerns associated with the failure of taper junctions. The use of large femoral heads and modular stems are now considered major risk factors for taper corrosion. I will summarise our laboratory and retrieval data on taper design and tribology in order to put in perspective the clinical use of modularity in hip arthroplasty. Modular junctions rely on a frictional interlock. The engagement obtained and resulting micromotion is strongly influenced by taper size, taper length/engagement, material, surface finish, neck length and offset. In our quest for thinner femoral necks, greater offsets and bigger femoral heads, we have inadvertently created an environment that can generate fretting corrosion at modular junctions and leads to premature implant failure. An inverted hip replacement setup was used similar to the specified ASTM test (ASTM F1875–98). Twenty-eight millimeter Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth finish. Wear and corrosion of taper surfaces were compared following a 10 million loading cycle. The surface roughness parameters on the head taper were significantly increased when the head-stem contact area was reduced. Similarly, the surface roughness parameters on the head taper were significantly increased when rough stem tapers were used. With rough male tapers the CoCr head taper became circumferentially ridged with distinct areas of pitting corrosion similar to that seen on some retrievals. In these tests similar surface morphology to that on retrieved femoral heads was seen on the female head taper. Thirty-six millimeter CoCr femoral heads were also coupled with either a CoCr or Ti stem with 12/14 tapers all with smooth finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. A proportional relationship between torque and corrosion was observed for both CoCr-CoCr and CoCr-Ti material combinations. In-vitro studies were used to evaluate the role of: taper size, angle mismatch, surface finish, and manufacturing tolerances on taper engagement. In-vitro loading analysis was performed to determine the bearing friction experienced by the taper connection. The component materials analysed were CoCr and Ti for stem design and CoCr/CoCr, ceramicized metal/CoCr, and CoCr/Ti for head/neck tapers. The high performance combinations included tapers with larger diameters, rougher surface finish, tighter tolerances and a proximal locking location. Loading studies demonstrate a 15 – 31% reduction in frictional torque (for 28, 36 and 40mm head sizes) using the ceramicized metal/XLPE couples compared to CoCr/XLPE couples. Retrieval studies were conducted to assess taper corrosion using the Goldberg system and SEM analysis. Two hundred-nine taper surfaces, with in-vivo time varying from 1 week and 10 years, were analysed showing that ceramicized metal femoral heads have a lower corrosion score compared to CoCr femoral heads. Understanding the key design and surgical factors that drive the performance of taper junctions is vital for the surgical community. There is a body of knowledge that supports appropriate taper use / modularity to help surgeons deal with complex situations. We must be careful not throw the baby out with the bathwater

Concerns with long-term fixation of cemented all-poly sockets have led to the near-universal acceptance of cementless fixation of the acetabulum. The sockets most often utilised today are bone-ingrowth porous metal, made of titanium, cobalt-chrome, or hyper-porous materials such as tantalum trabecular metal. Porous ingrowth sockets are extraordinarily reliable, with reports of 99–100% achieving stable fixation. The problem with sockets is not the fixation, but the bearing. Modular polyethylene liners are most commonly used, but wear on the primary bearing surface as well as backside wear can lead to osteolysis and late failure. Holes in the socket designed for supplemental screws act as a conduit for particles to enter the ace tabular bone where a cascade of inflammatory responses activate osteoclastic activity and bone destruction. One alternative is a socket without holes, using spikes or fins for additional stability. The concern here is that the socket may not be completely seated and the surgeon is unaware. Another alternative is the use of a monoblock acetabular component with the polyethylene molded to the metal shell. While excellent results are reported, the downside is an inability to exchange the polyethylene. Resurfacing sockets are also monoblocks, and some offer peripheral supplemental screws. Here again, incomplete seating may occur, leaving a gap behind the dome. Serial x-rays almost always reveal that this gap gradually fills in. Improvements in polyethylene, better locking mechanisms and alternative bearing materials such as ceramic and metal are the final steps to ensure acetabular durability