Wear debris induced osteolysis is a recognized complication in conventional metal-on-polyethylene hip arthroplasty. One method of achieving wear reduction is through the use of metal-on-metal articulations. One of the latest manifestations of this biomaterial combination is in designs of hip resurfacing which are aimed at younger, more active patients. But, do these metal-on-metal hip resurfacings show low wear when implanted into patients?. Using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy less than 1 micron) and a bespoke computer program, volumetric wear measurements for retrieved Articular Surface Replacements (ASR, DePuy) metal-on-metal hip resurfacings were undertaken. Measurements were validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was shown to be accurate to within 0.5mm3. Thirty-two femoral heads and twenty-two acetabular cups were measured. Acetabular cups exhibited mean volumetric wear of 29.00mm3 (range 1.35 - 109.72mm3) and a wear rate of 11.02mm3/year (range 0.30 - 63.59mm3/year). Femoral heads exhibited mean wear of 22.41mm3 (range 0.72 - 134.22mm3) and a wear rate of 8.72mm3/year (range 0.21 - 31.91mm3/year). In the 22 cases where both head and cup from the same prosthesis were available, mean total wear rates of 21.66mm3/year (range 0.51 - 95.50mm3/year) were observed. Revision was necessitated by one of five effects; early femoral neck fracture (4 heads), avascular necrosis (AVN) (2 heads, 1 cup), infection (1 head, 1 cup), adverse reaction to metal debris (ARMD) (19 heads, 18 cups) or ARMD fracture (6 heads, 2 cups). Mean paired wear rates for the AVN and infection retrievals were 0.51mm3/year and 3.98mm3/year respectively. In vitro tests typically offer wear rates for metal-on-metal devices in the region of 2-4mm3. Mean paired wear rates for ARMD and ARMD fracture were 17.64mm3/year and 68.5mm3/year respectively, significantly greater than those expected from in vitro tests. In the 4 cases of early fracture, only the heads were revised so a combined wear rate calculation was not possible. The heads exhibited mean wear rate of 8.26mm3/year. These high wear rates are of concern

Total Hip Arthroplasty (THA) is a well-established, cost-effective treatment for improving function and alleviating pain in patients who have disabling hip disease with excellent long-term results. Based on the excellent results, there is an ongoing trend for THA to be performed in younger and more active patients, having higher physical demands on their new total joints. Polyethylene (PE) wear and its biological consequences are one of the main causes of implant failure in THA. Macrophages phagocytise PE wear particles and this will result in osteolysis and loss of periprosthetic bone. The risk of these complications can be estimated in relation to the amount of volumetric wear based on two assumptions: that the number of PE particles dispersed in the peri-prosthetic tissues is controlled by the amount of PE wear; and that the development of osteolysis and the resulting aseptic loosening is triggered by these PE particles. Based on these assumptions, a model was developed to estimate the osteolysis-free life of a THA, depending on the Linear Wear Rate (LWR) and femoral head size of the PE bearing. A review of the literature was conducted to provide an estimate of the radiologic osteolysis threshold based on the volumetric wear of the PE bearing. This review demonstrates that this radiologic osteolysis threshold is approximated 670 mm3 for conventional PE. The osteolysis-free life of the THA was estimated by simply dividing this threshold volume by the annual Volumetric Wear Rate (VWR) of the bearing. The annual VWR is basically controlled by two parameters: (1) annual LWR and (2) head size, and was calculated by using published formulae. For 28 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 116.6 years / LWR: 25 µm/y => 46.6 years / LWR: 50 µm/y => 23.3 years / LWR: 100 µm/y => 11.6 years. For 40 mm heads, following osteolysis-free life was determined in function of the annual LWR. LWR: 10 µm/y => 57.1 years / LWR: 25 µm/y => 22.9 years / LWR: 50 µm/y => 11.4 years / LWR: 100 µm/y => 5.7 years. The osteolysis-free life determined by this model is in good agreement with the clinical results of PE bearings having a 28 mm head size and demonstrates that extreme low LWRs are mandatory to assure a descent osteolysis-free life for THA (PE bearings) using large heads, such as 40 mm. For such head sizes, small variations of the LWR may have large impacts on the osteolysis-free life of the THA

Wear of polyethylene is associated with aseptic loosening of orthopaedic implants and has been observed in hip and knee prostheses and anatomical implants for the shoulder. The reversed shoulder prostheses have not been assessed as yet. We investigated the volumetric polyethylene wear of the reversed and anatomical Aequalis shoulder prostheses using a mathematical musculoskeletal model. Movement and joint stability were achieved by EMG-controlled activation of the muscles. A non-constant wear factor was considered. Simulated activities of daily living were estimated from in vivo recorded data. After one year of use, the volumetric wear was 8.4 mm. 3. for the anatomical prosthesis, but 44.6 mm. 3. for the reversed version. For the anatomical prosthesis the predictions for contact pressure and wear were consistent with biomechanical and clinical data. The abrasive wear of the polyethylene in reversed prostheses should not be underestimated, and further analysis, both experimental and clinical, is required

Abstract. Introduction. Bipolar hemiarthroplasty(BPHA) for displaced intracapsular neck of femur fractures(DICNOF) is a controversial topic as conflicting evidence exists. The most common reason for revision to total hip arthroplasty(THA) from BPHA is acetabular erosion. In our study, we sought to quantify the direction of migration of the bipolar head within the first 3 years post-operatively. Methods. A proportional index in the horizontal and vertical planes of the pelvis were used to quantify migration. This method removed the need to account for magnification and rotation of the radiographs. Results. There were a total of 35 patients (8males, 27females) included, with an average followup of 2.3years (816days). 7 did not migrate, these were all female. For the remainder, per year of insertion, the average horizontal migration was 0.005769439 and the average vertical migration was 0.004543352, suggesting superomedial movement. Discussion. BPHA has been shown to provide results similar to those of THA in patients with DICNOF. The main cause of revision to THA is migration thought to be from loss of cartilage volume from mechanical wear, that causes pain. We have quantified this migration as minimal. None of our patients required revision to THA and none sustained dislocation or loosening in this followup period. This would fit with the meta-analyses looking at BPHA, which shows bipolar articulations reduce the amount of wear. We also identified a trend that in the female population migration is less likely to occur. This would add evidence to the theory that mechanical factors are significant in the volumetric wear caused by hemiarthoplasty. Conclusion. BPHA was found to be safe and effective in our cohort of patients with minimal migration and no need for revision at an average of 2.3years. Our data is concurrent with the literature in theorising that BPHA reduces wear at the prosthesis-cartilage interface

Background. Stress shielding and wear induced aseptic loosening cause failure in arthroplasty surgery. To improve survivorship, the use of a low modulus, low wearing biomaterial may be a suitable alternative to hard bearing prostheses, such as cobalt chromium (CoCr). There has been considerable research interest in the use of polyetheretherketone (PEEK) based on observed clinical success especially in spinal surgery. This study investigated the wear performance of PEEK, carbon reinforced PEEK (CFR-PEEK) and acetal as bearing materials in an all polymer total knee arthroplasty (TKA) using a unidirectional pin on plate test. Methods. The following material combinations were tested: PEEK vs. UHMWPE, CFR-PEEK vs. UHMWPE, PEEK vs. PEEK, CFR-PEEK vs. PEEK, CoCr vs. UHMWPE, PEEK vs. XLPE, CFR-PEEK vs. CFR-PEEK, PEEK vs. Acetal, Acetal vs. XLPE and CoCr vs. XLPE.Tribological couples tested (Pin vs. Plate) Using a previously validated modification of ASTM F732, 20mm diameter spherically ended pins with a radius of 25mm were articulated against 40mm diameter plates. A load of 1000N was applied to generate a contact stress of about 70MPa similar to contact stresses previously reported in the knee. The lubricant used was 25% newborn calf serum containing 0.3% sodium azide to retard bacteria growth and 20mM EDTA to prevent calcium deposition. Three repeats of pin on plate combinations (including 2 passive soak controls) were tested for 2 million cycles at a cycle frequency of 1Hz and a stroke length of 10 mm. Gravimetric wear was analysed every 250,000 cycles and results converted to volumetric wear using material density. Results. All CFR-PEEK articulations were stopped due to excessive wear of the counter-surfaces. Results showed a linear wear rate of UHMWPE and XLPE plates over the test period. PEEK vs. XLPE showed similar wear rate to metal on polyethylene (MoP) bearings. Conclusion. At stresses representative of the knee, PEEK pins when articulated against XLPE plates generated volumetric wear similar to that noted in MoP bearings

Material loss at the head-stem taper junction may contribute to the high early failure rates of stemmed large head metal-on-metal (LH-MOM) hip replacements. We sought to quantify both wear and corrosion and by doing so determine the main mechanism of material loss at the taper. This was a retrospective study of 78 patients having undergone revision of a LH-MOM hip replacement. All relevant clinical data was recorded. Corrosion was assessed using light microscopy and scanning electron microscopy, and graded according to a well-published classification system. We then measured the volumetric wear of the bearing and taper surfaces. Evidence of at least mild taper corrosion was seen in 90% cases, with 46% severely corroded. SEM confirmed the presence of corrosion debris, pits and fretting damage. However, volumetric wear of the taper surfaces was significantly lower than that of the bearing surfaces (p = 0.015). Our study supports corrosion as the predominant mechanism of material loss at the taper junction of LH-MOM hip replacements. Although the volume of material loss is low, the ionic products may be more biologically active compared to the particulate debris arising from the bearing surfaces

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm. 3. ; 730 to 1850) and high wear rates (mean 205 mm. 3. /year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene

Introduction. There is much current debate concerning wear and corrosion at the taper junctions of large head total hip replacements, particularly metal-on-metal hips. Is such damage a modern concern or has it always occurred in total hip replacement but not previously noted. To investigate this five explanted V40 Exeter femoral stems (Stryker Howmedica) were obtained following revision surgery at a single centre. In all cases, the 24–26 mm femoral heads were still attached. Hypothesis. In conventional ‘small head’ modular hip prostheses such as the Exeter, negligible wear and corrosion is seen at the taper junction of explanted devices. Methods. The articulating surface and the taper junction of each femoral heads was measured using a Mitutoyo LEGEX322 co-ordinate measuring machine (CMM) In each case a wear map was generated and the wear volume from the contact surface was calculated using a bespoke MATLAB program. The accuracy of such measurements has been previously shown to be within 0.5mm3. Results. Wear analysis of the articulating surfaces found unworn surfaces with each femoral head having less than 1 mm. 3. volumetric wear. All tapers had minimal wear with volumetric wear of less than 0.5 mm. 3. . Discussion and Conclusion. The wear volumes measured fall within the CMM measuring accuracy of 0.5mm. 3. Furthermore all tapers showed low wear volumes indicating that the taper junction had functioned correctly and distributed the load across the length of the truneon. Significance. This work adds to the growing evidence that taper problems in modern hip prostheses are associated with increasing head diameter and smaller taper dimensions

Ultra-high-molecular-weight polyethylene (UHMWPE) components for total joint replacement generate wear particles which cause adverse biological tissue reactions leading to osteolysis and loosening. Sterilisation of UHMWPE components by gamma irradiation in air causes chain scissions which initiate a long-term oxidative process that degrades the chemical and mechanical properties of the polyethylene. Using a tri-pin-on-disc tribometer we studied the effect of ageing for ten years after gamma irradiation in air on the volumetric wear, particle size distribution and the number of particles produced by UHMWPE when sliding against a stainless-steel counterface. The aged and irradiated material produced six times more volumetric wear and 34 times more wear particles per unit load per unit sliding distance than non-sterilised UHMWPE. Our findings indicate that oxidative degradation of polyethylene after gamma irradiation in air with ageing produces more wear

Metal-on-metal hip resurfacing prostheses are a relatively recent intervention for relieving the symptoms of common musculoskeletal diseases such as osteoarthritis. While some short term clinical studies have offered positive results, in a minority of cases there is a recognised issue of femoral fracture, which commonly occurs in the first few months following the operation. This problem has been explained by a surgeon's learning curve and notching of the femur but, to date, studies of explanted early fracture components have been limited. Tribological analysis was carried out on fourteen retrieved femoral components of which twelve were revised after femoral fracture and two for avascular necrosis (AVN). Eight samples were Durom (Zimmer, Indiana, USA) devices and six were Articular Surface Replacements (ASR, DePuy, Leeds, United Kingdom). One AVN retrieval was a Durom, the other an ASR. The mean time to fracture was 3.4 months. The AVNs were retrieved after 16 months (Durom) and 38 months (ASR). Volumetric wear rates were determined using a Mitutoyo Legex 322 co-ordinate measuring machine (scanning accuracy within 1 micron) and a bespoke computer program. The method was validated against gravimetric calculations for volumetric wear using a sample femoral head that was artificially worn in vitro. At 5mm3, 10mm3, and 15mm3 of material removal, the method was accurate to within 0.5mm3. Surface roughness data was collected using a Zygo NewView500 interferometer (resolution 1nm). Mean wear rates of 17.74mm3/year were measured from the fracture components. Wear rates for the AVN retrievals were 0.43mm3/year and 3.45mm3/year. Mean roughness values of the fracture retrievals (PV = 0.754nm, RMS = 0.027nm) were similar to the AVNs (PV = 0.621nm, RMS = 0.030nm), though the AVNs had been in vivo for significantly longer. Theoretical lubrication calculations were carried out which found that in both AVN retrievals and in seven of the twelve cases of femoral fracture the roughening was sufficient to change the lubrication regime from fluid film to mixed. Three of these surfaces were bordering on the boundary lubrication regime. The results show that even before the femoral fracture, wear rates and roughness values were high and the implants were performing poorly

Mismatch of bearing component centres and tension of soft tissues surrounding the hip joint can lead to component separation during gait cycle and cause the femoral head to contact the rim of an acetabular liner, which could increase wear and shorten lifespan of an implant. This study aims to investigate the contact and wear mechanics of a metal-on-polyethylene hip joint under dynamic separation by using Finite Element Analysis (FEA). A Pinnacle® cup with a Marathon neutral liner 36×56mm with a 45° inclination was constrained by a spring element in the medial-lateral axis. The spring was pre-compressed by 4mm to represent the corresponding translational mismatch of a simulator testing. Archard's law was used to predict wear over one ISO 14242-1 gait cycle. Contact pressure is proportional to the load input during the stance phase, associated with concentric contact condition; it increases threefold just before the swing phase (time C), reaching 46.2MPa, where edge loading occurs. Consequently, separation climbs to 3.54mm, which is comparable to the mathematical prediction (3.34mm) and dynamic FEA (3.2mm). The predicted volumetric wear after this gait cycle is 1.22 × 10–5 mm3. Dynamic separation between femoral head and acetabular liner can result in edge loading, consequently high contact pressure on the edge of a liner. In combination with cyclic loading, fatigue damage could take place and may be worth investigating in the future

Experimental simulation is the gold standard wear testing method for total knee replacements (TKR), with reliable replication of physiological kinematic conditions. When combined with a computational model, such a framework is able to offer deeper insight into the biomechanical and wear mechanisms. The current study developed and validated a comprehensive combined experimental and computational framework for pre-clinical biomechanics and wear simulation of TKR. A six-station electro-mechanical knee simulator (SimSol, UK), capable of replicating highly demanding conditions with improved input kinematic following, was used to determine the wear of Sigma fixed bearing curved TKRs (DePuy, UK) under three different activities; standard-walking, deep-squat, and stairs-ascending. The computational model was used to predict the wear under these 3 conditions. The wear calculation was based on a modification of Archard's law which accounted for the effects of contact stress, contact area, sliding distance, and cross-shear on wear. The output wear predictions from the computational model were independently validated against the experimental wear rates. The volumetric wear rates determined experimentally under standard-walking, deep-squat, and stairs-ascending conditions were 5.8±1.4, 3.5±0.8 and 7.1±2.0 [mm3/mc] respectively (mean ± 95% CI, n=6). The corresponding predicted wear rates were 4.5, 3.7, and 5.6 [mm3/mc]. The coefficient of determination for the wear prediction of the framework was 0.94. The wear predictions from the computational model showed good agreement with the experimental wear rates. The model did not fully predict the changes found experimentally, indicating other factors in the experimental simulation not yet incorporated in the framework, such as plastic deformation, may play an additional role experimentally in high demand activities. This also emphasises the importance of the independent experimental validation of computational models. The combined experimental and computational framework offered deeper insight into the contact mechanics and wear from three different standard and highly demanding daily activities. Future work will adopt the developed framework to predict the effects of patients and surgical factors on the mechanics and wear of TKR

Surgical interventions for the treatment of chronic neck pain, which affects 330 million people globally [1], include fusion and cervical total disc replacement (CTDR). Most of the currently clinically available CTDRs designs include a metal-on-polymer (MoP) bearing. Numerous studies suggest that MoP CTDRs are associated with issues similar to those affecting other MoP joint replacement devices, including excessive wear and wear particle-related inflammation and osteolysis [2,3]. A device with a metal-on-metal (MoM) bearing has been investigated in the current study. Six MoM CTDRs made from high carbon cobalt-chromium (CoCr) were tested in a six-axis spine simulator, under standard ISO testing protocol (ISO-18192-1) for a duration of 4 million cycles (MC). Foetal bovine calf serum (25%v/v), used as a lubricant, was changed every 3.3×10. 5. cycles and saved for particle analysis. Components were taken down for measurements after each 10. 6. cycles; surface roughness, damage modes and gravimetric wear were assessed. The mean wear rate of the MoM CTDRs was 0.24mm. 3. /MC (SD=0.03), with the total volume of 0.98mm. 3. (SD=0.01) lost over the test duration. Throughout the test, the volumetric wear was linear; no significant bedding-in period was observed. The mean pre-test surface roughness decreased from 0.019μm (SD=0.005) to 0.012μm (SD=0.002) after 4MC of testing. Prior to testing, fine polishing marks on the bearing surfaces were observed using light microscopy. Following 4MC of testing, these polishing marks had been removed. Consistently across all components, surface discolouration and multidirectional, criss-crossing, circular wear tracks, caused by abrasive wear, were observed. The wear results showed low wear rates exhibited by MoM CTDRs (0.24mm. 3. /MC), when compared CTDR designs incorporating metal-on-polymer bearings (0.56mm. 3. /MC) [4] as well as MoM lumbar CTDRs [5,6] (0.76mm3/MC – 6.2mm. 3. /MC). These findings suggest that MoM CTDRs are more wear resistant than MoP CTDRs, however the particle characterisation and biological consequences of wear remain to be determined

Polyethylene wear of joint replacements can cause severe clinical complications, including; osteolysis, implant loosening, inflammation and pain. Wear simulator testing is often used to assess new designs, but it is expensive and time consuming. It is possible to predict the volume of polyethylene implant wear from finite element models using a modification of Archard's classic wear law [1–2]. Typically, linear elastic isotropic, or elasto-plastic material models are used to represent the polyethylene. The purpose of this study was to investigate whether use of a viscoelastic material model would significantly alter the predicted volumetric wear of a mobile-bearing unicompartmental knee replacement. Tensile creep-recovery experiments were performed to characterise the creep and relaxation behaviour of the polyethylene (moulded GUR 4150 samples machined to 180×20×1 mm). Samples were loaded to 3 MPa stress in 4 minutes, and then held for 6 hours, the tensile stress was removed and samples were left to relax for 6 hours. The mechanical test data was used fit to a validated three–dimensional fractional Maxwell viscoelastic constitutive material model [3]. An explicit finite element model of a mobile–bearing unicompartmental knee replacement was created, which has been described previously [4]. The medial knee replacement was loaded to 1200 N over a period of 0.2 s. The bearing was meshed using quadratic tetrahedral elements (1.5 mm seeding size based on results of a mesh convergence study), and the femoral component was represented as an analytical rigid body. Wear predictions were made from the contact stress and sliding distance using Archard's law, as has been described in the literature [1–2]. A wear factor of 5.24×10. −11. was used based upon the work by Netter et al. [2]. All models were created and solved using ABAQUS finite element software (version 6.14, Simulia, Dassault Systemes). The fractional viscoelastic material model predicted almost twice as much wear (0.119 mm. 3. /million cycles) compared to the elasto-plastic model (0.069 mm. 3. /million cycles). The higher wear prediction was due to both an increased sliding distance and higher contact pressures in the viscoelastic model. These preliminary findings indicate the simplified elasto-plastic polyethylene material representation can underestimate wear predictions from numerical simulations. Polyethylene is known to be a viscoelastic material which undergoes creep clinically, and it is not surprising that it is necessary to represent that viscoelastic behaviour to accurately predict implant wear. However, it does increase the complexity and run time of such computational studies, which may be prohibitive

Knee arthroplasty with a rotating hinge knee (RHK) prosthesis has become an important clinical treatment option for knee revisions and primary patients with severe varus or valgus deformities and instable ligaments. The rotational axle constraints the anterior-posterior shear and varus-valgus moments, but currently used polyethylene bushings may fail in the mid-term due to insufficient creep and wear resistance of the material. Due to that carbon-fibre-reinforced (CFR) PEEK as an alternativ bushing material with enhanced creep, wear and fatigue behaviour has been introduced in a RHK design [Grupp 2011, Giurea 2014]. The objective of our study was to compare results from the pre-clinical biotribological characterisation to ex vivo findings on a series of retrieved implants. In vitro wear simulation according to ISO 14243-1 was performed on rotating hinge knee devices (EnduRo® Aesculap, Germany) made out of cobalt-chromium and of a ZrN multi-layer ceramic coating for 5 million cycles. The mobile gliding surfaces were made out of polyethylene (GUR 1020, β-irradiated 30 ± 2 kGy). For the bushings of the rotational and flexion axles and the flanges a new bearing material based on CFR-PEEK with 30% PAN fiber content was used. Analysis of 12 retrieved EnduRo. ®. RHK systems in cobalt-chromium and ZrN multi-layer in regard to. -. loosening torques in comparison with initial fastening torques. -. Optical, DSLR camera and stereo light microscope analysis. -. distinction between different wear modes and classification with a modified HOOD-score. -. SEM & EDX of representative samples. -. surface roughness and depth profilometry. with a focus on the four CFR-PEEK components integrated in the EnduRo. ®. RHK design. For the rotating hinge knee design with flexion bushing and flanges out of CFR-PEEK the volumetric wear rates were 2.3 ± 0.48 mm. 3. /million cycles (cobalt-chromium) and 0.21 ± 0.02 mm. 3. /million cycles (ZrN multi-layer), a 10.9-fold reduction (p = 0.0016). The UHMWPE and CFR-PEEK particles were comparable in size and morphology and predominantly in submicron size [5]. The biological response to representative sub-micron sized CFR-PEEK particles has been demonstrated in vivo based on the leucoyte-endothelian-cell interactions in the synovia of a murine intra-articular knee model by Utzschneider 2010. Schwiesau 2013 extracted the frequency of daily activities in hip and knee replacement patients from literature and estimated an average of 1.76 million gait cycles per year. Thus, the 5 million cycles of in vitro wear testing reflect a mean in vivo service life of 2.9 years, which fits to the time in vivo of 12–60 months of the retrieved RHK devices. The in vitro surface articulation pattern of the wear simulation tests are comparable to findings on retrieved CFR-PEEK components for both types of articulations – cobalt-chromium and ZrN multi-layer coating. For the rotating hinge knee design the findings on retrieved implants demonstrate the high suitability of CFR-PEEK as a biomaterial for highly loaded bearings, such as RHK bushings and flanges in articulation to cobalt-chromium and to a ZrN multi-layer coating

Systemic metal ion monitoring (Co;Cr) has proven to be a useful screening tool for implant performance to detect failure at an early stage in metal-on-metal hip arthroplasty. Several clinical studies have reported elevated metal ion levels after total knee arthroplasty (TKA), with fairly high levels associated with rotating hinge knees (RHK) and megaprostheses. 1. In a knee simulator study, Kretzer. 2. , demonstrated volumetric wear and corrosion of metallic surfaces. However, prospective in vivo data are scarce, resulting in a lack of knowledge of how levels evolve over time. The goal of this study was to measure serum Co and Cr levels in several types TKA patients prospectively, evaluate the evolution in time and investigate whether elevated levels could be used as an indicator for implant failure. The study was conducted at Ghent University hospital. 130 patients undergoing knee arthroplasty were included in the study, 35 patients were lost due to logistic problems. 95 patients with 124 knee prostheses had received either a TKA (primary or revision) (69 in 55 patients), a unicompartimental knee arthroplasty (7 UKA), a RHK (revision −7 in 6 patients) or a megaprosthesis (malignant bone tumours − 28 in 27 patients). The TKA, UKA and RHK groups were followed prospectively, with serum Co and Cr ions measured preoperatively, at 3,6 and 12 months postoperatively. In patients with a megaprosthesis, metal ions were measured at follow-up (cross-sectional study design). In primary knees, we did not observe an increase in serum metal ion levels at 3, 6 or 12 months. Two patients with a hip arthroplasty had elevated preTKA Co and Cr levels. There was no difference between unilateral and bilateral knee prostheses. In the revision group, elevated pre-revision levels were found in 2 failures for implant loosening. In both cases, ion levels decreased postoperatively. In revisions with a standard TKA, there was no significant increase in metal ions compared to primary knee arthroplasty. RHK were associated with a significant increase in Co levels even at short-term (3–12 months). The megaprosthesis group had the highest metal ion levels and showed a significant increase in Co and Cr with time in patients followed prospectively. With the current data, we could not demonstrate a correlation between metal ion levels, size of the implant or length of time in situ. In primary knee arthroplasty with a standard TKA or UKA, metal ion levels were not elevated till one year postoperatively. This suggests a different mechanism of metal ion release in comparison to metal-on-metal hip arthroplasties. In two cases of revision for implant loosening, pre-revision levels were elevated, possibly associated with component wear, and decreased after revision. With RHK, slightly elevated ion levels were found prospectively. Megaprostheses had significantly elevated Co and Cr levels, due to corrosion of large metallic surfaces and/or wear of components which were not perfectly aligned during difficult reconstruction after tumour resection. Further research is needed to assess the clinical relevance of metal ion levels in knee arthroplasty

It has been speculated that high wear at the head-stem taper may contribute to the high failure rates reported for stemmed large head metal-on-metal (LH-MOM) hips. In this study of 53 retrieved LH-MOM hip replacements, we sought to determine the relative contributions of the bearing and taper surfaces to the total wear volume. Prior to revision, we recorded the relevant clinical variables, including whole blood cobalt and chromium levels. Volumetric wear of the bearing surfaces was measured using a coordinate measuring machine and of the taper surfaces using a roundness measuring machine. The mean taper wear volume was lower than the combined bearing surface wear volume (p = 0.015). On average the taper contributed 32.9% of the total wear volume, and in only 28% cases was the taper wear volume greater than the bearing surface wear volume. Despite contributing less to the total material loss than the bearing surfaces, the head-stem taper junction remains an important source of implant-derived wear debris. Furthermore, material loss at the taper is likely to involve corrosion and it is possible that the material released may be more biologically active than that from the bearing surface

We compared and quantified the modes of failure and patterns of wear of 11 Mittelmeier and 11 Ceraver-Ostal retrieved alumina-alumina hip prostheses with reference to the corresponding clinical and radiological histories. Macroscopic wear was assessed using a three-dimensional co-ordinate measuring machine. Talysurf contacting profilometry was used to measure surface roughness on a microscopic scale and SEM to determine mechanisms of wear at the submicron level. The components were classified into one of three categories of wear: low (no visible/measurable wear), stripe (elliptical wear stripe on the heads and larger worn areas on the cups) and severe (macroscopic wear, large volumes of material lost). Overall, the volumetric wear of the alumina-alumina prostheses was substantially less than the widely used metal and ceramic-on-polyethylene combinations. By identifying and eliminating the factors which accelerate wear, it is expected that the lifetime of these devices can be further increased

In this prospective, randomised study, we have compared the wear rate of cemented, acetabular polyethylene cups articulating with either a 22 mm or a 32 mm cobalt-chromium head. We evaluated 89 patients who had a total of 484 radiographs. The mean follow-up period was 71.4 months (SD 29.1). All the radiographs were digitised and electronically measured. The linear wear rate was significantly higher during the first two years and decreased after this period to a constant value. We suggest that this is partly due to a ‘run-in’ process caused by irregularities between surfaces of the cup and head and an initial plastic deformation of the polyethylene. The mean volumetric wear was 120.3 mm. 3. /year for the 32 mm head, which was significantly higher than the 41.5 mm. 3. /year for the 22 mm heads. The mean linear wear rate was not significantly different. We were, however, unable to find radiological signs of osteolysis in the patients who had higher wear rates

Summary Statement. Wear of total knee replacement (TKR) is a clinical concern. This study demonstrated low-conformity moderately cross-linked-polyethylene fixed bearing TKRs showed lower volumetric wear than conventional-polyethylene curved fixed bearing TKRs highlighting potential improvement in TKR performance through design and material selection. Introduction. Wear of total knee replacement (TKR) continues to be a significant factor in the clinical performance of the implants. Historically, failure due to delamination and fatigue directed implant design towards more conforming implants to reduce contact stress. However, the new generations of more oxidatively-stable polyethylene have improved the long-term mechanical properties of the material, and therefore allowed more flexibility in the bearing design. The purpose of this study was to investigate the effect of insert conformity and material on the wear performance of a fixed bearing total knee replacement through experimental simulation. Methods. The wear of TKR bearings were investigated using a physiological six station Prosim knee wear simulator (Simulator Solutions, UK). Six samples of each test configuration (Sigma CR fixed bearing knees (DePuy Synthes, UK) were studied, and compared with previously reported data, tested under identical conditions (1, 2). The central axis of the implant was offset from the aligned axes of applied load and tibial rotation to replicate a right knee. High kinematics, under anterior-posterior displacement control was used for this study (3). The lubricant was 25% (v/v) calf serum supplemented with 0.03% (v/v) sodium azide solution in deionised water, as an antibacterial agent, and was changed approximately every 0.33Mc. Wear was assessed gravimetrically and moisture uptake accounted for using unloaded soak controls. Results. The wear rates for the moderately cross-linked inserts (XLK) were significantly lower than the conventional polyethylene (GVF) for all geometries (ANOVA, p<0.05). There was a significant reduction in wear rate as the insert geometry became less conforming for both materials (ANOVA, p<0.05). The wear scars areas were comparable in size and shape between materials, within a geometry group. The size of the wear scar changed with conformity, with the curved inserts showing the largest scars in both anterior-posterior and medial-lateral dimensions, and the flat inserts showing the smallest wear scars. Discussion/Conclusion. The introduction of a moderately cross-linked polyethylene insert was shown to significantly reduce the wear of a fixed bearing total knee replacement compared with a conventional material. There was a trend for reducing wear rate with reducing conformity for both materials, suggesting that reduced conformity results in higher contact pressures and reduced contact area, leading to a reduced surface for wear to occur. Both material and conformity were shown to have a significant impact on the wear of a fixed bearing TKR, and therefore provide opportunity for enhancing wear performance through material and design selection