INTRODUCTION. Precise determination of material loss is essential for failure analysis of retrieved hip cups. To determine wear, the measured geometry of the retrieval hast to be compared to its pristine geometry, which usually is not available. There are different approaches to generate reference geometries to approximate the pristine geometry that is commonly assumed as sphere. However, the geometry of press fit cup retrievals might not be spherical due to deformation caused by excessive press-fitting. The effect of three different reference geometries on the determined wear patterns and material loss of pristine and worn uncemented metal-on-metal hip cups was determined. METHODS. The surfaces of two cups (ASR, DePuy, Leeds; one pristine, one a worn retrieval) were digitized using a coordinate measurement machine (CRYSTA-Apex S574, Mitutoyo; 3 µm accuracy). Both cups were measured undeformed and while being deformed between a clamp. Three different methods for generating reference geometries were investigated (PolyWorks|Inspector 2018, InnovMetric). Method 1: A sphere with the nominal internal cup dimensions was generated. Method 2: A sphere was fitted to the measured data points after removing those from worn areas (deviation > 3 µm is defined as wear) to eliminate the influence of manufacturing tolerances on the nominal diameter. Method 3: Measurements, which displayed visual deformation in the computed wear pattern based on the best fit sphere, were fitted with an ellipsoid. The direction of the deformation axes and the amount of deformation were used to scale the best fit ellipsoid. Linear wear was calculated from the distance of the respective reference geometry to the measured point cloud. Finally, material loss is defined as the difference in volume of the reference geometry and the measured geometry. RESULTS. The method used for generating the reference geometry affected the determined wear greatly. Using the nominal manufacturing radius (larger than the best fit radius) for the worn cup falsely indicates deposit. This leads to approx. 39 % less wear volume compared to the best fit sphere analysis. Using an ellipsoid as reference geometry for both deformed cups improves the determination of the wear pattern and indicates areas of material loss better than a reference sphere. Additionally, the mistake in material loss determination is decreased, especially for the worn cup almost exactly to the wear volume analyzed with the best fit sphere before deformation. DISCUSSION. For correct determination of material loss best fit geometries instead of nominal sizes have to be used to compensate the differences due to manufacturing tolerances. Furthermore, deformation always has to be eliminated to generate correct wear patterns and volumes. Using an ellipsoid as reference geometry improves the outcome. For generating an even more accurate reference geometry, the exact behavior of the cup during deformation must be understood. Limitations to this method are cups that do not provide pristine areas in order to generate an appropriate best fit geometry. For any figures or tables, please contact authors directly

Introduction. In total joint replacement devices, material loss from the taper junctions is a clinical concern. Previous studies of explanted orthopedic devices have relied on visual scoring methods to quantify the fretting-corrosion damage on the component interfaces. Previous research has shown that visual fretting-corrosion evaluation is correlated to the volume of material loss [1], but scoring is semi-qualitative and does not provide a quantitative measure of the amount of material removed from the surface. The purpose of this study was to develop and validate a quantitative method for measuring the volume of material lost from the surfaces of explanted devices at the taper-trunnion junction. Methods. 10 new exemplar taper adapter sleeves (Ceramtec, Plochingen, Germany) were used for method validation. By using exemplar devices we were able to create clinically realistic taper damage in a controlled and repeatable manner using machining tools. Taper surfaces were measured before and after in vitro material removal using a roundness machine (Talyrond 585, Taylor Hobson, UK). Axial traces were measured on each taper surface using a diamond stylus. The mass of artificially removed material was also measured gravimetrically using a microgram balance (Sartorius, CPA225D, accuracy = ± 0.00003g). Surface profiles were analyzed using a custom MatLab script and Talymap software was used to provide 3D visualizations of the pattern of material loss. Calculated volumetric material loss was compared to the gravimetric value. A sensitivity analysis was conducted to determine the optimum number of traces to characterize the material loss from taper junctions. Results. Our calculations of material loss predicted over 99% of the variation in gravimetric material loss (Figure 1, r2 = 0.9962). Examples of the pattern of material removal from explanted components resembled the patterns reported in explants (Figure 2). The sensitivity analysis showed that a minimum of 24 axial profiles are required for measurements to stay within 2% of the volume calculated with 144 traces for cases with an axisymmetric wear pattern. Discussion. We have developed and validated a quantitative method for the material loss from taper junctions in orthopedic devices. Our sensitivity analysis showed that a minimum of 24 profiles are required to calculate volumetric material loss accurately, however a further sensitivity analysis is required to establish the minimum number of profiles required to accurately characterize “asymmetric” wear patterns. The measurement of 24 profiles takes approximately 20 minutes. The validation thus far has comprised material loss in an axisymmetric pattern. Work is underway to validate the evaluation of tapers with an asymmetric wear pattern. The axisymmetric and asymmetric patterns are realistic representations of wear patterns seen in explanted taper surfaces. This validated method of estimating material loss from taper junctions will be used in our ongoing research program to understand the mechanisms of fretting-corrosion in retrieved orthopaedic tapers

Background. Fretting corrosion at the junction of the modular head neck interface in total hip arthroplasty is an area of substantial clinical interest. This fretting corrosion has been associated with adverse patient outcomes, including soft tissue damage around the hip joint. A number of implant characteristics have been identified as risk factors. However, much of the literature has been based on metal on metal total hip arthroplasty or subjective scoring of retrieved implants. The purpose of this study was to isolate specific implant variables and assess for material loss in retrieved implants with a metal on polyethylene bearing surface. Methods. All 28mm and 32 mm femoral heads from a 12/14 mm taper for a single implant design implanted for greater than 2 years were obtained from our institutional implant retrieval laboratory. This included n = 56 of the 28 mm heads (−3: n = 10, +0: n = 24, +4: n = 13, and +8: n = 9), and n = 23 of the 32 mm heads (−3: n = 2, +0: n = 8, +4: n = 1, and +8: n = 6). There were no differences between groups for age, gender, BMI, or implantation time. A coordinate measuring machine was used to acquire axial scans within each head, and the resulting point clouds were analyzed with a custom Matlab program. Maximum linear wear depth (MLWD) was calculated as the maximum difference between the material loss and as-machined surface. Differences in MLWD for head length, head diameter, stem material, and stem offset were determined. Results. Within the 28 mm head diameter group, there was no difference (p = 0.65) in MLWD between head lengths (−3: 4.0 ± 1.7 µm, +0: 10.4 ± 15.2 µm, +4: 4.4 ± 1.7 µm, +8: 4.3 ± 1.8 µm). There was no difference (p = 0.12) between the 28 mm (6.7 ± 10.9 µm) and 32 mm (5.5 ± 6.2 µm) head diameters. There was also no difference (p = 0.97) between titanium (7.3 ± 11.4 µm) or cobalt-chromium (5.9 ± 5.6 µm) stems, and no difference (p = 0.20) between regular (7.0 ± 10.0 µm) or high-offset (5.7 ± 8.0 µm) stems. Discussion. The development of fretting corrosion at the head neck junction of metal on polyethylene total hip replacements is of substantial clinical importance. In a single taper design, head diameter, head length, stem material and stem offset were all not found to be contributory to magnitude of wear depth. This is in contrast to current literature, which is controversial regarding the role of head diameter, but head length is thought to be contributory. However, as this study using precise tools does not illustrate these proposed biomechanic factors of fretting corrosion, other factors influencing tribocorrosion such as trunnion surface finish, flexural rigidity, interface geometry and biochemical factors may need to be considered

Introduction. There is considerable interest in the orthopaedic community in understanding the multifactorial process of taper fretting corrosion in total hip arthroplasty (THA). Previous studies have identified some patient and device factors associated with taper damage, including length of implantation, stem flexural rigidity, and head offset. Due to the complexity of this phenomenon, we approached the topic by developing a series of matched cohort studies, each attempting to isolate a single implant design variable, while controlling for confounding factors to the extent possible. We also developed a validated method for measuring material loss in retrieved orthopaedic tapers, which contributed to the creation of a new international standard (ASTM F3129-16). Methods. Based on our implant retrieval collection of over 3,000 THAs, we developed independent matched cohort studies to examine (1) the effect of femoral head material (metal vs. ceramic, n=50 per cohort) and (2) stem taper surface finish (smooth vs. microgrooved, n=60 per cohort). Within each individual study, we adjusted for confounding factors by balancing implantation time, stem taper flexural rigidity, offset, and, when possible, head size. We evaluated fretting and corrosion using a four-point semiquantitative score. We also used an out-of-roundness machine (Talyrond 585) to quantify the material loss from the tapers. This method was validated in a series of experiments of controlled material removal on never-implanted components. Results. In the first study, the ceramic cohort exhibited a 92% reduction in cumulative volumetric loss from both the head and neck taper surfaces compared to the CoCr cohort (p < 0.001). In the CoCr cohort, there was greater material loss from femoral head tapers as compared with stem tapers (p < 0.0001). There was also a correlation between visual scoring and volumetric material loss (ρ = 0.67, p < 0.01). In the second study, taper damage was not different between the smooth and microgrooved taper cohorts when evaluated at the head bore (p=0.14) or the stem tapers (p=0.35). There was also no difference in material loss between the most damaged CoCr heads in the two cohorts (p>0.05). Conclusions. Our findings suggest that fretting and corrosion damage and material loss from the stem taper are mitigated, and on the head taper, eliminated with the use of a ceramic vs. metal femoral head. We also found that fretting and corrosion damage was insensitive to differences in stem taper surface finish and the presence of microgrooves. Although visual scoring was effective for preliminary screening to separate tapers with no or mild damage from tapers with moderate to severe damage, it was not capable of discriminating within the large range of material loss observed at the taper surfaces with high fretting-corrosion scores. Thus, for moderate to severely damaged conical tapers, direct measurement is necessary. A drawback of a matched cohort approach is that a large retrieval collection is necessary to effectively match an investigational group of implants with an appropriate control cohort. Notwithstanding this limitation, the matched cohort approach has been an effective approach to study the complex multifactorial problem of taper fretting and corrosion

Introduction. A common phenomenon occurring as a result of reverse total shoulder arthroplasties (RSA) is scapular notching. While bone loss of the scapula may be quantified using radiographic techniques,[1] the material loss on the humeral bearing has not been quantified. Depending on their functional biological activity, a high volume of polyethylene wear particles has been shown to be related to osteolysis, bone loss and ultimately, loosening of implants in other joints.[2] In order to understand the threshold for osteolysis in the shoulder, it is important to have a method that can accurately quantify the amount of material loss. The aim of this research was to (I) create and validate a method for quantifying material loss from a single humeral implant design which can then (II) be used to measure retrieved devices. Methods. Measurement of the surface topography of the implant was completed using coordinate measurement machine (CMM). The resulting point cloud was then imported into MATLAB and run through a custom algorithm to determine the volumetric wear of the humeral liner. Two never implanted humeral liners with an artificially damaged material loss were used for validation purposes. Each component was scanned three times, analyzed using the custom MATLAB program, and compared to gravimetric analysis (Figure 1). Following validation, an IRB-approved database was queried to identify 10 retrieved components of the same design which were then analyzed using the validated method. Results. All average measurements of the never implanted components were within +/- 5 mm. 3. of the gravimetrically determined values, providing a reasonable estimate of the volumetric wear (Figure 1). Ten retrieved components of a single design were analyzed using the same method and material loss ranged from immeasurable (within the accuracy limits) to approximately 90 mm. 3. (Figure 3). One short term duration implant (1.8 mos) exhibited approximately 78 mm. 3. of wear, resulting in a polyethylene dosage of more than 500 mm. 3. /yr. Discussion. The posterior-inferior wear pattern on the rim of these reverse shoulders appears consistent with repetitive scapular impingement. The significant wear of short duration implants indicates that wear associated with scapular notching may progress very quickly, resulting in large dose rates of debris in the joint space. However, the impingement may result in a more abrasive wear mechanism as opposed to an adhesive wear mechanism as seen in other joint wear environments. This may result in different size and shaped polyethylene particles with different biological activity. The algorithms presented in this work can be used to establish a dose-response relationship for scapular notching in RSA

Introduction:. Cemented femoral components have been used in hip replacement surgery since its inception. For many patients this works well, but recent retrieval studies. 1–4. and more fundamental studies. 5, 6. have highlighted the issues of damage and material loss from the both matt and polished cemented stems. Materials and methods:. This study will focus on a cohort of retrievals from the Southampton Orthopaedics Centre for Arthroplasty Retrieval Surgery (SOCARS). The cohort consisted of a number of hybrid modular total hip replacements with cemented femoral components, both from mixed and matched manufacturer stem and head combinations. Femoral stems were polished, collarless, tapered designs; head sizes ranged from 28–54 mm. For each femoral stem, samples of Palacos R + G cement (Heraeus Medical GmbH, Hanau, Germany) were retrieved from the proximal region of the cement mantle (Gruen zones 1 and 7), corresponding to both macroscopically damaged and undamaged surfaces of the stem. The areas of damage were determined using calibrated digital photography; damaged surfaces were then imaged in detail using an Alicona InfiniteFocus microscope (Alicona Imaging GmbH, Graz, Austria). The technique uses optical microscopy and focus variation technology to extract 3D morphology and depth information from the surface with a resolution of 10 nm. A series of measurements were made and two different analysis routes were used to provide volumetric material loss measurements from the stem surface. High-resolution microscopy and elemental analysis of the cement and stem surfaces was conducted via SEM and EDX to identify the mechanisms leading to material loss at the cement-stem interface. Results:. The results demonstrate that material loss from polished femoral stems results from a progressive tribocorrosion process; the major damage mechanism is thought to be the micro-motion between the femoral stem surface and zirconium dioxide radiopacifier agglomerates originating from the cement. No significant link was found between the extent of damage to the femoral stem and either the head size or the amount of wear occurring at the head-cup bearing surface. The scale of stem damage varied between implants but often exceeded the volumetric material loss measured at the bearing surfaces. Conclusions:. Tribo-corrosive damage to the femoral stems of cemented total hip prostheses is a major potential source of material loss in vivo; in severely affected arthroplasties, measurements of volumetric wear of the stem at the cement-stem interface were greater than at either the head-cup bearing surface or the taper junction. The mechanism of material loss in this study was identified as a wear-dominated tribocorrosion interaction between the cement and stem, with zirconium dioxide radiopacifier agglomerates within the cement providing the hard particles which damaged the surface of cobalt-chrome femoral stems

Utilization of reverse total shoulder arthroplasty (RTSA) has steadily increased since its 2003 introduction in the American market. Although RTSA was originally indicated for elderly, low demand patients, it is now being increasingly used to treat rotator cuff arthropathy, humeral fractures, neoplasms and failed total and hemi shoulder arthroplasty. There is, therefore, a growing interest in bearing surface wear of RTSA polyethylene humeral liners. In the current study, we examined humeral liners retrieved as part of an IRB approved study to determine the amount of bearing surface wear. We hypothesized that wear of the bearing surface by intentional contact with the glenosphere (mode I) would be minor compared to that produced by scapular notching and impingement of the humeral liner (mode II). Twenty-three retrieved humeral liners were retrieved at revision surgery after an average of 1.5 years implantation time. The average age at implantation was 68 years (range 50–85). Shoulders were revised for loosening (7), instability (6), infection (6), pain (2), and other/unknown reasons (2). The liners were scanned using microCT at a resolution of 50 µm and then registered against unworn surfaces to estimate the bearing surface wear depth. The depth of surface penetration due to impingement of the liner with surrounding structures was measured and the location of the deepest penetration was noted. Mode I wear of the bearing surface was detectable for five of the retrieved liners. The penetration depth was 100 µm or less for four of the liners and approximately 250 microns for the fifth liner. It was noted that the liners with discernable mode I wear were those with longer implantation times (average 2.4 years). Material loss and abrasion of the rim due to mode II wear was noted with measurable penetration in 18 of the liners. Mode II wear penetrated to the bearing surface in 11 liners. It was generally noted that volumetric material loss was dominated by mode II wear (Figure 1). In this study of short to medium term retrieved RTSA humeral liners, mode I wear of the bearing surface was a minor source of material loss. Mode II wear due to scapular notching or impingement of the rim was the dominant source of volumetric wear. This is in agreement with a previous study that we have performed on a smaller cohort of seven liners. It is noteworthy that we were able to detect measurable mode I wear for liners with moderate implantation times. The quantity of bearing surface wear that will be seen in long term retrievals remains unknown at this time

Introduction. Metal-on-polyethylene (MoP) is the most commonly used bearing couple in total hip replacements (THRs). Retrieval studies (Cooper et al, 2012, JBJS, Lindgren et al, 2011, JBJS) report adverse reactions to metal debris (ARMD) due to debris produced from the taper-trunnion junction of the modular MoP THRs. A recent retrospective observational study (Matharu et al, 2016, BMC Musc Dis) showed that the risk of ARMD revision surgery is increasing in MoP THRs. To the authors' best knowledge, no hip simulator tests have investigated material loss from the taper-trunnion junction of contemporary MoP THRs. Methods. A 6-station anatomical hip joint simulator was used to investigate material loss at the articulating and taper-trunnion surfaces of 32mm diameter metal-on-cross-linked polyethylene (MoXLPE) joints for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum (CoCrMo) femoral heads articulating against XLPE acetabular liners (7.5Mrad) were used with a diluted new-born-calf-serum lubricant. Each CoCrMo femoral head was mounted on a 12/14 titanium alloy trunnion. The test was stopped every 0.5Mc, components were cleaned and gravimetric measurements performed following ISO 14242-2 and the lubricant was changed. Weight loss (mg) obtained from gravimetric measurements was converted into volume loss (mm. 3. ) and wear rates were calculated from the slopes of the linear regression lines in the volumetric loss versus number of cycles plot for heads, liners and trunnions. Additionally, volumetric measurements of the head tapers were obtained using a coordinate measuring machine (CMM) post-test. The surface roughness (Sa) of all heads and liners was measured pre and post-test. At the end of the test, the femoral heads were cut and the roughness of the worn and unworn area was measured. Statistical analysis was performed using a paired-t-test (for roughness measurements) and an independent sample t-test (for wear rates). Results and Discussion. The mean volumetric wear rates for CoCrMo heads, XLPE liners and titanium trunnions were 0.019, 2.74 and 0.013 mm. 3. /Mc respectively. There was a statistically significant decrease (p<0.001) in the Sa of the liners post-test. This is in contrast to the femoral heads roughness in which no change was observed (p = 0.338). This head roughness result matches with a previous MoP in vitro test (Saikko, 2005, IMechE-H). The Sa of the head tapers on the worn area showed a statistically significant increase (p<0.001) compared with unworn, with an associated removal of the original machining marks. The mean volumetric wear rate of the head tapers obtained using the CMM (0.028 ± 0.016 mm. 3. /Mc) was not statistically different (p=0.435) to the mean volumetric wear rate obtained gravimetrically (0.019 ± 0.020 mm. 3. /Mc) for the femoral heads. Therefore, wear of the heads arose mainly from the internal taper. The mean wear rates of the CoCrMo taper and titanium trunnion are in agreement with a MoP explant study (Kocagoz et al, 2016, CORR). Conclusion. This is the first long-term hip simulator study to report wear generated from the taper-trunnion junction of MoP hips

The articulating surface replacement (ASR) XL stemmed total hip replacement and ASR resurfacing hip systems were recalled by DePuy due to a high prevalence of early failure. The ASR XL has a greater failure rate than the ASR resurfacing, which has been increasingly attributed to wear and corrosion at the taper interface between the female taper surface of the femoral head and the male taper (trunnion) of the femoral stem. The aim of this study was to quantify the prevalence and severity of taper corrosion in retrieved ASR XL hip components. A peer-reviewed subjective corrosion scoring system was used to quantify corrosion in a consecutive series of the 50 ASR XL hip components (head components – n=44; femoral stems – n=6) at our retrieval centre. Bearing surface wear (femoral head and acetabular cup combined) was quantified and a value of <5 microns was defined as low-wearing. Subsequent profilometry analysis was undertaken in the low-wearing hips to quantify material loss from the taper interface. 90% of components showed evidence of corrosion, with at least moderate corrosion observed in 58%. There were 17 low-wearing hips which had a median material loss from the taper interface of 3.51mm. 3. (range: 0.612–9.443). The median linear depth of material loss was 33μm (range: 8.5–78.0). No relationship was observed between taper corrosion and serum cobalt (r=0.204, p=0.2712) or chromium (r=0.146, p=0.432) metal ions. Wear and material loss from metal-on-metal (MoM) hips is associated with pseudotumour formation and adverse soft-tissue reactions. We have shown that taper corrosion is extremely common in failed ASR XL hips and that wear occurs in the same degree of magnitude as at the bearing surface also occurs at the taper interface. Therefore our findings support the emerging concept of ‘taper failure’, whereby the taper is the predominate reason for failure of MoM hips. Future work must determine the relative contributions of the bearing surface and the taper interface to serum cobalt and chromium metal ion levels

Introduction. Failure of the neck-stem taper in one particular bi-modular primary hip stem due to corrosion and wear of the neck piece has been reported frequently1, and stems were recalled. A specific pattern of material loss on the CoCr neck-piece taper in the areas of highest stresses on the proximal medial male taper was observed in a retrieval study of 27 revised Rejuvenate implants revised after 3 to 38 month time in situ (Stryker, Kalamazoo, MI, USA) (Figure 1). One neck piece exhibited additionally wear marks at the distal end of the flat male neck taper indicating contact with the female taper of the stem. The purpose of this study was to understand the observed failure scenario of bottoming-out by investigating the stem taper morphologies. Materials and Methods. The geometry of taper contact surfaces was determined using a Coordinate Measurement Machine (BHN 805, Mitutoyo, Japan). An algorithm based on the individual unworn areas of the respective taper surfaces was applied to all retrievals. One retrieval is additionally investigated by infinite focus microscopy (G4, Alicona, Austria) in the main wear areas on the neck piece taper, and the bottom, facing each other inside the junction (surfaces of the distal end of the male and the bottom of the female taper). Results. The bottom of the male neck piece taper showed a prominent patch surrounded by a corrosion area (Figure 2), similar to the pattern observed in the proximal taper articulation medial- proximally and lateral-distally (Figure 1). The bottom of the female titanium stem taper did not show material loss to this extent, but only slight scratches. The proximal male taper of the neck piece showed the usual corrosion pattern, with an elevated patch protruding inside the corrosion cavity (Figure 3, left). Contrarily to observations on other retrievals (Figure 3, right), the height of this patch did not reach the original surface level. The wear depth at the patch of the bottomed out taper was 93µm with wear reaching as deep as 170µm. Discussion. Only one of 27 retrieved neck pieces showed bottoming out. It can be speculated that the other retrievals were revised before this situation could occur. In the assembled situation, the initial space between the bottom faces of the stem taper is expectedly in the order of a few 100µm. During the observed wear process, permanent contact at patches on the neck piece prevents its reseating, until these localized structures give in to mechanical and electrochemical exposure. This end stage of failure only occurring in one explant indicates high clinical risks of the implants during earlier stages of intact patches, that are usually observed in retrievals. The formation of such patches has not been reported before, and might be characteristic for the wear and corrosion mechanism of the employed TMZF-CoCr combination, possibly due to the reduced stiffness of the TMZF Titanium. Acknowledgements. The research received funding from the European Union's Seventh Framework Program (FP7/2007-2013) under grant agreement GA-310477 (LifelongJoints)

Introduction. Wear debris induced osteolysis and loosening continue to cause clinical failure in total knee replacement (TKR). To improve longevity and reduce wear alternative materials have been examined. Carbon-fibre-reinforced poly–ether-ether-ketone (CFR-PEEK) has shown promising results in wear studies [1–2]. The aim of this study was to explore the use of CFR-PEEK and PEEK as alternative bearing materials for polyethylene in TKR through experimental knee joint wear simulation. Methods. Two novel materials were studied as an alternative to polyethylene as the tibial bearing surface in a TKR configuration using a Cobalt chrome femoral bearing in current clinical use. Six right Sigma CR fixed bearing TKRs (DePuy Synthes, UK) were paired with either PEEK or CFR-PEEK custom-made flat inserts (Invibio, UK) in a Prosim knee simulator (Simulator Solutions, UK). The tibial inserts were 14mm thick, to give an equivalent thickness to existing insert designs. A flat geometry was selected as this has previously been shown to yield low wear in polyethylene bearings [3]. The tests were conducted under High Kinematics, with anterior-posterior and internal-external displacement control [4]. Tests were conducted for three million cycles, lubricated with 25% bovine serum, with wear assessed gravimetrically at 1 and 3Mc. Images of the wear scars were recorded at completion of the study. Visual inspection of the tibial inserts was used to identify regions of wear damage for SEM analysis (EVO MA15-Smart SEM, Zeiss, Germany). Results. Extremely large material loss and wear was observed for both PEEK and CFR-PEEK inserts at 3Mc (Figure 1). The PEEK material showed higher volumetric loss than the CFR-PEEK. Wear rates of >200mm. 3. /Mc compare with less than 4 mm. 3. /Mc for polyethylene under the same conditions. [3]. Large, deep wear scars were observed on all plates (Figure 2a and b). Evidence of mechanical material failure was observed through SEM including material cracking, deformation and fibre pull-out (Figure 3a and b). Discussion. Wear simulator testing of flat PEEK and CFR-PEEK as potential replacements for polyethylene materials in a TKR configuration produced high material loss after 3Mc. This is in contrast to promising data reported in another study of the knee [5]. The present study examined a low-conformity condition. Previous studies have included hip and highly-conforming TKR designs; therefore the contact pressures would be lower than the current study. This study highlights these new materials may undergo mechanical failure at higher contact stress conditions

Introduction. We conducted independent wear analysis of retrieved metal on metal (MoM) hip components from around the world. All patients with resurfaced hips who developed adverse reactions to metal debris (ARMD) were found to have increased wear of the bearing surfaces. This was untrue in patients with large diameter (?36mm) MoM total hip replacements. This led us to search for other factors leading to ARMD. Methods. MoM THR explants retrieved from 78 patients suffering ARMD underwent full volumetric wear analysis of bearing surface and taper-junctions using coordinate measuring machine. Scanning electron microscopy (SEM) used to characterise material composition of specific areas. Results. 34 MoM THRs were found to have relatively low bearing surface wear (< 3mm. 3. /year). In each of these cases, material loss up to 60 microns wear depth was identified on the internal taper-junctions of femoral components. However, volumetric loss was rarely >5mm. 3. Similarly only 65% of metal ion levels of these patients were found to be greater than the MHRA guidance figure (7µg/L). Patterns of material loss at the tapers were consistent with antero-posterior force splaying open the taper-junction. This characteristic pattern was identified in number of commercially available devices (titanium and cobalt chromium stems). Soft tissue lesions were severe in patients found to have taper damage. Histology confirmed severe ALVAL with lymphoid neogenesis in majority cases, suggesting that wear debris from taper junctions may have greater potential to stimulate adverse immune response. Discussion. The results suggest that forces transmitted from large diameter hard-on-hard bearing surfaces are sufficient to cause mechanical damage to modular junctions with secondary localised corrosion. We urge caution in the use of these designs and recommend a re-evaluation of the stem head interface

Background. Previous studies have suggested that the modular junction of metal on metal (MoM) total hip replacements (THR) is an important source of metallic debris. Methods. We carried out a prospective study using custom techniques to analyse one of the largest collections of failed contemporary MoM devices in the world. All explants from patients who had suffered adverse reactions to metal debris (ARMD) were included in this study. These explants included: 82 36mm THRs, and 147 resurfacing head THRs and 140 resurfacing arthroplasties from several manufactures. Volumetric wear analysis of the bearing surfaces and taper junctions was carried out using a coordinate measuring machine. The relationships between total metallic loss and metal ion concentrations and the macroscopic and histological tissue appearance of THR patients were compared to those in resurfacing patients. Mann Whitney test for non-parametric data was used to assess significant differences between groups. Results. Resurfacing explants retrieved from patients who had suffered ARMD were found to have significantly higher median rates of volumetric wear than the THRs (10.16 versus 2.25mm. 3. /yr (p < 0.001)). Total volumetric material loss from taper junctions ranged from 0.01 to 21.55mm. 3. When volumetric taper wear was combined with bearing surface wear in the THR patients this total rate of material loss was still significantly less than in the resurfacing patients 2.52 versus 10.16mm. 3. /yr (p < 0.001)). Despite this, macroscopic tissue destruction and extent of ALVAL infiltration was found to be significantly greater in the THR patients. Conclusion. Taper debris appears to more readily stimulate a destructive immune cascade than debris from primary bearing surfaces. This cascade can culminate in catastrophic tissue necrosis when blood metal ion concentrations appear normal. MHRA guidance should distinguish clearly between MOM THRs and resurfacings

Introduction. Wear of polyethylene tibial inserts has been cited as being responsible for up to 25% of revision surgeries, imposing a very significant cost burden on the health care system and increasing patient risk. Accurate measurement of material loss from retrieved knee bearings presents difficult challenges because gravimetric methods are not useful with retrievals and unworn reference dimensions are often unavailable. Geometry and the local anatomy restrict in vivo radiographic wear analysis, and no large-scale analyses have illuminated long-term comparative wear rates and their dependence on design and patient factors. Our study of a large retrieval archive of knee inserts indicates that abrasive/adhesive wear of polyethylene inserts, both on the articular surface and on the backside of modular knees is an important contributor to wear, generation of debris and integrity of locking geometry. The objective of the current study is to quantify wear performance of tibial inserts in a large archive of retrieved knees of different designs. By assessing wear in a large and diverse series, the goal is to discern the effect on wear performance of a number of different factors: patient factors that might help guide treatment, knee design factors and bearing material factors that may inform a surgeon's choice from among the array of arthroplasty device options. Methods. An IRB approved retrieval database was queried for TKA designs implanted between 1997 and 2017. 1385 devices from 5 TKA designs were evaluated. Damage was ranked according to Hood's method, oxidation was determined through FTIR, and wear was determined through direct measurement of retrieved inserts using a previously established protocol. Design features (e.g. materials, conformity, locking mechanisms, stabilization, etc.) and patient demographics (e.g. age, weight, BMI, etc.) were cataloged. Multivariate analysis was performed to isolate factors contributing to wear, oxidation, and damage. Results. Wear and oxidation were both found to scale with time in vivo in conventional and crosslinked polyethylene. Wear rate was also found to scale with time in vivo, but was not found to be a function of oxidation. Regression shows patient age and female sex to correlate negatively with wear rate. Polished trays, crosslinked polyethylene, and constrained knee designs are all correlated with decreased wear rates. Discussion. While this study indicates that loosening and infection are predominant causes for TKA revision, wear related failure remains common. We believe this to be the largest existing comparative study of modern TKA wear rates. Insert wear is shown to correlate with several patient factors. Wear performance also varies significantly between knee designs, polyethylene material choice and tray surface finish. When compared to a historical standard for knee wear rates, all designs evaluated in the current study exhibited significant improvements in wear rates. Retrieval analysis can provide insight into implant and patient related factors that contribute to knee wear, with the goal of improving patient outcomes and best matching design decisions to patient populations

Introduction. The bearing surfaces of ceramic-on-ceramic (CoC) total hip replacements (THR) show a substantially lower wear rate than metal-on-polyethylene (MoP) THR in-vitro. However, revision rates for CoC THR are comparable with MoP. Our hypothesis that an explanation could be adverse reaction to metal debris (ARMD) from the trunnion led us to investigate the wear at both the bearing surfaces and the taper-trunnion interface of a contemporary CoC THR in an in-vitro study. Methods. Three 36mm CoC hips were tested in a hip simulator for 5 million cycles (Mc). BIOLOX. ®. delta ceramic femoral heads were mounted on 12/14 titanium (Ti6Al4V) trunnions. Wear of femoral heads, acetabular liners and trunnions was determined gravimetrically using the analytical balance. Roughness measurements (Sa) were taken on the articulating surfaces (pre and post-test) and on the trunnion surfaces (worn and unworn). Furthermore, Energy Dispersive X-ray Spectroscopy (EDX) was used to identify and quantify the wear debris present in the lubricant using scanning electron microscope (SEM). Results and Discussion. The total volumetric wear was 0.25 mm. 3. for CoC joints and 0.29 mm. 3. for titanium trunnions. The total wear volume of the titanium trunnions was in agreement with an explant study (Kocagoz et al, 2016, CORR) which quantified the volumetric material loss from retrieved trunnions with the total wear ranging from 0.0–0.74 mm. 3. The Sa values, pre-and post-test, for heads were 0.003 ± 0.002 and 0.004 ± 0.001 µm and for liners were 0.005 ± 0.001 and 0.005 ± 0.001 µm. Pre-and post-test measurements for Sa of heads (p = 0.184) and liners (p = 0.184) did not show a statistically significant change. The Sa of the trunnions on the unworn and worn areas showed a statistically significant decrease from 0.558 ± 0.060 to 0.312 ± 0.028 µm respectively (p < 0.001). Analysis of wear debris within the lubricant confirmed the presence of titanium. A recent clinical study (Matharu et al, 2016, BMC Musc Dis) found more ARMD in CoC hips than MoP hips. This is despite there being fewer metallic components in a CoC hip than a MoP hip. This in vitro study has shown that one source of metal debris in a CoC hip is the taper-trunnion junction. Conclusion. An explanation for wear related failures in ceramic-on-ceramic hip arthroplasty, despite the low wear arising at the articulating surfaces, may now exist; namely that titanium wear particles are generated from the trunnion. No other long-term hip simulator studies have measured wear at the taper-trunnion junction

Introduction. Corrosion at modular junctions of total hip replacements has been identified as a potential threat to implant longevity, resulting in efforts to determine appropriate countermeasures. Visual scoring and volumetric material loss measurements have been useful tools to elucidate various clinical and design factors associated with corrosion damage. However, corrosion involves electron exchange that results in chemical changes to biomedical alloys, and electrochemical assessment may therefore be a more appropriate approach to understand the phenomenon. The purpose of this pilot study was to electrochemically distinguish the severity of corrosion in retrieved femoral heads. A secondary goal was to identify the potential of electrochemical impedance spectroscopy (EIS) as a method to identify different forms of corrosion damage. Methods. Twenty femoral heads were identified from a larger study of total hip replacements, obtained as part of an ongoing multi- center IRB-approved retrieval program. Using a previously established 4-point scoring method, components were binned by taper damage: 10 components were identified as having severe damage, 7 with moderate damage and 2 with mild damage. One (1) unimplanted control was included to represent minimal corrosion damage. All components were then characterized using electrochemical impedance spectroscopy under the frequency domain: a 10 mV sinusoidal voltage, ranging from 20 kHz to 2 mHz, was applied to the taper of a femoral head (working electrode) filled with a 1M solution of PBS, a platinum counter electrode and a chlorided silver reference electrode. Absolute impedance at 2 mHz (|Z. 0.002. |), and max phase angle (θ) were assessed relative to taper damage severity. After least-squares fitting of the EIS data to a Randles circuit with a constant phase element, circuit elements: polarization resistance (Rp), CPE-capacitance, and CPE-exponent were also evaluated. The seven (7) most severely corroded components were further examined with scanning electron microscopy to identify corrosion modes. For all statistical analyses, significance was determined at alpha=0.05. Results. Taper damage was strongly correlated with both |Z. 0.002. | (ρ = −0.857, p<0.001) and CPE-capacitance (ρ=0.913, p<0.001). Taper damage was moderately associated with max phase angle (ρ= −0.483, p=0.031), CPE-exponent (ρ= −0.653, p=0.002) and Rp (ρ=0.556, p=0.011). Log-log plots of the strongest predictors of taper damage (|Z. 0.002. | and CPE- capacitance) identified some clustering among severely corroded components. SEM analysis identified evidence of grain/phase boundary corrosion on four components, all with log CPE-capacitance ≥ −4.4. Discussion. The results of this pilot study highlight that electrochemical impedance spectroscopy is useful in determining corrosion severity in retrieved femoral heads, and may also identify intergranular corrosion attack. For an undamaged taper, the self- passivating behavior of CoCrMo creates a surface that opposes charge transfer, but greater corrosion appears to compromise this barrier. The observed trend of low impedance but high capacitance for severely corroded components with intergranular corrosion may signal charge storage at the boundaries of individual grains. Additional work is underway to characterize this behavior

INTRODUCTION:. The use of tapered junctions in primary hip arthroplasty has excellent results. Large heads are being used to mitigate dislocation and optimize range of motion. The prevalence of larger heads, coupled with recent findings regarding corrosion artifacts at tapered surfaces, has spurred growing interest when considering revision rates. The purpose of this study was to determine if correlations exist between severity of corrosion artifacts and head size, head offset, time in vivo, orhead material in a 15 year retrieval database. METHODS:. Retrieved hip arthroplasty devices with CoCrMo or oxidized zirconium (OxZr) heads were investigated for corrosion artifacts in this study. Female tapered surfaces were scored independently by a panel according to the Goldberg system for assessment of corrosion. Exclusion criteria included less than 1 week in vivo, ceramic taper, and modular proximal stem sleeves. Evaluation was performed on only stem/head taper junctions. SEM analyses and a newly developed method of vertical straightness deviation (VSD) were used on a subset of devices as an additional measure to quantify corrosion within the taper contact region by measuring depth of material loss. RESULTS:. A total of 227 retrievals containing taper surfaces spanning 15 years were evaluated. Of these, 183 met the inclusion criteria (CoCrMo, n = 159; OxZr, n = 24). Time in vivo ranged from 1 week to 10 years. The majority of the head tapers were 12/14 in size. There was no correlation between head size and average Goldberg score (n = 183, R. 2. = 0.23). There was a parabolic correlation between head offset (9 offset sizes evaluated) and average Goldberg score (n = 156, R. 2. = 0.89), with the more negative offsets and the more positive offsets exhibiting higher scores. There was no correlation between time in vivo and Goldberg score (n = 104, R. 2. = 0.11). There was a correlation between head material and Goldberg score, with OxZr having a lower score as compared to CoCrMo heads (1.9 ± 0.6 vs. 2.5 ± 0.9, p = 0.002). VSD measurements made on CoCrMo heads with a Goldberg score of 4 showed that 5 of 6 CoCrMo heads had a measureable depth of material loss at the taper, with a maximum depth ranging from 8 to 103 microns. There were no OxZr heads with a Goldberg score of 4. SEM and VSD measurements corroborated scoring (Figures 1–3). CONCLUSIONS:. CoCrMo heads have 20+ years of clinical success, but as shown in this study may still generate a quantifiable amount of taper corrosion. Though impaction force, taper cleanliness, patient factors and other myriad multi-factorial issues may contribute to taper corrosion, in this study no correlation was observed for head size or time in vivo and Goldberg score. A correlation was found between head offset and Goldberg score. The use of an OxZr head material exhibited decreased corrosion by-products as compared to the traditional CoCrMo head material used in hip arthroplasty

Introduction. There have been increased concerns with trunnion fretting and corrosion and adverse local tissue reactions (ALTR) in total hip arthroplasty. We report on 11 catastrophic trunnion failures associated with severe ALTR requiring urgent revision arthroplasty. Methods. We retrospectively reviewed 10 patients with gross trunnion failure (n=11) and an additional 3 patients with impending trunnion failure. Results. All patients presented to the emergency department with severe pain, an inability to bear weight, and dramatic radiographs demonstrating implant failure. Patients were an average of 7.8 years from the initial index procedure. Implants were a cementless component with metal on polyethylene bearing from a single manufacturer with a 36mm femoral head size and a range of extended offset of 2.5 to 5.5 and neck length of +0 (n=1), +5 (n=5), and +10 (n=5). The implant was used during a limited time (2.5 years) by single surgeon in our practice using a posterior approach, with the last implant placed 7 years ago. Prior to revision, serum cobalt levels were elevated, typically more than chromium levels. Radiographs demonstrated failure of the implant with a dissociation of the head from the taper and large radiolucent fluid collections from the metal debris (Fig 1). Intraoperative findings and magnetic resonance imaging confirmed a diagnosis of ALTR with loss of abductors, and severe material loss from the taper (Fig 2). We estimate a conservative incidence of catastrophic trunnion failure in our series to be 2.2% (n = 636 total implanted). A femoral revision with a modular Wagner stem was performed, and when necessary the acetabulum was revised secondary to destruction of the locking mechanism from mechanical wear. Discussion and Conclusion. ALTR can occur in patients with catastrophic failure of their trunnion. Radiographs are dramatic. Serum metal ion levels and magnetic resonance imaging is comparable to adverse local tissue reaction in metal on metal bearing surfaces, corrosion at the head neck taper, and corrosion of dual modular taper stems. The initiating events leading to this mechanism of trunnion failure is unknown. We observed trunnion failure at large head sizes and at increased femoral head offsets. Other groups have reported an association of trunnion failure at increased neck length and head size with a variety of manufacturers. Based on our experience, we have been able to identify impending failure based on subtle radiographic criteria and elevated metal ion levels. A failure rate of 2% at 7.8 years is non-trivial. Impending trunnion failure should be considered as a possible diagnosis in a painful total hip arthroplasty with unknown etiology. Serum metal ion levels and magnetic resonance imaging should be obtained as part of the initial evaluation

The use of fourth generation ceramic as an orthopaedic biomaterial has proved to be a very efficient and has gained popularity for primary hip surgery in the last 8–10 years. Cumulative percentage probability of revision after 7 years for un-cemented CoC is 3.09% and for hybrid CoC is 2.00%, this compares favourably with traditional metal-on-UHMWPE un-cemented at 3.05% and hybrid at 2.35% (12th Annual Report - NJR, 2015). Such ceramic-on-ceramic hip prostheses are being implanted in ever younger, more active patients, and yet very few long-term large cohort retrieval studies are yet to be carried out due to the survivorship of the implants. It has been seen in previous studies that levels of wear in ceramic-on-ceramic bearing surface can be of the order of 0.2 mm. 3. /million cycles (Al-Hajjar, Fisher, Tipper, Williams, & Jennings, 2013). This is incredibly low when compared to studies that characterize wear in other bearing surface combinations. It has also been reported that an unusual stripe pattern of wear can occur in some in-vivo retrieved cups (Macdonald & Bankes, 2014) and it has further been postulated that this is caused by cup edge loading (Walter, Insley, Walter, & Tuke, 2004). The combined measurement challenge of stripe wear occurring at the edge of a low-wear ceramic-on-ceramic device is considerable, a solution to which is presented here. Current literature on wear measurement of such cases has been confined to in-vitro simulator studies and use of gravimetric measurement which by definition has limitations due to the lack of spacial characterisation. This paper details a novel method for measuring edge-wear in CoC acetabular liners. The method has been employed in an in-vitro study where it has been benchmarked against gravimetric measurements. These liners were measured on a CMM to determine the volume of material loss. The measurements were conducted as a blinded post-wear study akin to measurement of retrieved components. The most challenging part of this novel method was to create a reference geometry that replicates the free form edge surface of the ‘unworn’ cup using the residual post-wear surface. This was especially challenging due to the uncontrolled geometry at the cup edge and intersection of geometric features at this point. To achieve this, the geometry surrounding the wear patch was used to create a localized reference feature that minimised the effect of global form errors caused by hand polishing in the edge area. Furthermore, the reference geometry is compared with the measured surface to determine the linear penetration and volumetric wear loss. Result of this novel method can be seen in Fig 1. The findings have been compared to gravimetric results and a bar graph comparing two results can be seen in Fig 2. Overall the accuracy of the method for this cohort was 0.03–0.2 mm. 3. when compared to gravimetric reference measurements. This compares very favourably with previously published wear measurement methods and gives confidence in the ability to measure such small measurement volumes over complex geometry

Introduction. There are increasing reports of total hip replacement (THR) failure due to corrosion within modular taper junctions, and subsequent adverse local tissue reactions (ALTRs) to corrosion products. Modular junction corrosion is a multifactorial problem that depends on material, design, patient and surgical factors. However, the influence of alloy microstructure on corrosion has not been studied sufficiently. Especially for cast CoCrMo, there are concerns regarding microstructure variability with respect to grain size and hard-phase volume fraction. Therefore, it was the goal of this study to (1) identify different types of microstructures in contemporary implants, and (2) determine implications of alloy microstructure on the occurring corrosion modes. Methods. Fifteen surgically retrieved femoral stems made from cast CoCrMo alloy were analyzed for this study. Damage on the taper surfaces was investigated by scanning electron microscopy (SEM) and damage was assessed with the Goldberg Score. The alloy microstructure was evaluated by standard metallographic techniques. Alloy samples were sectioned off the femoral stem, and microstructural features were visualized by chemical etching. Cyclic potentio-dynamic polarization tests were carried out with alloy samples from two implants with different commonly occurring types of microstructures. Both had a similar grain size, but type 1 had no hard-phases, where as type 2 exhibited hard-phases along the grain boundaries, as well as intra-granular hard-phase clusters. Tests were performed in bovine serum at 37°C with a saturate calomel reference electrode and a graphite counter electrode. In vitro generated corrosion damage was then compared to in vivo generated damage features on the taper surfaces of the corresponding implants. Results. Tapers with high damage scores exhibited varying degrees of grain and phase boundary corrosion, along with fretting and pitting corrosion. In several cases thick chromium oxide films were observed. The metallographic analysis showed that nominally identical alloys (ASTM F75) exhibited a broad variability in grain size (250 micrometers to several millimeters), hard-phase volume fraction (0–6%), and hard-phase type (carbides and intermetallic phases). The corrosion tests revealed that the alloy without hard-phases (type 1) had a significantly higher pitting potential (p=0.001) than type 2 alloy without hard-phases. After testing, both alloys exhibited grain boundary corrosion. However, type 2 had a higher degree of material loss due to hard-phase detachment. Additionally, type 2 exhibited pitting within the grains around hard-phases, along with the formation of thick oxide films which was consistent with the lower pitting potential. The results also corresponded with the damage features on the corresponding tapers, where type 1 exhibited only mild damage features, and type 2 underwent severe grain and phase boundary corrosion along with thick oxide films (Figure 3). Discussion. It appears that the alloy microstructure drives local modes of corrosion. Additional phase boundaries due to hard-phase content promote corrosion. The fact that the same alloy can differ broadly even within the same design shows that material standards are currently not sufficient. Optimizing implant alloys will help to reduce in vivo corrosion processes, and subsequently the risk of implant failure due to ALTRs. For figures/tables, please contact authors directly.