Articulation of the polyethylene (PE) insert between the metal femoral and tibial components in total knee replacements (TKR) results in wear of the insert which can necessitate revision surgery. Continuous PE advancements have improved wear resistance and durability increasing implant longevity. Keeping up with these material advancements, this study utilises model-based radiostereometric analysis (mbRSA) as a tool to measure in vivo short-term linear PE wear to thus predict long-term wear of the insert. Radiographic data was collected from the QEII Health Sciences Centre in Halifax, NS. Data consisted of follow-up RSA examinations at post-operative, six-, 12-, and 24-month time periods for 72 patients who received a TKR. Implanted in all patients were Stryker Triathlon TKRs with a fixed, conventional PE bearing of either a cruciate retaining or posterior stabilised design. Computer-aided design (CAD) implant models were either provided by the manufacturer or obtained from 3D scanned retrieved implants. Tibial and femoral CAD models were used in mbRSA to capture pose data in the form of Cartesian coordinates at all follow-ups for each patient. Coordinate data was manually entered into a 3D modeling software (Geomagic Studio) to position the implant components in virtual space as presented in the RSA examinations. PE wear was measured over successive follow-ups as the linear change in joint space, defined as the shortest distance between the tibial baseplate and femoral component, independently for medial and lateral sides. A linear best-fit was applied to each patient's wear data; the slope of this line determined the annual wear rate per individual patient. Wear rates were averaged to provide a mean rate of in vivo wear for the Triathlon PE bearing. Mean linear wear per annum across all 72 patients was 0.088mm/yr (SD: 0.271 mm/yr) for the medial condyle and 0.032 mm/yr (SD: 0.230 mm/yr) for the lateral condyle. Cumulative linear wear at the 2-year follow-up interval was 0.207mm (SD: 0.565mm) and 0.068mm (SD: 0.484mm) for the medial and lateral condyles, respectively. Linear PE wear measurements using mbRSA and Geomagic Studio resulted in 0.056mm/yr additional wear on the medial condyle than the lateral condyle. Large standard deviations for yearly wear rates and cumulative measurements demonstrate this method does not yet exhibit the accuracy needed to provide short-term in vivo wear measurement. Inter-patient variability from RSA examinations is likely a source of error when dealing with such small units of measure. Further analysis on patient age and body mass index may eliminate some variability in the data to improve accuracy. Despite high standard deviations, the results from this research are in proximity to previously reported linear wear measurements 0.052mm/yr and 0.054mm/yr. Linear wear analysis will continue upon completion of >100 patients, in addition to volumetric PE wear over the entire articulating surface

The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery. Model-based RSA radiographs were collected for 106 patients who underwent primary TKR at a single institution. Supine RSA radiographs were obtained post-operatively and at 6-, 12-, and 24-months. Standing (weight-bearing) RSA radiographs were obtained at 12-months (n=45) and 24-months (n=48). All patients received the same knee design with a fixed, conventional PE insert of either a cruciate retaining or posterior stabilized design. Ethics approval for this study was obtained. In order to assess in vivo wear, a highly accurate 3-dimensional virtual model of each in vivo TKA was developed. Coordinate data from RSA radiographs (mbRSA v3.41, RSACore) were applied to digital implant models to reconstruct each patient's replaced knee joint in a virtual environment (Geomagic Studio, 3D Systems). Wear was assessed volumetrically (digital model overlap) on medial and lateral condyles separately, across each follow-up. Annual rate of wear was calculated for each patient as the slope of the linear best fit between wear and time-point. The influence of weight-bearing was assessed as the difference in annual wear rate between standing and supine exams. Age, BMI, and Oxford-12 knee improvement were measured against wear rates to determine correlations. Weight bearing wear measurement was most consistent and prevalent in the medial condyle with 35% negative wear rates for the lateral condyle. For the medial condyle, standing exams revealed higher mean wear rates at 1 and 2 years, supine, 16.3 mm3/yr (SD: 27.8) and 11.2 mm3/yr (SD: 18.5) versus standing, 51.3 mm3/yr (SD: 55.9) and 32.7 mm3/yr (SD: 31.7). The addition of weight-bearing increased the measured volume of wear for 78% of patients at 1 year (Avg: 32.4 mm3/yr) and 71% of patients at 2 years (Avg: 48.9 mm3/yr). There were no significant (95% CI) correlations between patient demographics and wear rates. Volumetric, weight-bearing wear measurement of TKR using model-based RSA determined an average of 33 mm3/yr at 2 years post-surgery for a modern, non-cross-linked polyethylene bearing. This value is comparable to wear rates obtained from retrieved TKRs. Weight-bearing exams produced better wear data with fewer negative wear rates and reduced variance. Limitations of this study include: supine patient imaging performed at post-op, no knee flexion performed, unknown patient activity level, and inability to distinguish wear from plastic creep or deformation under load. Strengths of this study include: large sample size of a single TKR system, linear regression of wear measurements and no requirement for implanted RSA beads with this method. Based on these results, in vivo volumetric wear of total knee replacement polyethylene can be reliably measured using model-based RSA and weight-bearing examinations in the short- to mid–term. Further work is needed to validate the accuracy of the measurements in vivo

Purpose. The purpose of this study was to examine the influence of weight-bearing on the measurement of in vivo wear of total knee replacements using model-based RSA at 1 and 2 years following surgery. Methods. Model-based RSA radiographs were collected for 106 patients who underwent primary TKR at a single institution. Supine RSA radiographs were obtained post-operatively and at 6-, 12-, and 24-months. Standing (weight-bearing) RSA radiographs were obtained at 12-months (n=45) and 24-months (n=48). All patients received the same knee design with a fixed, conventional PE insert of either a cruciate retaining or posterior stabilized design. Ethics approval for this study was obtained. In order to assess in vivo wear, a highly accurate 3-dimensional virtual model of each in vivoTKA was developed. Coordinate data from RSA radiographs (mbRSA v3.41, RSACore) were applied to digital implant models to reconstruct each patient's replaced knee joint in a virtual environment (Geomagic Studio, 3D Systems). Wear was assessed volumetrically (digital model overlap) on medial and lateral condyles separately, across each follow-up. Annual rate of wear was calculated for each patient as the slope of the linear best fit between wear and time-point. The influence of weight-bearing was assessed as the difference in annual wear rate between standing and supine exams. Age, BMI, and Oxford-12 knee improvement were measured against wear rates to determine correlations. Results. Weight bearing wear measurement was most consistent and prevalent in the medial condyle with 0–4% of calculated wear rates being negative compared to 29–39% negative wear rates for the lateral condyle. For the medial condyle, standing exams revealed higher mean wear rates at 1 and 2 years; supine, 16.3 mm. 3. /yr (SD: 27.8) and 11.2 mm. 3. /yr (SD: 18.5) versus standing, 51.3 mm. 3. /yr (SD: 55.9) and 32.7 mm. 3. /yr (SD: 31.7). The addition of weight-bearing increased the measured volume of wear for 78% of patients at 1 year (Avg: 32.4 mm. 3. /yr) and 71% of patients at 2 years (Avg: 48.9 mm. 3. /yr). There were no significant (95% CI) correlations between patient demographics and wear rates. Discussion and Conclusion. This study demonstrated TKA wear to occur at a rate of approximately 10 mm. 3. /year and 39 mm. 3. /year in patients imaged supine versus standing, respectively, averaged over 2 years of clinical follow-up. In an effort to eliminate the effect of PE creep and deformation, wear was also calculated between 12 and 24 months as 9.3 mm. 3. (standing examinations), This value is comparable to wear rates obtained from retrieved TKRs. Weight-bearing exams produced better wear data with fewer negative wear rates and reduced variance. Limitations of this study include: supine patient imaging performed at post-op, no knee flexion performed, and unknown patient activity level. Strengths of this study include: large sample size of a single TKR system, linear regression of wear measurements and no requirement for implanted RSA beads with this method. Based on these results, in vivo volumetric wear of total knee replacement polyethylene can be reliably measured using model-based RSA and weight-bearing examinations in the short- to mid–term. For any figures or tables, please contact authors directly

BACKGROUND:. Although most radiographs used for polyethylene wear measurements have been taken with the patient in the supine position in order to assess penetration by the femoral head into the acetabular polyethylene socket, we have questioned the effect of weight-bearing on the position of the head within the socket. The current study aimed to determine the effect of weight bearing, i.e. standing on the two-dimensional radiographic position of the femoral head within the socket. PATIENTS AND METHODS:. A total of three hundred and fifty patients (three hundred and eighty three hips) who had had a total hip arthroplasty had digital radiographs made a set of anteroposterior radiographs for each patient: one radiograph was made with the patient supine and one was made with the patient standing in full weight bearing on the replaced hip. The patients were divided into the following two groups: 1) seventy-five patients (eighty-three hips) with conventional polyethylene (CON) (group-1); 2) two hundred and seventy-five patients (three hundred hips) with highly cross-linked polyethylene (XPL) (group-2). The set of radiograph was taken at three weeks postoperatively and at the time of semiannual follow-up. The average ceramic femoral head penetration was measured with radiographs taken in the standing or supine position at the final follow-up and compared with those of three weeks postoperatively. A single researcher with use of a computerized measurement system performed all measurements on the radiographs of the two-dimensional position of the head. Follow-up period were 13.5 ± 1.0 (range. 11.0–15.5) years in group-1 and 7.6 ± 2.1 (range. 5.0–12.6) years in group-2. RESULTS:. Linear penetration rates in group-1 were 0.172 ± 0.069 mm/year in supine position and 0.178 ± 0.069 mm/year in standing position (p < 0.05, paired t-test; r. 2. = 0.88), and the rates in group-2 were 0.029 ± 0.024 mm/year and 0.035 ± 0.027 mm/year respectively (p < 0.0005, paired t-test; r. 2. = 0.16). The mean ceramic head penetration rate in XPL socket showed 80 to 83% reduction compared with those in CON. CONCLUSIONS:. We found significant difference between the average total ceramic femoral head penetration between supine and standing radiographs in using both CON and XPL socket. Standing radiographs were useful and recommended for polyethylene socket wear measurements. Figure legend. Fig. Wear measurement: With use of a computerized measurement system, the thickness of the polyethylene socket (a) was measured along a line connecting the center of the ceramic femoral head to the outer border of the socket at its shortest distance. The wear rate was determined by comparing the thickness in the latest follow up radiograph with the thickness in the initial postoperative radiograph at the same location. Each radiographically measured value was corrected for magnification by a factor derived from comparing the diameter of the ceramic head on the radiograph (b) with its known diameter of 22.225 mm

Introduction. Periprosthetic osteolysis following total hip arthroplasty is caused mainly by polyethylene wear particles and necessitates revision surgery at some stage even in the presence of well-fixed implants. Therefore, methods to estimate the polyethylene wear become important, with manual wear measurement methods as the main outcome measurement even in the presence of computer-assisted measurement methods on account of easy availability and simplicity in their use with reasonable accuracy. The purposes of this study were to quantify the accuracy and reproducibility of the slide presentation software method on clinical radiographs and to compare it with that of the previously described Livermore's method, and to determine the usefulness of the slide presentation software methods for highly cross linked polyethylene wear measurement. Materials and Methods. 81 hips out of 61 patients who underwent primary total hip arthroplasty between October 2000 and January 2006 were retrospectively evaluated for polyethylene wear by two independent observers using the Livermore's and the slide presentation software methods. All the hips were implanted with highly cross linked polyethylene acetabular liners with cementless acetabular components. The 28 mm sized cobalt chrome alloy femoral heads were used in all cases. The mean age of the patients was 50.8 years(range, 27–73 years), and the mean follow-up period was 6.6 years (range, 2–11 years). Paired radiographs were analyzed using the Livermore's and the slide presentation software method. For the Livermore's methods, radiographs were magnified to 200%, printed, and readings taken with digital calipers with an accuracy of 0.01 mm(Figure 1). For the slide presentation software method, we used Microsoft Office PowerPoint software(Microsoft Corp., Redmond, WA, USA) as described in a previous our study(Figure 2). Results. The mean polyethylene wear rate in 81 hips measured by the Livermore's method was found to be 0.071±0.12 and 0.081±0.09 mm/year by observer 1 and 2 respectively. The mean polyethyelene wear rate measured by slide presentation software method was found to be equally 0.069±0.07 mm/year by observer 1 and 2. Interobserver and intraobserver variance were evaluated using Pearson correlation coefficient. Correlation coefficients for interobserver variance were 0.802 for the Livermore's method and 0.979 for the slide presentation software method. Correlation coefficient for intraobserver variance were 0.777 for the Livermore's method and 0.965 for the slide presentation software method in observer 1, 0.303 for the Livermore's method and 0.941 for the slide presentation software method. The mean time consumed in each radiographic measurement with the Livermore's method was 15.52 minutes (range, 10.67–22 minutes) as compared to 9.55 minutes (range, 5.42–13.5 minutes) measured with the slide presentation software method (p < 0.001). Conclusion. The slide presentation software method was more accurate in serial intra-observer measurements and more reproducible in inter-observer readings for polyethylene wear than the traditional Livermore method, and was simple to use and less time consuming. Not all orthopaedic surgeons have access to CT for measuring polyethylene wear, hence the use of this type of manual method becomes a necessity on account of its easy availability and repeatability in serial measurements

Introduction. Reverse total shoulder arthroplasty (RTSA) is a semi-constrained joint replacement with an articulating cobalt-chromium glenosphere and ultra-high molecular weight polyethylene (PE). Because of its limited load bearing, surgeons and implant manufacturers have not elicited the use of highly cross-linked PE in the shoulder, and to date have not considered excessive PE wear in the reverse shoulder a primary concern. As the number of shoulder procedures is expected to grow exponentially in the next decade, however, it is important to evaluate how new designs and bearing materials interact and to have an understanding of what is normal in well-functioning joint replacements. Currently, no in vivo investigation into RTSA PE wear has been conducted, with limited retrieval and simulation studies. In vitro and in silico studies demonstrate a large range in expected wear rates, from 14.3 mm. 3. /million cycles (MC) to 126 mm. 3. /MC, with no obvious relationship between wear rate and polyethylene diameter. The purpose of this study is to evaluate, for the first time, both volumetric and linear wear rates in reverse shoulder patients, with a minimum six-year follow-up using stereo radiographic techniques. Methods. To date, seven patients with a self-reported well-functioning Aequalis Reversed II (Wright Medical Group, Edina, MN, USA) RTSA implant system have been imaged (mean years from surgery = 7.0, range = 6.2 to 9). Using stereo radiographs, patients were imaged at the extents of their range of motion in internal and external rotation, lateral abduction, forward flexion, and with their arm at the side. Multiple arm positions were used to account for the multiple wear vectors associated with activities of daily living and the shoulder's six degrees of motion. Using proprietary software, the position and orientation of the polyethylene and glenosphere components were identified and their transformation matrices recorded. These transformation matrices were then applied to the CAD models of each component, respectively, and the apparent intersection of the glenosphere into the PE recorded. Using previously validated in-house software, volumetric and maximum linear wear depth measurements were obtained. Linear regression was used to identify wear rates. Results. The volumetric and linear wear rates for the 36 mm PE liners (n = 5) were 39 mm. 3. /y (r. 2. = 0.86, range = 24 to 42 mm. 3. /y) and 0.09 mm/y (r. 2. = 0.96, range = 0.08 to 0.11 mm/y), respectively. Only two patients with 42 mm PE liners were evaluated. For these, volumetric and linear wear rates were 110 mm. 3. /y (r. 2. = 0.81, range = 83 to 145 mm. 3. /y) and 0.17 mm/y (r. 2. = 0.99, range = 1.12 to 1.15 mm/y), respectively. Conclusion. For the first time, PE wear was evaluated in the reverse shoulder in vivo. More patients are required for conclusive statements, but preliminary results suggest first order volumetric and linear wear rates within those predicted by simulation studies. It is interesting to note the increased wear with larger PE size, likely due to the increased contact area between congruent faces and the potential for increased sliding distance during arm motion

The PowerPoint (2007 Version; Microsoft, Redmond, Wash) method is reported to have improved repeatability and reproducibility and is better able to detect differences in radiographs than previously established manual wear measurement methods. In this study, the PowerPoint method and the Dorr and Wan method were used to calculate the polyethylene liner wear volume. The wear volumes of retrieved polyethylene liners calculated from the 3D laser scanning method were compared with each method. This study hypothesized that the wear volume calculated by the PowerPoint method would correlate well with the wear volume measured by 3D laser scanning method. Between March 2004 and June 2009, 22 polyethylene liners from 20 patients were collected during revision Total hip arthroplasty(THA). Exclusion criteria included (1) missing an early primary postoperative radiograph or prerevision radiograph, (2) evidence of acetabular loosening or migration, (3) existence of significant mismatch between early primary postoperative radiograph and prerevision radiographs on vertical axis, and (4) liner wear-through. After applying these exclusion criteria, 17 retrieved polyethylene liners from 16 patients were included in this study. Wear volumes were calculated using the PowerPoint, the Dorr and Wan methods by 3 independent experienced observers who were unaware of the study design, and 3-dimensional (3D) laser scanning methods. Spearman correlation coefficients for wear volume results indicated strong correlations between the PowerPoint and 3D laser scanning methods (range, 0.89–0.93). On the other hand, Spearman correlation analysis revealed only moderate correlations between the Dorr and Wan and 3D laser scanning methods (range, 0.67–0.77). The PowerPoint method is an efficient tool for the sequential radiologic follow-up of patients after THA. The PowerPoint method can be used to monitor linear wear after THA and could serve as an alternative method when computerized methods are not available

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.

Polyethylene wear represents a significant risk factor for the long-term success of knee arthroplasty [1]. This work aimed to develop and in vivo validate an automated algorithm for accurate and precise AI based wear measurement in knee arthroplasty using clinical AP radiographs for scientifically meaningful multi-centre studies. Twenty postoperative radiographs (knee joint AP in standing position) after knee arthroplasty were analysed using the novel algorithm. A convolutional neural network-based segmentation is used to localize the implant components on the X-Ray, and a 2D-3D registration of the CAD implant models precisely calculates the three-dimensional position and orientation of the implants in the joint at the time of acquisition. From this, the minimal distance between the involved implant components is determined, and its postoperative change over time enables the determination of wear in the radiographs. The measured minimum inlay height of 335 unloaded inlays excluding the weight-induced deformation, served as ground truth for validation and was compared to the algorithmically calculated component distances from 20 radiographs. With an average weight of 94 kg in the studied TKA patient cohort, it was determined that an average inlay height of 6.160 mm is expected in the patient. Based on the radiographs, the algorithm calculated a minimum component distance of 6.158 mm (SD = 81 µm), which deviated by 2 µm in comparison to the expected inlay height. An automated method was presented that allows accurate and precise determination of the inlay height and subsequently the wear in knee arthroplasty based on a clinical radiograph and the CAD models. Precision and accuracy are comparable to the current gold standard RSA [2], but without relying on special radiographic setups. The developed method can therefore be used to objectively investigate novel implant materials with meaningful clinical cohorts, thus improving the quality of patient care

Each in vivo wear measurement method for total hip arthroplasty (THA) has strengths and weaknesses. The authors have developed a new manual wear measurement method (PowerPoint [PP] method) and validated that the PP method was found to have better repeatability, reproducibility and pick up differences in the radiographs than the previously established manual wear measurement methods. The primary aim of this study was to evaluate the reliability of the PP method by retrieval study. 17 retrieved polyethylene (PE) liners (16 patients) were enrolled in this study. The wear volumes of retrieved PE liners from clinical radiographs were calculated by the PP and Dorr and Wan method and they were compared with the wear volume of retrieved PE liners calculated by the triangulation three-dimensional (3D) laser scan. Spearman correlation coefficients results between PP method and 3D laser scan revealed excellent correlations (0.89 to 0.93). The Intraclass Correlation Coefficients values of the PP method showed excellent correlations (0.95 to 1.00). We suggest that the PP method will be a viable new technique for measuring wear of THA and a supplement method when computerized methods are not available

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. Highly cross-linked (HXL) polyethylene has demonstrated clinical advantages as a wear resistant acetabular bearing material in total hip arthroplasty (THA) [1]. In vitro wear testing has predicted a tenfold reduction in the wear rate of HXL polyethylene, as compared to its conventional, non-HXL counterpart [2]. To date, radiographic studies of head penetration represent the state-of-the-art in determining clinical wear of polyethylene hip liners [3]. However, as the amount of wear drops to very low levels, it becomes important to develop a precise and reliable method for measuring wear, facilitating a comparison of clinical results to expectations. This study focuses on locating and quantifying the maximum linear wear of retrieved acetabular poly liners using a coordinate measuring machine (CMM). Specifically, HXL liners are compared to a baseline of conventional, non-HXL bearings. Methods. An IRB-approved retrieval laboratory received 63 HXL acetabular bearing retrievals from 5 manufacturers with in vivo durations of 1.01–14.85 years. These were compared with 32 conventional, non-HXL controls (including gas plasma, gamma-barrier and EtO) from 3 manufacturers with in vivo durations of 1.03–20.89 years. Liners were mounted in a tripod of axial contacts with the liner face positioned in a vertical plane. Each bearing was scanned with a CMM dual-probe head, with one horizontal probe scanning the articular surface and the other scanning the non-articular, sequentially. Surface-normal wall thickness values along each latitude were calculated using a custom developed algorithm (Figure 1). Because the liners are axially symmetric as manufactured, deviation in wall thickness at a given latitude represents linear wear [4]. Results. Total wear penetration for the HXL liners ranged from 0.02 to 1.03 mm, and for the conventional, non-HXL controls ranged from 0.07 to 6.85 mm. The HXL liners had an average linear wear rate of 0.02 mm/year, compared to 0.20 mm/year for the conventional, non-HXL controls (Figure 2). The direction of maximum wear, as measured in degrees from the cup pole, ranged from 8.32 to 73.86 degrees. Differences in wear rates as a function of crosslinking dose, as well as presence/absence of a lip can be identified. Discussion. This wear measurement study of retrievals is the first application of a novel CMM technique to locate and quantify wear in HXL liners compared to conventional polyethylene controls. The study confirms the expectations of a tenfold reduction in wear rates that were based on in vitro testing [2]. The results are consistent with those of radiographic studies that have documented lower wear of HXL polyethylene in the hip compared to conventional polyethylene [3]. However, the current technique offers higher precision and reliability, and eliminates the large proportion of negative wear measurements common amongst radiographic methods. A sufficient number of liners have been measured to begin to differentiate wear between different radiation doses

Introduction. Temporary use of antibiotic-impregnated polymethylmethacrylate (PMMA) bone cement spacers in two-stage revisions is considered to be standard of care for patients with a chronic infection of a joint replacement. Spacers should be wear resistant and load-bearing to avoid prolonged immobilisation of the patient and to reduce morbidity. Most cement spacers contain barium sulphate or zirconium dioxide as radio-opaque substrate. Both are quite hard materials that may negatively influence the wear behaviour of the spacer. Calcium carbonate is another radio-opaque substrate with lower hardness potentially increasing the wear resistance of the spacer materials. The purpose of the study was to compare a prototype PMMA knee spacer (calcium carbonate loaded) with a commercially available spacer (containing barium sulphate) regarding the wear performance and particle release in a knee wear simulator. Material and Methods. Spacer K (TECRES, Italy) was used as barium sulphate (10%) containing spacer material. A prototype material (Heraeaus Medical, Germany) with 15% calcium carbonate was compared. Both were gentamicin impregnated, ready-made for clinical application (preformed) and consist of a tibial and a femoral component. Force-controlled simulation was carried out on an AMTI knee simulator. The test parameters were in accordance to ISO 14243–1 with a 50% reduced axial force (partial weight bearing). Tests were carried out at 37 °C in closed chambers filled with calf serum. Tests were run for 500,000 cycles at a frequency of 1 Hz. For wear analysis, gravimetric wear measurements according to ISO 14243–2 and wear particle analysis according to ASTM F1877–05 were performed. Results. Fig. 1 presents the results of the gravimetric wear measurements. For the Spacer K cement a mean articular wear mass of 375.53±161.22 mg was determined after 500.000 cycles (femoral components: 149.55±17.30 mg, tibial components: 225.98±153.01 mg). The prototype cement showed lower mean total wear of 136.32±37.58 mg (femoral components: 74.32±33.83 mg, tibial components: 61.99±15.74 mg). However, a statistically significant lower wear rate was only seen for the femoral components (p=0,027). In Fig. 2 isolated PMMA wear particles are shown and the morphological characteristics are given in Tab. 1. Discussion and conclusion. The prototype material showed better wear performance in terms of gravimetric wear and particle release. Thus calcium carbonate seems to be a promising material as radio-opaque substrate in PMMA spacers. Nevertheless, the wear amount released from both spacer materials is much higher as compared to conventional total knee replacements with polyethylene inserts. In this context biological reactions against PMMA particles and an increased release of cytokines have been reported in vitro [1] and furthermore, the promotion of osteolysis has been shown in vivo in the presence of PMMA particles [2]. As a clinical consequence we suggest excessive debridement during removal of the cement spacer components to reduce the risk of third body wear for the final joint replacement. Beside the wear performance further studies are essential to prove the mechanical stability and the antibiotic release kinetics for the prototype cement

Introduction. Fretting corrosion at the taper interface has been implicated as a possible cause of implant failure. Using in-vitro testing, fretting wear observed at tapers of retrieved implants may be reproduced (Marriott, EORS-2014). In order to reduce time and cost associated with experimental testing, a validated finite element method (FE) can be employed to study the mechanics at the taper. In this study we compared experimental and representative FE simulations of an accelerated fretting test set-up. Comparison was made by between the FE wear score and volumetric material loss from the testing. Methods. Experimental test set-up: An accelerated wear test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet stems with smooth 4° Type-1 tapers were combined with Ti6Al4V Magnum +9 mm adaptors using a 2 or 15 kN assembly force. The head was replaced with a custom head fixture to increase the offset and apply a torque at the taper interface. The stems were potted according to ISO 7206-6:2013. The set-up was submerged in a test medium containing PBS and 90gl-1 NaCl. The solution was pH adjusted to 3 using HCl and maintained at 37°C throughout the tests. For each assembly case, n=3 tests were cyclically loaded between 0.4–4 kN for 10 Million cycles. Volumetric wear measurements were performed using a Talyrond-365 roundness measurement machine. The FE model was created to replicate the experimental set up. Geometries and experimental material data were obtained from the manufacturer (Biomet). The same assembly forces of 2 and 15 kN were applied, and the same head fixture was used for similar offset and loading conditions. The 4 kN load was applied at the same angles in accordance with ISO 7206-6:2013. Micromotions and contact pressures were calculated, and based on these a wear score was determined by summation over all contact points. Results. The FE wear score showed a significant drop after an assembly force of 15 kN has been applied. The micromotion scores were similar, and the contact pressure was higher due to the larger assembly force. The volumetric wear measurements did not show a significant difference between the two assembly cases due to the large variation in measured values. A downward trend can be observed when applying higher assembly forces, similar to the trend seen at the FE wear score (figure 1, table1). Discussion. This study shows a correlation between experimental and FE simulation, however highlights the difficulty in validating a FE model with complex in-vitro experiments. Due to the nature of experimental testing, it is impossible to remove all sources of error associated with the set-up. The use of a single static load and the absence of fluids and corrosion processes means that the full mechanics of the wear process could not be fully replicated. Despite these deficiencies the general trends and wear patterns observed in the experimental setup were reproduced. Further studies will focus on including the interplay between the aforementioned properties, to provide a better simulation of the fretting processes occurring at the taper junction

Introduction. It is important to measure 2-dimensional (2D) polyethylene wear in total hip arthroplasty (THA) accurately in order to estimate value of wear performance. However, wear vector direction is usually defined in a coordinate system specific manner, which sometimes leads to confusion and makes it difficult to compare measures between techniques. We systematically evaluated the influence of four different coordinate system definitions for the measurement of 2D wear in acetabular cups form radiographs. Materials and Methods. We performed 2D wear measurement of 152 hips that underwent THA using a 26mm CoCr femoral head with the same design of cementless acetabular shell between September 2003 and March 2005. All hips received either a CPE liner (76 hips, gamma sterilized at 25 kGy) or a XLPE liner (76hips, 10Mrad e-beam irradiation, EtO sterilized) randomly during the surgery. The average follow-up was 81.6±8.2 months. Supine AP radiographs obtained postoperatively at 6 months and final follow-up were assessed for each femoral head penetration and angle using Roman v1.70 software (. http://www.cookedbits.co.uk/roman/. ). The wear magnitude and angle between the two follow-ups was calculated using four coordinate system definitions:. #1; the line tangent to both ischiums was defined as 0 degrees, with wear directed medially defined as positive and wear detected laterally defined as negative. (Martell; JBJS Vol79-A No11 p1635–41). #2; wear directed toward the liner (Zone 1 and Zone 2) defined as positive and away from it as negative (Zone 3 and Zone 4). (Wan; CORR No 449 p267–224). #3; wear vector magnitude angle ranging between 0 and 360, starting from the medial part of the line (x axis). (Greedink; JBJS Vol90-B p839–46). #4; wear vector between 0 and 180, directed towards the liner, was identical with coordinate #3. The vector between 180 and 360, directed away from the liner, was analyzed into the positive cosine magnitude. (Modified #3). Results. There were 74 (48.7%) negative wear cases using coordinate definition #1 and 49 (32.2%) using coordinate definition #2. There were no statistically significant differences between average penetration rates for CPE and XLPE groups using the 4 coordinate definitions, except when negative values were included [Fig.1]. Discussion and Conclusions. Wan et al reported nearly 50% of 2D wear measurement showed negative values as a sequel to error in radiographic quality and measurement. In some studies, negative values were eliminated from the average penetration, or only wear vector magnitude was used and reported as the median of penetration. However, negative values of wear result simply from differences of coordinate system definition. For example, seven cases in the CPE group showed small focal osteolysis at final follow up in this study. All osteolysis cases were detected as negative wear using coordinate definition #1, and as positive wear with the other coordinate definitions [Fig.2]. Our coordinate system definition (#4) is more sensible when the wear vector is directed partially outward because it eliminates negative values and correctly reports the head displacement as wear

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated with a mean follow-up of 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant level over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR after twenty years

Radiostereometric analysis (RSA) has become the gold standard technique for measuring implant migration and wear following joint replacement due to its high measurement precision and accuracy. However, RSA is conventionally performed using two oblique radiographic views with the presence of a calibration cage. Thus, a second set of radiographs must be acquired for clinical interpretation, for example anterior-posterior and cross-table lateral views following total hip arthroplasty (THA). We propose a modification to the RSA setup for examining THA, in which RSA measurements are performed from anterior-posterior and lateral views, with the calibration cage images acquired separately from the patient images. The objective of the current study was to compare the accuracy and precision of the novel technique to the conventional technique using a phantom. X-ray cassette holders were developed to enable simultaneous acquisition of anterior-posterior and cross-table lateral radiographs with the patient in a supine position in the RSA suite. A Sawbones phantom with total hip implant components was attached to a micrometer-driven stage. The femoral component was translated known distances relative to the acetabular cup in all planes, mimicking head penetration due to wear. Double RSA examinations were acquired for each increment using the traditional and novel radiograph orientations. Translations were measured from the radiographic images using RSA software. For both techniques, accuracy was calculated by comparing the measured translations to the known translation from the micrometer, and reported as the 95% confidence interval. Precision was measured by comparing the measured translations between the double exams, and reported as the standard deviation. Accuracy was greater for the conventional technique in the inferior-superior axis (p = 0.03), greater for the novel technique in the anterior-posterior axis (p = 0.01), and equivalent in the medial-lateral axis (p = 0.06). Overall accuracy for both the conventional and novel techniques was identical at ±0.022 mm. Precision was equivalent between both techniques for the medial-lateral (p = 0.68), inferior-superior (p = 0.14), and anterior-posterior axes (p = 0.86). Overall precision for the conventional technique was ±0.127 mm and for the novel technique was ±0.095 mm. Utilising standard clinical radiograph view angles within an RSA exam had no detrimental effect on wear measurement accuracy or precision. This reduces the barriers to implementing RSA imaging in routine follow-up of arthroplasty patients, potentially greatly increasing the numbers of patients that can have quantitative data on implant performance. Future applications can involve applying more clinically relevant radiograph view angles to RSA exams of the knee and shoulder

Introduction. Variations in component position can lead to dynamic separation and edge loading conditions. In vitro methods have been developed to simulate edge loading conditions and replicate stripe wear, increased wear rate, and bimodal wear debris size distribution, as observed clinically [1, 2]. The aim of this study was to determine the effects of translational and rotational positioning on the occurrence of dynamic separation and severity of edge loading, and then investigate the wear rates under the most severe separation and edge loading conditions on an electromechanical hip joint simulator. Materials and Methods. A hip joint simulator (ProSim EM13, Simulation Solutions, UK) was set up with 36mm diameter ceramic-on-ceramic (BIOLOX®delta, PINNACLE®, DePuy Synthes, UK) hip replacements. Three axes of rotation conditions (ISO 14242-1 [3]) was applied to the femoral head. This study was in two parts. I) A biomechanical test was carried out at 45° (n=3) and 65° (n=3) cup inclination angles with 1, 2, 3 and 4 (mm) medial-lateral translational mismatch between the centres of the head and cup. The amount of dynamic separation displacement between the head and cup was measured using a position sensor. The severity of edge loading was determined from the area under the axial force and medial-lateral force outputs during the time of separation [4]. II) A wear test was carried out at 45° (n=6) and 65° (n=6) cup inclination angles for three million cycles with translational mismatch of 4mm between the head and cup. The lubricant used was diluted new-born calf serum (25% v/v). Volumetric wear measurements were undertaken at one million cycle intervals and mean wear rates were calculated with 95% confidence limits. Statistical analysis was carried out using ANOVA and a t-test with significance levels taken at p<0.05. Results. Dynamic separation increased significantly with 3mm (p<0.01) and 4mm (p<0.01) translational mismatch at a 45° cup inclination angle (Figure 1). At 65° the separation increased significantly as the translational mismatch increased from 1mm to 4mm (p<0.01). The most severe edge loading conditions occurred at a 65° cup inclination angle with 4mm of translational mismatch (p<0.01, Figure 2). Mean wear rates were greater at a 65° cup inclination angle compared with a 45° cup inclination angle (p<0.01, Figure 3). Conclusion. Different levels of rotational and translational mismatch affected the separation between the head and cup during gait. Higher levels of translational mismatch and a steeper cup inclination angle may lead to more severe edge loading conditions and increased wear of ceramic-on-ceramic bearings in vivo. A new preclinical testing approach was developed to study the effects of edge loading due to variations in rotational and translational surgical positioning under ISO loading and angular displacement conditions. The first stage comprised of biomechanical tests to determine the occurrence and severity of edge loading in a range of component positions. The second stage investigated the tribological performance of the bearing surface under the worst case edge loading conditions

Introduction. The long-term wear performance of highly cross-linked polyethylene (HXLPE) in cemented total hip arthroplasty (THA) has rarely been reported. Here we report a prospective randomized comparative analysis of radiographic wear after a minimum follow-up of 10 years in cemented THAs with either HXLPE or conventional polyethylene (CPE), and assess its clinical relevance. Patients and Methods. From 1999 to 2001, we conducted 94 primary cemented THAs with a 22.225-mm head at our hospital as part of a prospective randomized trial. All surgeries were performed using a direct lateral approach with a trochanteric osteotomy (Dall's approach). The patients were divided into 4 groups. Twenty-six hips in group A were implanted with CPE sockets against zirconia heads and Charnley-type stems. HXLPE sockets (Aeonian, Kyocera Medical Corp) were implanted in all hips in the other 3 groups. Twenty-five hips in group B were implanted with zirconia heads and KC stems (Kyocera Medical Corp), 23 hips in group C with zirconia heads and distal cylindrical stems, and 20 hips in group D with stainless steel heads and C-stem (DePuy Inc). The sockets were highly cross-linked by gamma irradiation at a dose of 35 kGy, heat annealed at 110ºC, and sterilized with 25 kGy of gamma irradiation in nitrogen. For radiographic evaluation, anteroposterior radiograms were taken for each patient annually, and every two years postoperatively for wear analyses. Two-dimensional head penetration was measured on each postoperative radiogram using a computer-aided technique. Results. Wear measurements were performed for 59 cases followed up over 10 years. Linear wear rates were 0.138±0.074 (mm/year±SD) for group A, 0.010±0.015 for group B, 0.013±0.020 for group C, and 0.012±0.027 for group D. Linear wear rates differed significantly between group A and other groups, and no significant difference was found among groups B, C, and D. There were four revision cases. Among them, two sockets of group A were revised for aseptic loosening at 7 and 14 years postoperatively with linear wear rates of 0.749 and 0.153 mm, respectively. Two stems of group B and C were revised for aseptic loosening at 10 and 9 years postoperatively with linear wear rates of 0.007 and 0.041 mm, respectively. There were no other cases with aseptic loosening in any group. Osteolysis was found in 10 cases (group A: 7, group B: 1, group C: 1, group D: 1), and there was a significant difference in linear wear rates between the cases with and without osteolysis (0.157±0.083 and 0.030±0.053 mm/year±SD respectively). Discussion. The two revision cases of HXLPE did not have aggressive socket wear, and possibly cement fracture caused osteolysis and stem instability. The results of this study indicate that there is a significant difference in wear rate between CPE and HXLPE, and it was evident that PE wear was associated with osteolysis and aseptic loosening of the socket

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