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

Polyethylene (PE) wear particle induced osteolysis remains a major cause of failure in total hip arthroplasty (THA), so that routine clinical measurement of wear stays important. Crosslinked PE promises very low wear rates so that measurement accuracy becomes increasingly important to distinguish alternative materials. The rising use of large femoral heads causes lower linear head penetration also requiring improved accuracy. Digital x-rays and wear measurement software have become standard, but during archiving and exchange of x-rays, image format, resolution or compression are often changed without knowing the effects on wear measurement. This study investigates the effect of digital x-ray resolution and compression on the accuracy of two software programs to measure wear. The 8-year post-op digital x-rays of 24 THA patients (Stryker ABG-II, 28mm metal femoral head against Duration or conventional PE) were taken from the hospital PACS (Philips Diagnost H, AGFA ADC Solo, Siemens Medview) as DICOM at 5.1 MPix resolution. Images were converted to compression-free TIFF format using Irfanview V4.1. Wear (linear head penetration) was measured using Roman V1.7 and Martell Hip Analysis Suite 7.14. The x-rays were smoothened (Irfanview V4.1, Median Filter: 3) as recommended in literature for compatibility with Martell’s edge detection algorithm. Wear was measured twice by two independent observers at original format and resolution and then once by a single observer at three subsequently halved resolutions (2.6, 1.3, 0.65MPix) and three jpeg compressions (90%, 50%, 20%). Intra- and inter-observer reliability (R) was compared to the reliability of measuring manipulated images (Pearson’s r). The mean absolute wear differences (AD) were calculated versus the original x-ray. The mean total wear was 0.98+/−0.59mm (0.3–2.4mm) equaling an annual of wear rate of 0.11mm/yr. Using Roman, Intra-R (0.97) and Inter-R (0.96) were high and AD low (0.10 and 0.20mm). Reduced image resolution caused the R to drop only slightly to 0.95 (2.6MPix), 0.92 (1.3MPix) and 0.94 (0.65MPix) while AD remained low (< 0.20mm). Also compression hardly affected R (90%:0.96, 50%: 0.94, 20%:0.93) nor AD (< 0.20mm). Using Martell Intra-R (0.99) and Inter-R (0.87) were also high but dropped with reducing resolution (0.82, 0.72, 0.34, AD: 0.4–1.1mm) but hardly with increased compression (0.95, 0.92, 0.94, AD< 0.20mm). Low resolution and high compression do not have to be critical for wear measurement accuracy and reliability when edge detection is performed by a trained human eye. This way interpolating the ball and cup perimeters and locating their centers can be performed at accuracy below pixel size (ca. 0.40mm at 0.65MPix). Automatic edge detection is less robust to reducing resolution but performs at high compression. If image size needs to be reduced compression is preferable to reducing resolution

Wear of the polyethylene liner in Total hip arthroplasty (THA) is associated to aseptic component loosening. With low wear bearing surfaces and metal backing in acetabular components the manual methods of measurements have not fared well. Computerized methods increased the ease and accuracy of wear measurement. The average clinician has no access to these methods. In this study we proposed to develop a method of manual wear measurement (PowerPoint – PP method) using a simple office PC and. quantify its accuracy and reproducibility. compare the accuracy with Livermore and Dorr method and. determine the accuracy in different degrees of wear. The study population was divided into class 1 (C1), Class 2 (C2) and Class 3 (C3) group. C1 group had 20 patients who had undergone liner change for high wear. This class simulated a high wear situation. C2 group had 24 patients who were implanted with HXLP. This class simulated very low wear situation. 10 patients were included in C3 group. The same 6week postoperative radiograph was paired as a set of x rays for analysis. This mimics a zero wear situation. PP method had more consistency with Livermore method for C1 group. For C2 and C3 groups all the three methods did not provide consistent results. The correlation coefficient values for wear measurement by PP method showed good correlation between observers in C1 and C2 wear (P values < 0.05). For C3 with true zero wear there was poor correlation between the observers (r −0.659, 0.028, 0.638). The paired T test P values for all classes and both observers were > 0.05. There was no statistically significant difference in the reading of the two observers. Pearson correlation coefficient for all methods showed good correlation for C1and C2 groups. All the methods had errors while measuring true zero in C3. The one way ANOVA analysis was done to identify the ability of the three methods differentiate between C2 and C3. The PP method had the ability (P value < 0.05) to differentiate between C1, C2 and C3. The Dorr’s and Livermore’s methods could only differentiate the C1 from C2andC3. Computerized methods have certain limitations. Matthew Collier et al reported a mean linear wear rate of 0.4(0.04–0.86) and 0.27 (0.01–0.56) by computerized methods in radiographs with true zero wear. In C3 group the average wear rate by PP method was 0.22 ± 0.206 mm. In PP method ability to work at 400% magnifications, ability to correct for rotation on X axis, grouping function of PowerPoint program leads to less chances of errors. PP method has a good reproducibility for clinical use (r> 0.930). The ability of the PP method to differentiate between C2 and C3 should make it a preferred manual method of wear assessment. The PP method has limitations. The least measurement is limited by diameter of the femoral head. It cannot be utilized for wear analysis in cup loosening or migration. It can be regarded as a supplement to the existing methods of manual wear measurements

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

We have developed and tested the accuracy of a completely automated method for polyethylene (PE) wear measurement of digitised antero-posterior and lateral radiographs. New computer algorithms have been developed to measure PE wear on digitised hip radiographs. The only user input required is the file name of the x-ray. Validation was performed by simulation of PE wear in an acrylic phantom. Radiographs were analysed with the new software and results were compared to know penetration of the femoral head. Accuracy using 10 antero posterior and lateral phantom radiographs was within ±0.08mm (95% CI) of the real femoral head penetration. There was no inter or intra-observer error (identical results with all measurements). Perhaps most importantly, this system gave accurate results in 94% of 600 clinical radiographs of variable quality. Only 74% of this same group of radiographs were considered of sufficient quality to allow reliable manual measurement. This new method of PE wear measurements eliminated inter and intra-observer error, allowing comparison of wear results between different institutions. Accuracy is improved, but still limited by resolution of the scanned image

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

Aims

A retrospective study was conducted to measure short-term in vivo linear and volumetric wear of polyethylene (PE) inserts in 101 total knee arthroplasty (TKA) patients using model-based radiostereometric analysis (MBRSA).

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

Introduction: Wear of the polyethylene (PE) acetabular component is widely regarded as the primary factor limiting the longevity of total hip arthroplasties (THA). To compare wear patterns of different polyethylene inserts computer assisted measurement techniques for in vivo polyethylene wear were developed. This study was performed to investigate which software out of four programs is most precise and easy to use in daily clinical practice. Materials and Methods: 24 anteroposterior digital radiographs of patients with a THA (Stryker ABG-II with N2Vac and Duration PE inserts in metal backed cups) with an average of 8.0 years follow-up were measured twice by a blinded single observer for linear wear (head penetration) in a single image analysis. Four computer assisted wear measurement methods were compared, the commercially available Martell Hip Analysis suite 7.14 and Rogan Hyperview, a not yet available Rogan beta-version called View Pro-X and Roman v1.70, freely available software to download from the internet. While both Rogan software can read the DICOM format from the hospital image server, images had to be converted for Martell (greyscale TIFF only) and Roman (any format). The annual wear rates were compared and intra-observer variability was calculated as the difference between both measurements (precision). The average time it takes to measure one image (without format conversions) was documented and practicality of daily clinical use was evaluated. Results: The annual wear rates measured were (mean +/− SD): Martell=0.09+/−0.21,, Hyperview=0.14 +/−0.10, Pro-X=0.12+/−0.07 Roman=0.12 +/−0.06. Martell was the only method measured negative wear (7/24 cases). The precision was (mean +/− SD): Martell = 1.74+/−1.53, Hyperview = 0.36 +/−0.92, Pro-X = 0.10+/−0.11 Roman = 0.08 +/−0.08. The average measuring time per image was: Martell = 94s, Hyperview = 94s, Pro-X = 92s Roman = 158s. Discussion: The Roman method is the most precise and easiest to use in daily practice, but takes the longest time to measure. The Rogan View Pro-X software is nearly as precise and easy to use but not on the market yet. It is an improvement over the Hyperview which looses precision by using a elliptical interpolation necessary for non-metal backed cups instead of circular interpolation which is more precise for metal backed cups. The Mar-tell method produced the intolerable low precision and in some cases “negative wear”. Only on large patient groups it may produce realistic average wear rates. We found out that the Martell edge detection method, originally developed for scanned analogue x-rays, functions inferiorly with digital images, the coming hospital standard. Image processing (smoothening) of the digital x-rays did increase accuracy and precision. We recommend the Roman software, a digital version of the Livermore method, for precision, ease of use and cost

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

Ultra-high molecular weight polyethylene (UHMWPE) is a commonly used as bearing material in joint replacement devices. UHMWPE implants can be hard to see on a standard X-ray because UHMWPE does not readily attenuate X-rays. Radiopaque UHMWPE would enable direct imaging of the bearing both during and after surgery, providing in vivo assessment of bearing position, dislocation or fracture, and potentially a direct measure of wear. The X-ray attenuation of UHMWPE was increased by diffusing an FDA approved contrast agent (Lipiodol) into UHMWPE parts (Zaribaf et al, 2018). The aim of this study was to evaluate the optimal level of radiopacity for a UHMWPE bearing.

Samples of un-irradiated medical grade UHMWPE (GUR 1050) were machined into 4mm standard medium Oxford Unicompartmental bearings. Samples were immersed in Lipiodol Ultra Fluid (Guerbert, France) at elevated temperatures (85 °C, 95 °C and 105 °C) for 24 h to achieve three different levels of radiopacity.

A phantom set-up was used for X-ray imaging; the phantom contained two perspex rods to represent bone, with the metallic tibial tray and polyethylene bearing fixed to the end of one rod and the metallic femoral component fixed to the other rod. Radiographs of the samples were taken (n=5) with the components positioned in full extension. To ensure consistency, the images of all the samples were taken simultaneously alongside an untreated part.

The results of our ongoing study demonstrate that the radiopacity of UHMWPE can be enhanced using Lipiodol and the parts are visible in a clinical radiographs. The identification of the optimal treatment from a clinical perspective is ongoing; we are currently running a survey with clinicians to find the consensus on the optimal radiopacity taking into account the metallic components and alignment. Future work will involve a RSA study to assess the feasibility of measuring wear directly from the bearing.

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique.

In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year.

The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

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.

The aim of the study was to measure in-vivo the 10-year linear and volumetric polyethylene wear of a fully congruent mobile bearing unicompartmental knee arthroplasty (OUKA).

We studied six OUKA’s that had all been implanted 10 years previously. Each patient was examined in even double leg stance at a range of knee flexion angles, in a calibration cage. A stereo pair of X-ray films was acquired for each patient at 0°, 15° and 30° of flexion. The films were analysed using an RSA style calibration and a CAD model silhouette-fitting technique. The position and orientation of each femoral and tibial component was found relative to each other and the bearing position inferred. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. The volumetric wear is calculated from the measured linear wear and the known surface area of the bearing. In addition eight control patients were examined less than 3 weeks post-operation where no wear would be expected.and 30We studied seven OUKA’s that had all been implanted at least 10 years previously. A stereo pair of X-ray films was acquired for each patient at 0 Results: The control group showed no measured wear. The seven OUKA’s had an average maximum depth of linear penetration of 0.40 mm at a mean follow-up of 10.9 years. The linear wear rate was 0.033 mm/year. The volumetric material loss was 79.8 mm3. If a steady gradual material loss is assumed, 8 mm3 of UHMWPE was lost per year.

Polyethylene particulate wear debris continues to be implicated in the aetiology of component loosening and implant failure knee following arthroplasty. The OUKA employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. The results from this in-vivo study confirm that the device has low 10-year linear and volumetric wear in clinical practice. This may protect the device from component loosening in the long term.

Ceramic heads and highly cross-linked polyethylene (HXLPE) as bearing surface materials have been introduced to reduce the production of polyethylene wear particles. The present study hypothesized that the wear rate of HXLPE could be further reduced when combined with a ceramic head. The purpose of this study was to compare the in vivo wear of Longevity HXLPE against cobalt-chromium and zirconia heads after a minimum 5-year follow-up.

A prospective cohort study was performed in 102 cementless total hip arthroplasties (THAs) with the Longevity HXLPE socket (Zimmer) between June 2000 and October 2001. Same prostheses were used in all cases both acetabular cups (Trilogy; Zimmer) and femoral stems (Versys Fiber Metal Taper; Zimmer). 26-mm zirconia heads (NGK) or 26-mm cobalt-chromium heads (Zimmer) were randomly used in 51 hips each. A minimum 5-year follow-up was completed for 47 hips with zirconia heads and 46 hips with cobalt-chromium heads. Two-dimensional linear wear of Longevity HXLPE was measured using computer-assisted methods (PolyWare) on annual x-rays, and total head penetration rates and steady state wear rates were calculated. In addition, periprosthetic osteolysis was evaluated.

At a mean 6-year follow-up, the total head penetration rates were 0.034±0.016 mm/year (zirconia) and 0.031±0.015 mm/year (cobalt-chromium). The steady state wear rates were −0.01 mm/year (zirconia) and −0.01 mm/year (cobalt-chromium). No significant difference was seen between the two groups (p=0.4 and p=0.91). Osteolysis was not observed around prostheses in any hips.

In conclusion, no advantage was seen for the zirconia head compared with the cobalt-chromium head in this time period.

The authors propose a manual measurement method for wear in total hip arthroplasty (PowerPoint method, PP-method) based on the well-known PowerPoint software. In addition, the accuracy and reproducibility of the devised method were quantified and compared with two methods previously described by Livermore and Dorr, and accuracies were determined at different degrees of wear. The 57 hips recruited were allocated to; Class 1 (retrieval series), Class 2 (clinical series), and Class 3 (a repeat film analysis series). The PP method was found to have good reproducibility and to better detect wear differences between classes. The devised method can be easily used for recording wear at follow-up visits, and could be used as a supplementary method when computerized methods cannot be employed.

Level of evidence: Diagnostic study, level –II

We present minimum 20 year results of a randomized, prospective double blinded trial (RCT) of cross-linked versus conventional polyethylene (PE), using a computer assisted method of PE wear measurement. After Ethics Committee approval, 122 patients were enrolled into an RCT comparing Enduron (non cross-linked PE) and highly cross-linked Marathon PE (DePuy, Leeds, UK). Other than the PE liners, identical components were used, a Duraloc 300 metal shell with one screw, a 28mm CoCr femoral head and a cemented Charnley Elite femoral stem. All patients were followed with anteroposterior (A∼P) and lateral radiographs at 3 days, 6 weeks, 3 months, 6 months, 1, 2, 3, 4, 5, 10 and 20 years. PE wear was measured with PolyMig, which has a phantom validated accuracy of ± 0.09mm. At minimum 20 year follow-up, 47 patients had died, 5 of which had been revised prior to their death. Another 32 patients were revised and alive, leaving 43 patients unrevised and alive (15 Enduron, 28 Marathon). No patients were lost to follow-up, but 2 were not able to be radiographed (dementia), leaving 41 patients (15 Enduron, 26 Marathon) available for PE wear measurement. After the bedding-in period, Enduron liners had a wear rate of 0.182 mm/year, and Marathon liners had a wear rate of 0.028 mm/year. At 20 years follow-up, 37 patients had required revision. Patients with conventional PE had three times the revision rate (28/37) of those who received XLPE (9/37). This is the longest term RCT showing substantially improved clinical and radiological results when XLPE is used as the bearing surface

Ceramic bearing fracture is a rare complication following implantation using modern day ceramic bearing materials. Revision bearing options in such cases is debated, with the choice between ceramic-on-ceramic and ceramic-on-polyethylene bearings. Revision to a hard on soft bearing raises concerns about potential catastrophic wear secondary to a third-body reaction caused by the fractured ceramic particles. Data was collected retrospectively from the NJR, electronic patient records, revision database and picture archiving and communication system. Templating software was used to determine linear wear between first post-operative radiograph and the latest available follow up. Univariate analysis was used to examine patient demographics and the wear rates for revision of ceramic bearing fractures to ceramic on polyethylene components. The intra and inter-rater reliability of wear measurements was calculated. There were twelve patients identified as meeting the inclusion criteria. The average age at revision was 62 years (54–72). There were 6 liner and 6 head fractures revised to delta ceramic heads and cross-linked polyethylene acetabular components. The most frequently used head size was 32mm. At mean follow up of 3.8 years (0.5 6.1 years), median 4.4 years, linear wear rate was calculated at 0.08± 0.06 mm/year. Both intra-rater and inter-rater reliability was excellent with ICC scores of 0.99 at all timepoints. Revision to ceramic on polyethylene (CoP) bearings following ceramic fracture does not cause early catastrophic wear at early follow up. It appears safe to use this hard on soft bearing combination, given that wear rates are comparable to what is expected in a primary hip replacement setting. Longer follow up is required to establish if this trend persists