Introduction. Patella implant research is often overlooked despite its importance as the third compartment in a total knee replacement. Wear and fracture of resurfaced patellae can lead to implant failure and revision surgeries. New simulation techniques have been developed to analyze the performance of patella designs as they interact with the trochlear groove in total knee components, and clinical validation is sought to ensure that these simulations are appropriate. The objective of this work was to subject several patellar designs to patient-derived deep knee bend (DKB) inputs on a 6 degree of freedom (DOF) simulator and compare the resultant wear scars to clinical retrievals. Materials and Methods. Previously reported DKB profiles were developed based on in vivo patellofemoral data and include a wide range of patient variability. The profiles chosen for this body of work were based on the stress in the patellar lateral facet; maximizing this stress whilst maintaining the ability to run the profile stably on the simulator. Load/kinematic profiles were run on three patellar designs (n=3 per group) for 220,000 cycles at 0.8Hz on an AMTI VIVO joint simulator. A comparison cohort of clinically retrieved devices of the same design was identified in an IRB-approved database. Exclusion criteria included gross delamination, cracking secondary to oxidation, and surgeon-reported evidence of malalignment leading to mal-tracking. 29 Patellae were included for analysis: PFC. ®. All Poly (n=14), ATTUNE. ®. Anatomic (n=6), and ATTUNE. ®. Medialized Dome (n=9). Mean in vivo duration was 70.1 months. Patellae were analyzed under optical microscope in large-depth-of-field mode to map the surface damage profile. Burnishing ‘heat-maps’ were generated for retrievals and simulated patellae by normalizing the patellar size and overlaying silhouettes from each component of the same type using a custom-developed MatLAB code. Results. Burnishing heat-map comparisons between retrievals and simulator specimens for each of the three designs were compared. Retrievals show more variation than simulator devices, however the general loci and relative area of burnished regions is closely aligned for each of the three designs. The retrieved and simulated burnishing scar heat-maps on all-poly PFC. ®. patellae are centered medio-laterally with a wider profile on the lateral aspect. The burnishing marks are continuous. A similar observation may be made of the ATTUNE. ®. medialized dome, retrievals and simulator specimens, though the contact areas appear to be more concentrated away from the apex. The anatomic patellae show two primary regions of contact, and minimal burnishing at the apex. The simulator specimens likewise show two principal regions of contact. Discussion. Wear scar analysis shows that joint simulation on AMTI VIVO yields clinically relevant wear patterns across a variety of device types. Clinically relevant damage provides insight that load and motion inputs to the simulator deliver results that may be used to interpret in vivo performance or analyze future designs and/or materials. This qualitative surface contact analysis will help to inform future quantitative mass loss and fatigue failure studies. For any figures or tables, please contact authors directly

INTRODUCTION. Finite element analysis (FEA) is widely used to study micromotion between the glenoid baseplate and bone, as a pre-clinical indicator for clinical stability in reverse total shoulder arthroplasty (rTSA). Various key parameters such as the number, length, and angle of screws have been shown to influence micromotion [1]. This study explores the influence of screw preloads, an insufficiently studied parameter. Specifically, two rTSA configurations with 18mm and 48mm peripheral screws (PS) were analyzed without screw preloads, followed by analysis of the 48mm PS configuration with an experimentally measured screw preload. METHODS. FEA models were created to simulate a fixation experiment inspired by ASTM F2028-14. The rTSA configurations used here have a superior and an inferior PS. The assemblies were virtually implanted into a synthetic bone block as per surgical technique. Sliding contacts were defined to model the interface between screw threads-bone, and between baseplate-bone. To determine the screw preload experimentally, the 48mm screw (n=5) was inserted through a hole in a metal plate, which rested on top of a Futek washer load cell, placed on top of the foam block with a predrilled pilot hole (Figure 1). The screw was inserted using a torque driver until the average human factors torque for the screw driver handle was reached. The resulting axial compressive load due to screw insertion was measured by the washer load cell. Two step analyses were performed using Ansys version 17.2 for 18mm and 48mm PS, where 756N axial and shear loads were applied sequentially. The model with the 48mm PS was then analyzed in a four step analysis; preload inferior and superior screws, followed by applying the axial and shear loads (Figure 2). Peak overall micromotion including tangential and normal components at the baseplate-bone interface was compared for all three models. RESULTS. From the experimental study, the mean screw preload for the 48mm screw was determined to be 141±8 lbs. Peak micromotion was predicted at the inferior edge of the baseplate (Figure 3A). In the two models without screw preloads, the model with the 48mm PS predicted 42% lower micromotion than the model with the 18mm PS. The 48mm PS model predicted 63% further reduction in micromotion by including the preload for the two PS. Figure 3B presents the micromotion comparison between these three models. DISCUSSION. This study demonstrates the significant influence that screw preload can have on evaluating either absolute values or differential performance of rTSA micromotion within the same design family. It further demonstrated that the inclusion of preload in simulation can have as much (or greater) impact on micromotion as other key parameters such as shorter versus longer screws. These findings indicates that it is important to include appropriate values of screw preloads in simulations when comparing designs with different number of peripheral screws or studying the effects of including a central screw on rTSA micromotion

Introduction:. There is substantial range in kinematics and joint loading in the total knee arthroplasty (TKA) patient population. Prospective TKA designs should be evaluated across the spectrum of loading conditions observed in vivo. Recent research has implanted telemetric tibial trays into TKA patients and measured loads at the tibiofemoral (TF) joint [1]. However, the number of patients for which telemetric data is available is limited and restricts the variability in loading conditions to a small subset of those which may be encountered in vivo. However, there is a substantial amount of fluoroscopic data available from numerous TKA patients and component designs [2]. The purpose of this study was to develop computational simulations which incorporate population-based variability in loading conditions derived from in vivo fluoroscopy, for eventual use in computational as well as experimental activity models. Methods:. Fluoroscopic kinematic data was obtained during squat for several patients with fixed bearing and rotating platform (RP) components. Anterior-posterior (A-P) and internal-external (I-E) motions of the TF joint were extracted from full extension to maximum flexion. Joint compressive loading was estimated using an inverse-dynamics approach. Previously-developed computational models of the knee, lower limb, and Kansas knee simulator were virtually implanted with the same design as the fluoroscopy patients. A control system was integrated with the computational models such that external loading at the hip and ankle were determined in order to reproduce the measured in vivo motions and compressive load (Fig. 1). Accuracy of the model in matching the in vivo motions was assessed, in addition to the resulting joint A-P and I-E loading. The external loading determined for a broader range of patients can subsequently be utilized in a force-controlled simulation to assess the robustness of implant concepts to patient loading variability. The applicability of this work as a comparative tool was illustrated by assessing the kinematics of two PS RP designs under three patient-specific loading conditions. Results:. External hip and ankle loading conditions were determined for each computational model that reproduced in vivo A-P, I-E and flexion-extension joint motions and estimated compressive load. For example, RMS accuracy of 0.4 mm, 0.2° and 0.7° were achieved for A-P, I-E and flexion, respectively (Fig. 1, 2). There was good agreement in both trend and magnitude of joint loads predicted from the externally-loaded models compared to telemetric measurements. Comparative analysis of two designs under multiple loading conditions illustrated variability in joint mechanics as a result of design factors and variation between subjects for the same design (Fig. 3). Discussion:. Pre-clinical evaluation of new devices under physiological joint loading conditions is crucial to robust functionality across the TKA population. The loads applied to a TKA system will affect fixation, wear, and functional performance. Harnessing in vivo kinematic data to develop population-based loading profiles will facilitate development of a platform for comprehensive design-phase evaluation of prospective designs. In addition, loading conditions for experimental simulators can be developed in order to test new devices under the range of variability likely to be encountered in vivo

The design of every post-surgical knee arthroplasty study begins with the question “How soon after surgery should we assess the patients?”. The consensus, based primarily upon clinical rating systems, is that patients' scores reach a plateau roughly one year after surgery, and that observations performed at that time should be indicative of the long-term behavior of the joint. This is satisfactory for long-term studies of clinical performance. However, when new devices are introduced there is a need to determine as quickly as possible if the device performs as designed. Waiting a year or more after surgery to characterize a device's performance may place additional patients at risk of receiving an inferior design, or may delay widespread availability of a superior design. The goal of this study was to assess knee arthroplasty patients at 6–12 weeks, 6 months and 1 year after surgery to determine if their tibiofemoral kinematics changed during functional activities. A total of 13 patients (7 female) were recruited from an ongoing clinical study to participate in this IRB-approved sub-study. All subjects received fixed-bearing, cemented, posterior-cruciate-retaining total knee arthroplasty of the same design from a single surgeon. Subjects averaged 69 years, 169cm tall, and 28 BMI. Subjects were studied at 6–12 weeks, at 6 months and at 12 months post-surgery, when they showed an average clinical flexion of 106°, 113° and 115°, respectively. Subjects' knees were observed using pulsed-flat-panel-fluoroscopy during three activities: lunging to maximum flexion with their foot placed on a 20cm step, kneeling to maximum flexion on a padded bench, and step-up/down on a 20cm step without progression of the contralateral limb. Model-image registration was used to register 3D geometric models of the implants with their radiographic projections based upon measured projection parameters. 3D knee kinematics were derived from the registered models, including joint angles and the antero-posterior translation of the medial and lateral condyles relative to the tibial baseplate. There were no statistically significant changes in knee kinematics between the 6–12 week and 6 month, and 6-month and 12-month visits during the kneel and lunge activities (Table 1). Similarly, there were no pair-wise differences in tibial rotation or condylar translation during the dynamic step activity at any flexion angle (Figure 1). Traditional thinking suggests studies of knee mechanics should be performed at least one year after surgery to make observations that are predictive of long-term joint function. In three different functional activities, we could not demonstrate significant changes in knee kinematics between 6–12 weeks and 6 months, nor between 6 months and 12 months. If these results can be confirmed in a larger subject cohort, and for a range of TKA designs, then functional follow-up studies of novel knee arthroplasty designs might be justified as early as 6–12 weeks after surgery, making it possible to accelerate confirmation devices are performing in patients as designed. For any figures or tables, please contact the authors directly

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

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

Adequate fixation of implant components is an important goal for all arthroplasty procedures. Aseptic loosening is one of the leading causes of revision surgery in total knee arthroplasty. Radiostereometric analysis (RSA) is an imaging technique to measure implant migration, with established migration thresholds for well-fixed, at risk, and unacceptably migrating components. The purpose of the present study was to examine the long-term fixation of a cemented titanium fixed bearing polished tibial baseplate. Patients enrolled in a previous two-year prospective trial were recalled at ten years. All patients received a cemented, posterior-stabilised total knee replacement of the same design implanted by one of three surgeons. Of the original 35 patients, 16 were available for long-term follow-up, with one patient lost to follow-up, nine patients deceased, and a further nine patients unwilling to return to the clinic. Each patient underwent RSA imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes as well as maximum total point motion (MTPM) was compared between all time points (baseline, six weeks, three months, six months, one year, two years) up to the ten year follow-up visits. Outcome scores including the Knee Society Score (KSS), WOMAC, SF-12, and UCLA Activity Score were recorded. At ten years, the mean migrations of the tibial component were less than 0.1 mm and 0.1 degree in all planes relative to the post-operative RSA exam. There was no significant difference in tibial component migration between time points. However, MTPM increased significantly over time (p = 0.002), from 0.23 ± 0.18 mm at six weeks to 0.42 ± 0.20 mm at ten years. At one year, 13 patients had an acceptable MTPM level, three patients had an ‘at risk’ level, and no patient had an ‘unacceptable’ level. No patients were revised at ten years. WOMAC and KSS were significantly improved (p < 0.0001) at the latest follow-up compared to pre-operatively, but there was no difference in SF-12. The median UCLA Activity Score at latest follow-up was six (range, two to eight). The tibial baseplate demonstrated solid fixation at ten years. No patients had an unacceptable MTPM level at one year and no patients were revised at ten years, supporting the use of RSA to predict long-term loosening risk. The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries

Non-large head Metal-on-metal (MoM) hip replacements were seen as a solution to concerns about implant wear in younger patients. Mid-term loosening of once well-fixed hydroxyapatite (HA) coated femoral stems was recently observed in select MoM patients upon revision surgery. Accordingly, an implant retrieval study was undertaken to examine the incidence of aseptic loosening of in HA-coated femoral stems with MoM, ceramic on ceramic (CoC) and metal on polyethylene (MoP) bearing couples. A single-centre implant retrieval lab reviewed 44 hydroxyapatite (HA)-coated titanium wedge taper stems of the same design retrieved over a period of 9 years. Ten were MoM articulations, 23 MoP and 11 CoC. Head sizes ranged from 28 to 40 with only four 40mm heads, all of which were MoM. Reason for revision, duration of implantation, femoral head size, patient age and body mass index was recorded for each retrieval. Goldberg corrosion scores were determined for the taper surfaces of each retrieval, with ‘0’ indicating no corrosion and ‘3’ indicating severe corrosion. Logistic regression analysis, Wilcoxan Rank Sum and Fischer's exact test were used for statistical analysis. Aseptic loosening was the listed reason for revision in 18 of 44 cases. MoM bearing was associated with increased probability of aseptic loosening (Odds ratio 7.1 (95%CI 1.1–47.0) p=0.042). Severity of corrosion was also associated with aseptic loosening (Odds ratio 2.75 (95%CI 1.1–6.6) p=0.02). Head size and patient age had no correlation. Median time to revision of implants for aseptic loosening was 4.5 years (range: 4.2–7.0 years) for MoM versus 1.4 years (range: 0.3–3.0) for other bearing couples (p=0.004). Aseptic loosening was categorised as early (<=2 years) or mid-term (>2 years). No MoM hips were revised for aseptic loosening in the first 2 years while 8 of the 11 mid-term revisions had MoM articulations (p=0.004). Taper corrosion was more severe in mid-term aseptic loosing cases (p=0.049). MoM HA-coated hip replacements appear to be associated with increased mid-term aseptic loosening compared to other bearing couples. Patients with MoM HA-coated hip replacements should be monitored regularly beyond the initial 1 to 2 years following surgery. Future analyses will examine the presence and progression of femoral radiolucency prior to revision surgery to determine an approximate timeline of stem loosening in this patient cohort. This research highlights the importance of implant retrieval programs to assess post-revision implant characteristics for early identification of possible device issues

Background. Total ankle arthroplasty (TAA) is an alternative to ankle arthrodesis, replacing the degenerated joint with a mechanical motion-preserving alternative. Implant loosening remains a primary cause of TAA revision, and has been associated with wear-mediated osteolysis. Differing implant designs have a major influence on the wear performance of joint replacements. Providing a range of implant sizes allows surgeons a greater intra-operative choice for varying patient anatomy and potential to minimise wear. Minimal pre-clinical testing exists in the literature that investigates the effect of implant size on the wear behaviour. The aim of this study therefore was to investigate the effect of two different implant sizes on the wear performance of a TAA. Materials & Methods. Six ‘medium’ and six ‘extra small’ BOX® (MatOrtho Ltd, UK) TAA implants, of the same conceptual design and polyethylene insert thickness, were tested in a modified 6 station pneumatic knee simulator. 5 million cycles (Mc) of wear simulation were completed for each implant size, under kinematics aiming to replicate an ankle gait cycle (Figure 1) [1]. The simulator used had six degrees of freedom, of which four were controlled. The maximum axial load was 3150N, equivalent to 4.5 times body weight of a 70kg individual. The flexion profile ranged from −15° plantarflexion to 15° dorsiflexion. Rotation about the tibial component ranged from −2.3° of internal rotation to 8° external rotation, and anterior/posterior (AP) displacement ranged from 3.1 mm anterior to −0.9 mm posterior displacement. The lubricant used was 25% bovine serum supplemented with 0.04% sodium azide to prevent bacterial degradation. The wear of the TAA polyethylene inserts were determined gravimetrically after each Mc, with unloaded soak controls used to compensate for the uptake of moisture by the polyethylene. Results. There were no significant differences (P = 0.872) in the mean wear rates (± 95% confidence limits) between the medium (11.00 ± 3.06 mm3/Mc) and extra small (10.64 ± 4.61 mm3/Mc) implant sizes (Figure 2). An observation of insert surfaces showed clear signs of abrasive wear and burnishing (Figure 3). There was evidence of polyethylene transfer and scratching on the tibial components, while talar components displayed fine linear scratching in similar directions for both implant sizes. Conclusions. The wear rates of both implant sizes are comparable to the wear rate (13.30 ± 2.50 mm3/Mc) of a previous wear study, which was conducted on ‘medium-sized’ Corin Zenith TAAs, under the same simulator conditions for 2 Mc [1]. The wear rates for both implant sizes are substantially lower than the wear of four ‘small-sized’ BOX® ankles (18.60 ± 12.80 mm3/Mc) for 2Mc [2]. The considerable difference in wear rates may be due to the lower forces, higher AP and deionised water as the test lubricant [2], which does not replicate the features of the natural synovial fluid and produce tribological artefact. The results from this study suggest that under the same kinematic and kinetic conditions, the wear rates are unaffected by a change in TAA implant size

Introduction. Acetabular cup deformation is an important topic in today's THA and was investigated for a variety of metal cup designs (e.g. 1,2,3). Cup deformation caused by press-fit forces can have negative effects on the performance of such systems (e.g. high friction, metal ion release). When considering new materials for monolithic acetabular cups - such as ceramics - detailed knowledge about the deformation behaviour is essential to ensure successful performance. Therefore, the deformation behaviour of monolithic ceramic cups was investigated. Materials and Methods. Testing was conducted with monolithic ceramic cups (under development, not approved) of size 46mm and 64mm. One cup design of each size had a constant wall thickness of 3.0mm and an offset of 0.0mm (center of rotation on front face level), the other design was lateralized with an offset of 3.5mm (46mm) or 5.0mm (64mm), leading to an increased wall thickness. First, 3 cups of each design were impacted into 1.0mm underreamed Sawbones® blocks (pcf 30, geometry: see (2)). Second, all cups were quasi-statically assembled into the Sawbones® blocks of the same design using a material testing machine. Third, the cups were placed in a two-point-loading frame (acc. to ISO/DIS 7206–12:2014(E)) and a load of up to 1kN was applied. The inner diameter of all cups was measured under unloaded and loaded conditions for all scenarios using a coordinate measurement machine at 9 locations of each cup, 1.5mm below the front face (Fig.1). As the diametrical deformation (unloaded inner diameter – loaded inner diameter) was not normally distributed a Wilcoxon test was performed to statistically analyse the deformation differences of the different cup designs (p<0.05). Results. Impaction or quasi-static assembly of the cups into Sawbones® showed similar deformation behaviour (Fig.2). With increasing cup size the deformation increased by up to 81% (p<0.001) and lateralization reduced the deformation by up to 85% (p<0.001). Two-point-loading showed the same deformation behaviour. Deformations of up to 215 µm were measured (Fig.3). Increasing the cup size increased the deformation by up to 105% (p<0.001) and lateralization reduced the deformation by up to 77% (p<0.001). Discussion. Stiffening the cups by lateralization fairly reduced cup deformation and can help avoiding negative effects resulting from cup deformation. In comparison to metal cup designs the maximum deformation values for the lateralized ceramic cups are by up to 70 % smaller (3). Due to the lower deformation the clearance range could be narrowed in comparison to metal cups. Therefore, it might be possible to more precisely predict the friction and wear behaviour of ceramic on ceramic resurfacing systems

Unicompartmental knee replacements (unis) offer an early option for the treatment of osteoarthritis. However there is no standard method for measuring the wear of unis in the laboratory. Most knee simulators are designed for TKA, for which there is an ISO standard. This study is about a wear method for unis, applied to a novel unicompartmental knee replacement (design by PSW). It has a metal-backed UHMWPE femoral component to articulate against a monoblock metallic tibial component. The advantage is reduced resection of strong bone from the proximal tibia for more durable fixation. The femoral component resurfaces the distal end of the femur to a flexion arc of only 42°, the area of cartilage loss in early OA (Fig. 1). We compared this novel bearing couple to the same design but with the usual arrangement of femoral metal and tibial plastic. Our hypothesis was that the wear of the reversed materials would be comparable to conventional and within the range of TKR bearings. The test was conducted on a 4-station Instron-Stanmore force-controlled knee simulator. Both specimen groups (n=4 each) were highly crosslinked UHWMPE stabilized with vitamin E. On each of the four stations, one uni system was mounted on the medial side and one on the lateral, as if a standard TKR was being tested. The ISO-14243-1 walking cycle force-control waveforms were applied for 5 million cycles (Mc) at 1Hz, but with the maximum flexion during the swing phase (usually 58°) curtailed to 35° to maintain the contact within the arc of the femoral component. In-vivo this implant would be inlaid into the distal medial femoral condyle and the articulating surface immediately transitions into native cartilage. In our test set-up there was no secondary surface as such. The reduced flexion occurred during the swing phase where compressive load was low and the effect on the wear would be negligible. Wear was measured gravimetrically at many intervals and corrected by the weight gain of extra two active soak controls per group. After 5 Mc, the average rates of gravimetric weight loss from the UHMWPE femoral and tibial bearings were 4.73±0.266 mg/Mc and 3.07±0.388 mg/Mc, respectively (statistically significantly different, p=0.0007) (Fig. 2). No significant difference was found in wear between medial and lateral placement for specimens of the same type, although the medial side generally wore more. Although the plastic femorals of the reverse design wore more than the plastic tibials, the wear was still low at <5 mg/Mc. The range for typical TKRs using ultra-high molecular weight polyethylene, tested under the same conditions in our laboratory has been 2.85–24.1 mg/Mc. In summary, we adapted the ISO standard TKA wear test for the evaluation of unis, and in this case, a uni with reversed materials. Based on the wear results, this type of ‘early intervention’ design could therefore be a viable option, offering simplicity with less modular parts as well as load sharing with the native articular cartilage

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

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

Introduction. In Total Knee Arthroplasty (TKA) a proper choice of the implant size is mandatory in order to guarantee the success of the prosthesis, although the tribological behavior TKA is strongly influenced by the implant design. Retrieval analysis of failed total knee prosthesis is essential to investigate the wear mechanism leading to osteolysis and loosening of the implant. Assessments from retrieval studies constitute crucial information in the effort to improve prosthesis functionality and reduce the risk of revision. The aim of the present study was to investigate the correlation among different implant sizes of retrieved TKA and patients' variables such as Body Mass Index (BMI) in terms of surface modifications and morphology change, in order to examine prosthesis properties and performances. In particular, this study can improve the understanding of the tribological behavior of total knee prosthesis and it can help the surgeon to select the best implant size of TKA considering patient's variables. Methods. Twelve retrieved total knee prostheses of the same design but with different sizes were investigated. These prostheses were all cemented, fixed and posterior stabilized. These prostheses were explanted from 12 patients after a mean of 3.2 years (from 1.1 to 7.4 years). These patients had undergone a primary TKA at our hospital between 2005 and 2010; there were 10 women and 2 men with a mean age of 68 years (ranging from 48 to 77 years) at implantation. A qualitative assessment of wear patterns and surface damages was performed on femoral components and polyethylene inserts. Roughness analyses were obtained on femoral components to assess surface modifications. Surface roughness of the metallic femoral components was performed with a contact rugosimeter. Following an internal protocol, thirty measurements were acquired from each condyle. Two roughness parameters were take into account: Ra (the Mean Roughness, i.e. the arithmetical mean value of the deviations of the roughness profile about the centre line) and Rsk. (i.e. the skewness, indicates the prevalence of peaks or valleys and quantifies the asymmetry of the profile variation from the mean line). Prostheses time in-vivo and patient details were known. Results. Results from roughness studies were compared among the specimens and then matched. In Figures 1 and 2 there are showed the Ra and Rsk values measured on the retrieved femoral prosthesis. The correlation between implant size, surface roughness and morphological alterations were found and showed that prosthesis size is a significant factor on the TKA overall performance. Moreover, differences were highlighted through the specimens characterized by different time in-vivo. Discussion. No previous study, to the best of authors' knowledge, was addressed to examine the implant size of retrieved total knee prosthesis in terms of surface and morphological modifications. The present study, however, has some limitations due to the small number of retrieved TKAs and the lack of information on the level of activity of the considered patients. This study can give a novel insight into tribological mechanisms leading to knee prosthesis failure and it can also offer indications for improving its functionality

Introduction:. Severe bone loss creates a challenge for fixation in femoral revision. The goal of the study was to assess reproducibility of fixation and clinical outcomes of femoral revision with bone loss using a modular, fluted, tapered distally fixing stem. Methods:. 92 consecutive patients (96 hips) underwent hip revision surgery using the same design of a modular, fluted, tapered titanium stem between 1998 and 2005. Fourteen patients with 16 hips died before a 2-year follow-up. Eighty hips were followed for an average of 11.3 years (range of 8 to 13.5 years). Bone loss was classified as per Paprosky's classification, osseointegration assessed according to a modified system of Engh et al, and Harris Hip Score was used to document pain and function. Serial radiographs were reviewed by an independent observer to assess subsidence, osseointegration and bony reconstitution. Results:. The average patient age was 68 years at the time of surgery (range 40 to 91). 80% hips had at least Paprosky type 3A proximal bone loss and 41% had an associated proximal femoral ostoetomy. Pre-operative Harris Hip scores (HHS) averaged 50.368 (range 22 to 72.775) and improved to an average HHS of 87.432 (range 63.450 to 99.825) at last follow-up. The HHS improved an average of 37.103 points (range 13.750 to 58.950). Radiographically, osseointegration was evident in all hips. No hips had measurable migration beyond 5 mm. 61%) hips had evidence of bone reconstitution and 27% demonstrated diaphyseal stress shielding. One well-fixed distal stem was revised for stem fracture, and two proximal segments were revised for recurrent dislocation. Conclusion:. Reproducible fixation and clinical improvement were consistently achieved with this stem design in the setting of femoral bone loss

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

While short stem designs are not a new concept, interest has surged with increasing popularity of less invasive techniques. If the goal of the tapered stem is to load preferentially proximally, why do we need a stem at all? Perhaps the only reason to use a tapered, long stem is to prevent varus; however, studies have shown that varus malalignment of a tapered stem does not affect results. Short stems are easier to insert, especially when using an anterior approach such as the anterior supine intermuscular in which the proximal femur is elevated anteriorly from the wound during stem insertion. Femoral preparation can be accomplished with straightforward broaching of the canal, without use of reamers. Short stems are bone conserving. They violate less femoral bone stock, providing more favorable conditions should a revision be required. However, ease of insertion and bone conservation matter little if not supported by clinical results. Thus, we reviewed our early experience with 2094 patients undergoing 2457 primary THA using short, tapered titanium, porous plasma spray-coated femoral components since January 2006 at our center. The TaperLoc Microplasty stem (Biomet, Warsaw, IN) has been used in 1881 THA, and the TaperLoc Complete Microplasty stem (Biomet) in 576. Patient age averaged 63.6 years. Increased offset was used in 1990 hips (81%). The surgical approach was less invasive direct lateral (LIDL) in 1194 THA (49%), anterior supine intermuscular (ASI) in 1117 (46%), and standard direct lateral (Std) in 146 (6%). Follow-up averaged 20 months. Thirty-five stems (1.4%) have been revised: 15 for infection (12 LIDL, 3 ASI), 1 same day revision for intraoperative femoral shaft perforation (Std), 1 at 3 days for patellar dislocation (LIDL), 2 for early subsidence (1 LIDL, 1 ASI), 13 for periprosthetic femoral fracture (1 Std, 12 ASI), 2 for aseptic loosening (1 LIDL, 1 ASI), and 1 stem well fixed (ASI) removed for loose cup and unable to disarticulate trunnion. What lessons have we learned? First, we usually require one or two diameter sizes larger with short porous tapered stem versus the standard length version of the same design. The surgeon should be aggressive with sizing, pushing to the largest size possible. Use the broach like a rasp. Drive the component in valgus during insertion. Upon seating the component, do a trial reduction using the shortest available neck length. The component will generally sit slightly prouder than the broach and may require additional effort to seat completely. Conservation of existing bone stock, compatibility with soft-tissue sparing surgery, more physiologic loading of the proximal femur, and versatility with varying femoral anatomy make the short taper an attractive implant option. The tapered wedge short stem represents the natural evolution of joint arthroplasty to a smaller, less-invasive, and more efficient implant

Demand for TKR surgery is rising, including a more diverse patient demographic with increasing expectations [1]. Therefore, greater efforts are being devoted to laboratory testing. As a result, laboratory testing may set a clinical performance presumption for surgeons and patients. For example, oxidized ZrNB (Oxinium) femoral components have been projected to show 85% less wear than CoCr femoral components in bench-top testing [2]. However, recent clinical data show no difference in outcomes between Oxinium® and CoCr for the same design [3]. While it does not show lagging peformance for the Oxinium components, it does call into question the predictive ability of simulation. To better understand the performance of these two materials, a non standardized simulator evaluation was conducted. One commercially available design (Legion PS) was evaluated with two variations of femoral component material (n = 3/material) Oxinium® and Cobalt Chromium. All testing was conducted using a 7.5 kGy moderately crosslinked UHMWPE (XLPE). A 6-station knee simulator was utilized to simulate stair-climbing kinematics. The lubricant used was Alpha Calf Fraction serum which was replaced every 0.5 million cycles for a total of 5 million cycles. Soak controls were used to correct for fluid absorption and statistical analysis was performed using the Student's t-test. Total wear rate results for the tibial inserts are shown in Figure 1. There was no statistical difference in volume loss (p = 0.8) or wear rate (p = 0.9) for the Oxinium® system when compared to the CoCrsystem under stair-climbing kinematics. Visual examination revealed typical wear scars and features on the condylar surfaces, including burnishing. These results corroborate the recent clinical data showing no difference between Oxinium® components and their CoCr analogs [3]. The kinematics used here are not a combination of normal level walking with stair-climbing conditions as was published originally for the Oxinium® material [2], but stair-climbing kinematics only. Even though the stair-climbing profile utilized here does not represent standardized kinematics, it provided results that are in line with clinical observations for these femoral materials. Logic suggests that a combined duty cycle is more representative of patient behavior so there must be additional test factors contributing to the prediction previously reported. The goal of bench top testing is to simulate actual clinical performance so test models must be validated as clinicaly relevant in order to be predictive. Furthermore, the results of this test indicate that the different femoral materials evaluated in this study do not alter the wear characteristics of this TKR. This is further supported by a similar previous study showing the relative contribution of design versus materials in terms of wear behavior [4]. The main determination comes from clinical evidence, and as it has been demonstrated by Kim, et al [3], there is no significant difference in the clinical results of the two TKR devices analyzed

An attempt to analyse whether impaction allografting without cement is more or less satisfactory than the technique with the addition of cement is compromised by conflicting reports of where the migration actually occurs. In some cemented series distal migration of the prosthesis within the cement mantle has been recorded as well as migration of the whole cement/prosthesis construct into the graft. Two prospective consecutive series of revision hip arthroplasties by a single surgeon:- Group 1; Uncemented impaction grafting revision hip replacement in a series of 30 patients (33 hips). Group 2; Cemented impaction grafting revision hip replacement in a series of 30 patients (31 hips). Group demographics were similar. Each case used the same design of hip implant with the only difference in design being a proximal hydroxyapatite coating used on the uncemented implants. Follow-up ranged from 2 to 17 years for the uncemented group and from 1 to 11 years for the cemented group. A validated hip scoring system was employed at regular follow up incorporating pain and functional assessment. Migration rates for the uncemented group were 0 to 15 mm for 30 hips; however 3 hips were revised early due to excessive migration. 3 hips sustained early complications (1 fracture, 1 dislocation, 1 varus malposition of stem). Migration rates for the cemented group were 0 to 9 mm for 29 hips, however the remaining 3 hips were revised due to excessive migration (up to 33mm). Although similar results were obtained in terms of success and also pain and function scores, marginal improvement in results did occur with the cemented series overall. Statistical significance was not reached however. More sinkage occurred in the uncemented group overall, the majority occurring in the first 6 post-operative months. Part of the improvement with the cemented series results may be explained by the improved techniques achieved whilst performing the uncemented series. These results from a single surgeon demonstrate that the method is highly technique dependent and relies on adequate graft impaction. With sufficient graft and an appropriate prosthetic design, cement is not essential to the early success of this method. However, the extent of the initial migration did not accurately predict a successful outcome for the procedure. The absence of cement removes any confusion as to the location of any migration

INTRODUCTION. Mobile-bearing knee prostheses have been designed in order to provide less constrained knee kinematics compared to fixed-bearing prosthesis. Currently, there is no evidence to confirm the superiority of either of the two implants with regard to walking performances. It has been shown that subjective outcome scores correlate poorly with real walking performance and it has been recommended to obtain an additional assessment of walking ability with objective gait analysis. OBJECTIVES. We assessed recovery after total knee arthroplasty (TKA) with mobile- and fixed-bearing between patients during the first postoperative year, and at 5 years follow-up, using a new objective method to measure gait parameters in real life conditions. METHODS. 56 patients with mobile- and fixed-bearing of the same design were included in this randomised controlled double-blinded study and evaluated pre- and post-operatively at 6 weeks, 3 months, 6 months 1 year and 5 years. At each visit a WOMAC and Knee Society Score were calculated and each participant completed an EQ-5D questionnaire. To assess the patients' gait five miniature angular rate sensors mounted respectively on the sacrum and each shank and thigh measured lower limb movement and rotation. The patients walked 30 metres on a flat surface and gait parameters were recorded with a small ambulatory device in order to carry out an objective gait analysis. RESULTS. Objective recovery was strongly correlated with patients' age. When the whole population was considered, there was no significant difference between groups at any time in objective gait parameters. After separating the population according to their age (less than 71 years old, compared to those of more than 71 years old) a secondary analysis showed that the bearing type can lead to opposite results in different age groups. At five years follow-up, most of the recorded gait parameters (stride length, knee max rotation speed, shank and thigh range of motion, and limp) showed better results for mobile bearing in younger patients, while better gait performances were found systematically with fixed-bearing TKA in older patients. CONCLUSION. To our knowledge, this is the first study where similarly designed posterior-stabilised knee replacements with fixed- and mobile-bearing have been compared with gait analysis in real-life conditions. We observed systematically differences between mobile and fixed bearing groups, which are confirmed by multivariate analysis. Our results suggest that older patients might not benefit from a mobile bearing TKA and that extended age controlled study should be performed to identify an age, above which fixed bearing should not be the recommended choice. Before choosing the bearing type, surgeons should take into account the age of the patient