Introduction. A tibial insert with choices in size, thickness, and posterior slope is proposed to improve ligament balancing in total knee arthroplasty. However, increasing posterior slope, or the angle between the distal and proximal insert surfaces, will redistribute ultra-high molecular weight polyethylene (UHMWPE) thickness in the sagittal plane, potentially affecting wear. This study used in-vitro testing to compare wear for a standard cruciate-retaining tibial insert (STD) and a corresponding 6° sloped insert (SLP), both manufactured from direct-compression molded (DCM) UHMWPE. Our hypothesis was slope variation would have no significant effect on wear. Methods. Two of each insert (STD and SLP) were tested on an Instron-Stanmore knee simulator with a force-control regime. The gait cycle and other settings followed ISO 14243-1 and -2, except for reference positions. The STD insert was tilted 6° more than the SLP insert to level the articular surfaces. Wear was gravimetrically measured at intervals according to strict protocol. Results. No statistical difference (p=0.36) in wear rates was found for the STD (9.5 ±1.8 mg/Mc)) and SLP (11.4 ±0.5 mg/Mc) inserts. Discussion. The overall wear rate measured was higher than previously published rates for implants similar to the STD inserts. This may result from increased shear loads due to the shift in reference position and 6° slope. This is the first time the effect of tibial insert slope on wear has been evaluated in-vitro. For inserts made from DCM UHMWPE with a slope limited to 6°, this test suggests altering tibial insert slope has an insignificant effect on wear

Due to increased life expectancy of human population, the amount of total knee replacements (TKR) is expected to increase. TKR reached a high grade of quality and safety, but most often it fail because of aseptic implant loosening caused by polyethylene (PE) wear debris. Wear is generated at the articulating surfaces, e.g. caused by three body particles, like bone fragments or bone cement particles. The aim of this experimental study was to compare the wear of tibial PE inserts combined with metallic and ceramic femoral components at three body wear situation induced by polymethylmethacrylate (PMMA) and zirconia (ZrO2) particles from the bone cement. Wear testing was performed for 5 Mio load cycles, using tibial standard PE inserts combined with the same CR femoral component, in two different materials, Cobalt Chromium (CoCrMo) and Biolox delta ® ceramic (Multigen Plus Knee System, Lima Corporate, Italy). A knee wear simulator, according to ISO 14243 (EndoLab GmbH, Rosenheim, Germany), was used to carry out the tests. The tests were performed in temperature-controlled test chambers at 37 °C, containing calf serum with a protein content of 30 g/l. Polymethylmethacrylate (PMMA) and zirconia (ZrO2) bone cement particles (Palacos R ®) were manufactured to a size of 30 μm. The three body particles were added at all stations onto the articulating surface of the tibial PE insert (7mg per condyle) at every 500,000 cycles. Wear was determined gravimetrically and the surfaces of tibial inserts were analysed by scanning electron microscope (SEM) after finishing the 5 million cycles. Furthermore, roughness of the PE insert surfaces and the articulating surfaces of the different femoral components were detected and the PE wear particles were analysed by SEM. The average gravimetrical wear rates of the tibial PE inserts in combination with CoCr and Biolox delta ® ceramic femoral components amounted to 6.4 ± 0.9 mg and 2.6 ± 0.4 mg per million cycles, respectively. Beside bone cement particles on the articulating surface of the PE inserts, polished surfaces and scratches were detected by SEM. In comparison to the untreated surfaces of the PE inserts at both material pairings the surface roughness at the articulating areas showed deep scratches and polished regions. Analyses of the metallic femoral components showed scratches at the articulating surfaces, none on ceramics. The present study pointed out the effect of femoral component material in an abrasive three body wear situation on the wear properties of TKR. The wear simulator tests showed that wear of PE inserts under three body wear conditions, in combination with ceramic femoral components, was significantly lower than with metallic femoral components. With regard to anti-allergic properties, ceramic femoral components are promising products for TKR

Introduction. While clinically successful for decades, CR TKA is persistently compromised by inconsistent PCL function. Problems of mid-flexion instability, incomplete knee flexion, erratic kinematic behavior and posterior instability, not seen with PS devices, raise concerns about the consistency of the technique, and the devices used. Most TKA systems offer at least 2 different geometries of tibial inserts to address this clinical problem. We hypothesize these problems are a result of compromise of PCL anatomy. To avoid compromise to the PCL 3 steps are required: 1) The slope of tibial resection must be less than 5°; 2) the depth of tibial resection must be based off the insertion footprint of the PCL, not the deficiencies of the tibial articular surface; and 3) the tibial insert must be modified to allow intraoperative balancing of the PCL. Results. The CR Slope ™ implants and technique (Exactech) (“Posterior Cruciate Referencing Technique (PCRT)”) reflect this philosophy and have allowed consistent surgical intervention without PCL release and without multiple inserts. We present data identifying, the footprint, and the instrument and technique modifications that allow for predictable identification of the depth and angle of resection. At 2 years post implantation in the first 100 patients implanted, the study group has demonstrated similar operative time, LOS and Oxford knee scores (OKS), while ROM averaged 5° greater, and time to achieved flexion was decreased. Conclusion. The PCRT offers a new conceptual and clinical approach to predictable CR TKA

Introduction. Oxidized zirconium (OxZr) is used as a ceramic surface for femoral components in total knee arthroplasty (TKA). The aim of this study was to investigate its performance by examining retrieved femoral components and their corresponding PE inserts in matched comparison with conventional chrome/cobalt/molybdenum alloy (CrCoMo). Methods. 11 retrieved posterior stabilized (PS) TKA with an OxZr femoral component were included. From a cohort of 56 retrieved TKA with CrCoMo femoral components, pairs were matched according to duration of implantation, patient age, reason for revision, and BMI. The retrieved tibial polyethylene (PE) inserts were analyzed for wear using the Hood classification. Femoral components were optically viewed at 8–32x magnification and screened for scratching, pitting, delamination, and striation. Profilometry was performed to measure surface roughness of the OxZr components using a non-contact white light profiler. Results. The prostheses were in situ for a mean of 18.5±10.6 (OxZr) and 19.5±14.3 (CrCoMo) months (p=0.41). None of these cases were revised for problems directly related to the use of OxZr. There was one reaction to the implant in the CrCoMo group. The average wear of the tibial PE inserts was significantly lower with OxZr components (41.5±16.8 vs. 60.1±22.0, p=0.01). The average wear score in the visual analysis of the femoral components was significantly lower for the OxZr (1.6±1.3 vs. 9.5±0.6, p=0.005). Discussion and Conclusion. Femoral components made of OxZr are less sensitive to in vivo wear damage than those of CrCoMo. PE inlays show significantly less in vivo wear damage in combination with an OxZr femoral component

Introduction. Vitamin E stabilization of radiation crosslinked UHMWPE is done by (1) blending into the resin powder, consolidating and irradiating or (2) diffusing into already consolidated and irradiated UHMWPE and terminally gamma sterilizing. With blending, a higher radiation dose is required for crosslinking to the same level as virgin UHMWPE. With diffusion, the vitamin E amount used is not limited by the crosslink density, but, vitamin E is exposed to terminal sterilization dose of 25–40 kGy, less than the 100–150 kGy used with blending, which may decrease the grafting of the antioxidant onto the polymer. We investigated the efficiency of grafted vitamin E against squlene-initiated accelerated aging. Methods. Medical grade GUR1050 UHMWPE with vitamin E (0.1 wt%) was irradiated to 150 kGy. Tibial knee insert preforms were irradiated to 100 kGy, diffused with vitamin E using a doping and homogenization procedure. This UHMWPE was used either before or after gamma sterilization. One set of machined blocks (10 × 10 × 6 mm; n = 6) were extracted in boiling hexane for 4 days, then dried. The extracted blocks were doped with squalene at 120°C for 2 hours. One block each was analyzed after doping. The rest were accelerated aged at 70°C and 5 atm. of oxygen for 6 (n = 2) and 14 days (n = 3). Thin sections (150 micron thick) were microtomed and analyzed by Fourier Transform Infrared Spectroscopy to determine a vitamin E index (1245–1275 cm. −1. normalized to 1850–1985 cm. −1. ) and an oxidation index (1700 cm. −1. normalized to 1370 cm. −1. ) after extraction with boiling hexane for 16 hours and drying. Results. After extraction, 92% of the original vitamin E was removed from diffused and sterilized UHMWPE and 99% of the vitamin E was removed from the diffused and unsterilized UHMWPE. Vitamin E content of the blended, irradiated UHMWPEs could not be detected. As a result of accelerated aging in the presence of squalene, all extracted vitamin E-stabilized UHMWPEs showed increased oxidation except diffused, sterilized UHMWPE. The small amount grafted vitamin E in these samples (8%, ∼0.02 wt%) protected irradiated UHMWPE under these conditions. All vitamin E-stabilized, extracted UHMWPEs showed higher oxidative stability than irradiated and melted virgin UHMWPE in the presence of squalene. In the blended, irradiated UHMWPE, there was less effective vitamin E compared to the diffused, sterilized UHMWPE due to the high dose irradiation. Conclusions. Radiation grafting of vitamin E onto UHMWPE was effective against squalene initiated oxidation in accelerated aging. Vitamin E-diffused, sterilized UHMWPE showed no oxidation and diffused, unsterilized UHMWPE and blended, irradiated UHMWPE showed higher oxidative resistance than irradiated/melted UHMWPE