Backside wear of tibial polyethylene components is affected by gait pattern: A knee simulator study using rare earth tracer technology.

The aim of this study was to determine the effect of two in-vivo-determined gait patterns, one with low and one with high anteroposterior (AP) motion, on total and backside polyethylene insert wear in comparison with the ISO (International Organization for Standardization) standard 14243-3. In order to differentiate and accurately quantify topside and backside wear, a novel technique was employed where different lanthanide tracers were incorporated into the polyethylene during manufacture. Wear particle analysis was conducted following established protocols. For all tested liners and motion protocols, the chemically calculated wear rates correlated closely with gravimetrically determined wear. Both in vivo motion groups displayed higher wear rates than the ISO group following the order of the AP motion amplitudes. Backside wear for ISO constituted 2.76% ± 0.90% (mean ± SE) of the total wear, increasing significantly to 15.8% ± 3.2% for the low AP and further increasing to 19.3% ± 0.95% for the high AP motion protocol. The mean wear particle sizes were under 200 nm for all three motion patterns, being largest for the protocol with high AP motion. Particle release from the low and high AP gait patterns was 1.9 to 2.8 times that from the ISO protocol. Testing for the proportion of backside wear across various activities of daily living should be an important consideration in evaluating knee prostheses wear.

Articulation of an alumina-zirconia composite ceramic against living cartilage - An in vitro wear test.

BACKGROUND: There is interest in minimally invasive solutions that reduce osteoarthritic symptoms and restore joint mobility in the early stages of cartilage degeneration. The aim of the present study was to evaluate an alumina-zirconia composite (AZC) as a counterface for articulation against live cartilage explants in comparison to the clinically relevant cobalt-chromium (CoCrMo) alloy. METHODS: A four-station bioreactor designed to articulate against living tissue in an incubator was used for testing. Twelve 32 mm AZC and twelve 32 mm CoCrMo femoral heads with equal surface roughness made up both test groups. Each head articulated against a cartilage disk harvested from stifle joints of 24-week old steers. Test samples and free-swelling control cartilage samples were cultured in Mini ITS medium. Testing was conducted 3 h daily over 10 days applying a contact load of approximately 2 MPa. PG/GAG and hydroxyproline were analyzed using biochemical assays. Additionally, chondrocyte survival and Mankin score analyses were performed on histological slides. RESULTS: Cells stayed alive during the course of the experiment, with cell survival values close to 80% at test completion in the superficial zone. There was no significant difference between AZC and free-swelling control tissue. However, cell count values were inferior for CoCrMo (p = 0.003). Tested tissue suffered mostly structural abnormalities. The PG/GAG content in medium was not different between CoCrMo and AZC (p = 0.315); however, the hydroxyproline release into medium was nearly 30% higher for CoCrMo (p = 0.024). CONCLUSION: Based on average values, AZC induces less cell and tissue damage than CoCrMo. However, only the hydroxyproline measurements reached statistical significance, partially due to substantial scatter within both groups.

Effect of europium(II) stearate on the mechanical properties and the oxidation resistance of UHMWPE.

The objective of this pilot study is to investigate the effect of europium(II) stearate additive on the mechanical properties and oxidation resistance of an ultra-high molecular weight polyethylene (UHMWPE), which has been used as an articulating surface in prosthetic devices for many years. It is hypothesized in this study that combining the UHMWPE with lanthanide stearates could enhance oxidation resistance, leading to better preservation of the material's mechanical integrity. Compression molded UHMWPE was doped at 0, 375 and 750 ppm of europium(II) stearate, γ-irradiated to 35 kGy in a nitrogen atmosphere, and accelerated aged in accordance with the ASTM standard F2003-02. Non-irradiated and nonaged samples were used as controls. Miniature samples were comparatively tested for mechanical properties using the small punch test. Oxidation indices (OIs) were obtained through the FTIR spectroscopy on thin film sections of all irradiated samples. The UHMWPE doped with the europium(II) stearate had the same small punch test curve shape as the conventional UHMWPE control; the ultimate displacement remained unchanged (approximately 4.33±0.02 mm), while the ultimate load and work-to-failure exhibited only small changes (<7.5% and <5.0%, respectively). The doped material was more resistant to oxidation than the control material, retaining 83% of its as-irradiated work-to-failure after irradiation and accelerated aging, versus only 53% for the control. Accelerated aging changed the average oxidation index of the control group from 0.07 to 0.40; whereas the average oxidation indices changed from 0.03 to 0.15 and from 0.05 to 0.13 for the 375 ppm and the 750 ppm doped condition, respectively.