Comparison of ISO 14243-1 to ASTM F3141 in terms of wearing of knee prostheses.

BACKGROUND: The wear properties of knee implants need to be thoroughly evaluated prior to clinical use to ensure implant longevity. ISO 14243-1:2009 and ASTM F3141-17 are the two standards typically used for evaluating wear, with the ISO standard being more common; ASTM F3141-17 was first released in 2015. The aim of this study is to compare differences between these two standards in terms of wearing on a knee prosthesis. METHODS: Using finite element analysis based on Archard's law, this study evaluated anterior-posterior and internal-external motion, contact area, contact force, contact stress, volumetric wear rate, wear depth, and wear distribution on the knee prosthesis. FINDINGS: The results show that simulations performed according to ASTM F3141 produced knee kinematics that were more similar to human gait. The maximum wear depth occurred on the medial side of the tibia. However, the region of peak contact stress did not always correspond with the region of the maximum wear depth, indicating that considering the contact stress alone is not sufficient for evaluating wear as the sliding distance also plays an important role. The resulting wear region from the ASTM F3141 simulation was smaller but deeper than the wear region from the simulation per ISO 14243-1. However, the volumetric wear rates were very similar, with 13.48-55.26 mm3/million for ASTM F3141 and 13.64-54.9 mm3/million for ISO 14243-1. INTERPRETATION: The resulting rate of wear is almost identical between ISO 14243-1 and ASTM F3141. However, there are differences in wear contours and wear depth.

Effects of knee simulator control method and radiation dose on UHMWPE wear rate, and relationship between wear rate and clinical revision rate in National Joint Registry.

The wear rate of five types of cruciate-retaining artificial knee joint ultrahigh-molecular-weight polyethylene (UHMWPE) inserts was examined using two custom-made knee joint simulators satisfying ISO 14243-1 (load control) and ISO 14243-3 (displacement control). The wear rate of knee joints composed of a UHMWPE insert and a Co-Cr-Mo alloy or oxidized zirconium femoral component linearly increased with increasing number of wear cycles, and the volumetric wear rate per million cycles was approximately 6-18 mm3/Mc. The wear rate was the lowest in the highly crosslinked knee joint irradiated at 90 kGy (Scorpio) among the five UHMWPE inserts. The extent of oxidation in UHMWPE after a knee simulator test of up to 5 × 106 cycles was small. The load-controlled wear rates measured in this work were close to the displacement-controlled wear rates reported in the literature. The effect of the control method on the wear rate was small for Nexgen and Scorpio knee joints. However, it was larger for the PFC Sigma knee joint having a high curvature of the surface. The wear rate of various knee joints made of highly crosslinked UHMWPE (XLPE) markedly decreased when they were subjected to a radiation dose of 40 kGy or more. The 10-year cumulative percentage revision rate since the primary operation slightly decreased with decreasing volumetric knee simulator wear rate for conventional UHMWPE (CPE) and XLPE knee joint inserts. The XLPE knee joint was shown to exhibit reduced in vivo wear and lower rates of revision for total knee replacement. On the other hand, Nexgen and PFC Sigma (both CPE) knee joints showed the lowest revision rate in the AOA and NJR national joint replacement registries. The volumetric wear rates of 3 mm3/Mc for XLPE and 15 mm3/Mc for CPE knee joint inserts are recommended as a goal for the development of new knee joints.

Regression models to predict the behavior of the coefficient of friction of AISI 316L on UHMWPE under ISO 14243-3 conditions.

Friction is the natural response of all tribosystems. In a total knee replacement (TKR) prosthetic device, its measurement is hindered by the complex geometry of its integrating parts and that of the testing simulation rig operating under the ISO 14243-3:2014 standard. To develop prediction models of the coefficient of friction (COF) between AISI 316L steel and ultra-high molecular weight polyethylene (UHMWPE) lubricated with fetal bovine serum dilutions, the arthrokinematics and loading conditions prescribed by the ISO 142433: 2014 standard were translated to a simpler geometrical setup, via Hertz contact theory. Tribological testing proceeded by loading a stainless steel AISI 316L ball against the surface of a UHMWPE disk, with the test fluid at 37 °C. The method has been applied to study the behavior of the COF during a whole walking cycle. On the other hand, the role of protein aggregation phenomena as a lubrication mechanism has been extensively studied in hip joint replacements but little explored for the operating conditions of a TKR. Lubricant testing fluids were prepared with fetal bovine serum (FBS) dilutions having protein mass concentrations of 5, 10, 20 and 36 g/L. The results were contrasted against deionized, sterilized water. The results indicate that even at protein concentration as low as 5 g/L, protein aggregation phenomena play an important role in the lubrication of the metal-on-polymer tribopair. The regression models of the COF developed herein are available for numerical simulations of the tribological behavior of the aforementioned tribosystem. In this case, surface stress rather than film thickness should be considered.