Hu X Q, Wood R J K, Taylor A, Tuke M A
National Centre for Advanced Tribology at Southampton (nCATS), School of Engineering Sciences, University of Southampton, UK.
Proc Inst Mech Eng H. 2011 Nov;225(11):1061-9. doi: 10.1177/0954411911419061.
Clearance is one of the most influential parameters on the tribological performance of metal-on-metal (MOM) hip joints and its selection is a subject of considerable debate. The objective of this paper is to study the lubrication behaviour of different clearances for MOM hip joints within the range of human physiological and pathological fluid viscosities. The frictional torques developed by MOM hip joints with a 50 mm diameter were measured for both virgin surfaces and during a wear simulator test. Joints were manufactured with three different diametral clearances: 20, 100, and 200 microm. The fluid used for the friction measurements which contained different ratios of 25 percent newborn calf serum and carboxymethyl cellulose (CMC) with the obtained viscosities values ranging from 0.001 to 0.71 Pa s. The obtained results indicate that the frictional torque for the 20 microm clearance joint remains high over the whole range of the viscosity values. The frictional torque of the 100 microm clearance joint was low for the very low viscosity (0.001 Pa s) lubricant, but increased with increasing viscosity value. The frictional torque of the 200 microm clearance joint was high at very low viscosity levels, however, it reduced with increasing viscosity. It is concluded that a smaller clearance level can enhance the formation of an elastohydrodynamic lubrication (EHL) film, but this is at the cost of preventing fluid recovery between the bearing surfaces during the unloaded phase of walking. Larger clearance bearings allow a better recovery of lubricant during the unloaded phase, which is necessary for higher viscosity lubricants. The selection of the clearance value should therefore consider both the formation of the EHL film and the fluid recovery as a function of the physiological viscosity in order to get an optimal tribological performance for MOM hip joints. The application of either 25 per cent bovine serum or water in existing in vitro tribological study should also be revised to consider the relevance of clinic synovial fluid viscosities and to avoid possible misleading results.
间隙是影响金属对金属（MOM）髋关节摩擦学性能的最重要参数之一，其选择是一个备受争议的话题。本文的目的是研究在人体生理和病理流体粘度范围内，MOM髋关节不同间隙的润滑行为。对直径为50 mm的MOM髋关节在原始表面以及磨损模拟器测试过程中产生的摩擦扭矩进行了测量。制造的关节具有三种不同的径向间隙：20、100和200微米。用于摩擦测量的流体包含不同比例的25%新生小牛血清和羧甲基纤维素（CMC），所得粘度值范围为0.001至0.71 Pa·s。所得结果表明，20微米间隙关节的摩擦扭矩在整个粘度值范围内都保持较高。100微米间隙关节在极低粘度（0.001 Pa·s）润滑剂下的摩擦扭矩较低，但随着粘度值的增加而增加。200微米间隙关节在极低粘度水平下的摩擦扭矩较高，然而，它随着粘度的增加而降低。得出的结论是，较小的间隙水平可以增强弹性流体动力润滑（EHL）膜的形成，但这是以在行走的卸载阶段阻止轴承表面之间的流体恢复为代价的。较大间隙的轴承在卸载阶段允许更好地恢复润滑剂，这对于高粘度润滑剂是必要的。因此，间隙值的选择应同时考虑EHL膜的形成和作为生理粘度函数的流体恢复，以便获得MOM髋关节的最佳摩擦学性能。在现有的体外摩擦学研究中，25%牛血清或水的应用也应进行修订，以考虑临床滑液粘度的相关性，并避免可能产生误导性的结果。
