Significance and Use
5.1 This test procedure provides a method of evaluating the frictional torque and friction factor of artificial hip joint bearings under the stated in-vitro test conditions.
5.2 Friction is not simply a materials property. The specimen system and the effects on its friction are multi-factorial, including the materials and processing of the components, the design and assembly of the components, the test parameters, and environmental factors (lubricant, temperature, etc.).
5.3 The procedure may be used as a standardized method of measuring friction for a particular system, or as a method of investigating the effects of specific test parameters such as hip sizes, designs, radial clearance, different lubricants, clamping (nonuniform sphericity), misalignments during installation, etc.
5.4 The procedure may be used to study the variation of friction with time as the specimens wear, which is particularly useful for samples that undergo a transition from “run-in” to “steady-state” wear behavior. Since the motion and load waveforms are identical to those specified in ISO 14242-1:2014, standardized friction and wear measurements may be combined and viewed in the correct perspective where they affect each other.
5.5 Frictional torque, and in particular the maximum value, are useful to assess the torques that may compromise fixation, or cause disassociation of modular components in acetabular cup or liner/shell assemblies through a lever-out or torsion-out mechanism.
5.6 Friction factor is a useful parameter for comparison of materials and designs, and provides insights into the lubrication regime operating in the implant system. Friction factor measurement may also be able to detect acetabular liner deformation (clamping referred to earlier).
Scope
1.1 This test procedure provides a method of evaluating the frictional torque and friction factor of artificial hip joint bearings used in Total Hip Replacement systems. The method presented here was based on a published study, first as a conference paper in 2008 (1)2 and then as a peer-reviewed journal paper (2). The method is compatible with and is capable of being carried out during actual wear testing of total hip replacement implants on wear simulators equipped with multiple degrees of freedom force and moment sensors.
1.2 Although the methodology described does not replicate all physiological loading conditions, it is a means of in-vitro comparison of the frictional torque and friction factor of artificial hip joint bearings used in Total Hip Replacement systems under the stated test conditions.
1.3 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
