Significance and Use
5.1 This test procedure provides a method of evaluating the frictional torque and friction factor of hip replacement bearings.
5.2 The procedure may be used as a standardized method of measuring friction to investigate the effects of specific test parameters such as hip materials, sizes, designs, radial or diametral clearance, different lubricants, different deformation levels of the acetabular cup, clamping (non-uniform sphericity), damaged/scratched bearings, artificial ageing, misalignments during installation, etc.
5.3 Friction torque, and in particular the maximum value, is useful to assess the applicable torques that may compromise fixation, or even risk disassociation of modular components in the acetabular cup or liner/shell assemblies through a lever-out or torsion-out mechanism.
5.4 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).
5.5 The loading and motion of a hip replacement in vivo differ from the loading and the motion defined in this standard. The amount of frictional forces in vivo will, in general, differ from the frictional forces evaluated by this standard test method. The results obtained from this test method cannot be used to directly predict in vivo performance. However, this standard is designed to allow for in-vitro comparisons for different hip designs, when tested under similar conditions.
5.6 Although this test method can be used to investigate the many variables listed in 1.2 and 5.2, it does not either provide a method to determine beforehand the combination of these variables that will produce the worst-case couple(s) among a range of sizes; the worst-case testing condition(s) for “normal” or “adverse” conditions; or provide specific methods to deform the acetabular cup, simulate Mode 3 wear conditions (for example, third-body particles, scratched heads), or artificially aged materials. As these methods are not included in the standard and if they are to become the subject of the investigation then it is up to the user to justify the couple(s) selected and method(s) used in the test and, if necessary, provide a rationale for how the “worst-case” couple(s) and method(s) were selected to represent clinically relevant “normal” and “adverse” conditions as part of the report.
Scope
1.1 This test procedure provides a method of determining the frictional torque and friction factor of artificial hip joint bearings used in total hip replacement (THR) systems under laboratory conditions using a reciprocal friction simulator. This test method specifies the angular movement between the articulating components, the pattern of applied force, and the way data can be measured and analyzed.
1.2 Many variables can be investigated using this test method including, but not limited to, the effect of head size, different inclination/version angles, different deformation levels of the acetabular cup, bearing clearances, lubrication, scratched heads, and artificial ageing.
1.3 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.
