New Practice for Measurement of Contact Area and Contact Pressure in Total Knee Replacements
1. Scope
The standard would specify the loading conditions to use for Tibiofemoral Contact Area and contact pressure testing. The standard would also contain methodologies for establishing worst case size combination to test and stipulate that a worst-case analysis must be done for the entire compatibility chart range of the device to evaluate the smallest contact area and highest contact stress pairing of devices.The standard will also specify methodologies for calibrating, validating, and verifying any type of contact area and stress measurement technology while giving specific reference to examples of common used modes (Pressure sensitive film, electronic resistive based flexible film tekscan or equivalent) and express considerations to take in terms of accounting for drift, hysteresis, self-heating, equilibration, pre-conditioning, frequency of calibration, material couples and calibration setup, and other technical aspects required for getting consistent results from these sensors. The standard would provide some insight into using these common well-known tools.
Keywords
Wear, Contact stress, Delamination
Rationale
Contact Area and Contact Pressure testing has been recommended in FDA Guidance and ASTM F2083 Total Knee specification. This testing is recommended to understand potential for wear behavior in a total knee implant system and helps support worst case analysis for wear testing.Little guidance on the method is given in the standards currently, and only the angles of flexion are specifically recommended. These often do not match reported literature. Literature references are provided but no standard test method exists as a standard. Therefore published literature explores many methods (film vs digital film vs ultrasound etc.) and loading conditions and size combinations of implants, mostly undisclosed, and this offers a poor comparator between devices. Loading conditions, angles, and methods must be consistent to make a meaningful comparison.
