ASTM F1800-19 Standard Practice for Cyclic Fatigue Testing of Metal Tibial Tray Components of Total Knee Joint Replacements

The ASTM F1800-19 Standard Practice for Cyclic Fatigue Testing of Metal Tibial Tray Components in Total Knee Joint Replacements, developed by the American Society for Testing and Materials (ASTM) , describes a procedure for fatigue testing of metallic tibial trays used in knee joint replacements using a cyclic, constant amplitude force. It applies to tibial trays covering both the medial and lateral plateaus of the tibia. This practice may require modifications to accommodate other tibial tray designs.

This application is intended to provide useful, consistent, and reproducible information on the fatigue performance of metallic tibial trays with an unsupported condyle. The results are applicable to laboratory testing conditions and may not correlate with in vivo performance.

For the purposes of this standard, the following terms and definitions apply:

• The anteroposterior centerline is the line passing through the center of the tibial tray, parallel to the sagittal plane and perpendicular to the load application line. For asymmetric tibial tray designs, the appropriate center of the tibial tray should be determined by the investigator and a rationale should be provided.
• The fixture centerline is the line passing through the center of the fixture, parallel to the anteroposterior centerline. This line represents the separation between the supported and unsupported portions of the test fixture.
• The mediolateral centerline is the line passing through the center of the tibial tray, parallel to the coronal or frontal plane and perpendicular to the line of load application. For asymmetric tibial tray designs, the appropriate center of the tibial tray should be determined by the investigator and a rationale should be provided.
• The moment arm is the perpendicular distance between the mediolateral centerline of the tibial component and the line of load application.
• The moment arm is the perpendicular distance between the anteroposterior centerline of the tibial component and the line of load application.

This application is used to describe the effects of materials, manufacturing, and design variables on the fatigue performance of metallic tibial trays subjected to cyclic loading for a relatively large number of cycles.

In vivo loading of tibial tray designs is generally different from the loading described in this exercise. The results obtained here cannot be used to directly predict in vivo performance. However, this exercise is designed to allow comparisons between the fatigue performance of different metallic tibial tray designs when tested under similar conditions.

To ensure that fatigue data on tibial trays are comparable, reproducible, and relatable across laboratories, it is essential to establish uniform procedures.

The selected test component must have the same geometry as the final product and be in finished condition.

The tibial tray should be mounted as a cantilever beam. Care should be taken to ensure that the fixation of the tibial tray does not produce abnormal stress concentrations that could alter the failure mode of the part. A possible installation involving fixation of the lower surface or clamping of the upper surface is shown in the figures included in the standard. If necessary, bone cement or other high strength epoxy may be used in the supported direction of the tibial tray to prevent loosening during testing. There should be a minimum of 5 mm clearance between the lower surface of the loaded compartment on the tibial tray and any part of the fixture.

The tibial tray should be positioned so that the anteroposterior centerline and the fixture centerline are aligned with an accuracy of 61 mm in the x-direction and 62 degrees in the xy-plane.

If the tibial tray design includes a central spine or other protrusion, only the medial or lateral half of the spine is supported.

A spacer made of plastic with sufficient rigidity and creep resistance (e.g., ultra-high molecular weight polyethylene, acetal copolymer) must be placed between the tibial tray and the load applicator. The spacer must include a spherical recess or groove for the spherical indentation. This groove must be greater than or equal to the diameter of the spherical indentation and is included to minimize the possibility of fracture of the spacer under load. The spacer must have a minimum thickness of 6 mm, measured at the dome of the sphere, and a diameter of 13 mm.

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