Standard Guide for Wear Assessment of Prosthetic Knee Designs in Simulator Devices

1.1 This guide covers a laboratory method for evaluating the wear properties of materials or devices, or both, that are being considered for use as the bearing surfaces of human knee joint replacement prostheses. The knee prostheses are evaluated in a device intended to simulate the tribological conditions encountered in the human knee joint.

1.2 The methods described in this guide are intended to apply to a number of fundamentally different types of knee wear simulators. These include apparatuses which are designed to apply some combination of axial load, flexion/extension angular motion, AP displacement or shear force, and tibial rotational displacement or torque to femoral and tibial wear test specimens.

1.3 Since the knee simulator method permits the use of actual implant designs, materials, and physiological load/motion combinations, it can represent a more physiological simulation than basic wear-screening tests, such as "pin-on-disc" (Test Method F732) or "ring-on-disc" (ISO-6474).

1.4 It is the intent of this guide to rank the combination of implant designs and materials with regard to material wear-rates, under simulated physiological conditions. It must be recognized, however, since there are many possible variations in the in vivo conditions, a single laboratory simulation with a fixed set of parameters may not be universally representative (1,2)

1.5 The reference materials for the comparative evaluation of candidate materials, designs, and processes shall be the wear rate of extruded or compression-molded ultra-high molecular weight (UHMW) polyethylene (Specification F648) bearing against standard counter faces [cobalt-chromium-molybdenum alloy (Specification F75); thermomechanically processed cobalt chrome (Specification F799 or F1537)], having typical prosthetic-quality surface finish and geometry similar to those with established clinical history. These reference materials will have been tested under the same wear conditions as the candidate materials.