With the frequent use of modular knee systems today, component integrity at the modular interface is often questioned. Many knee systems use modular stem extensions that attach to the tibial or femoral component. The use of these modular stems raise issues about the fatigue integrity of the construct, fretting of the modular connection, and modular attachment strength. These must be addressed through testing in order to validate the safety and efficacy of a product. Three test methods that can be used to investigate the fatigue integrity of the modular tibial tray and stem interface will be discussed. The three test methods discussed are the Cantilever Test, the Unsupported Stem Test, and the Partial Bone Support Test. Each of these test methods is compared and contrasted on their ability to mimic clinical conditions, ease of use, and ease of analysis. The test methods attempt to address several issues relevant to modular tibial stem extensions. The presentation of the test methods is meant to provide information on current stem extension testing in order to fuel the emergence of a standardized testing protocol.