60 patients undergoing total knee arthroplasty were randomized to surgery with either the Triathlon cruciate-retaining (CR) total knee system or the Triathlon posterior-stabilized (ie. cruciate-sacrificing; PS) total knee system. The purpose of this study was to evaluate migration and micromotion of the tibial tray between the two devices for up to two years after surgery. In terms of translation, there was no significant difference between groups in medial-lateral translation, although significant differences were found in caudal-cranial translation and posterior-anterior translation. In PS prostheses, migration was more cranially and posteriorly, while CR prostheses migrated more caudally and anteriorly. No significant differences between groups were observed in component rotation/ micromotion and clinical outcome over 2-year follow-up.