Improving implant longevity is an eminent challenge in joint replacement surgery with aseptic loosening as the major reason for early failure necessitating revision surgery in both total hip and total knee arthroplasty (THA and TKA). Analysis of implant fixation by measuring migration with roentgen stereophotogrammetric analysis (RSA) has shown that the loosening process starts at very early onset after implantation. Implants showing relative high migration during the first post-operative year are prone to failure and subsequent revision later on. However, it is still not crystallized how specific implant characteristics or the surgical procedure affect the implant migration pattern and what degree of initial migration is acceptable without jeopardizing longevity of implant fixation at 10-20 years. In this thesis the migration pattern in relation to longevity of both cemented and cementless stems in THA, the influence of mobile-bearings in TKA on migration and survival, and methods to instantly evaluate implant fixation by inducible displacement have been studied.Atlantic Innovation Fund (Atlantic Canada Opportunities Agency); Biomet; Dutch Arthritis Association; European Information and Communication Technologies Community Seventh Framework ProgrammeLUMC / Geneeskund