Study design and methods Comparison of prosthesis migration of cemented versus uncemented dual-mobility cup fixation Objective: Investigate prosthesis migration and polyethylene wear of cemented and cementless Avantage® dual-mobility acetabular components (Biomet Inc.) in elderly patients and correlate migration measurements with radiological evaluation of implant placement/cementation quality, with bone quality at the time of surgery (osteoporotic/osteopenic/normal bone), and with functional outcome after two years. The migration pattern and magnitude will predict the likelihood of later aseptic loosening and revision.