 4. MB-RSA measurements of migration of the femoral component. A MB-RSA system will be used; a technique in which the position of the prosthesis is assessed by matching a virtual projection of a 3D-model of the prosthesis to the actual radiographic projection. It does not require former times special implants with attached markers. The patients will be x-rayed within the first postoperative week and subsequently at 3 months, 6 months, 1 year, 2 years and 5 years using 2 fixed X-ray tubes with the patient in supine position and a uniplanar calibration cage will be used. The precision of the measurements of migration will be estimated from sets of double X-rays of patients n12 included in the study. 