Total hip replacement is a very cost effective procedure to enhance life quality in a group of patients. In the period 2000-2004 7-8000 procedures were preformed, 13% were revisions (1). Historically, many different principles have been used from the first resurfacings to cemented and uncemented total hip replacements as we know them today. In 2000, 28 different femoral stems and 26 different acetabular components were in regular use in Norway. There are several well-documented cemented acetabular components, but no such uncemented cup. On the femoral side there are several well-documented stems both cemented and uncemented. (2).

From the late 1990's a reverse hybrid (uncemented stem and cemented cup) is being more frequently used. In 2004 a total of 276 reverse hybrid hips were done and the trend is increasing. (1). This technique is solely based on experience and the fact that one combines the better of two principles (cemented and uncemented). There is no scientific evidence that this technique is as good or better than a cemented THR.

One of the potential problems with hydroxyapatite coated components is that it is suspected that it may increase wear due to the particle theory. (3,4). There are no prospective randomised controlled RSA and DXA studies that conclude on this matter. This is such a study and our hypothesis is that there is no difference in wear or osteolysis between the methods.

Inclusion Criteria:

• Osteoarthritis
• Indication for THR

Exclusion Criteria:

• Significant anatomical abnormalities
• Rheumatoid artheritis, dysplasia, fracture sequela