In order to investigate the role of acetabular cup screw holes for the transport of osteolysis-inducing particles in a total hip arthroplasty articulation, the investigators compare the amount of bone loss around acetabular cups with and without holes. Bone loss is measured with computed tomography at 7 years and 15 - 18 years of follow-up.

Particles generated by wear and corrosion within an artificial hip articulation can cause biologically mediated bone loss in the surrounding pelvis. Particles can be found within immunologically active cells inside bone lesions. Holes intended for screw fixation in uncemented acetabular cups are believed to be a main route for these particles from the articulation into the pelvic bone. Using pressfit, screws are not always necessary for a successful fixation of an uncemented cup. The investigator's hypothesis is that a pressfit fixated cup without screw holes will display a decreased amount of periacetabular osteolysis compared to a cup with screw holes. Therefore, 95 hips (90 patients) were randomized to receive either pressfit cups without screw holes or the same type of cup with screw holes. The occurence and size of periacetabular osteolysis will be compared between the two groups. In addition, since the patients will have a computed tomography examination at 7 years and between 15 and 18 years the investigator will also analyze development of periacetabular osteolysis over time. The different cups were paired with three different types of femoral stems. Also, articulation wear and cup and stem fixation will be analyzed using radiostereometry.

Inclusion Criteria:

• primary or secondary osteoarthritis

Exclusion Criteria:

• Inflammatory osteoarthritis, hip joint infection