The purpose of this study is to compare two surface materials (tantalum versus titanium fiber mesh) of acetabular components in hip arthroplasty.

In younger patients, acetabulum components are most often implanted without the use of cement. A direct ingrowth of bone to the implant is crucial to the attainment of good results in those cases where cement is not employed. A new implant material (tantalum) has shown better properties than the implant material which is in use today (titanium). The advantages of tantalum implants are greater porosity, reduced stiffness and a higher friction coefficient than with titanium implants.

Hypothetically, the higher porosity of tantalum should enhance bone ingrowth due to better osteoconductivity in terms of:

1. less migration of the acetabulum component, as evaluated by RSA;
2. increased BMD in the bone surrounding acetabulum components;
3. fewer postoperative complaints on the Harris Hip Score and visual analog scale scores.

The migration of acetabulum components will be evaluated by RSA. The follow-up RSA will be scheduled for week 1, as well as 3 months, 12 months and 2 years after surgery. Bone mineral density around the implanted femoral component will be examined by DEXA scan at week 1, as well as 1 year and 2 years after surgery.

Inclusion Criteria:

• Patients with primary arthritis in the hip.
• Patients with sufficient bone density to allow uncemented implantation of a femoral component.
• Informed patient consent in writing.

Exclusion Criteria:

• Patients with neuromuscular or vascular disease in the affected leg.
• Patients found upon operation to be unsuited for uncemented acetabulum component.
• Patients who regularly take non-steroid anti-inflammatory drugs (NSAID) and cannot interrupt intake for the postoperative phase of the study.
• Patients with fracture sequelae.
• Female patients of childbearing capacity.
• Hip joint dysplasia.
• Sequelae to previous hip joint disorder in childhood.