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.