The study aims at comparing the effect of hollow or solid centralizer designs on the long time fixation behaviour of hip prosthesis stems that are polished, tapered and collarless. In a prospective, controlled and randomized study comprising two groups of 30 patients/hips each, the patients will be followed up by RadioStereometric Analysis (RSA) for ten years. In completion general health questionnaires as well as hip specific scoring instruments will be used to evaluate patient satisfaction and outcome.The hypothesis of the study is that the different centralizers will result in different migration patterns of the stems, which might affect the risk for late aseptic loosening.

Inclusion Criteria:

• Primary osteoarthritis of the hip necessitating primary hip replacement
• Charnley classification group A and B
• Age 60 - 85 years old at the inclusion time of the study.

Exclusion Criteria:

• Secondary osteoarthritis
• Rheumatoid arthritis
• Malignant disease
• Severe osteoporosis
• Earlier fracture or operation in the hip to be operated on
• Peroperative fracture
• Ongoing corticosteroid (oral) or immunosuppressive medication
• Personal disorders (dementia, alcohol or drug abuse etc) suspected of making completion of the trial uncertain.