In this prospective randomized four-armed study the investigators aim to compare wheter 3-D planning, which necessitates preoperative CT acquisition and sophisticated planning together with engineers, results in measurable benefits in terms of objective and subjective outcome values in a collective of patients undergoing primary total hip replacement.

Hypothesis:

1. When compared to 2-D planning, 3-D planning of a THR results in better hip reconstruction, better subjective and clinical outcome and better longevity of total hip implants.
2. When compared to a non-anatomical stem, an anatomical stem allows better hip reconstruction, better subjective and clinical outcome and better longevity of total hip implants.

Patients sent to our outpatient clinic for eventual primary THR are informed about this study and written patient information given to them. When patients decide to undergo primary total hip replacement, patient's questions with respect to this study are discussed in the outpatient clinic and patients willing to participate included.

Block randomization using closed envelopes for age categories 40-50, 50-60, 60-70 years will be conducted to assign the participant to one of the four study arms.

Patients will be blinded for the type of stem and method of planning. Investigators are blined in terms of methods of planning. In terms of stem design, investigators can not be blinded since their visibility on x-ray does not allow it.

The preoperative investigation includes routine investigation and an additional CT scan plus evaluation of the "University of California at Los Angeles" (UCLA) activity level and "Short Form Health 36" (SF-36) score. The same applies for the postoperative investigation and 3 months. The follow-up visits at 1, 5 and 10 years are routine investigations with additional UCLA and SF-36 Scores.

Inclusion Criteria:

• patients aged 40-70 years scheduled for primary THR
• signed written informed consent.

Exclusion Criteria:

• Charnley class B and C
• ASA score >2
• pregnancy
• gross hip deformity making complex hip reconstruction (greater trochanter advancement, acetabular augmentation, femoral osteotomy, use of cemented or revision stem) necessary
• immature patients and patients incompetent to judge