There have been no previously published clinical randomized studies comparing Primoris®, short stem, hip prosthesis with standard uncemented hip arthroplasty in relation to bone density and function development. This is the subject for this study.

The overall purpose of this study is to show whether the Primoris® hip prosthesis results in a smaller loss of bone density than standard hip prosthesis, which in the longer term may result in an improved survival of prosthesis No. 2 after revision / replacement of a Primoris® hip prosthesis.

The primary outcome is periprosthetic bone quality in Primoris® hip prosthesis compared to standard hip prosthesis measured by DXA scanning.

The secondary outcomes are to assess:

1. The hip function measured by gait analysis.
2. Hip strength at pressure gauge.
3. Prosthetic migration / migration measured by radio-stereometric analysis (RSA).
4. Patient satisfaction measured by PROMs.

Inclusion Criteria:

Women ≤ 45 years or men ≤ 55 years with hip osteoarthritis, suitable for hip prosthesis.

Patients who wish to participate in the project and give written consent after oral and written information.

Exclusion Criteria:

1. Patients with previous bone disease, metabolic disease, including diabetes, or the use of drugs that affect bone density.
2. Smoking more than 20 cigarettes daily
3. Patients with fracture in the femur or acetabulum.
4. Patients who do not understand the given patient information
5. Competing disorder requiring treatment with antiinflammatory drugs (NSAIDs, steroid, cytostatics).
6. Estimated residual life <10 years
7. Rheumatoid arthritis or other arthritis (eg psoriasis arthritis).
8. Previous surgery on the relevant hip joint.
9. Co-Morbidity (ASA Group 3-5).
10. Neurological disorder that compromises motor skills and rehabilitation.
11. Pregnancy.
12. Osteoarthritis secondary to mb. Calvé-Legg-Perthes / Avascular Caput Necrosis, Epiphysiolysis Capitis Femoris and Multiple Epiphysic Dysplasia.
13. Acetabular dysplasia with secondary subluxation (Crowe grade II to IV).
14. Previously detected osteoporosis or osteoporosis detected by current DXA scanning.
15. Ongoing treatment with osteoporosis medicine (bisphosphonates, estrogen receptor modulators and parathyroid hormone, etc.).
16. Aseptic caput necrosis (posttraumatic, idiopathic).
17. Varus or valgus deformity in proximal femur (collum angle <125 ° or> 145 °.)
18. Collum femoris assessed too retro- or anteverted.