Hemiarthroplasty of the hip is standard treatment of femoral neck fractures (hip fractures). Hemiarthroplasty means replacing the hip joint with a metal prosthesis. Unipolar prostheses has a one-piece design where the hip movement occurs between the prosthesis and the acetabulum (hip socket). A bipolar prosthesis has an additional artificial joint between the two components of the prosthesis. Both treatments are clinically proven and common around the world. No clinical trial has proven benefits of one or the other prosthesis design. The investigators want to measure the differences in acetabular wear using these two prostheses, using radiostereometric measurements.

Patients 70 years or older presenting to our hospital with an acute femoral neck fracture are eligible for inclusion. 15 patients in each group will be recruited. One group receives a unipolar hemiarthroplasty and 15 receives a bipolar arthroplasty. Tantalum markers are placed around the acetabulum during surgery. Follow-up intervals are at 3, 12 and 24 months with radiostereometric evaluation (radiographs) and clinical evaluation.

Inclusion Criteria:

• Displaced femoral neck fracture
• 70 years or older
• Ambulatory status: No walking aids
• No mental illness or impaired cognitive function

Exclusion Criteria:

• Pathological fracture (malignant disease)
• Ongoing systemic or local infection
• Radiologically presence of acetabular wear (osteoarthrosis)