This is the world's first national orthopedic randomized controlled trial (RCT) involving 19 out of 21 departments in Denmark. Each year, 7,000 patients suffer a hip fracture. This is a severe condition leading to 25% mortality after 1 year and 40% do not recover to the same functional level. The aim is to compare two surgical treatment methods (metal fixation versus artificial hip) in patients above 65 years with an undisplaced femoral neck fracture. The hypothesis is that even though an artificial hip is a larger surgical procedure than metal fixation of the broken bone, the artificial hip is more stable with less pain due the lack of a healing broken bone and therefore leads to a better and quicker mobilization after surgery. Better mobilization is one of the most important factors for decreasing mortality. We have chosen a pragmatic RCT design by using the local departmental implants. We hope that the knowledge from this study will therefore easily be implemented afterwards.

This is the world's first national orthopedic randomized controlled trial (RCT) involving 20 out of 21 departments in Denmark. The aim is to compare two surgical treatment methods (internal fixation (IF) versus arthroplasty) in patients above 65 years with an undisplaced femoral neck fracture (FNF).

Each year, 7,000 patients suffer a hip fracture. This is a severe condition leading to 25% mortality after 1 year and 40% do not recover to the same functional level. Undisplaced FNF is treated with internal fixation in order to aid in fracture healing. However, approximately 10% in Denmark will suffer a reoperation and two RCT's have demonstrated 20-21% reoperations. In comparison, the reoperation frequency was 5-7% for arthroplasty that also demonstrated slightly faster mobilization which is one of the most important factors for decreasing mortality. The hypothesis is therefore that even though arthroplasty is a larger surgery they benefit from the lack of fracture healing, less pain and faster mobilization.

Patients are included in the emergency department and are electronically randomized to either IF or arthroplasty before the surgery. The design is a pragmatic RCT using the implants which are available in the departments. Furthermore, the postoperative treatment protocol is "business as usual" thereby investigating the precise effect of the intervention in real clinical conditions. In addition to a great external validity this allows for easy implemented after study results. The primary outcome is a validated functional score 1 year after surgery and the sample size is calculated to 330 patients. Secondary outcome measures are additional functional assessments and questionnaires, health related quality of life and pain assessment.

We have set up a steering committee consisting of researchers and senior surgeons with a representative from each region. In addition, all but 1 hospital has a representative in project group. The project is therefore anchored in the entire Denmark.

Inclusion Criteria:

• Age ≥ 65 years old
• Undisplaced femoral neck fracture
• Posterior tilt (18) less than 20 degrees
• NMS (13) = 5 and above, indicating an ability to walk
• Cognitive intact in order to achieve informed consent

Exclusion Criteria:

• The fracture is pathological
• The patient does not speak Danish

Due to Danish regulation direct data sharing is not possible.

The surgeon, theater staff and patient cannot be blinded due to the nature of two very different types of surgery. However, the assessors will be blinded for type of surgery.