Introduction. Undisplaced femoral neck fractures have been given little attention in the literature. By using data from the Norwegian Hip Fracture Register, this study investigates risk for reoperation and the clinical results, including pain, patient satisfaction, and quality of life, after undisplaced femoral neck fractures in elderly patients. Material and Methods. Data on 4,468 patients over 70 years of age with undisplaced femoral neck fractures operated with internal fixation (IF) were compared to 10,289 patients with displaced femoral neck fractures treated with IF (n = 3,389) or bipolar hemiarthroplasty (n = 6,900). The evaluation was based on number of reported reoperations and patients' assessment (visual analogue scales concerning pain (0–100) and patient satisfaction (0–100), and quality of life (EQ-5D)) four and twelve months postoperatively. The patients were followed for 0–1 year. The Cox multiple regression model was used to construct adjusted survival curves. Subanalyses were performed on undisplaced femoral neck fractures to investigate different risk factors for reoperation. Results. The survival rate of implants after one year was 89% after screw fixation for undisplaced fractures, 79% after screw fixation for displaced fractures, and 97% after hemiarthroplasty for displaced fractures (Kaplan Meier). Adjusted for age, sex, ASA-classification, and cognitive function the displaced fractures operated with internal fixation had higher risk of reoperation compared to the undisplaced fractures operated with internal fixation (RR 1.92, 95% CI: 1.69–2.17; p<0.001). The displaced fractures operated with hemiarthroplasty had a lower risk of reoperation compared to the undisplaced fractures (RR 0.32, 95%CI: 0.27–0.38; p<0.001). Patients treated with IF for undisplaced fractures were more satisfied, had less pain, and higher quality of life compared to patients treated with IF after displaced fractures (p<0.05). The patients treated with bipolar hemiarthroplasty for displaced fractures had, however, the least pain, were most satisfied, and reported the highest quality of life. Discussion and Conclusion. The clinical outcome after undisplaced femoral neck fractures treated with screw fixation was better than the results of screw fixation for displaced fractures, but poorer than the clinical results for patients with displaced femoral neck fractures operated with a bipolar hemiarthroplasty. However, the differences in clinical outcome were smaller than what is considered to be of clinical importance. One year postoperatively screw osteosynthesis of undisplaced femoral neck fractures in elderly patients still seems to be a good alternative
