INTRODUCTION: Ankle fracture surgery is a common procedure, but the influence of anaesthesia choice on postoperative pain and quality of recovery is poorly understood. Some authors suggest a benefit of peripheral nerve block (PNB) in elective procedures, but the different pain profile following acute fracture surgery and the rebound pain on cessation of the PNB both remain unexplored. We present an ongoing randomised study aiming to compare primary PNB anaesthesia with spinal anaesthesia for ankle fracture surgery regarding postoperative pain profiles and quality of recovery.METHODS AND ANALYSIS: AnAnkle Trial is a randomised, dual-centre, open-label, blinded analysis trial of 150 adult patients undergoing primary internal fixation of an ankle fracture. Main exclusion criteria are habitual opioid use, impaired pain sensation, other painful injuries or cognitive impairment. The intervention is ultrasound-guided popliteal sciatic (20 mL) and saphenal nerve (8 mL) PNB with ropivacaine 7.5 mg/mL, and controls receive spinal anaesthesia (2 mL) with hyperbaric bupivacaine 5 mg/mL. Postoperatively all receive paracetamol, ibuprofen and patient-controlled intravenous morphine on demand. Morphine consumption and pain scores are registered in the first 27 hours and reported as an integrated pain score as the primary endpoint. Pain score intervals are 3 hours and we will use the area under curve to get a longitudinal measure of pain. Secondary outcomes include rebound pain on cessation of anaesthesia, opioid side effects (Opioid-Related Symptom Distress Scale), quality of recovery (Danish Quality of Recovery-15 score) and pain scores and medication days 1-7 (diary).ETHICS AND DISSEMINATION: The study has been approved by the Regional Ethics Committees in the Capital Region of Denmark, the Danish Data Protection Agency and the Danish Health and Medical Authority. We will publish the results in international peer-reviewed medical journals.TRIAL REGISTRATION NUMBER: AnAnkle Trial is registered in the European Clinical Trials Database (EudraCT 2015-001108-76).