BackgroundClosed reduction of upper limb fractures and/or dislocations are common in the emergency department (ED), which involves physically re-aligning the injured part prior to immobilisation. As this is painful, numerous techniques are available to provide regional anaesthesia to ensure patient tolerance. A Bier block (BB) is typically performed as part of routine care. An alternative technique gaining interest in the ED is ultrasound-guided supraclavicular block (UGSCB), which involves injecting local anaesthetic around the brachial plexus at the supraclavicular fossa under ultrasound guidance. It is unclear whether UGSCB is effective and safe when performed in the ED.MethodsSUPERB (SUPraclavicular block for Emergency Reduction versus Bier block) is a prospective open-label, non-inferiority randomised controlled trial that compares the effectiveness of UGSCB versus BB for closed reduction of upper limb fractures and/or dislocations. Adult patients presenting with an upper limb fracture and/or dislocation that requires emergent closed reduction in the ED will be eligible. After screening, participants will be randomised to either UGSCB or BB. Once regional anaesthesia is obtained, closed reduction of the injured part will be performed and appropriately immobilised. The primary outcome is maximal pain experienced during closed reduction measured via a visual analogue scale (VAS). Secondary outcomes include baseline and post-reduction pain, patient satisfaction, total opioid requirement in ED, ED length of stay, adverse events and regional anaesthesia failure.DiscussionExisting evidence suggests UGSCB is effective when performed in the operating theatre by trained anaesthetists. SUPERB will be the first randomised controlled trial to elucidate the effectiveness and safety of UGSCB in the ED. The findings have the potential to provide an alternative safe and effective option for the management of upper extremity emergencies in the ED.Trial registrationThis trial has been registered on 21 October 2022 with Australia and New Zealand Clinical Trials Registry (ACTRN12622001356752).