Background The Bedside Ultrasound Conducted in Kids with distal upper Limb fractures in the Emergency Department (BUCKLED) trial is a multicentre, randomised, open-label, non-inferiority study comparing point-of-care ultrasound to x-ray as the initial imaging modality in children with clinically non-angulated distal forearm injuries. Objective The purpose of this document is to minimise bias by defining and making publicly available our analysis approach prior to completing the study and reviewing or analysing the trial data. Methods We developed a statistical analysis plan (SAP) for reporting and analysing the BUCKLED trial including our approach to expected protocol deviations, withdrawals, missing data, and loss to follow up. Study methods are described using a previously published study protocol. Broad statistical analysis principles are outlined. Primary and secondary trial outcomes are described, along with appropriate methods for statistical comparison. Results This report pre-specifies the SAP for the primary outcome of upper limb function at 4 weeks, using an intention-to-treat analysis with a hypothesis of non-inferiority. Results of a per-protocol analysis will also be reported. Subgroup analyses will include diagnostic category and age category and secondary outcomes will include cost, quality of life, satisfaction, pain, adverse events, rates of imaging, Emergency Department length of stay, treatment time and diagnostic accuracy. Methods of statistical comparison are outlined. Conclusion This report describes the SAP for the BUCKLED trial, to minimise analysis bias and ensure transparency and internal validity for the findings of this randomised controlled trial.

The authors have declared no competing interest.

ACTRN12620000637943

grants from the Emergency Medicine Foundation (Grant ID: EMPJ-222R31-2019), Wishlist Sunshine Coast Hospital Foundation 2019, Queensland Health Research Scholarship (Round 2, 2020), and the Gold Coast Health Study Education and Research Trust Fund (July 2020, journal publication fees). Funding is managed by the coordinating site Gold Coast University Hospital and Griffith University. The Trial Sponsor is the Research Governance Officer, GCHResearch@health.qld.gov.au.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Children's Health Queensland Hospital and Health Service Human Research Ethics Committee gave ethical approval for this work.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

All datasets used and/or analysed during the BUCKLED RCT will be available from the corresponding author of that paper upon reasonable request and after requestees meet criteria stipulated by the approving ethics committee.