Assessing the changes in outcome measurements in randomized controlled trials of regional anesthesia interventions: a registry-publication comparison study

Background Regional anesthesia (RA) is increasingly used due to its safety and effectiveness in reducing postoperative pain and opioid use. As in other areas of clinical research, transparent and consistent outcome reporting is important for interpreting trial evidence. This study assessed the extent and nature of temporal changes to prespecified outcomes in interventional RA trials registered on ClinicalTrials.gov after the implementation of the Final Rule and the Food and Drug Administration Amendments Act 801. Methods We conducted a registry-based cross-sectional analysis of RA trials initiated between January 2017 and December 2024. Eligible trials enrolled adults, were interventional in design, had posted tabular results on ClinicalTrials.gov, and were linked to a peer-reviewed publication. Using ClinicalTrials.gov version histories, we compared the earliest and most recent registry records to identify modifications in outcome definitions, timing and classifications. Changes were categorized by type, timing and interpretive impact. Disclosure of modifications in registry records and publications was assessed. Results Among 74 eligible trials, 91.9% exhibited at least one substantive outcome change between registry versions. Among trials with substantive outcome modifications, the most recently entered substantive modification occurred after primary completion in 47.1% and after publication in 51.5%, and none were disclosed. Changes to both primary and secondary outcomes were common, with 37.8% of trials exhibiting high-impact modifications. Minor rewording was the most frequent change type, though often accompanied by more substantive shifts in outcome measurement tools, timepoints, or classifications. Secondary outcomes were more frequently added or removed than primary outcomes. Discussion In this sample of 74 RA trials, differences between the earliest and most recent registered outcome fields were common, including changes involving primary outcomes. For most of these trials, the most recently entered substantive modification occurred after primary completion or publication and was not explicitly explained in the associated publication. These findings describe the frequency and timing of registry modifications but cannot determine why the changes occurred or whether they influenced the reported results.