A consensus-based classification of minor complications, major complications, and failure after anterior cruciate ligament reconstruction: A modified delphi study

INTRODUCTION: The aim of this study was to establish a consensus-based classification of postoperative events following anterior cruciate ligament reconstruction (ACLR), clearly distinguishing no complication/normal clinical course, minor complication, major complication, and failure, using a structured Delphi methodology among international experts in anterior cruciate ligament (ACL) surgery. METHODS: A three-round modified Delphi process was conducted involving international high-volume ACL surgeons. An initial set of statements addressing potential postoperative events after ACLR was developed by a working group based on clinical expertise and contemporary literature. Panelists classified each statement as no complication/normal clinical course, minor complication, major complication, or failure. Consensus was predefined as ≥75% agreement within a single category. Statements reaching consensus were retained, whereas non-consensus statements were revised and re-evaluated in subsequent rounds. RESULTS: Thirty-nine experts completed the first and second Delphi rounds, and 30 (76.9%) completed the third round. The initial 52 statements were expanded to 67 in round two and refined to 46 in round three. Consensus was achieved for 14 statements (26.9%) in round one, 21 statements (31.3%) in round two, and 20 statements (43.5%) in round three. Overall, consensus was reached for 55 statements, forming the final classification framework. The panel clearly distinguished graft failure-defined as graft insufficiency or symptomatic instability-from major complications requiring surgical intervention or associated with substantial morbidity, and from minor complications or expected postoperative findings. Notably, traumatic graft rupture following a clearly documented new injury was not considered a postoperative complication. CONCLUSIONS: This international Delphi consensus establishes a standardized and clinically meaningful classification of postoperative events following ACLR. By clearly distinguishing no complication, minor complication, major complication, and failure, this framework provides a shared language that may improve consistency in outcome reporting, facilitate comparison across studies, and enhance the interpretability of clinical research and registry data. LEVEL OF EVIDENCE: V, expert consensus.