A Consensus-Based Classification of Minor Complications, Major Complications, and Failure After ACL Reconstruction: A Modified Delphi Study

<h2>Abstract</h2><h3>Introduction</h3> To establish a consensus-based classification of postoperative events following anterior cruciate ligament (ACL) reconstruction, clearly distinguishing no complication/normal clinical course<b>,</b> minor complication<b>,</b> major complication<b>,</b> and failure, using a structured Delphi methodology among international experts in ACL surgery. <h3>Methods</h3> A three-round modified Delphi process was conducted involving international high-volume ACL surgeons. An initial set of statements addressing potential postoperative events after ACL reconstruction was developed by a working group based on clinical expertise and contemporary literature. Panelists classified each statement as <i>no complication/normal clinical course</i>, <i>minor complication</i>, <i>major complication</i>, or <i>failure</i>. 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. <h3>Results</h3> 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. <h3>Conclusions</h3> This international Delphi consensus establishes a standardized and clinically meaningful classification of postoperative events following ACL reconstruction. By clearly distinguishing no complication<b>,</b> minor complication<b>,</b> major complication<b>,</b> 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. <h3>Level of Evidence</h3> Level V, expert consensus.