F2 and hemorrhagic disease: (2) Retrospective design and missing data: The retrospective nature of the study and the lack of some data (small number of PLIF cases (more risk of nerve root injury than TLIF), bleeding disorders, surgeon experience, preoperative blood predictors (active partial thromboplastin time (APTT), prothrombin time (PT), and other clotting factors were not routine preoperative laboratory) limit the model's comprehensiveness.