Hidden blood loss and the influential factors after intramedullary nail fixation of extra-articular tibial fractures - a retrospective cohort study

•A significant amount of hidden blood loss exists in intramedullary nailing fixation for extra-articular tibial fractures.•Male sex, small medullary cavity, and long-time surgical duration might increase hidden blood loss.•The effect of hidden blood loss should be taken into account when the surgeon fixed the extra-articular tibial fractures.