Abstract： Objective:To study the therapeutic effects of hyperbaric oxygen（HBO）on postoperative delirium in elderly patients with middle and lower tibial fractures and its impact on serum insulin-like growth factor-1（IGF-1）and matrix metalloproteinase-9（MMP-9）.Methods:A total of 106 elderly patients with middle and lower tibial fractures admitted to our hospital between August 2020 and September 2022 were randomly assigned to either a control group（53 cases）or a treatment group（53 cases）. The control group was treated with tibial intramedullary nail fixation；while the treatment group additionally received HBO pretreatment for three days before the surgery and HBO therapy for seven days following the surgery. The heart rates（HR）and mean arterial pressure（MAP）levels were measured in both groups before anesthesia（T1），before surgery（T2），30 minutes after surgery（T3），and two hours after surgery（T4），respectively. The visual analogue scale（VAS）scores and the mini-mental state examination（MMSE）scale scores of both groups were recorded on the 1st，3rd，and 7th days after surgery. The confusion assessment method for the ICU（CAM-ICU）scale was used to diagnose delirium in patients within seven days after surgery.Results:The differences in HR and MAP levels between the two groups at T2，T3，and T4 were statistically significant（all P<0.05）. The incidence of delirium seven days after surgery in the treatment group（5.66%）was significantly lower than that in the control group（22.64%）（ χ2=6.627， P=0.007）. The VAS scores of the treatment group were significantly lower than those of the control group on the 3rd and 7th days after surgery；while the MMSE scores were significantly higher than those of the control group（all P<0.05）. The serum IGF-1 levels of the treatment group were significantly lower than those of the control group on the 3rd and 7th days after surgery；while the MMP9 levels were significantly higher than those of the control group（all P<0.05）. Conclusion:Preoperative HBO therapy and continued HBO therapy after surgery may significantly reduce the incidence of postoperative delirium in elderly patients with middle and lower tibial fractures through regulating serum IGF-1 and MMP9.