Objective:To investigate the clinical value of thromboelastogram in early diagnosis of deep vein thrombosis (DVT) in patients undergoing free flap surgery of lower extremity.Methods:A retrospective study was conducted to analyze the 192 patients undergoing surgical repair of soft tissue defects at lower extremity with free anterolateral femoral flap at Department of Orthopaedics, Tongji Hospital from January 2018 to June 2022. There were 117 males and 75 females, with an age of (45.6±12.7) years and an area of skin defects ranging from 5 cm × 3 cm to 18 cm × 9 cm. The patients were divided into 2 groups according to whether DVT occurred on the first day after surgery. In the DVT group of 22 patients, there were 14 males and 8 females, with an age of (47.7±14.3) years; in the DVT-free group of 170 patients, there were 103 males and 67 females, with an age of (45.3±12.5) years. The 2 groups were compared in terms of reaction time, coagulation time, maximum amplitude and coagulation angle in the thromboelastogram. Diagram of receiver operating characteristic (ROC) curves was used to evaluate the predictive value of thromboelastography in assessing the risk of DVT after surgery.Results:The 2 groups were comparable because there was no significant difference in the baseline information or operation time between them ( P>0.05). The reaction time [(5.21±0.85) min] and coagulation time [(1.12±0.30) min] in the DVT group were significantly shorter than those in the DVT-free group [(6.48±0.06) min and (1.60±0.03) min], and the maximum amplitude [(71.45±1.17) mm] and coagulation angle [69.54° (64.59°, 76.64°) ] in the DVT group were significantly larger than those in the DVT-free group [(66.63±0.40) mm and 64.92°(54.11°, 74.21°)] (all P<0.05). The optimal cut-off points in the ROC diagram were 5.46 min at reaction time, 1.52 min at coagulation time, 72.31 mm at maximum amplitude and 59.89° at coagulation angle. The sensitivity and specificity of detecting DVT on the first day after surgery were 80.7% and 71.6%, respectively, according to the combination of the best cut-off points in the ROC diagram and all the indexes in the thromboelastogram. Conclusion:Thromboelastogram is of a great value for the diagnosis of lower extremity DVT, and of a positive significance for the prevention of serious complications after surgery in patients undergoing free flap surgery of lower extremity.