Abstract： Objective:To investigate the value of preoperative MRI measurements of hamstring (semitendinosus+gracilis) tendon cross-sectional area in predicting intraoperative graft diameter for anterior cruciate ligament reconstruction (ACLR).Methods:A total of 265 preoperative MRI were retrospectively collected in the Third Affiliated Hospital of Southern Medical University from January 2013 to August 2020 for patients who underwent single-bundle ACLR of hamstring tendon. Patients were divided into a graft diameter≥8 mm group (129 patients) and a graft diameter<8 mm group (136 patients) according to intraoperative graft diameter. The cross-sectional areas of the semitendinosus and gracilis tendons were measured at the largest level of the femoral condyle on preoperative MRI cross-sectional images, and the two were summed to obtain the cross-sectional area of the hamstring tendon. The independent samples t-test was used to compare the differences in the cross-sectional area of each tendon between the graft diameter≥8 mm group and the graft diameter<8 mm group. The Spearman correlation analysis was used to assess the correlation between tendon cross-sectional area and intraoperative graft diameter. Multi-factor logistic regression analysis was used to screen the influence of tendon cross-sectional area on intraoperative graft diameter. The effectiveness of intraoperative graft diameter≥8 mm was assessed by plotting the receiver operating characteristic curves. Results:Intraoperative measurement of graft diameter was 7.5 (7.5, 8.0) mm. The cross-sectional area of the popliteal tendon was (21.4±4.6) mm 2 in the graft diameter≥8 mm group and (15.6±3.7) mm 2 in the graft diameter<8 mm group. Statistically significant differences were found in the cross-sectional areas of the semitendinosus, soleus and hamstring tendons between the graft diameter≥8 mm group and graft diameter<8 mm group ( t=-10.26, -10.29, -11.47, P<0.001). Intraoperative graft diameter was positively correlated with the cross-sectional area of the semitendinosus, gracilis, and hamstring, with correlation coefficients of 0.57 ( P<0.001), 0.58 ( P<0.001), and 0.62 ( P<0.001), respectively. Multi-factor logistic regression showed that popliteal tendon cross-sectional area was a predictor of intraoperative graft diameter (OR=1.45, 95%CI 1.32-1.59, P<0.001). The area under the curve for popliteal tendon cross-sectional area to predict intraoperative graft diameter≥8 mm was 0.838 (95%CI 0.792-0.885), with a critical value of 20.0 mm 2, a sensitivity of 0.581, and a specificity of 0.941. Conclusion:The measurement of the cross-sectional area of the hamstring muscle on preoperative MRI can predict the diameter of the autologous hamstring graft of ACLR.