Objective:To study the morphologic features of the fusion site of proximal tibial epiphysis in normal adults and analyze its potential clinical value based on Mimics three-dimensional (3D) reconstruction.Methods:CT images of knee joint of 68 patients without obvious abnormalities of lower limbs were retrospectively analyzed in electronic database of our hospital from June 2020 to June 2021, including 41 males and 27 females. The mean age of the patients was 38.7±8.4 years (range, 25-55 years), and the mean body mass index (BMI) was 25.3±4.0 kg/m 2 (range, 18.75-41.8 kg/m 2). Mimics 3D reconstruction technique was used to reconstruct the 3D model of the proximal tibia and epiphyseal fusion site. The relationship between the surface area of epiphyseal fusion site and age and BMI was studied, and the changes of cortical thickness and density at epiphyseal fusion site were also explored. Results:The fusion site of adult epiphyseal reconstructed by Mimics 3D reconstruction is a complex wavy surface structure in 3D space. The surface area of the epiphyseal fusion site was 2,994.7±645.3 mm 2 (range, 1,704.0-4,650.0 mm 2) obtained by 3-Matic Research 12.0. The fusing area of male epiphysis was 3 269.3±533.9 mm 2 than that of female 2,577.6±578.7 mm 2, the difference was statistically significant ( t=5.06, P<0.001). However, there was no significant correlation between the epiphyseal fusion site surface area and age ( R2=0.02, P=0.268) and BMI ( R2=0.04, P=0.125). Mimics software was used to obtain the CT values of bone cortex at the epiphysis line and the distal end of the epiphysis line at 10 mm and 20 mm levels as 451.059±74.953 Hu, 1,018.412±125.732 Hu and 1,414.162±107.848 Hu, respectively. The thickness of bone cortex was 1.814±0.090 mm, 2.511±0.089 mm and 3.189±0.185 mm at 10 mm and 20 mm layers of epiphysis line and distal epiphysis line, respectively. Conclusion:In this study, Mimics 3D reconstruction technique was used to visualize the fusion site of the proximal tibial epiphysis in normal adults. The epiphyseal fusion site of adult is a undulating plate-like structure, and the cortical bone density of epiphyseal fusion site is low and thin, theoretically, it is easy to fracture under indirect violence.