A posterior tibial slope angle over 12 degrees is critical to epiphyseal fracture of the proximal tibia: Three-dimensional finite element analysis

Introduction: The effects of the proximal tibial slope angle on the proximal tibial epiphysis remain unknown. To elucidate those effects, we investigated the strain distribution in proximal tibial epiphysis with different proximal tibial slope angles and proximal tibial epiphysis closure periods using finite element analysis. Materials and methods: The finite element models of the proximal tibia were reconstructed from CT images and consisted of cancellous/cortical bone and epiphyseal plate. The variations in proximal tibial slope angle (range: 6–16°) and four closure variations in proximal tibial epiphysis (open, semi-open, semi-closed, and closed) were prepared. The loading force on the medial and lateral joint surface, and the tensile force by the patellar tendon were applied to the models, and the distal area of the tibia was fixed. The ratio of the equivalent strain in semi-open/semi-closed proximal tibial epiphysis to the strain in open proximal tibial epiphysis on different proximal tibial slope angles were calculated. Results: The strain ratio between the semi-open/semi-closed and open proximal tibial epiphysis models indicated significant differences between 6 or 8° of proximal tibial slope angle and 12, 14, and 16° of proximal tibial slope angle models. In the increased proximal tibial slope angle model, a hoop-shaped strain in the closing proximal tibial epiphysis was found, and the maximum strain was found in the tibial tubercle. Discussion: During epiphyseal closure, adolescents with an increased proximal tibial slope angle over 12° are significantly at risk for suffering from proximal tibial epiphyseal fractures compared with those under 10°.