Fig. 1

The method to calculate the fracture line angle (FLA) and depict the depression. a The FLA is determined by measuring the included angle between BF and major fracture line MN. B is the middle point of the posterior cruciate ligament’s insertion on the tibial plateau; F is the medial 1/3 point of the tibial tuberosity. BF is used as the reference line to determine the major FLA. b The depression zone is depicted with a certain gray value and transparency level. The red points at the border are the position with ≥2 mm depression, but not all the borders are of less than 2 mm of depression