Figure 2: The proper entry point for the femur and the insertion of the IM rod (a) on a 3-D femur model. The line 1 connecting the two points represents the anatomic axis. The point 3 at which the axis intersected the distal articular surface was determined to be the proper entry point. (b) The AIN, the center of the femoral trochlear groove, and the trochlear point were shown on the distal articular surface. (c) The offset of the point 3 to AIN was measured in two directions. The epicondylar axis was identified by two points in 3-D model and projected in this cross section. (d) The IM rods were in the femoral canal in different directions. IM: Intramedullary; AIN: Apex of the intercondylar notch; 3-D: Three dimensional; Points 1&2: at 10 cm and 20 cm proximal to the knee joint surface in the femur.