Preoperative planning of the osteotomy. Lines a, b, c, d and e are drawn. Line a is the plane of the tibial plateau. Line b is the distal lateral axis of the tibial shaft (DTA). Line c is vertical to line a. It starts at point Z, that separates the anterior 1/5th and the posterior 4/5ths of the tibial plateau. Line d (the proximal tibial axis, PTA) starts from point Z with a posterior inclination of 7⁰ relative to line c. The tilt angle of the right tibial plateau (RT-angle) is formed by the intersection between the line a and line b (DTA). The true center of rotation and angulation (true-CORA, point trC) of the deformity is the intersection between line b (DTA) and line d (PTA). The CORA of the osteotomy (osteotomy-CORA, point otC) is placed on the dorsal tibial cortex, about 1 cm distal to the true-CORA. Line e is the plane of the osteotomy. The osteotomy starts 1 cm below the tibial tubercle (TT) and exits at the osteotomy-CORA (otC).