The aim of our study is to determine the variation of the angle of tibial osteotomy by internal opening in genu varum, as well as to analyse mathemathically the modification that must be made to the orientation of the upper tibial epyphisis when the osteotomy associates to the frontal correction a modification in the sagittal plane.this study leads to the realization of tables which can be used in partice in the implementation of the tibial osteotomies Our support software surgery using a new equation by which this program gives us precisely the entry point of the spindle on the medial cortex which direction to take, on the corner of the outer cortex osteotomy and the angle of correction needed to be made during the surgical procedure on a 2D plane and this is tailored to each patient.