Varus malalignment combined with an increased posterior tibial slope (PTS) in the ACL deficient knee is a frequent pathology; yet, treatment for this condition remains challenging. The presented biplanar osteotomy technique allows to simultaneously address both components of malalignment in a single step. A detailed preoperative planning is best achieved by means of a digital planning software and constant intraoperative imaging is performed to verify the correction angle. A bony wedge is resected along with the extension osteotomy according to the preoperative planning and the medial-opening tibial osteotomy site is filled with bone allograft. Two bicortical lag screws are placed in anterior-posterior direction to secure the extension osteotomy, whereas a plate fixation is used for the medial-open osteotomy.