62 patients with medial knee osteoarthritis or osteonecrosis who were scheduled for opening-wedge high tibial osteotomy were randomized to the procedure using either combined CT-based and image-free navigation technology or conventional techniques to create the correction angle. The primary purpose of this study was to evaluate if navigation allowed for fewer coronal and sagittal outliers on postoperative computed tomography (CT). No significant difference at 2 years was noted between groups in the incidence of femorotibial angle outliers or in the clinical outcome measures assessed. However, the conventional group had a significantly greater number of tibial posterior slope outliers, and a significantly greater number of outliers in both planes.