This study is a randomized clinical trial that will compare two surgical techniques for patients with knee osteoarthritis and varus deformity who are candidates for medial opening wedge high tibial osteotomy. The goal is to evaluate whether using patient-specific 3D-printed surgical guides improves the accuracy of the bone cut compared with the conventional technique performed with anatomical landmarks and fluoroscopy. A total of 50 adult patients will be randomly assigned to one of two groups: conventional osteotomy or osteotomy assisted by patient-specific instrumentation (PSI). The main outcome is the accuracy of the osteotomy cut, measured by comparing preoperative planning with the postoperative CT scan. Secondary outcomes include leg alignment, surgical time, radiation exposure, complications, and functional recovery assessed with validated questionnaires (KOOS, WOMAC, IKDC, EQ-5D) and gait analysis using depth cameras. Patients will be followed for up to 12 months after surgery to evaluate clinical and radiological outcomes.