The accurate reduction of tibial plateau malunions can be challenging without guidance. In this work, we report on a novel technique that combines 3D computer-assisted planning with patient-specific surgical guides for improving reliability and accuracy of complex intra-articular corrective osteotomies. Preoperative planning based on 3D bone models was performed to simulate fragment mobilization and reduction in three cases. Surgical implementation of the preoperative plan using patient-specific cutting and reduction guides were evaluated, benefits and limitations of the approach were identified and discussed. The preliminary results are encouraging and show that complex intra-articular corrective osteotomies can be accurately performed with this technique. For selective patients with complex mal-unions around the tibia plateau this method might be an attractive option, with the potential to facilitate the most accurate correction possible.