Abstract:[Objective] To investigate the accuracy and efficacy of 3D printed patient-specific instrumented (PSI) high tibial osteotomy (HTO) for medial knee osteoarthritis (KOA) , by comparing with traditional HTO . [Methods] A retrospective study was conducted on 35 pa- tients who underwent medial open wedge HTO for medial KOA in our department from January 2019 to February 2021. Based on preopera- tive doctor-patient communication, 17 patients received 3D printed PSI HTO (the 3D group), while the remaining 18 patients underwent the traditional HTO (the traditional group) . The documents regarding to perioperative period, follow-up and radiographs were compared be- tween the two groups. [Results] All patients in both groups had the surgical procedures performed smoothly. The 3D group proved signifi- cantly superior to the traditional group in terms of total length of surgical incision, operative time, blood loss, fluoroscopy times, walking time and postoperative hospital stay (P<0.05) , whereas without significant differences between them in the occurrence of early complica- tions (P>0.05) . All the patients were followed up from 12 to 18 months with a mean of (14.34±2.03) months. The 3D group resumed full weight-bearing activity slightly earlier than the traditional group, despite of no statistically significant difference between them (P>0.05) . The VAS and HSS scores and knee extension range of motion (ROM) in both groups significantly improved over time (P<0.05) , which were not statistically significant between them at any matching time point (P>0.05) . Radiographically, the weight bearing line ratio (WBLR) , me- dial proximal tibial angle (MPTA) and Kellgren- Lawrence (K- L) classification significantly improved, whereas the posterior tibial slope (PTS) remained unchanged in both groups postoperatively compared with those preoperatively (P<0.05) . At 6 and 12 months after surgery, the 3D group was significantly superior to the traditional group in terms of WBLR and MPTA (P<0.05) , whereas no a statistical difference in K-L grade between them (P>0.05) . By the time of latest follow-up, bony healing achieved in all the patients, which was not significantly different between the two groups (P>0.05) . [Conclusion] Compared with conventional osteotomy, 3D printed PSI OWHTO has advantages of fewer intraoperative fluoroscopy, shorter operative time and more accurate alignment of lower extremity correction.