Accurate correction with a novel patient-specific instrument for medial opening wedge high tibial osteotomy

Introduction: Patient-specific instruments (PSIs) have been introduced to enhance the accuracy of medial opening wedge high tibial osteotomy (MOWHTO). This study aimed to evaluate the accuracy of a newly developed PSI and its impact on postoperative clinical outcomes. Methods: Forty patients with varus alignment who underwent MOWHTO using the newly developed PSI were retrospectively analyzed for accuracy of correction. Radiographic evaluations, including hip-knee-ankle angle (HKA) and medial proximal tibial angle (MPTA) were performed using long-leg standing radiographs preoperatively and at 6 months postoperatively. Overall error was defined as the difference between the planned and achieved HKA (ΔHKA), while surgical error was defined as the difference between the planned and achieved MPTA (ΔMPTA). Planning error was defined as the difference between overall error and surgical error. For each type of error, positive values indicated over-correction, while negative values indicated under-correction. Knee Injury and Osteoarthritis Outcome Score (KOOS) data were collected and compared between preoperative and 12-month postoperative assessments. Results: The mean planned HKA was 182.4° ​± ​0.3°, and the achieved HKA was 182.6° ​± ​1.5° (p ​= ​0.382). The mean planned MPTA was 93.1° ​± ​1.9°, and the achieved MPTA was 92.8° ​± ​1.9° (p ​= ​0.358). The overall error was 0.2° ​± ​1.5° (38% under-correction and 62% over-correction). Surgical error (ΔMPTA) averaged −0.3° ​± ​1.1° (55% under-correction and 45% over-correction), while planning error averaged 0.6° ​± ​1.1° (30% under-correction and 70% over-correction). All KOOS subscales showed a statistically significant improvement at 12 months postoperatively compared to preoperative scores (p ​< ​0.001). Conclusion: The newly developed PSI workflow proved to be an accurate method for planning and performing MOWHTO. While overall error was low, the observed tendencies for surgical under-correction and planning over-correction highlight the need for careful consideration of these factors to optimize outcomes in the future. Level of evidence: Level IV, Retrospective Case Series.