Accurate and reproducible coronal and sagittal alignment correction using patient-specific instrumentation in medial opening wedge high tibial osteotomy

OBJECTIVES: This study aimed to evaluate the accuracy of a newly developed patient-specific instrumentation (PSI) system in both the coronal and sagittal planes, with a particular focus on the reproducibility of the planned posterior tibial slope angle (PTSA). METHODS: Sixty-eight patients (55 males and 13 females; mean age: 47.6 ± 6.0 years) who underwent PSI-assisted medial opening wedge high tibial osteotomy (MOWHTO) were retrospectively analyzed. The hip-knee-ankle angle (HKA) was measured on long-leg standing radiographs and PTSA on lateral radiographs, pre-operatively and at 6 months postoperatively. Coronal correction accuracy was assessed as the difference between planned and achieved HKA values (overall error). Sagittal correction error was defined as the difference between the planned and achieved changes in the PTSA. This error was evaluated within each planned PTSA strategy (no change, PTSA increase, and PTSA reduction) using a one-sample Wilcoxon signed-rank test. RESULTS: The mean overall error in coronal alignment was 0.0° ± 1.6° (range: -4.9°-3.9°), with 55 of 68 cases (81%) falling within the ±2° acceptable range. In the sagittal plane, the mean change in the PTSA was 0.2° ± 1.5° (range: -3.7°-4.9°), and the mean sagittal correction error was 0.6° ± 1.7° (range: -3.0°-5.8°), with 55 of 68 cases (81%) within ±2°. Among the three subgroups, only the PTSA reduction group showed a statistically significant deviation from zero (p < 0.001). CONCLUSION: The newly developed PSI workflow demonstrated high accuracy in both coronal and sagittal alignment correction and reliably reproduced the intended posterior tibial slope in most cases. However, planned reductions in the PTSA were less consistently achieved, indicating that slope-decreasing corrections are less reliable and reflect the technical demands of surgical execution, even when using PSI-assisted MOWHTO. LEVEL OF EVIDENCE: level of evidence was IV.