Three-dimensional relationships between secondary changes and selective osteotomy parameters for biplane medial open-wedge high tibial osteotomy

Abstract Purpose To assess the axial rotational change of distal tibia and posterior tibial slope (PTS) change after OWHTO in 3-D planes and to identify the causal relationship on the effect of variation in the posterior slope angle and rotational errors. Methods A total of 21 patients (23 knees) underwent OWHTO and were evaluated with 3D–CT before and after surgery. Medial proximal tibial angle in the coronal plane, PTS in the sagittal plane, and rotational axis in axial plane were evaluated and compared between pre- and post-operative 3D models constructed by applying reverse-engineering software. As a selective osteotomy parameter, hinge axis and gap ratio were measured in the postoperative 3D models Results The increasing tendency of internal rotation of the distal tibia after OWHTO was positively related to hinge axis (β = 0.730, p = 0.001, R2 = 0.546) and gap ratio (β = − 0.283, p = 0.001, R2 = 0.520), which also showed statistically significant linear correlations to PTS changes after multivariate regression analysis that controlled for the rotational change of the distal tibia (hinge axis: β = 0.443, p = 0.006; gap ratio: β = 0.144, p = 0.017). Conclusion Hinge axis more posterolaterally was related to a greater increase in internal rotation after biplane medial open-wedge HTO, and hinge axis and gap ratio were significant predictors of PTS change after rotational change was controlled for. Hinge axis has to be considered an important independent variable for limiting unintended axial rotation change as well as PTS change as secondary. Clinical relevance The relationship of the hinge axis with the rotational change and its influence to PTS change, acknowledged from by-product of the statistical analysis, might provide a deeper understanding of HTO, and should have constitutional effects on the development of HTO procedures and implants.