How to avoid unintended increase of posterior slope in navigation-assisted open-wedge high tibial osteotomy

Open-wedge high tibial osteotomy (HTO) with navigation provides accurate axial alignment correction in the frontal plane but can cause an unintended increase of the proximal tibial slope. This study examined the plausibility of preserving the original posterior slope of the proximal tibia during navigation-assisted open-wedge HTO. Three-dimensional virtual HTO preserving the original posterior slope was simulated and the opening gaps measured. Forty cases of navigation-assisted open HTO for unicompartmental osteoarthritis were performed maintaining an anterior opening gap measuring 67% of the posterior gap. The posterior slope of the proximal tibia was compared before and after surgery. In virtual surgery, a ratio of 0.67 between the anterior and posterior opening gap was needed to maintain the original slope. In navigation-assisted HTO, the mechanical axis was corrected to 2.9 degrees valgus (range, 0.5 degree-6.2 degrees) with fewer outliers (12.5%), and the posterior slope was maintained. The posterior slope was 7.9 degrees +/- 2.3 degrees preoperatively and 8.3 degrees +/- 2.8 degrees postoperatively (P > .05). The normal tibial posterior slope can be maintained if the anterior opening gap is approximately 67% of the posterior opening gap during the navigation-assisted HTO.