Background

Tibial slope and its effect on cruciate ligament strain is increasingly appreciated. A prior systematic review demonstrated that medial opening wedge proximal tibia osteotomies have a tendency to increase the posterior tibial slope by 2 degrees.

Methods

Proximal tibia osteotomies were performed on 10 fresh frozen cadaveric knees using a commercially available guide to generate a medial opening wedge osteotomy with a purely lateral hinge. Coronal plane correction was performed using both 5mm and 10mm trapezoidal wedged osteotomy plates. Techniques that maximized the posterior to anterior gap ratio were done to minimize the effect on tibial slope. These included posterior plate placement, a trapezoidal, sloped plate, and forced knee extension during plate fixation to help close the anterior gap. Anterior and posterior gap widths were measured during each state. Medial proximal tibia angle and posterior tibial slope were measured pre-osteotomy and after both 5mm and 10mm wedged implants using anteroposterior and lateral standard fluoroscopic images. Three independent observers performed all radiographic measurements and intraclass correlation coefficients were calculated.

Results

The 5mm and 10mm trapezoidal wedged osteotomy plates increased the medial proximal tibia angle by a mean of 3.5 and 7 degrees, respectively. The 5mm and 10mm trapezoidal wedged osteotomy plates decreased the posterior tibial slope by a mean of 1.0 and 0.6 degrees, respectively. The mean gap ratio percentage of the 5mm and 10mm trapezoidal wedged osteotomy plates was 67% and 70%, respectively. Good intraobserver reliability was found for both the medial proximal tibia angle (ICC = 0.897, [0.821-0.946]) and the tibial slope measurements (ICC = 0.761,[0.672-0.826]).

Conclusions

Contrary to prior evidence, medial opening wedge proximal tibia osteotomies can maintain tibial slope irrespective of coronal correction by utilizing a lateral hinge, placing a trapezoidal plate posteriorly, and fixation during forced knee extension. With careful consideration of the importance of tibial slope, medial opening wedge proximal tibia osteotomies do not increase posterior slope.