Medial open wedge high tibial osteotomy: the effect of the cortical hinge on posterior tibial slope.

Background: High tibial osteotomy can affect the posterior tibial slope in the sagittal plane because of the triangular configuration of the proximal tibia. However, the effect of the location of cortical hinge on posterior tibial slope has not been previously described.

Hypothesis: Posterolateral location of the cortical hinge will increase posterior tibial slope after medial open wedge osteotomy, and lateral location of the cortical hinge will not affect the change of the posterior tibial slope.

Study Design: Controlled laboratory study.

Methods: We performed incomplete valgus open wedge osteotomy on 12 paired knees of 6 fresh-frozen human cadavers (age, 63.4 + or - 7.5 years) using an OrthoPilot navigation system. The left and right legs of each specimen were randomly assigned to a posterolateral (group A) or a lateral (group B) cortical hinge group. Changes in mean medial proximal tibial angle, posterior tibial slope, and opening wedge angle were measured and compared after surgery.

Results: In group A, mean medial proximal tibial angle changed from 84.37 degrees + or - 2.8 degrees to 93.48 degrees + or - 3.06 degrees (P = .028); mean posterior tibial slope increased significantly from 8.71 degrees + or - 0.81 degrees to 12.16 degrees + or - 0.84 degrees (P = .031); and mean wedge angle was 1.92 degrees + or - 0.46 degrees . In group B, mean medial proximal tibial angle changed from 82.98 degrees + or - 2.53 degrees to 90.89 degrees + or - 3.25 degrees (P = .027); mean posterior tibial slope changed from 9.19 degrees + or - 1.11 degrees to 9.78 degrees + or - 1.27 degrees (P = .029); and mean wedge angle was 7.25 degrees + or - 0.72 degrees .

Conclusion: The location of the intact cortical hinge affects the posterior tibia slope. During medial open wedge osteotomy, the change of posterior tibial slope was larger in the posterolateral than in the lateral cortical hinge group.

Clinical Relevance: To prevent the unintentional increase of the posterior tibial slope, special attention should be paid to locate the intact cortical hinge on the lateral, not the posterolateral, side of the tibia.