Summary

Increase in the posterior tibial slope was prevented with appropriate uni- or bi-planar osteotomy with a simple distraction at the most posterior gap.

Abstract

Background

The tibial slope usually increases after open wedge high tibial osteotomy (OWHTO), and this increase could be related to incomplete osteotomy of the posterolateral cortex. If incomplete osteotomy is performed at the posterolateral side, the opening gap is dominantly increased at the anterior side, leading to an unnecessary increase in the posterior slope. For a good natural gap ratio, appropriate osteotomy of the posterior cortex is important. However, to date, the most appropriate osteotomy length or ratio of the posterior cortex has not been accurately established.
Purpose/Hypothesis: We aimed to 1) determine the length of the osteotomy and opening gap at the anterior and posterior side, 2) compare between uni- and bi-planar osteotomy, and 3) evaluate the relationship between extent of the osteotomy and change of the posterior tibial slope. The hypothesis of this study were that 1) anterior cortical osteotomy would be larger in the uni-planar osteotomy, 2) gap ratio would be larger in the bi-planar osteotomy, and 3) maintenance of the slope would be closely related to the length of posterior cortical osteotomy.

Methods

A prospective comparative study of 24 uni-planar and 30 bi-planar osteotomies was performed. To evaluate the length of osteotomy, osteotomy lines of the anterior and posterior cortex were analyzed in the 3D surface models. For slope measurement, the intramedullary axis of the proximal tibia (slope P), posterior cortical line of the proximal tibia (slope C), and anterior cortical line of the proximal fibula (slope F) were used. Analysis of the changes in the posterior tibial slope was performed independently using a pre- and post-operative lateral plane radiograph.

Results

In the uni-planar osteotomy, ratio of the osteotomized length to the total cortical length aligned with the osteotomized plane were larger in the anterior cortex (0.91 in uni-planar vs 0.46 in bi-planar, p=0) and posterior cortex (0.97 in uni-planar vs 0.79 ratio in bi-planar, p=0). Further, the posterior tibial slope was maintained in both groups and the ratios between the anterior and posterior gap in both groups were 0.57 and 0.63 ratio, respectively: The maintenance of the slope was not related to any specific variables. Additionally, these phenomena did not differ between those who underwent uni- and bi-planar osteotomy.

Conclusion

Increase in the posterior tibial slope was prevented with appropriate uni- or bi-planar osteotomy with a simple distraction at the most posterior gap. However, in the uni-planar osteotomy, ratio of the osteotomized length to the total cortical length was larger in both anterior and posterior cortex.
Level of Evidence: Level of evidence, III, Case-Control study
Keywords: Proximal tibia, High tibial osteotomy, Slope, Osteotomy