Summary

Thickness of the posterolateral bony bridge was smaller compared to the observed thickness on the AP radiograph image that is routinely used for the follow up.

Abstract

Background

Most osteotomies of the open wedge high tibial osteotomy (OWHTO) are started from the 3-4 cm below portion of the anteromedial aspect of the proximal tibia along the natural tibial slope as similar as possible and end around just above portion of the proximal tibiofibular joint. Anatomically, lateral tibial plateau shows convexity at the central portion on the sagittal plane. However, abrupt down slope occurs at the posterior part of the posterolateral (PL) aspect of the lateral tibial plateau. It could imply that bony bridge of the PL side would be smaller than that of the anterolateral or central area of the around lateral hinge.

Hypothesis

The hypotheses of this study were 1) the thickness of the bony bridge that measured on the plain AP radiograph would be larger than that of the 3D CT images, 2) the thickness would be smaller if osteotomy is started more distally, osteotomy slope is increased on the coronal plane, or reverse slope occurs on the sagittal plane, and 3) biplanar osteotomy would show larger bony bridge.

Methods

From 2012 to 2014, a prospective comparative study was performed with 30 patients who received uniplanar osteotomy (Group I) and 35 patients who received biplanar osteotomy (Group II). For measurement of the proximal wedge, postoperative AP radiograph and 3D CT images were used. In the AP radiograph, medial and lateral bony bridge thicknesses were measured. In the 3D CT, the anterior and posterior images parallel to the coronal plane were selected for the evaluation. Coronal osteotomy slope was measured with the anterior image of the 3D CT scan. Sagittal osteotomy slope was measured with the sagittal section of the CT scan.

Results

Differences between the lateral bony bridge thicknesses measured in AP radiograph and the posterolateral posterolateral bony bridge thicknesses measured in 3D CT were statistically significant in both groups. The coronal osteotomy slopes showed negative correlation with statistical significance in the biplanar osteotomy group (correlation coefficient: -0.31 (n.s.) in the uniplanar and -0.45 (p<0.01) in the biplanar). Differences of the sagittal osteotomy slope from the native tibial slope showed negative correlation in the biplanar osteotomy group (correlation coefficient: -0.38 (n.s.) in the uniplanar and -0.46 (p=0.01) in the biplanar).

Conclusion

Thickness of the posterolateral bony bridge was smaller compared to the observed thickness on the AP radiograph image that is routinely used for the follow up. The thickness would be getting smaller if osteotomy is performed with an abrupt angle on the coronal plane and reverse slope on the sagittal plane. Therefore, osteotomy with abrupt angle on the coronal plane and reverse slope on the sagittal plane should be avoided for the proper thickness of the posterolateral bony bridge.
Level of Evidence: Level III
Keywords: Proximal tibia, High tibial osteotomy, Bony wedge, Thickness