Quantifying the effect of hinge axis orientation on the posterior tibial slope angle during medial opening wedge high tibial osteotomy

Abstract

Introduction

Research has suggested that rotating a medial open wedge high tibial osteotomy hinge axis internally or externally can change the posterior tibial slope and may create abnormal loading patterns through the tibia.

Objectives

(1) To develop and validate a finite element model that estimates posterior tibial slope following a medial opening wedge high tibial osteotomy with a prescribed hinge axis; (2) use the model to evaluate the effect hinge axis rotation has on the posterior tibial slope and medial mechanical proximal tibia angle; and (3) quantify the effect of rotating the hinge axis on the stress and strain response within the anterior and posterior regions of the hinge.

Methods

Five tibia finite element models were reconstructed from computed tomography scans of 5 cadaveric specimens. Three different hinge axis rotations were tested (15° external rotation, neutral, and 15° internal rotation) in each of the 5 models and the resulting posterior tibial slope, stresses, and strains were analyzed.

Results

A 15° externally rotated hinge significantly increased the posterior tibial slope angle compared with the preoperative alignment. The 15° externally rotated hinge experienced greater stresses and strains in the posterior region of the hinge, while the 15° internally rotated hinge experienced higher stresses and strains in the anterior region of the hinge.

Conclusions

The orientation of the medial open wedge high tibial osteotomy hinge can be manipulated to alter the posterior tibial slope but that changes in the stresses can also occur and this should be considered in the presurgical planning phase to reduce the risk of complications (eg, lateral cortical fractures).