Summary

In this study, the contact stress on the lateral tibial plateau was increased by the fibular osteotomy. There is possibility, the simple fibular osteotomy can improve the osteoarthritis knee function.

Abstract

Introduction

High tibial osteotomy is a commonly used method to treat knee varus deformities due to osteoarthritis of the knee.
In the present study, a knee joint model was created by matching images from CT and MRI for a healthy knee to reproduce the bones, cartilage and meniscus, and evaluated the changes the contact stress with and without the fibular using a 3D finite element method.
Subjects and Methods
CT and MRI were performed for a healthy knee, and bone regions on images from MRI were registered for the femur and tibia, using the positions of bones on CT as a reference Analysis was performed using Mechanical Finder software (version 7.0, extended edition; Research Center of Computational Mechanics, Tokyo, Japan).
Next, bone axes of the femur and tibia were rotated 5 degree each in the adduction direction, and changes in corresponding stress on the tibiofemoral cartilage were examined(with and without the fibular).
Load conditions were set envisioning a person weighing 600 N standing on one leg, then tripling that load to 1,800 N. For load conditions, the lower end of the tibia was completely immobilized, assuming a uniform load of 1,800 N from the head of the femur. Material properties were set as follows: for bone, Young’s modulus was set at 0.2 and Poisson’s ratio at 0.3; for the meniscus, Young’s modulus was set at 0.059 and Poisson’s ratio at 0.49; and for cartilage, Young’s modulus was set at 0.005 and Poisson’s ratio at 0.46.

Result
As the varus increase, the stress was increased at the anteromedial area of the medial condyle of femur, and at the posteromedial area of the medial condyle of tibia. And by the fibular osteotomy the contact stress on the lateral tibial plateau was increased. The average stress on the lateral tibial plateau were 0.67MPa/mm2 (with the fibular at 0 degree), 0.72MPa/ mm2 (without the fibular at 0 degree), 0.2MPa/mm2 (with the fibular at 5 degree), 0.3 MPa/mm2 (without the fibular at 5 degree), 0.04 MPa/mm2 (with fibular at 10 degree), 0.04 MPa/mm2 (without fibular at 10 degree), respectively.

Discussion

In this study, the contact stress on the lateral tibial plateau was increased by the fibular osteotomy. There is possibility, the simple fibular osteotomy can improve the osteoarthritis knee function. Moreover, analysis in which MRI and CT images are matched is believed to provide a more accurate shape for the soft tissues than analysis using only CT, while analysis matching the two types of images is thought to result in more accurate bone morphology than analysis of images from MRI alone.