Summary

.A three-dimensional finite element model (3D-FEM) of a patient who underwent OWHTO was created from MRI images, and the change in equivalent stress applied to the meniscus before and after surgery was examined. It was found that the maximum equivalent stress in the medial meniscus decreased after OWHTO.

Abstract

【Purpose】 Medial meniscus posterior root tear (MMPRT) causes knee osteoarthritis (KOA) by disrupting the hoop function of the meniscus. Recently, combined surgery with open wedge high tibial osteotomy (OWHTO) for repairing MMPRT is recommended to reduce the load on the repair site. In this study, we created a three-dimensional finite element model (3D-FEM) from magnetic resonance imaging (MRI) images of a patient who underwent OWHTO, and examined the change in equivalent stress applied to the regions of meniscus before and after surgery.

【Methods】The subject was a patient (60 years old, male, BMI: 27.4 kg/m2) who underwent unilateral OWHTO. 3D images were extracted from the MRI images using SYNAPSE VINCENT, and 3D-FEM was constructed using HyperMesh (Altair, HyperWorks). Then, CAE software (Swanson Analysis Systems, Inc.) was used for finite element analysis. As a constraint, the entire bottom surface of the meniscus was completely fixed to the tibia. The medial and lateral meniscus were divided into five regions; anterior, middle and posterior segments, anterior horn and posterior horn. Anterior and posterior horn was defined within 1cm from tibia insertion. The contact surfaces of the femur, cartilage, meniscus and tibia were fixed, and only the distal surface of the tibia was completely fixed. An axial pressure of 1150 N was applied from the proximal femur, and the maximum equivalent stress of each segment in the 3D-FEM model before and after surgery was calculated.

【Results】The maximum equivalent stress of the medial meniscus was 2.9MPa at the anterior horn, 13.2MPa at the anterior segment, 5.2MPa at the middle segment, 28.6MPa at the posterior segment, and 1.1MPa at the posterior horn before surgery, and 1.2MPa at the anterior root, 10.1MPa at the anterior segment, 7.8MPa at the middle segment, 15.5MPa at the posterior segment, and 0.9MPa at the posterior horn after surgery. The maximum equivalent stress of the posterior segment of the medial meniscus was reduced by 45.8% and that of the posterior horn by 16.2%, after surgery. The maximum equivalent stress of the lateral meniscus was 22.6MPa at the anterior segment, 10.5MPa at the middle segment, and 8.4MPa at the posterior segment before surgery, and 7.5MPa at the anterior segment, 10.0MPa at the middle segment, and 4.4MPa at the posterior segment after surgery.

【Discussion】 In the analysis using 3D-FEM, the maximum equivalent stress of the medial meniscus was reduced in all sections except the middle segment. Mechanical stress and shear force can cause degeneration and tearing of the posterior root of the medial meniscus. In this study, the maximum equivalent stress of the posterior horn of the medial meniscus decreased after OWHTO, and load reduction was achieved.

【Conclusion】Analysis using 3D-FEM created from MRI images demonstrated that the maximum equivalent stress of the medial meniscus posterior horn was reduced by 16.2% after OWHTO.