Abstract
Introduction
Although total knee replacement became a widespread procedure for the purpose of knee reconstruction, osteotomies around the knee were regularly performed. Total knee arthroplasty should be performed for advanced arthritis of the knee. With the advent of biplanar open wedge high tibial osteotomy (HTO) combined with locking plate fixation, HTO has been expanded and its surgical outcome has been improved in recent years. However, post-operative joint-line obliquity has been raised as a concern with this procedure, which may affect the outcome especially in the knees with severe varus deformity. Hence the purpose of this study is to analyze the compression and shear stresses in the knee cartilage with joint line obliquity after HTO.
Methods
Using a three-dimensional computer aided design software, the digital knee model with soft tissues was developed. The geometrical bone data used in this study were derived from commercially available human bone digital anatomy media (3972 and 3976, Pacific Research Laboratories, Inc., WA, USA). The three-dimensional knee model was transferred to finite element model. Material properties of the soft tissues and bones were derived from previous studies. The loading condition was adjusted to the load during a single-leg stance of the gait cycle, which resulted in an axial compressive load of 1200 N. Two different conditions were subjected to the analysis: normal alignment and joint-line obliquity after HTO. For the normal alignment, a static force of 1200 N was applied along the mechanical axis. For the joint-line obliquity models, a single force of 1200 N was applied rotating force directions in the frontal plane from the normal direction by 2.5º, 5º, 7.5º, and 10º, respectively.
Results
The maximum values of the axial stresses in the cartilages for the normal condition showed almost same values in medial and lateral compartments. In the joint-line obliquity models, the maximum axial stress values in the medial compartment did not exhibit substantial change up to the level of 7.5º obliquity, while a rise in maximum stress value was observed for the model with 10º obliquity. The shear stress showed a different tendency. In the joint-line obliquity models, a steep rise of laterally directed shear stress in the medial compartment was observed for models with obliquity of 5º or more.
Discussion
The shear stress in the medial cartilage increased to almost twice as high as the normal knee level for the joint- line obliquity model with an inclination of 5º. The maximum shear stress values increased in accordance with the obliquity angle. The elevated stress could be deleterious to the cartilage. In such large amount of correction by tibial osteotomy leads to unfavorable mechanical environment in the knee. For those severe situations, double-level osteotomy, which retains anatomical knee joint line by simultaneous femoral and tibial osteotomies, should be considered to correct the joint-line obliquity.
