Analysis of the distribution of mechanical load on the plate and lateral hinge of a valgus-producing open wedge high tibial osteotomy during weight-bearing by simulating consolidation. Finite element study

Introduction: High tibial osteotomy (HTO) is indicated for managing isolated medial knee osteoarthritis in a young patient with a metaphyseal deformity of the proximal tibia. In a medial open-wedge HTO, maintaining the integrity of the hinge is crucial for consolidation and preservation of the correction. Based on a validated model and preliminary results, the objective of this work was to measure and monitor the distribution of mechanical load on a locking fixation plate and the lateral hinge of an HTO using a finite element (FE) model during different phases of consolidation evolution, simulating single leg weightbearing.

Hypothesis: The working hypothesis was that with increasing consolidation, the stresses significantly decrease on both the plate and the lateral hinge, but with greater magnitudes on the plate and approaching zero on the hinge.

Materials and methods: A validated numerical model of a high tibial osteotomy (HTO) fixed with a locking plate on a real proximal tibial geometry (using Autodesk Fusion 360 and Altair HyperWorks software) was used. An axial load equivalent to one body weight was applied. Five scenarios were considered, resulting in five different models by varying, in the FE model, the Young's modulus of the trabecular and cortical bone, which allows for simulating the evolution of consolidation. Consolidation scenarios were tested by varying the mechanical properties of the HTO gap filling: 25% of normal bone properties, then 50%, 75%, and finally 100%, which is hypothetically considered as remodeled bone. The primary outcome measure was the maximum stress value in the areas of interest (Von Mises stresses, in MPa), specifically at the plate and lateral hinge.

Results: The decrease (in %) is major as early as the simulation of 25% consolidation in both areas of interest: a reduction of 91% on the plate and 93% on the hinge. The reduction in absorbed stresses continues in both areas, but with a more pronounced decrease on the plate. It is noteworthy that from 50% consolidation, under these experimental conditions, stresses remain comparable on the hinge, especially between 75% and 100% consolidation.

Discussion: The hypothesis is confirmed with a more marked decrease on the plate and approaching zero on the hinge, which seems logical in a consolidation process. Comparison with the literature is challenging, as only one finite element study has analyzed the influence of consolidation on the stresses absorbed by an HTO plate, but with different consolidation thresholds and without studying the hinge. This study has limitations: the model construction conditions, it is a finite element computer study, and the weight-bearing simulation for this study was static, which does not address the distribution of stresses during walking, this model is defined for a given valgus HTO plate and a specific opening and does not allow for extrapolation to distal femur opening osteotomies nor in clinical practice.

Conclusion: The hypothesis is confirmed; however, further studies are needed to validate these numerical results: an experimental part on instrumented cadaveric bone and comparative studies of fixation plates are necessary.

Level of evidence: V; expert opinion, controlled laboratory study.