Pre-Planning of High Tibial Osteotomy: The Effect of Ligamentous Tissues (A Finite-Element experiment)

High tibial osteotomy (HTO) is a common surgical procedure for treatment of patients with varus malalignment. The success rate of the procedure is strongly dependent on the quality of correction. The purpose of this study was to simulate the HTO in a patient with varus deformity in order to explore the interactions between the wedge angle, the mechanical axis, and the knee joint configuration.
A finite-element model of the knee joint of a patient with varus deformity was developed. The geometry was obtained using the whole limb CT scans and the knee MR images. The bones were assumed as rigid bodies, the articular cartilage and the meniscus as elastic solids, and the ligaments as nonlinear springs. A 600N force was applied at the femoral head in the line of the mechanical axis and the resulting knee configuration was investigated. The HTO was simulated by insertion of wedges with different angles beneath the tibial plateau and application of the resulting alteration of the loading axis in the model.
The results indicated that the actual change of the mechanical axes was always smaller than was predicted by a geometric pre-planning approach that does not consider the effect of soft tissue on the post-operative configuration of the knee joint.
It was suggested that subject-specific models can improve the results of the HTO by simulating the operation before surgery and determining the optimal wedge angle that locates the mechanical axis in the middle of the knee.