# Geometrical Planning of the Medial Opening Wedge High Tibial Osteotomy--An Experimental Approach
## 4 Discussion  
The geometric planning of the OWHTO in general and the optimal position of the intersection point between the medial-lateral articular line and the corrected mechanical axis are approached in literature by performing preoperative and postoperative evaluations. The preoperative evaluations are usually performed through 3D modeling and CAE (computer aided engineering) simulations and seek the optimization, from a geometric point of view, of the geometrical parameters that characterize the correction (CORA, initiation point of the cut of the osteotomy plane, correction angle) [29], as well as the optimization of the stability of the assembly consisting in the tibia--on which the OWHTO was performed, and the TomoFix osteosynthesis plate [30; 31; 32]. A preoperative method can also consist of synthesizing clinical trials as presented in [21], as previous experiences regarding the evolution and the stability of the intervention can offer clues for optimizing the geometrical planning of the surgery. Postoperative experimental evaluations, regarding the stability of the joint on which the surgery occurred, were performed less frequently because they present a series of limitations. The most important one consists in the fact that the experimental tries cannot be performed 'in vivo' on human bones, thus it is necessary to perform the surgery on bovine juvenile bones that have a very similar mechanical behavior. Despite these limitations, the fact that the evaluations are actually performed by using experimental methods on a real bovine bone-TomoFix plate assembly, they can provide a better indication of the surgical outcome, as they provide actual feedback on the behavior of such an assembly. A very important element in this sense is the fact that the bovine bone used has a heterogeneous structure (cortical and spongy), similar to human bone. Figure 12: Variations of the minor strain \(\epsilon_{2}\) (modulus values) during medial and offset loading (Fujisawa point). The research carried out in the present paper is considered to contribute to the optimization of the geometric planning of the medial opening wedge high tibial osteotomy. The experimental results are a considerable argument in this regard. The results obtained in the experiments provide consistent information on the choice of the optimal position of the intersection point between the medial-lateral articular line and the corrected mechanical axis. The variations of the force relative to the deformation shown in Figures 6 and 7 reveal a better stability of the system in the case of the intersection at the Fujisawa point, resulting in a displacement smaller by almost one millimeter compared to the midpoint of the joint. The parabolic variation between force and deformation in the case of the Fujisawa point also indicates a better load-bearing capacity and--as can be seen from the graph for high value forces (700-1000 N)--the increase in the displacements is small (approximately 0.23 mm). In the case of the other loads, at the same range of variation of the force, the increase in the displacements is 4 times higher. The analysis of the local strains and displacements leads to similar findings. It is easily noticed that the highest stresses in terms of mechanical strength occur when the stress is closer to the middle of the tibial plateau, both strains (major and minor) doubling their values compared to the offset loading (in Fujisawa point) under the conditions of the same 1000 N load. In both medial and offset (Fujisawa point) loadings, the maximum values of the main and secondary strains appear in the hinge area of the OWHTO. The progressive evaluation of the major and minor strains during medial and offset loading corresponding to a stroke of 25% (a), 50% (b), 75% (c), and 100% (d) of the total loading stroke is important, taking into account the fact that the load in the knee is variable while walking. Another conclusion is that an overcorrection of the mechanical axis is beneficial and gives better stability in all four stages of loading.