Elsevier

The Journal of Arthroplasty

Volume 31, Issue 9, September 2016, Pages 2025-2030
The Journal of Arthroplasty

Basic Science
The Valgus Inclination of the Tibial Component Increases the Risk of Medial Tibial Condylar Fractures in Unicompartmental Knee Arthroplasty

https://doi.org/10.1016/j.arth.2016.02.043Get rights and content

Abstract

Background

Medial tibial condylar fractures (MTCFs) are a rare but serious complication after unicompartmental knee arthroplasty. Although some surgical pitfalls have been reported for MTCFs, it is not clear whether the varus/valgus tibial inclination contributes to the risk of MTCFs.

Methods

We constructed a 3-dimensional finite elemental method model of the tibia with a medial component and assessed stress concentrations by changing the inclination from 6° varus to 6° valgus. Subsequently, we repeated the same procedure adding extended sagittal bone cuts of 2° and 10° in the posterior tibial cortex. Furthermore, we calculated the bone volume that supported the tibial component, which is considered to affect stress distribution in the medial tibial condyle.

Results

Stress concentrations were observed on the medial tibial metaphyseal cortices and on the anterior and posterior tibial cortices in the corner of cut surfaces in all models; moreover, the maximum principal stresses on the posterior cortex were larger than those on the anterior cortex. The extended sagittal bone cuts in the posterior tibial cortex increased the stresses further at these 3 sites. In the models with a 10° extended sagittal bone cut, the maximum principal stress on the posterior cortex increased as the tibial inclination changed from 6° varus to 6° valgus. The bone volume decreased as the inclination changed from varus to valgus.

Conclusion

In this finite element method, the risk of MTCFs increases with increasing valgus inclination of the tibial component and with increased extension of the sagittal cut in the posterior tibial cortex.

Section snippets

Methods

The present study was performed in accordance with a fully validated FEM model of the proximal tibia [10]. Digital 3-dimensional data of the left tibia (Sawbone fourth-generation composite tibia; Pacific Research Laboratories, Inc, Vashon, Washington) were used to construct FEM models. In each of the FEM models, 112,110 to 757,170 nodes were placed depending on calculating status of analysis. A model of the left UKA tibial component was created from a commercially available design, TRIBRID

Results

The stress distributions on the exterior proximal cortical surface of the tibia in each model are shown in Figure 4. In all 15 models, a larger area of von Mises stress concentration was observed on the medial tibial metaphyseal cortex, and relatively smaller areas of principal stress concentration were observed on the anterior and posterior cortices in the corner of cut surfaces.

On the medial tibial metaphyseal cortex, the von Mises stress increased for the 2° extended cut and furthermore for

Discussion

Fracture of the medial tibial condyle after UKA is a serious complication and may be associated to surgical technique. The fracture lines of MTCFs begin from the corner of the tibial bone cut surfaces and reach the medial tibial metaphyseal cortex 6, 7. In the present FEM study, stress concentrations were observed on the medial tibial metaphyseal cortex and the anterior and posterior tibial cortices in the corner of cut surfaces in all models. Thus, we believe that the model generated in this

Conclusions

We investigated the effect of the coronal alignment of the tibial component and the notching of the posterior cortex on the stress concentration of the tibial cortex in UKA. The valgus inclination of the tibial component with the extended sagittal bone cut increased remarkably the stress concentration on the medial tibial metaphyseal cortex and the posterior tibial cortex. Placement of the tibial component using a large valgus inclination may increase the risk of MTCFs.

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No external funding was provided for this study.

One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.02.043.

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