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

Background: Medial tibial condylar fractures (MTCFs) are a rare but serious complication after uni-compartmental 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 degrees varus to 6 degrees valgus. Subsequently, we repeated the same procedure adding extended sagittal bone cuts of 2 degrees and 10 degrees 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. bThe extended sagittal bone cuts in the posterior tibial cortex increased the stresses further at these 3 sites. In the models with a 10 degrees extended sagittal one cut, the maximum principal stress on the posterior cortex increased as the tibial inclination changed from 6 degrees varus to 6 degrees 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. (C) 2016 Elsevier Inc. All rights reserved.