Implant design in total knee arthroplasty is a key factor for the recovery of function and mobility of the joint. However, there is a lack of knowledge on the complex relationship between design features and the biomechanical situation. The posterior inclination of the tibial plateau (tibial slope) has a known functional impact on knee joint kinematics. In the native knee it shows high inter-individual differences, which is inadequately considered in total knee arthroplasty. We investigated the effects of the separate and combined variation of the medial and lateral tibial slope on knee joint kinematics in an in vitro setup. Therefore, the medial and lateral inserts of a knee implant were parameterised and the initial slope was gradually varied to +4°, +2° (posterior) and -2°, -4° (anterior). The variations were manufactured by using polymer based rapid prototyping. The effects on semi-active tibiofemoral and patellofemoral kinematics were studied and quantified in terms of the Root Mean Square Error and Pearson’s Correlation coefficient. The overall largest effect was observed on tibiofemoral internal-external rotation by the variation of the lateral insert. The anterior-posterior translation was predominantly effected by the combined variation. Nevertheless, the lateral variation showed greater influence than medial. In contrast, changes in patellofemoral kinematics were small. Our findings suggest that in total knee arthroplasty the lateral tibial slope has a larger functional effect than the medial tibial slope. Thus, functional design optimization should focus on the lateral insert.
© 2018 the author(s), published by Walter de Gruyter Berlin/Boston
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