Influence of the posterior tibial slope on the flexion gap in total knee arthroplasty

Adjusting the joint gap length to be equal in both extension and flexion is an important issue in total knee arthroplasty (TKA). It is generally acknowledged that posterior tibial slope affects the flexion gap; however, the extent to which changes in the tibial slope angle directly affect the flexion gap remains unclear. This study aimed to clarify the influence of tibial slope changes on the flexion gap in cruciate-retaining (CR) or posterior-stabilizing (PS) TKA.

The flexion gap was measured using a tensor device with the femoral trial component in 20 cases each of CR- and PS-TKA. A wedge plate with a 5° inclination was placed on the tibial cut surface by switching its front–back direction to increase or decrease the tibial slope by 5°. The flexion gap after changing the tibial slope was compared to that of the neutral slope measured with a flat plate that had the same thickness as that of the wedge plate center.

When the tibial slope decreased or increased by 5°, the flexion gap decreased or increased by 1.9 ± 0.6 mm or 1.8 ± 0.4 mm, respectively, with CR-TKA and 1.2 ± 0.4 mm or 1.1 ± 0.3 mm, respectively, with PS-TKA.

The influence of changing the tibial slope by 5° on the flexion gap was approximately 2 mm with CR-TKA and 1 mm with PS-TKA.

This information is useful when considering the effect of manipulating the tibial slope on the flexion gap when performing CR- or PS-TKA.