Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration

Abstract

Background: Restoration of natural knee kinematics for a designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty (TKA). In different posterior-stabilized TKAs, there are wide variations in tibiofemoral surfaces and post-cam design. However, it is not known whether these design variations preserve natural knee kinematics. The purpose of this study was to determine the most appropriate tibiofemoral surface and post-cam designs to restore natural knee kinematics of the TKA.

Methods: A subject-specific finite element knee modal was used to evaluate tibiofemoral surface and post-cam design. Three different posts in convex, straight, and concave geometries were considered with a fixed circular cam design in this study. In addition, this post-cam design was applied to three different surface conformities for conforming, medial pivot, and subject anatomy mimetic tibiofemoral surfaces. We evaluated the femoral rollback, internal-external rotation, and quadriceps muscle force under a deep-knee-bend condition.

Results: The three different tibiofemoral conformities showed that the convex post provided the most natural-knee-like femoral rollback. This was also observed in internal rotation. In surface conformity, subject anatomy mimetic tibiofemoral surfaces showed the most natural -knee-like kinematics and quadriceps force.

Conclusions: This study confirmed that convex post design and subject anatomy mimetic tibiofemoral surfaces provided the most natural-knee-like kinematics. This study suggested that post-cam design and tibiofemoral surface conformity should be considered in conventional and customized TKA.

Keywords: Conformity; Finite element analysis; Patient-specific implant; Post-cam design; Total knee arthroplasty.

Fig. 1

3D FE knee joint model developed from imaging data used in this study

Fig. 2

Three different custom-designed cams in the tibial component

Fig. 3

Development of customized femoral component: (a) three patient-specific “J” curves in sagittal planes; (b) patient’s anatomic curves in coronal planes; (c) surface geometry for femoral component using the articulating curves

Fig. 4

Conventional and customized PS-TKAs with different TF joint conformity designs by applying the curvature radius ratio in the coronal, medial, and lateral planes

Fig. 5

Comparison of internal tibial rotation with previous study for validation of the TKA model

Fig. 6

Comparison of femoral rollback in (a) Conformed Customized PS-TKA, (b) Medial Pivot Customized PS-TKA, and (c) Anatomic Articular Surface Customized PS-TKA with regard to different cam designs in the tibial component and (d) straight post designed tibial component with regard to different conformity designs in the tibial component under deep-knee-bend

Fig. 7

Comparison of internal rotation in (a) Conformed Customized PS-TKA, (b) Medial Pivot Customized PS-TKA, and (c) Anatomic Articular Surface Customized PS-TKA with regard to different cam designs in the tibial component and (d) straight post designed tibial component with regard to different conformity designs in the tibial component under deep-knee-bend

Fig. 8

Comparison of quadriceps force in (a) Conformed Customized PS-TKA, (b) Medial Pivot Customized PS-TKA, and (c) Anatomic Articular Surface Customized PS-TKA with regard to different cam designs in the tibial component and (d) straight post designed tibial component with regard to different conformity designs in the tibial component under deep-knee-bend