Purpose: Implantation of prosthetic tibio-femoral components in hyperextension is a well-established and effective procedure, but whether prosthetic orientation in the sagittal plane has any effects on the postoperative kinematics remains unclear. The purpose of this study is to explore how the aforementioned hyperextension affects knee kinematics.
Methods: Validated computational dynamic TKA models were established. Based on representative literatures and actual operation specifications, femoral and tibial components were assembled with 0° or 5° of hyperextension. Dynamic data, including the timing of cam-post engagement, anterioposterior femoral translation and tibial axial rotation coupling with knee flexion, were recorded for analysis.
Results: 5° of femoral component hyperextension delayed cam-post engagement by an angle of 2°. Nevertheless, a 5° posterior slope of the tibial component resulted in a 38° delay in engagement. Comparing this with the femoral component at the same angle of hyperextension, the tibial component could more evidently assist in the prevention of paradoxical femoral anterior translation and the promotion of tibial internal rotation through early flexion.
Conclusion: Tibio-femoral components in hyperextension did significantly alter postoperative kinematics, especially for the tibial component. These results suggest that the degree of tibial posterior slope cutting should be more highly scrutinized intraoperatively.
Level of evidence: II.