Three-dimensional kinematics during deep-flexion kneeling in mobile-bearing total knee arthroplasty.

We performed an in vivo radiographic analysis of tibiofemoral and polyethylene (PE) insert motions during weight-bearing kneeling beyond 120° of flexion in one high-flexion knee arthroplasty design to determine if kinematics changed over time and if axial rotation occur between the PE insert and the tibial baseplate. Twenty knees implanted with a posterior-stabilized rotating-platform (RP) knee arthroplasty were postoperatively evaluated at 3, 6, and 12 months. The averaged flexion angles were 122°, 129°, and 131° at 3, 6, and 12 months, respectively, showing that the improvement of flexion was achieved up to 6 months. The femoral condyles translated posteriorly from extension to maximum flexion. There was a significant increase in AP translation of femoral lateral condyle in the maximum flexion kneeling between 12 months and the two other intervals (p=0.0003 at 3 months and p=0.016 at 6 months), while no differences in those of medial condyle between all intervals. Almost all rotation occurred at the surface between the tibial baseplate and the PE insert (p=0.0479 at 3 months, p=0.0008 at 6 months, and p=0.0479 at 12 months), almost no rotation occurred at the surface between the PE insert and the femoral component. There were significant increases in the amount of internal rotation angle during full flexion between the tibial component and the PE insert up to 12 months. Knees implanted with this RP knee arthroplasty design show deep-flexion knee kinematics that are consistent with the implant design intent.