Abstract
Background
Mobile-bearing (MB) total knee prostheses have been developed to achieve lower contact stress and higher conformity compared to fixed-bearing total knee prostheses. However, little is known about the in vivo kinematics of MB prostheses especially the motion of the polyethylene insert (PE) during various daily performances. And the in vivo motion of the PE during stairs up and down has not been clarified. The objective of this study is to clarify the in vivo motion of MB total knee arthroplasty including the PE during stairs up and down.
Patients and methods
We investigated the in vivo knee kinematics of 11 knees (10 patients) implanted with PFC-Sigma RP-F (DePuy). Under fluoroscopic surveillance, each patient did stairs up and down motion. And motion between each component was analyzed using two- to three-dimensional registration technique, which used computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components, and PE (implanted with four tantalum beads intra-operatively) from single-view fluoroscopic images. We evaluated the range of motion between the femoral and tibial components during being grounded, axial rotation between the femoral component and PE, the femoral and tibial component, and the PE and tibial component during being grounded.
Results
The mean flexion angle of being grounded during stairs up was 72.0° ï1/2ž 8.74° (Max, Min). The femoral component relative to the tibial component demonstrated 8.77° external rotation during stairs up. The PE relative to the tibial component demonstrated 8.23°external rotation and the femoral component relative to the PE demonstrated 3.93°external rotation during stairs up. The average ROM during stairs down was from 40.8° to 5.75° (Max, Min). The external rotation of the femoral component relative to the tibial component was 4.73° during stairs down. The tibial component rotated 6.36° relative to the PE and the femoral component rotated 3.95° relative to the PE. In both two movement, there was a positive correlation between the femoral component relative to the tibial component and the PE relative to the tibial component in terms of axial rotation at each flexion angle.
Discussion and conclusion
In this study, we evaluated the in vivo motion of the PE during stairs up and down. there was a positive correlation between the femoral component relative to the tibial component and the PE relative to the tibial component about axial rotation at each flexion angle.
