Symmetrical cruciate-retaining versus medial pivot prostheses: The effect of intercondylar sagittal conformity on knee kinematics and contact mechanics.

Background: A total knee arthroplasty should restore the mechanical function of the knee and enable patients to perform desired daily activities. The joint kinematics and contact mechanics performance are important determinants of the success of total knee arthroplasty devices. The purpose of this study was to determine the effect of intercondylar sagittal conformity on kinematics and contact mechanics.

Methods: An explicit dynamic finite element method was used to investigate the differences in the performances of constrained cruciate-retaining (CR), unconstrained CR, and medial pivot designs during gait, squatting, descending stairs, and climbing stairs. The predicted kinematic results were verified through an in vitro experiment during the gait cycle.

Results: The results confirmed that the medial pivot design improved the kinematic behavior with no paradoxical anterior motion, which was found in the unconstrained prosthesis during the four activities. However, a small femoral internal rotation was found during gait (3.9°), descending stairs (2.2°), and climbing stairs (3.6°), which may produce anterolateral pain. An enlarged contact area and a lower peak contact pressure were observed on the medial side of the medial pivot prosthesis. Conversely, on the lateral side of the medial pivot prosthesis, the contact area and peak contact pressure were equal to those of the unconstrained prosthesis, which could potentially result in wear.

Conclusion: In summary, although the medial pivot prosthesis may provide qualitatively similar kinematics as the average measurements of tibiofemoral motion, further in vivo analysis and long-term studies on the femoral internal rotation and high contact pressure on the lateral side are still required.