The Effect of Component Design and Tibial Tray Orientation on Weight-Bearing Postoperative Kinematics for Total Knee Arthroplasty: A Parametric Analysis of Multiple Variables.

Abstract

Considerable work has been done to improve outcomes in total knee arthroplasty (TKA), yet there remains a lack of consensus for proper target component alignments and design, particularly of the tibial tray. Furthermore, isolation of variables is difficult to do clinically. This study used a preoperative planning tool and a validated forward mathematical model of the knee to examine the effects of different TKA design features and tibial tray orientations (posterior tibial slope [PTS] and axial orientation) on femorotibial kinematics. The three-dimensional tool contains reconstructed bone and soft-tissue geometry for 10 unique subjects, each implanted with three different cruciate-retaining TKAs. Mechanical alignment with PTS of 6° was the control group, 5° internal/external rotation, and 0, 3, and 9° PTS of the tibial tray were experimental groups. Each subject underwent a deep knee bend from full extension to 120° flexion. Examined parameters include femorotibial condylar motion, medial collateral ligament forces, lateral collateral ligament forces, posterior cruciate ligament forces, and femorotibial contact mechanics (force, area, and stress). The PTS had no effect on kinematics, whereas internal/external rotation did (P < 0.001). More bearing conformity resulted in greater sensitivity to malalignment in contact mechanics and had the highest ligament forces, while less bearing conformity resulted in greater paradoxical anterior motion of the lateral condyle, with the least conforming system experiencing 8.6 ± 4.8 mm of motion. Component design plays a critical role in producing desirable clinical outcomes, and there exists a balance between conformity and nonconformity that is optimal. Internal/external rotation of the tibial tray must be further standardized and studied to ensure stability and natural knee mechanics.