In vivo kinematics of mobile-bearing knee arthroplasty in deep knee bending motion.

The current study aimed to analyze kinematics during deep knee bending motion by subjects with fully congruent mobile-bearing total knee arthroplasties allowing axial rotation and anteroposterior (AP) gliding. Twelve subjects were implanted with Dual Bearing Knee prostheses (DBK, slot type: Finsbury Orthopaedics, Surrey, UK). These implants include a mobile-bearing insert that is fully congruent with the femoral component throughout flexion and allows axial rotation and limited AP translation. Sequential fluoroscopic images were taken in the sagittal plane during loaded knee bending motion. In vivo kinematics were analyzed using a two- to three-dimensional registration technique, which uses computer-assisted design models to reproduce the spatial position of femoral and tibial components from single-view fluoroscopic images. The average femoral component demonstrated 13.4 degrees external axial rotation for 0-120 degrees flexion. On average, the medial condyle moved anteriorly 6.2 mm for 0-100 degrees flexion, then posteriorly 4.0 mm for 100-120 degrees flexion. On average, the lateral condyle moved anteriorly 1.0 mm for 0-40 degrees flexion, then posteriorly 8.7 mm for 40-120 degrees flexion. The typical subject exhibited a lateral pivot pattern from extension to 60 degrees flexion and a central pivot pattern from 60 degrees to 100 degrees flexion, patterns that are not usually observed in normal knees. Subsequently from 100 degrees to 120 degrees flexion, a rollback pattern was reproduced in which bilateral condyles moved backward.