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° external axial rotation for 0–120° flexion. On average, the medial condyle moved anteriorly 6.2 mm for 0–100° flexion, then posteriorly 4.0 mm for 100–120° flexion. On average, the lateral condyle moved anteriorly 1.0 mm for 0–40° flexion, then posteriorly 8.7 mm for 40–120° flexion. The typical subject exhibited a lateral pivot pattern from extension to 60° flexion and a central pivot pattern from 60° to 100° flexion, patterns that are not usually observed in normal knees. Subsequently from 100° to 120° flexion, a rollback pattern was reproduced in which bilateral condyles moved backward.