In vivo determination of posterior femoral rollback for subjects having a NexGen posterior cruciate-retaining total knee arthroplasty

This study determines the in vivo kinematics during a deep-knee bend activity for subjects implanted with a posterior cruciate-retaining total knee arthroplasty having asymmetric geometries. Of 20 subjects, 19 experienced posterior femoral rollback (PFR) of the lateral condyle (average -3.9 mm), and 13 subjects experienced PFR of the medial condyle (average -3.1 mm). As a result of the lateral condyle rolling further posterior than the medial condyle, on average, subjects experienced 1.4degrees of normal axial rotation. Of 20 subjects, 10 experienced normal axial rotation, whereas 10 experienced an opposite rotation pattern. Condylar lift-off occurred predominantly with the lateral condyle. Contrary to previous in vivo studies, the subjects in this study experienced consistent PFR of the posterior cruciate-retaining total knee arthroplasty. It can be hypothesized that having asymmetric femoral condyles may lead to PFR with increasing knee flexion.