Observations of femoral rollback in cruciate-retaining knee arthroplasty

The current study evaluated kinematics of the knee during a stair-climbing activity after total knee arthroplasty. All patients received a posterior cruciate ligament retaining prosthesis of the same design, having an anatomically shaped femoral component and an unconstrained tibial insert. All patients had the same surgical technique done by two experienced surgeons. Patients had some posterior femoral rollback and screw-home type axial rotations during weightbearing activities. However, patients treated by different surgeons had different patterns of tibiofemoral motions. In Group 1, rollback occurred early in the flexion range and was maintained until 80 degrees flexion. In Group 2, the lateral condyle had rollback in early flexion, but both condyles translated forward as flexion increased to 80 degrees. An anatomic femoral component seems to be necessary to produce consistent early femoral rollback. However, soft tissue balance can have a significant effect on the kinematics of sagittally unconstrained posterior cruciate retaining total knee arthroplasty, because it may vary among surgeons.