Computer modeling to predict effects of implant malpositioning during TKA.

Computer-assisted surgery has focused on alignment of implants and soft tissue balancing but the end results during surgery as they pertain to long-term function of the implants are not yet realized. One parameter that continues to be variable despite the use of computer navigation is the placement of the implants in the transverse plane. The objective of this study was to determine whether implant and anatomic registrations could be used in a computer model (LifeMOD/KneeSIM, LifeModeler, Inc., San Clemente, California) to show differences in the resulting contact patterns of the medial and lateral condyles of the polyethylene insert. The simulations included tibiofemoral and patellofemoral contact, passive soft tissue (medial and lateral collateral, and posterior cruciate ligaments, as well as the capsular tissues), and active muscle elements (quadriceps and hamstrings). Components of a fixed-bearing cruciate-retaining total knee (Columbus knee system; B. Braun Aesculap, Tuttlingen, Germany) were imported into the model. The systems were subjected to one 60-second cycle of a lunge. Both the femoral and the tibial components were positioned in 5° of internal or external rotation in varying combinations and the resulting kinematics analyzed. The resulting kinematics showed variations in anteroposterior translation of the lateral and medial femoral condyles that resembled several of those reported in the literature for individual patients with a cruciate-retaining knee implant system.