The influence of contemporary knee design on high flexion: a kinematic comparison with the normal knee.

Although >90% of total knee arthroplasties are associated with a good-to-excellent outcome, some patients have difficulty adjusting their gait to accommodate the new articulations inherent in contemporary implant designs. Paradoxical motions inclusive of anterior sliding and lateral pivot are examples of aberrant kinematics in total knee arthroplasty. A computational kinematic simulator measured the motion attained by six contemporary total knee arthroplasty designs. Results were compared with the in vivo kinematic data from healthy knees (i.e., knees with no history of surgery) in deep flexion1. Three designs employing a tibial post and a femoral cam as the motion control mechanism were evaluated, including the Legacy LPS-Flex Fixed Bearing (Zimmer, Warsaw, Indiana), the Journey (Smith and Nephew, Memphis, Tennessee), and the Vanguard PS (Biomet, Warsaw, Indiana). Three designs that did not employ a tibial post and femoral cam mechanism were also evaluated, including the MRK (Finsbury, Leatherhead, United Kingdom), the Duracon (Stryker Orthopaedics, Mahwah, New Jersey), and the Triathlon (Stryker Orthopaedics). All six designs have a fixed plateau and are currently available for clinical use in the United States. LifeMOD/KneeSIM (LifeModeler, San Clemente, California), a dynamic, validated musculoskeletal modeling system, was utilized in this study. KneeSIM provides a musculoskeletal modeling environment of the left leg of a nominal-size patient in which activities such as walking gait, lunge, stair ascent and descent, and deep-knee bend may be simulated. Activities are propelled by muscle forces and constrained by the soft tissues. Solid models of scanned geometries of the total knee arthroplasty component are arranged in the joint space to reflect a successful virtual surgery (Fig. 1). A specified activity is then simulated, and animations and plots of component and soft-tissue positions, forces, and moments are generated. Factors influencing kinematic function and stability of the knee joint, including surgical technique, component placement and …