Three-Dimensional Dynamic Simulation of Total Knee Replacement Motion During a Step-Up Task

[+] Author and Article Information
Stephen J. Piazza

Center for Locomotion Studies and Departments of Kinesiology and Mechanical & Nuclear Engineering, Pennsylvania State University, University Park, PA 16802

Scott L. Delp

Biomechanical Engineering Division, Mechanical Engineering Department, Stanford University, Stanford, CA 94305

J Biomech Eng 123(6), 599-606 (Jul 31, 2001) (8 pages) doi:10.1115/1.1406950 History: Received March 02, 1999; Revised July 31, 2001
Copyright © 2001 by ASME
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(A) The three-dimensional body model used to simulate step-up. The swing foot passes through the step because knee and ankle motion in the swing leg were not modeled. The stance knee was fitted with a total knee replacement and the stance foot was fixed to the step throughout the simulation. (B) Illustration of the six body segments modeled. (C) Orientation of each of the six segment-fixed coordinate systems.
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Flow chart describing the organization of the simulation. Implant motions were determined by using the SD/FAST software package to create differential equations of motion. These equations were numerically integrated to calculate motions while forces were computed and applied that represented the actions of muscles and ligaments and the effects of prescribed motion. SD/FAST input files and routines that computed muscle and ligament forces during the simulation were created using Dynamics Pipeline, a second software package.
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EMG data that has been rectified, filtered, averaged, and smoothed. These seven curves were used to prescribe the activation input of 11 of the 13 musculotendon actuators. The two remaining actuators, representing tensor fascia lata and sartorius, received no activation input.
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Knee flexion versus time during step-ups performed by a normal subject (dashed line and shaded area represent the mean and one standard deviation above and below the mean), and simulated knee flexion (solid line)
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Simulated and measured forces at the prosthetic knee plotted against knee flexion angle. Net intersegmental forces at the knee in the present simulation (solid curves) were defined as the difference between resultant muscle force and the articular contact force 44. Corresponding net intersegmental forces, averaged over five patients with posterior cruciate-substituting knee implants, were reported by Banks et al. 36 (dashed curves with shading representing ± one standard deviation). All forces have been normalized by body weight (BW). The components of the tibiofemoral articular contact forces (dash-dot curves) are also presented. (A) Superior–inferior forces. Positive net force indicates a net upward force applied to the tibia and positive articular contact force indicates a force applied to the tibia downward along its long axis. (B) Anterior–posterior forces. Positive net force is in the anterior direction and positive articular contact force indicates a posteriorly directed force applied to the tibia. (C) Medial–lateral forces. Positive net force is in the lateral direction and positive articular contact force indicates a medially directed force applied to the tibia.
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Anteroposterior positions of the lowest points on the lateral (top) and medial (middle) femoral condyles relative to the tibial component, and the minimum distance separating the femoral cam and tibial spine (bottom). Anteroposterior condyle positions are specified relative to the anteroposterior midline of the tibial component (anterior positive). Dashed lines with shading are the mean lowest-point positions (±one standard deviation) and spine-cam separations measured by Banks et al. 15 in patients who had received the same implant as that modeled in the present study.
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Ratios of patellar ligament force (Fpl) to quadriceps force (Fq) computed during the present simulation and measured in cadavers 454647.




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