ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

The z-axis is aligned with the tibia tray stem and points in the inferior direction
(compression). The x-axis points in the lateral direction and the y-axis points in the
anterior direction. Figure 3 compares predicted ground reaction forces versus measured
ground reaction forces during the prosthetic squat simulation for both the right and left
feet. Predicted muscle forces and measured rectified raw EMG signals for major
muscles crossing the knee are shown in Fig. 4.
a.) b.)
Figure 2: Comparison of measured “e-tibia” and predicted “model” knee forces (a.) and
torques (b.) for two cycles of a dual limb squat. The z-axis is aligned with the tibia tray
stem, the x-axis points in the lateral direction, and the y-axis points in the anterior direction.
a.) b.)
Figure 3: Comparison of measured and predicted ground reaction forces for the right foot
(a.) and left foot (b.) for the dual limb squat. The z-axis is the vertical axis, the x-axis is
medial-lateral, and the y-axis is anterior-posterior.
Figure 4: Predicted forces for muscles crossing the knee and measured rectified raw EMG.
The prosthetic model overpredicts tibia compressive force when the subject
rises from the deepest portion of the squat (~ 3.5 seconds and ~ 5.8 seconds) (Fig. 2a).
This overprediction corresponds to forces produced by the gastrocnemius muscles that
do not match measured muscle activations (Fig. 4). The subject favors her right leg
while standing (0 – 2.1 s) and the prosthetic simulation captures this in the ground
reaction forces (Fig. 3a and Fig. 3b), but the model underpredicts reaction forces on the
right foot and overpredicts reaction forces on the left foot during the two squats.
Figure 5 shows the tibia plateau during the deepest portion of the squat for
forward dynamics simulation of the natural model. The lateral meniscus exhibits
subluxation during the squat for both partial and full ACL transection. For the partial
and full ACL transection, the femur moves several millimeters in the posterior and
lateral direction prior to the squat. The femur pulls the meniscus in the posterior-lateral