Biomedical Engineering Reference
In-Depth Information
Table 7.1
Overview of falling scenarios for maximum stress in the femur No. 4 has additional
ground contact with the second foot to balance the fall. No. 5 induces stress via maximum knee
flexion.
No.
Direction
Stance/Gait
Ground contact
1
Forwards
Stance
Both knees
2
Forwards
Stance
One knee
3
Forwards
Gait
One knee
4
Forwards
Gait
One knee and foot
5
Backwards
Gait
Hands
Calculated and measured time-dependent moments revealed good agreement in
the best case, and only general agreement in the worst case observed (Fig.
7.3
). Pat-
terns andmagnitudes of moments showgood agreement within the trials of individual
subjects; whereas as a group, the subjects show only general agreement. Absolute
differences in moments range from a maximum of 30%BWM for about 10% of the
gait cycle in the best (subject SK, Fig.
7.3
c), to a maximum of more than 50%BWM
over around 40% of the gait cycle in the worst case (subject VE, Fig.
7.3
d). The
RMSD observed for the resultant moment was 27%BWM.
As presented, forces obtained in the simulation showed a good agreement with
the measured loads despite the moments showing a somewhat lower accuracy which
is still accurate enough for most clinical applications. Therefore, the model was
considered to be fully validated for calculations of resultant forces and moments.
7.7.1 Biomechanical Application of the MBS—Stress Resultants
in Different Cases of Falling
Once the model was validated, it was driven by kinematic and kinetic data from a
healthy subject who mimicked the five documented falling scenarios of amputees as
listed in Table
7.1
and illustrated by an example in Fig.
7.5
.
The essential motion data as well as ground reaction forces for driving and loading
the model are acquired with the same motion capturing set-up as for the validation
study [
78
,
79
]. The PlugInGait marker set and model for the lower extremity (kine-
matic model V 2.3) was used to generate the kinematic data [
79
]. It consists of 16
reflective markers with a 14mm diameter attached to anatomical landmarks: supe-
rior/anterior spina illiaca, thigh, lateral epicondyle, shank, lateral malleolus, and sec-
ond metatarsal head and on the calcaneous for left and right leg (Fig.
7.2
b). No knee
alignment device was used. Captured marker data were processed (VICON-Nexus
1.5.1, VICONMotion Systems Ltd., Oxford, UK) and trajectories were labeled using
the PlugInGait model. Kinematic datawere post-processedwith aWoltring-filter with
a mean squared error (MSE) setting of 10.
