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

Error in position [mm]
Error in position [mm]
6
4
2
RASIS
0 0.2 0.4
6
4
2
LASIS
0 0.2
Time [s]
0.4
6
4
2
6
4
2
RPSIS
0 0.2 0.4
LPSIS
0 0.2
Time [s]
0.4
Error in position [mm]
Error in position [mm]
7
6
5
4
3
2
LFE
1
0 0.2 0.4
7
6
5
4
3
2
MFE
1
0 0.2
Time [s]
0.4
Figure 2. Error in position (distance) relative to the underlying bone marker. (*) symbols represent
the original skin landmarks while the continuous line represents the proposed procedure. The figure
on the left is for pelvis landmarks while the other on the right is for those of the femur.
The previous procedure was repeated for 5 different simulation repetitions of different
random sinusoidal function phase angles. Results are shown in Table 1.
Rep.
No.
Pelvis landmarks
Rigid model Skin
RASIS RPSIS LASIS LPSIS RASIS RPSIS LASIS LPSIS
Femur landmarks
Rigid model Skin
LFE MFE LFE MFE
1 28.5 33.0 30.1 30.5 38.6 39.5 40.2 40.2 26.8 39.7 43.4 43.2
2 27.2 29.2 26.9 28.0 35.7 37.9 36.6 36.3 42.5 41.5 43.7 42.1
3 25.0 26.0 23.0 23.3 37.5 39.1 37.0 39.4 39.1 40.4 43.7 43.7
4 28.2 13.8 28.3 14.2 37.0 40.2 38.0 37.5 25.3 38.0 43.2 44.5
5 27.0 24.9 25.2 22.0 38.7 36.7 36.2 35.9 26.5 35.8 44.9 41.8
Table (1). Errors in landmark positions before and after implementing the proposed rigid body
model for different 5 repetitions.
As can be seen in Table 1, a significant reduction the errors in the positions of pelvis
landmarks has been obtained after implementing the proposed procedure for all the
repetitions. A similar procedure was followed for the femur, and the results are depicted in
Fig. 2 and Table 1.
5. CONCLUSION
A recent study shows that conventional methods for obtaining rigid body kinematics from
landmark trajectories based on an optimization process may not reduce the STA. In this
article we have introduced a method for the calculation of rigid body kinematics for the
lower extremity. Starting from the angular velocity and acceleration of the body, the
orientation of a local reference system attached to the body, represented by three
consecutive rotations around fixed axes, is integrated after adequate transformation. This