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

GO , L
4. APPLICATION ON SIMULATED MODEL
r r R r
G G G L
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To illustrate the previous relations a simulated model of the lower limb was built in MSC-
ADAMS dynamic simulation software. It consists of a model for the pelvis and another one
for the femur. The motion of this simulated model was estimated from the 3D location
(position and orientation) of the pelvis and hip angles of an actual task measured at the IBV
laboratory. To simulate the soft tissue artifact in the pelvis landmarks four spheres were
fixed to it by spherical joints as shown in Fig. 1. These are Right and Left Antero-Superior
Iliac Spines (RASIS y LASIS) and Postero-Superior Iliac Spines (RPSIS and LPSIS).
RASIS
RPSIS
LPSIS
LASIS
Figure 1. Bone model with the four spheres located at the anatomical landmarks of the pelvis. The
small dots on the surface of the spheres simulate pelvis landmarks or skin landmarks.
The size of each sphere approximately simulates the curvature of the surface of the bone at
the corresponding anatomical point, and its range of motion, two rotations around to two
perpendicular axes, produces a variation in the relative distance between landmarks fixed
on the sphere’s surface similar to that one of the actual task. Two sources of errors were
deduced from the actual task. Firstly, noise from the cameras superimposed on the STA. In
the simulated model the first was assumed to be random and of a uniform distribution with
a maximum amplitude of ±2 mm. And the second, the STA, was assumed to be sinusoidal
with one cycle and amplitude of the same order of magnitude as the real one (at most 6 mm
as measured), and a random phase angle.
Now, based on the previous data obtained from simulation, and applying the relations
introduced in the previous section, the trajectories of the landmarks of the pelvis were
reconstructed in the global reference system. And in order to quantify the improvement
after the application of this method, a comparison has been established between the
positions of the landmarks before and after reconstructing their movements, both relative to
their positions on the underlying pelvis bone. Results are shown in Fig. 2.
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