Biomedical Engineering Reference
In-Depth Information
Table 10.1
Range of motion of the left hip joint and estimated GRF magnitude on the right foot.
Angles are reported in deg and force in newton (N)
Movement
Flex/Ext (
∈
)
Abd/Add (
∈
)
Int/Ext rot (
∈
)
GRF = % BW (N)
Arabe.
0
/
36
.
1
±
9
.
8
0
/
32
.
1
±
6
.
6
0
/
79
.
5
±
6
.
4
97
.
4
±
2
.
0
Circum.
52
.
4
±
26
.
1
/
0
0
/
37
.
9
±
24
.
8
0
/
22
.
5
±
9
.
1
95
.
9
±
7
.
8
Dev.Av.
71
.
3
±
17
.
1
/
0
0
/
22
.
2
±
7
.
9
0
/
34
.
8
±
8
.
1
95
.
4
±
10
.
4
Dev.Lat
72
.
9
±
35
.
8
/
0
0
/
54
.
5
±
15
.
3
0
/
11
.
3
±
28
.
5
96
.
0
±
4
.
6
Gra.Pl.
70
.
9
±
49
.
4
/
0
0
/
8
.
7
±
1
.
7
0
/
1
.
5
±
7
.
1
48
.
0
±
3
.
1
Walk.S-P
30
.
6
±
10
.
9
/
0
0
/
12
.
2
±
3
.
6
0
/
10
.
4
±
6
.
1
95
.
7
±
8
.
3
Fig. 10.10
Curves
of angles and loads for bending movement. Angles are expressed in degree and
loads in % BW
To build the biomechanical model, the mechanical properties of soft tissue are
considered. Given (i) the significant difference of the Young modulus between the
labrum (20 MPa), articular cartilage (12 MPa) and cortical bone (17GPa) [
8
] and
(ii) the small mechanical role of trabecular bone [
16
], bone deformation will be
minimal (0.01-0.1%) compared to cartilage deformation [
66
]. Therefore, it is more
convenient to consider bones as rigid surface structures to reasonably simplify the
model and considerably reduce computation times [
17
].
Then, the subject-specific deformable models of the soft tissue consist of two
tetrahedral meshes (see Fig.
10.3
). The first mesh (18k Tet) is composed of both
the labrum and acetabulum cartilage, for which the tetrahedral elements of each
cartilage are defined with mechanical properties specific to the tissue type. The
second mesh (7k Tet) exclusively represents the femoral cartilage. Such modeling
(2 meshes instead of 3) reduces the computation of collision detection. External
surfaces of tetrahedral meshes are extracted to define the boundary conditions in the
simulation model: vertices of the first mesh attached to the hip bone are considered as
fixed, while those of the second mesh attached to the femur will transfer loads. Since
soft tissues are characterized by large deformations, which are tackled by the used
simulation model, mesh elements of the labrum, acetabulum and femoral cartilages
are parameterized with appropriate mechanical behavior [
67
,
68
].
