Biomedical Engineering Reference
In-Depth Information
A finite element model for the lower
cervical spine
A
A parametric study was conducted to determine the
variations in the biomechanical responses of the spinal
components in the lower cervical spine (Yoganandan
et al.,
1997). Axial compressive load was imposed uniformly on
the superior surface of the C4-C6 unit. The various
components were assumed to have linear isotropic and
homogeneous elastic behavior and appropriate material
parameters were taken from the literature. A detailed 3D
FE model was reconstructed from 1.0-mm CT scans of
a human cadaver, resulting in a total of 10,371 elements
(
Fig. 3.1.3-7A
). The results show that an increase in
elastic moduli of the disks resulted in an increase in
endplate stresses and that the middle C5 vertebral body
produced the highest compressive stresses (
Fig. 3.1.3-
7B
). The model appears to confirm clinical experience
that cervical fractures are induced by external compres-
sive forces.
B
Maneuver
Low sit-to-stand
Normal sit-to-stand
Tie
Leg cross
Stoop
Post. disloc. maneuvers
Pivot
Roll
Ant. disloc. maneuvers
Overall series
No. of trials
No. of dislocations
% of trials dislocating
FEA of indentation tests
on pyrolytic carbon
47
55
69
64
42
277
58
19
77
353
41
33
31
22
6
133
23
12
35
168
87
64
45
34
14
48
40
63
45
47
Pyrolytic carbon (PyC) heart valves are known to fail
through cracks initiated at the contact areas between
leaflets and their housing. In
Gilpin
et al.
(1996)
, this
phenomenon is simulated with a 5.1-mm steel ball
indenting a graphite sheet coated on each side with PyC,
similar to the makeup of real heart valves. Two types of
contacts were analyzed: when the surface material is thick
(rigid backing) and when it is fairly thin (flexible backing).
Fig. 3.1.3-6 (A) Finite element model of a contemporary 22-mm
modular THA system. (B) Table of FE dislocation predictions of
the seven challenge maneuvers simulated. (Reproduced with
permission from
Nadzadi et al., 2003
.)
1.5
C4
C5
C8
1.0
0.5
0.0
1.7
3.4
6.8
A
B
Disk Annulus Modulus (MPa)
Fig. 3.1.3-7 Finite element model of the C4-C6 unit of the lower cervical spine: (A) mesh showing 3D solid elements and (B) plot of
vertebral body stress as a function of disk annulus moduli. (Reproduced with permission from
Yoganandan et al., 1997
.)
