Biomedical Engineering Reference
In-Depth Information
The fixation components, including plate and screw, were made of titanium alloy (Ti6Al4V). The
Young's modulus and Poisson's ratio of Ti6Al4V were 114 GPa and 0.3, respectively.
During this simulation, the anterior longitudinal ligament and the entire disc were completely
removed, and then the intervertebral space was replaced with the allograft bone and was considered
totally fused to the adjacent vertebrae. The bone-screw interface was considered completely inte-
grated and constrained. The loading and boundary conditions were the same as the intact healthy
cervical spine.
16.3.2 c
erVical
S
pinal
m
otion
after
a
nterior
f
uSion
After spinal fusion, the ability for motion was almost fully lost at the operative level (C4-C5) for all
the spinal motions (Figure 16.5). The rotation motions imposing the moment load were 0.1°, 0.1°,
0.3°, 0.3° during flexion, extension, axial rotation, and lateral bending, respectively. At the adjacent
level, the motions only increased by 3% during lateral bending at C5-C6, and only decreased by 6%
during flexion at the common site.
The results showed that spinal fusion will restrain motion at the operative segment under moment
loading, but has a limited effect at the adjacent segment. Since there was complete loss of motion
at the operative level and limited compensatory motion at the adjacent level, motions of the entire
segment (C3-C6) decreased by between 30% and 36% during all spinal motions.
16.3.3 i
influence
of
S
pinal
f
uSion
on
f
acet
J
oint
The adjacent discs transfer load through the vertebral body, and the facet joints and posterior
ligaments transfer load through the posterior elements. The facet joints and posterior ligaments,
particularly the capsular ligament, have been shown to play a significant role in torsion, transverse
shear, and extension.
Flexion
Extension
335
335
FE (intact)
330
330
FE (fusion)
FE (fusion)
FE (ProDisc-C)
225
225
FE (ProDisc-C)
220
220
FE (Mobile-C)
115
115
110
110
5
5
0
0
To tal
C3-C4
C4 -C5
C5-C6
To tal
C3-C4
C4 -C5
C5-C6
Axial rotation
Lateral bending
335
335
330
330
225
225
220
220
115
115
110
110
5
5
0
0
To tal
C3-C4
C4 -C5
C5-C6
To tal
C3-C4
C4 -C5
C5-C6
FIgure 16.5
Spinal motions after different surgical reconstructions.
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