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study, the inferior endplate of the C6 vertebrae was constrained by fixing all degrees of freedom
in the intact healthy model (Panjabi et al. 2001). An axial precompression of 74 N was applied at
the center of the superior endplate of the C3 vertebrae. This precompression simulated the in vivo
loading due to head weight and the reaction of cervical muscles, as a simplified “follower load.”
A 1.8-Nm moment was imposed on the superior endplate surface of C3 vertebrae in the three
anatomical planes to simulate flexion, extension, left-right lateral bending, and left-right axial
rotation (Panjabi et al. 2001).
16.2.2 V
alidation
of
tHe
i
ntact
H
ealtHy
c
erVical
S
pine
In general, a validated model is one that matches previously observed experimental behavior. There
are many ways to validate a cervical spine model. The most important model parameters to validate
are those that will be studied later during simulation (Bowden 2006). For example, in the present
study, the model was used to predict spinal kinematics and intradiscal pressure; then the spinal
kinematics and intradiscal pressure were validated, but validation of cortical stress was not neces-
sary (Griffin 2001). An important consideration during the validation step is directly related to the
subject-specific nature of biological modeling. However, the large variation in material and geo-
metric considerations between individuals warrant such considerations. Most cervical models were
validated against published experimental data from different subjects, since it is difficult to perform
subject-specific validation experiments.
In the present study, the rotational motions in the intact healthy cervical spine imposing 1.8 Nm
in the three anatomic planes (Figure 16.3) fell into the standard deviation of in vitro experimental
data (Panjabi et al. 2001; Finn et al. 2009). In detail, the range of motion (ROM) was greater than
the average value of Panjabi's in vitro testing at the C3-C4 level and less at C4-C5 and C5-C6 during
Flexion
Extension
112
112
In vitro (Panjabi, 2001)
110
110
In vitro (Finn, 2009)
FE (Intact)
8
8
6
6
4
4
2
2
0
0
C4-C5
C4-C5C5-C6
C5-C6
C3-C4
C3-C4
C3-C4C4-C5
C4-C5
C5-C6
5-C6
Axial rotaion
Lateral bending
112
112
110
110
8
8
6
6
4
4
2
2
0
0
C3-C4
C4-C5
C4-C5C5-C6
C5-C6
C3-C4
C3-C4C4-C5
C4-C5C5-C6
C5-C6
FIgure 16.3
Model validation: comparison of spinal motion with experimental data.
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