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

Figure 2
In order to account for different daily activities, different simulations were performed:
(i) M1 model was loaded with vertical loads of 2000N and 500N and with 10Nm
moments in flexion, extension, lateral bending and torsion; (ii) M2 model was loaded as
M1; (iii) M3 model was loaded as M1 and M2, excluding extension, lateral bending and
torsion where the cage contribution to a different load sharing was thought to be
negligible.
In order to compare the state of stress arising in the rods after the implant in the spine
with the one arising using the configuration according to standards, also in this case, for
each simulation, both the location of the most stressed points in traction and the
correspondent value of VM were extrapolated.
4. RESULTS
4.1 Validation of the ISO and ASTM procedure
Results regarding the validation of S1 and S2 models are reported in Table 1 in terms of
maximum strain and stiffness K of the construct (expressed as applied force F divided
by the vertical displacement U): differences were found to be lower than 8%, thus
confirming the appropriateness of the model.
S1
(ISO)
S2
(ASTM)
Exp
[strain]
KExp
[N/mm]
FEM %
KFEM %
mean±SD
[strain] Diff.
mean±SD
[N/mm] Diff.
SG1
SG2
2066±5.10
2065±5.19
2088,68
2069,80
1,09%
465,47±1.25
0,23%
463,39 -0,45
SG1
SG2
1339±3.26
1354±1.95
1418,92
1451,81
5,96%
7,23%
90,82±0.56 85,10 -6,30
Table 1
4.2 Comparison between standard configuration and physiological environment
Table 2 reports both the maximum of VM (in MPa) in the rods in traction calculated in