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

Table 1: Analysis conditions
Static analysis with a mesh solid (tetrahedral).
Number of elements = 164006, Number of nodes = 249478
Pressure load = 1.9 MPa (Load on the upper surface of the L4 lumbar vertebral body.
Value of load is known from the literature. [11] )
Fixed constraint (Defined at the bottom surface of the L5 vertebral body.)
Contact surface conditions: Bonded Surfaces, Contact surfaces between internal rod
and external sheath of the reinforced rod were allowed to slip.
Analysis configurations are shown in Figure 6. Model type A was the same as a
conventional design: the interbody spacer and the rod were made of a Ti alloy. Model
type C was configured with the PEEK interbody spacer and the reinforced rod. The
physical properties of the materials of each part are shown in Table 2.
Figure 6: Synopsis of analyzed models
of the artificial vertebral body.
Table 3: List of material physical properties.
6. RESULTS OF FEM SIMULATIONS AND DISCUSSION
6.1 Comparisons of the Equivalent Strain of Model Types A and C
We analyzed the equivalent strain of the Ti alloy and PEEK artificial vertebral bodies
(Figure 6). In Figure 6.1, the strain on the vertebral body near the interbody spacers in
model type C was less than the similar strain in model type A. Changing the materials of
the interbody spacer from Ti to PEEK is valid for reducing vertebral body damage.
In Figure 6.2, the strain of the interbody spacer was very low for model type A. In
model type C, the interbody spacer was more distorted than model type A. Therefore we
can expect to see mechanical stimulation of bone growth.
In model type A (Figure 6.2), high strain was seen in the center of the Ti rod. In model
type C, the entire reinforced rod was deformed. The reinforced rod provided low
resistance to longitudinal deformation, which allowed the artificial vertebral body to
have a more appropriate mechanical deformation, e.g., the vertebral bodies moved
parallel to each other.