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

3.2 Changing the Materials of the Interbody Spacer
Traditional interbody spacers need a large peephole because Ti interbody spacers have
low x-ray permeability. However, stress concentrations can occur around the peephole,
which may lead to damage of the intervertebral spacer.
We changed the material of the interbody spacer from a Ti alloy to PEEK, which has
high x-ray permeability. Because of this, the large peepholes were changed to small
holes, for a more even dispersion of stress (Figure 3). PEEK is a biocompatible plastic
which is approved by the US Food and Drug Administration (FDA), and is useful in the
clinical treatment.
Figure 3: Illustration of PEEK interbody spacer filled with Polyvinyl formal.
4. ROD DESIGN
The purpose of the screws and rods attached to the rear are to suppress the rotation of
the vertebral body, therefore, the rods must be strong against bending. We proposed a
reinforced rod made of two types of PEEK materials (Figure 4). Our design consisted of
an inner rod with a high Young’s modulus PEEK and an outer sheath of a low Young’s
modulus PEEK. The purpose of this is to provide high resistance to bending but low
resistance to longitudinal deformation.
PEEK (A)
PEEK (C)
5. CONDITION OF FEM SIMULATION
The structure of the analytical model
consisted of the vertebral body, the
interbody spacers, the rods and the screws.
Almost all artificial vertebral body
replacement surgeries have been between
the fourth lumbar (L4) and the fifth lumbar
(L5) of lumbar spine. [10] Therefore, we
adopted the lumbar vertebral body, L4 and
L5, shown in Figure 5 for the simulation.
Figure 4: Illustration of the reinforced rod. The rod
has a structure that combines PEEK materials of two
different Young's modulus. The Young's modulus of
PEEK(A) is higher than the Young's modulus of
PEEK(C).
Lumber
Lumber
Scre
Analysis conditions are shown in Table 1.
Fixed
(L5)
w
Figure 5: Illustration of the L4 & L5
lumbar spine FEM model.
(L4)
Interbody
spacer
Load 1.9MPa
Scre
w
Rod