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

1. ABSTRACT
FEM analysis of an artificial vertebral body
composed of biocompatible plastic
K. Shimazu 1 , Y. Nakanishi 2 , Y. Nakamuta 3 ,
H.Mizuta 4 , A. Sei 5 , W. Togami 6 , H. Higaki 7
Posterior lumbar interbody fusion is one of the treatments for vertebral disease.
Generally, the constituent materials of the artificial vertebral body compose of an
interbody spacer, rods, and screws, and use Ti alloys which have a higher Young’s
modulus than bone. Therefore, a mechanism to induce bone healing from dynamic
stimulation is not realized. Also, there is an issue of instability from high stress
concentrations between the bone and the interbody spacer. In order to realize dynamic
stimulation, we propose the materials of the interbody spacer and rod be changed to the
biocompatible plastic polyetheretherketone (PEEK), which has selectable material
properties. These implants were designed to allow strain in the direction of the spine by
combining PEEK materials of different Young's modulii. To increase stability, the
interbody spacer was designed to distribute the stress by attaching to the cover of a
conventional spacer. An FEM analysis was performed using a CAD model of the
artificial vertebral body. A Ti alloy and PEEK were used as the constituent materials of
the interbody spacer and rod, and the artificial vertebral body design concept was
assessed. The results of this study show the change in strain in the direction of the spine
on the interbody spacer and rods could be verified when the material was changed from
a Ti alloy to PEEK.
2. INTRODUCTION
Posterior lumbar interbody fusion is one of the treatments for vertebral body disease,
osteoporotic vertebral compression fracture and lumbar disc herniation. It is an
operative method in which the diseased vertebral body is replaced with an artificial
vertebral body. [1], [2], [3] Generally, the constituent materials of the artificial vertebral
body, are composed of an interbody spacer, rods, and screws, and use Ti alloys which
have a higher Young’s modulus than bone (Figure 1, left). However, artificial vertebral
body replacement surgery has many issues; (1) the autogenous bone graft is at risk for
complications such as bleeding, pain and infection, (2) the interbody spacer impairs
osseous tissue generation and (3) the material of the interbody spacer is radio opaque
[4], [5], [6]
making it difficult to see inside the region of interest.
Other studies have shown that hydrophilic porous plastic inserted into the interbody
spacer can be used to avoid the need to insert autologous bone and also to avoid bone
comminution. [7] In this paper, we change the materials of the interbody spacer and the
1 Student, Department of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto City,
Kumamoto Prefecture, Japan.
2
Professor, Graduate School of Science and technology, Kumamoto University, Kurokami 2-39-1,
Kumamoto City, Kumamoto Prefecture, Japan.
3
Student, Department of Engineering, Kyusyu University, 6-10-1 HAKOZAKI, HIGASHI-KU,
FUKUOKA, 812-8581, JAPAN
4
Professor, Orthopedics, Kumamoto University Hospital, Honjo 1-1-1, Kumamoto City, Kumamoto
Prefecture, Japan.
5
Lecturer, Kumamoto University Hospital, Honjo 1-1-1, Kumamoto City, Kumamoto Prefecture, Japan.
6
Student, Kumamoto University Hospital, Honjo 1-1-1, Kumamoto City, Kumamoto Prefecture, Japan.
7
Professor, Department of Engineering, Kyusyu Sangyo University, Kokadai 2-3-1, Higashi, Hukuoka
City, Hukuoka Prefecture, Japan.