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

3. MATERIALS AND METHODS
A CAD model of a left human tibia obtained from the VAKHUM public dataset was
used to simulate the bone fragments for FEM analysis (3) . Screws and two custom plate
models were designed in Autodesk Inventor. Both models were locking plates with
six in line screw holes. Plate A was designed to test a single material, e.g., medical
grade titanium alloy (6Al-4V) or PEEK, and Plate B contained an inner reinforcement
of titanium alloy to increase the deformation resistance of the PEEK thermoplastic (Fig.
1). The reinforcement was designed in response to a previous study where a standard
PEEK plate was found to produce excess motion in the fracture gap (1) .
1
2
(3)
(4)
5
6
Proximal
Figure 1: Plate A - Standard Plate. Plate B - Reinforced Plate. (Including
screw numbers.)
A
Static FEM compression analyses were performed in
Inventor with the tibia loaded proximally and fixed distally.
Load approximated a person of 80 kg and was distributed
between the medial and lateral tibial plateaus following load
distribution estimations previously published by Kettlekamp, et
al. (Fig. 2). A 3 mm osteotomy was applied at the center of the
diaphysis between the proximal and distal bone fragments
about which the plate was centered. A 3 mm gap was chosen to
better elucidate the effects of the load upon the constructs. The
fracture plates were placed medially and four screws (#1, #2,
#5, #6) were used to fasten the plate to the bone. The two
central holes (#3, #4) of the six plate screw holes were left
open to simulate the surgical procedure of bridging the fracture
gap to not further damage the fracture area. Contact between
screw heads and the plate was “bonded” and contact between
1
2
5
B
Distal
6
Lateral
Proximal
Distal
Medial
Figure 2: Construct model
used in FEM analysis
showing proximal loads.
(Medial: 220 MPa,
Lateral: 93 MPa)
Table 1: Construct configurations for analysis.
Configuration Label Plate Type Plate Material Screw Material
Reinforced-Pk-Pk Ti Reinforced PEEK PEEK
Reinforced-Pk-Ti Ti Reinforced PEEK Titanium
Standard-Pk-Pk Standard PEEK PEEK
Standard-Ti-Ti Standard Titanium Titanium