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

the screw shaft and bone fragments was “shrink fit / no sliding.” Contact between bone
fragments was “separation” and, for plate b, contact between the plate and
reinforcement was “sliding / no separation.” Inventor uses a “tetra 10” style mesh (4
physical points and 10 nodes for interpolation) and produced an average of 886,220
nodes and 580,979 elements for the models. A local mesh of 0.5 mm was applied to
regions of interest, such as screw-to-bone contacts, to provide for higher accuracy
results. Four constructs were analyzed with configurations shown in table 1. Material
properties used in the FEM analysis are displayed in table 2.
4. RESULTS
Disp. [mm]
5
4
3
2
1
0
Max Fragment Displacement within Gap
Proximal Fragment Distal Fragment
Figure 3: Maximum bone fragment displacement
within the osteotomy.
Equivalent Strain [-]
0.05
0.04
0.03
0.02
0.01
0
Table 2: Material properties used in FEM analysis.
Material Young’s Modulus [GPa] Poisson’s Ratio Yield Strength [MPa]
Titanium 102.81 0.36 275.60
PEEK 13.00 0.44 355.00
Cortical Bone 12.50 0.30 83.40
Reinforced-Pk-Pk Reinforced-Pk-Ti Standard-Pk-Pk Standard-Ti-Ti
Max Osteotomy Surface Strain
Proximal Fragment Distal Fragment
Figure 5: Maximum equivalent strain on the bone
fragment surfaces within the osteotomy.
Stress [MPa]
Stress [MPa]
Bone fragment displacement within the osteotomy is largest in constructs which contain
screws made of PEEK thermoplastic and lowest in the Standard-Ti-Ti construct (Fig. 3).
In the analysis, the three constructs using PEEK as the plate material closed the 3 mm
gap at the lateral side (plate opposite) of the fracture gap. The Standard-Ti-Ti construct
700
600
500
400
300
200
100
0
9000
6000
3000
0
Max Osteotomy Surface Stress
Proximal Fragment Distal Fragment
Figure 4: Maximum Von Mises stress found on the
bone fragment surfaces within osteotomy.
Screw 1
Max Stress by Material & Part
Screw 2
Screw 5
Screw 6
Construct Component
(Reinf.)
Plate
Figure 6: Maximum stress for each part of each
construct. (Inner Ti reinforcement of the reinforced
PEEK plate included.)