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

occur with an IFM of up to 3 mm. The high IFM for this analysis is most likely due to
the size of the plate relative to its anatomical position and the loads placed upon it.
Usually, fracture plates used in a high load diaphyseal fracture are as long as possible so
that load may be distributed over the length of the plate and over more screws. A short
plate is used in this study with the hope of emphasizing problem areas.
The Standard-Ti-Ti construct had excessively high stress at the #5 screw head. The
bearing yield strength of medical grade titanium is just under 1500 MPa which means
that this high stress would lead to construct failure 7 . The position of this extremely high
stress is at the head of the screw near the bottom of the plate. It appears that a stress
riser formed between the plate and screw in that location due to contact between the two
parts when the construct was deformed under load. It is possible that a larger, or ovalshaped,
exit hole on the plate would alleviate this problem.
Figures 4 and 5 show that PEEK plates, standard and Ti reinforced, all had gap closure
and all had similar stress and strain magnitudes per bone fragment. The Standard-Ti-Ti
construct did not allow total gap closure, therefore very little stress or strain is found
within the gap. Wolff’s law, and Dr. Frost’s subsequent Mechanostat model, state that
bone remodels itself based on the mechanical deformation, or strain, placed upon it.
This lack of stress and strain within the osteotomy in the all-titanium construct may
prevent remodeling from occurring. Results would likely differ in a non-gap analysis
but fracture gaps often occur in real world conditions. The fracture gap is used here may
simulate an extreme example of this but is used for reasons previously stated.
A limitation of this study is the isotropic representation of bone in the FEM analysis
when it is actually an anisotropic material. The accurate representation of tibial
morphology aided in the translation of forces throughout the length of the bone
fragments but the anisotropic properties of bone are required for a more accurate
simulation. Another possible limitation is the small plate design for the anatomical
position of the analysis. Often, these types of fractures are treated with an
intramedullary nail or a plate that spans much of the length of the diaphysis. In the case
of a long bone fracture plate system, the number of screws used is greater than what the
plate in the current study can accommodate. More screws help to distribute the load
evenly along the length of the plate. This is a likely reason for the relatively high IFM
and stress results in this analysis. Finally, mechanical tests should be performed to
validate the results of the FEM analysis. These tests are planned for the near future.
While none of the constructs are shown to be absolutely superior to another, we believe
that a Ti-reinforced, PEEK construct is a viable competitor to traditional metallic
fracture plating. Titanium and stainless steel materials have proved to be highly
effective orthopedic implant materials but the problem of stress shielding is one of their
biggest drawbacks, especially in osteoporotic bone. It has, however, proved difficult to
find a better combination of biocompatibility and strength. Here we show that a
composite of PEEK and titanium materials deforms more than a titanium construct,
which then initiates contact between bone fragments. The contact created an increase in
gap stress and strain, which may instigate the bone remodeling response. On the other