Biomedical Engineering Reference
In-Depth Information
2.3
Model Accuracy and Strength Characteristics
The accuracy of both methods, has been quantitatively validated [32] and CT seems
to be slightly more accurate in the reconstruction of skeletal characteristics, especially
when examining longer bones.
The reverse engineered models can be employed to determine the strength charac-
teristics of the examined area through FEA simulations, indicating apparent fracture
risks [33]. The main advantage of these methods is associated to the high degree of
geometrical customization, as this approach considers patient specific characteristics.
Figure 2 (left side) indicates the compressive response of a cancellous bone sample
[34] under compressive load at a 2.5% strain. The porosity of the sample amounted to
88% and an apparent density to 0.247 gr/cm 3 . These calculations ease the determina-
tion of critical areas, where strut buckling will gradually deteriorate the strength cha-
racteristics of the sample ultimately causing fractures. It is however notable that CT
reconstructed models require extensive data manipulation and simulation expertise to
acquire the desired result, while each model is highly customized and thus not appli-
cable to anyone but the examined individual.
Fig. 2. FEA calculated strength characteristics of a CT reconstructed bone sample and MRI
reconstructed femur
The right side of the figure 2, indicates the stress distribution on a MRI reverse en-
gineered human femur. The model was bound at a lower section of the femur and
loaded by a 2317N joint force (inclined by 24 o to the coronal plane and 6 o to the sagit-
tal one) and an abductor muscle force of 703N (inclined by 28 o to the coronal plane
and 15 o to the sagittal one).
Such a model can indicate the apparent fracture risk in the femoral neck area, and
even though MRI is widely considered as a state of the art imaging technique, this
approach is subject to further restrictions. These limitations are not associated to the
geometrical characteristics of the described anatomy, but rather to the mechanical
properties of the reverse engineered tissue. As MRI reconstructed models merely
represent cortical/cancellous bone allocation and not the micostructural characteristics
of trabecular bone, they have to consider bulk material properties for the cancellous
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