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Bone Strength Prediction with Spinal Cord
Injury
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Principal Investigator: Dennis R. Carter, PhD
Co-Investigators: Gary S. Beaupré, PhD and B. Jenny Kiratli,
PhD
The primary goal of the proposed study is to determine an accurate method
for estimation of bone strength in the midshaft and distal femur using a
minimum amount of pQCT data. The secondary goal is to compare the results of
this method with those obtained with bone mineral densitometric measurements
and calculated geometric properties derived from DXA images. The results will
be expected to help identify those individuals at a high risk of fracture. This
will have particular relevance for individuals with SCI who commonly suffer
fractures of the midshaft and distal femur.
In order to achieve these objectives, the following tasks have been
completed:
- A 2D finite element method to determine bone stresses caused by bending and
torsional moments was developed; bone inhomogeneity is taken into account. A
distributable software application that embodies this method is almost
complete. The application imports pQCT or CT section images and automatically
processes them to create a FE mesh, which is consequently solved to determine
local stresses and strains; bending/torsional rigidity and strength metrics are
computed as well.
- A combined torsion and bending load-testing device was designed and
prototyped. The device has the ability to apply torsional and three point
bending loads independently from each other using separate controller and
actuator assemblies. Loads can be applied either under displacement/angle
control or under force/torsion control. Special attention was paid to the
elimination of unwanted moments caused by the bone's shape irregularity.
- 41 cadaveric femurs have been obtained so far, all meeting the study
inclusion criteria. 17 of them have been dissected and 4 of them have been
embedded partially in acrylic cement (at both ends) in order to fit the
housings of testing device. 20 of the femurs have been DXA scanned in order to
determine T scores.
- A quantitative evaluation of the pQCT modality accuracy was performed,
different scanning parameters have been examined as well as their impact on
acquisition time, signal to noise ratio, beam-hardening effects, radiation
dosage. Relations between the reported voxel values and bone apparent density
were drawn based on both experimental and theoretical data.
Next steps for the coming year include:
- The completion of the cadaver femur preparation process (acquisition,
dissection, bone cement casting) and scanning using the pQCT modality;
- integration of the custom testing device with the available material
testing system, calibration and validation;
- bone testing to failure in different modes (pure bending, pure torsion,
combined bending & torsion);
- evaluation & comparison of experimental results to the model (produced
by the finite element program) results; and,
- initiation of the clinical part of the study, by recruiting SCI patients
and control subjects.
Funding Source: Department of Veterans Affairs – Merit Review
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