Medical Imaging as a Bone Quality Determinant and Strength Indicator of the Femoral Neck - Biomedical Engineering Systems and Technologies - page 192

bone. As the mechanical properties of bone vary significantly among the human
population, a model not considering these patient specific strength characteristics,
may prove to be highly inaccurate.

3 DXA Strength Indicator of the Femoral Neck

3.1 Materials and Methods

This part of the study, was conducted on femoral neck samples, harvested from pa-
tients undergoing total hip replacement due to osteoarthritis. In order to determine the
samples' structural integrity, standard X-rays (anterior- posterior) of the pelvis were
taken preoperatively in all cases. Patients with a sort femoral neck, large cysts in neck
region or previous surgeries in proximal femur were excluded from the study.
Overall 30 patients (27 female and 3 male) were considered as representative can-
didates for this study and thus subjected to DXA, to catalogue their proximal femur
bone mineral density. The average age of these patients was 63.7 years (57- 76 years).
During the surgical procedure and after a 45 o osteotomy, femoral heads were re-
moved and stored at -60 o C until evaluation. A plane bone slice with 6mm thickness
was harvested from the femoral neck (see figure 3) as two parallel blades, mounted on
a mechanical saw at a 6mm distance, simultaneously entered the proximal femur. This
ensured similarity among all specimens while producing parallel piped specimens,
directly employable in compression tests.

Fig. 3. Considered bone specimen and reverse engineered model

Mechanical testing was performed on an electric INSTRON Testing system. To de-
termine the specimens' strength characteristics, all samples were subjected to uniaxial
compression, until failure. A cross-head traveling speed of 0.6mm/s was selected and
the maximum travelling distance (upon contact) was set to 5mm in order to avoid
contact of the moving cross-head and the fixed base plate. To reduce friction, the
sample-actuator contact areas were lubricated. The displacement of the cross-head
was measured by means of an inductive sensor, at an accuracy of 1 µ m.