Biology Reference
In-Depth Information
TABLE 14.1 Cross-Sectional Measurements
Measurements
a.
Total cross-sectional area
b.
Cross-sectional area of cortical bone
c.
Cross-sectional area of medullary canal
d.
2nd moments of inertia (area) I
x
and I
y
perpendicular through centroid
d
I
x
for mediolateral direction, Iy for
anteroposterior direction
e.
Product of inertia about x and y axes translated to centroid
f.
Second moments of area about principal axes
g.
Angle between translated x and y axes and principal axes
h.
Maximum distance along major axis from area of centroid to outer perimeter
i.
Maximum distance along minor axis from area of centroid to outer perimeter
j.
Polar moment of area
JorI
p
d
approximating torsional rigidity
¼
k.
Centroid
d
center of cortical area
Adapted from SLICE (
Nagurka and Hayes, 1980
)
analyze the geometric properties of bone cross-sections. All that is needed is an image of the
bone cross-section for the analysis. This program is available as a free download from the
website of the International Society of Biomechanics (
http://isbweb.org/software/
imamorph.html
)
. The algorithms used to calculate these properties are available in the publi-
cation by
Nagurka and Hayes (1980)
. The geometric shape measurements that are automat-
ically calculated using SLICE are listed in
Table 14.1
. SLICE can be used to analyze the outline
of cut bone or a DICOM image (Digital Imaging and Communications in Medicine) from
a CT scan.
There is some subjectivity in measurement when deciding whether to include the trabec-
ular bone of the endosteum in the calculation of the cross-sectional properties.
Burr and Pio-
trowski (1982: 341)
caution against this: “Including cancellous bone in calculations of
structural properties of bone cross-sections may cause the strength and stiffness of the
bone to be exaggerated.” They have two arguments for why it overestimates strength. First,
the trabecular bone is closer to the neutral axis and so has a smaller contribution for overall
structural properties in terms of bending and torsion. Second, the trabecular bone has much
lower compressive strength than cortical bone, and thus overestimates the overall area (
Burr
and Piotrowski, 1982
).
MEDICAL IMAGING
For research in human skeletal biology, medical imaging provides nondestructive analysis
in order to reveal the biomechanical properties of bone, including the internal shape and
