Biology Reference
In-Depth Information
intends to investigate the mechanical properties of bone from multiple perspectives (e.g.,
both macrostructure and the material property of bone density) is able to offer a more holistic
perspective of the functional adaptation of the human skeleton. For my dissertation, I was
interested in the functional morphology of body mass, especially the effects of obesity. My
first step in this process was to take courses in biomechanics to gain a better understanding
of human movement and the different forces that can affect bones. If you are also interested
in functional morphology, this is an essential first step in graduate school. My goal was to
analyze the shape changes of the weight-bearing bones of the lower limb, so I investigated
the differences in the biomechanics of movement in normal weight and obese subjects. There
are significant variations in gait patterns between the two groups as a result of weight, so my
predictions about how the bone would alter as a result of this difference in gait developed out
of the knowledge gained during my graduate level biomechanics coursework.
At the University of Tennessee, I had access to the William M. Bass Donated Human Skel-
etal Collection, which is a very large and documented collection of skeletons of modern indi-
viduals with known age, sex, height, weight, and other antemortem data. This collection
represents a broad spectrum of body size from a body mass index (BMI
kg/m
2
) of only
16 (severely underweight) to a BMI of 87 (an individual who weighed over 600 pounds).
The next step in my research logistics was to decide on a methodology. I wanted to
develop a holistic perspective of the functional effects of body mass on the skeleton, looking
at both the material properties of bone density and the macrostructural properties of bone, so
I chose to pursue both DEXA and CT. I then developed partnerships with the Radiology
Department at the University of Tennessee Medical Center, the Department of Exercise
Science, and the Department of Biomedical Engineering, in addition to my existing affiliation
with the Department of Anthropology, which houses the skeletal collection. The Department
of Exercise Science houses a DEXA scanner and the Radiology Department has several CT
machines. The Biomedical Engineering Department provided research funding and expertise
in the three-dimensional analysis of the DICOM images. In addition to the actual data collec-
tion and analysis, my role was to act as a liaison between these departments, to be responsible
for the care and analysis of the skeletal remains during the scanning procedure, to negotiate
the necessary costs, and to coordinate the scanning logistics.
ΒΌ
Bone Density Scanning
To conduct the bone density scans, I focused on just the femur. I chose the femur specifi-
cally because it is a weight-bearing bone of the lower leg, which would presumably exhibit
the greatest changes in bone density in response to body mass. Each dry femur was placed in
a plastic container 65 cm long, 14 cm tall, and 11 cm wide. A 2 cm thick cube of low-density
foam was placed under the lesser trochanter to make the shaft approximately parallel to the
table surface (as recommended by
Ruff, 1981
). Both distal condyles were set directly on the
bottom of the box. Leveling the femur in this way better approximates anatomical position.
There is a slight natural rotation of the proximal femur in the living body that this method
does not account for. As a result, the lesser trochanter is visible in the density scans, which
would not be the case in living individuals.
The DEXA machine is designed to recognize living individuals, so an individual's age is
calculated by entering their birth date in the user interface. To compensate for this, we
