Biology Reference
In-Depth Information
of trabecular and 25
e
30 percent of cortical bone mass with advancing age, whilst men lose
15
e
45 percent of trabecular and 5
e
15 percent of cortical bone” (Francis, 1998). Cortical
bone loss is accelerated following menopause, whereas the trabecular bone loss is relatively
constant throughout adult life (Zhang-Wong and Seeman, 2002).
Weight-bearing exercise increases bone density at a slower rate than it increases in muscle
mass. Calcium supplementation does not appear to have much of an effect on perimeno-
pausal women's bone density and may have other physiologic side effects. The dramatic
decrease in estrogen appears to be a more significant factor in maintaining bone metabolism
at menopause. Ancestry also plays a significant role in bone density. African American
women are less prone to osteoporosis than European American women and tend to have
much greater bone density throughout life (
Nelson et al., 2000; Saeed et al., 2009
). It appears
that this distinction is more related to genetics than environment, as another study of individ-
uals from Niger showed increased bone density compared to European and Asian popula-
tions despite chronically low intake of calcium in the Niger sample (
VanderJagt et al.,
2004
). Body mass index also plays a role in bone density (
Gibson et al., 2004; Looker et al.,
2007; Miyabara et al., 2007; Wu et al., 2007; Moore and Schaefer, 2011
).
CR
OSS-SECTIONAL GEOMETRIC SHAPE ANALYS
IS
Three decades ago, Ledley et al. (1974) noted that the only noninvasive method for recon-
structing cross-sections sufficiently for biomechanical analysis was through computed tomo-
graphic (CT) scanning. The same is still true today (
O'Neill and Ruff, 2004
) with even better
quality images, faster scanning time, and reduced cost. The resultant 3-D radiographs can be
converted into 3-D computer surface models, which facilitate highly sophisticated shape
analyses. Three-dimensional computer models enable automation of research, and thus the
simultaneous, quantitative interpretation of shape variation in the skeleton. Before medical
imaging methods, destructive analysis (or a fortuitous bone fracture in an archaeological
specimen) was the only means of directly analyzing the 3-D shape of both the internal and
external structures of bone.
Research studies on shape variation in the skeleton that have used cut bone cross-
sections have investigated diverse topics ranging from age changes in the skeleton
(
Burr and Piotrowski, 1982
) to the prediction of minimum critical force for fracture risk
of the clavicle (
Harrington et al., 1993
).
Bridges (1985)
conducted cross-sectional geometric
analysis on the humerus and femur of males and females from archaeological samples
dating to the Archaic (6000
e
1000 B.C.) and the Mississipian (1200
e
1500 A.D.) prehistoric
time periods in North America. The results of her research surprisingly revealed that the
females actually had larger humeral cross-sections than males during the Mississipian
period. This was likely the result of the division of labor in which females manually
ground corn
d
an activity not practiced by the hunters and gatherers of the Archaic period
(
Bridges, 1985
).
Traditional methods for studying the cross-sectional geometry of a bone were to simply
cut the bone. An excellent and detailed description of methods for how to determine the loca-
tion of each slice and to make the cross-sectional cuts for the femur is provided by
Ruff (1981)
.
Nagurka and Hayes (1980)
developed the computer algorithm SLICE to automatically