Biology Reference
In-Depth Information
FIGURE 8.2
Butterfly fracture illustrating the direction of force.
(
Nordin and Frankel, 1989
). This force causes the material to narrow and lengthen. In bones,
failure occurs at a microscopic level by the pulling apart of the osteons at the cement lines
(areas of joining osteons) (
Nordin and Frankel, 1989
). Understanding that the bone will fail
initially in the area of tension is also a key concept in fracture pattern interpretation. For
example, a specific type of fracture commonly referred to as a butterfly or a wedge fracture
is a great example of using fracture biomechanics for fracture pattern analysis. As the bone is
loaded in a perpendicular direction, areas of both compression and tension are formed. The
bone will fail first in the area of the tension, since bone is commonly weaker in tension than in
compression, as discussed earlier. The fracture will then radiate back towards the area of
compression, constantly changing due to the changing biomechanics of the bone as the frac-
ture advances. While the moment-by-moment progression of this type of fracture is complex,
a simple understanding of where the areas of tension and compression in the bone are can
give an anthropologist the knowledge needed to correctly identify the direction of force
(
Figure 8.2
).
T
YPES OF TRAUMA IN THE HUMAN SKELETON
Historically, bone fractures have always been “classified” into the three separate categories
of blunt, ballistic, and sharp trauma. These classifications serve to aid both pathologists and
anthropologists in understanding the mechanism of injury; however, a proper understanding
of the biomechanics behind the classification system is necessary to avoid confusion and
incorrect interpretation of the fracture patterns.
Blunt Trauma
Blunt trauma is commonly thought of in terms of a slower loading force applied to tissue,
such as is seen in cases of assault, battery, or even motor vehicle accidents. When examining
bone that has been fractured by a blunt force type of mechanism, there are clues that the
pathologist or anthropologist can identify. First, there is usually a clear sign of impact, which
is the area where the fractures first originate from (
Kroman et al., 2011
). Two types of
