BLUNT FORCE 
BLUNT FORCE Blunt force traumas can be defined as "relatively low-velocity
impacts over a relatively large surface area" (Galloway 5). This
type of trauma can be caused by either static or dynamic loading.
Static loading is where a force is gradually applied; in these cases it
is the weight that is significant. An example of this would be the
weight of the topsoil over a burial (see pseudo
trauma). Dynamic loading is when the force is suddenly applied
and here is is not the weight, but the velocity of the weapon that is important.
For example, a hammer that is placed on top of a person's head will not
cause severe damage, but if the hammer is brought down on a person's head
with enough speed, injuries can be produced (see hammer
trauma).
DETERMINING THE DIRECTION OF THE FORCE:
Image courtesy of Dirkmaat, Lab Methods
INWARD AND OUTWARD BENDING:
A bone's elasticity allows it to resist some force and it is only when this ability to flex is surpassed that blunt force trauma will occur. No matter what, however, when a bone is hit it will bend inward at the site of impact (inward bending) and outward (outward bending) at other points.
The
large arrow shows the site of inbending, white the smaller areas show radiating
fractures occurring where there is outbending.
Image courtesy of Dirkmaat, Lab Methods
FRACTURE CHARACTERISTICS:
Different
factors effect what will happen when bone is hit with blunt force.
Possible bone reaction includes:
A.) A piece of bone (referred to as a plug) is being forced into the cranium.
B.) There is inward bending occurring with a fracture starting to emerge from the inner table and moving out.
C.) Here there is a crushing of the outer table and diploe, while the inner table is left untouched.
D.) There is inward bending of the outer table as
there was in (B), but in this case the inner table and diploe are shattered.
Image courtesy of Dirkmaat, Lab Methods
FRACTURE FORMATION:
A.)
The blunt object hits the skull causing inward and outward bending of the
vault. Fractures are beginning to form.
B.) Radiating fractures spread away from the impact site.
C.) The blunt object bends a pieces of bone inward.
D.) Concentric fractures now form.
Image courtesy of Dirkmaat, Lab Methods
PUPPE'S RULE:
See gunshot wounds.
GUNSHOT FRACTURES VERSUS BLUNT FORCE FRACTURES:
See gunshot
wounds.
Click on photos below for a larger view and explanation of each:
Photos courtesy of OsteoInteractive at http://www-medlib.med.utah.edu/kw/osteo/index2.html