152 Forensic dentistry
in the majority of such cases. The extremities, especially the hands
and forearms, and occasionally the legs, may bear defensive inju-
ries as well. Therefore, all bones should be examined, to the extent
possible, before cleaning and again afterward. Care must be taken
when macerating remains not to remove or damage the periosteum.
Blade marks are often seen in this fibrous tissue sheath overlaying
undamaged bone cortex. These injuries are best viewed in oblique
light under low-power magnification, or under oblique fluorescence.
Defects may be captured for comparison before further cleaning by
making a cast with polysiloxane or similar material. Unlike ballistic
metal, blades rarely transfer any of their substance to bone. However,
when a sharp edge is applied to a bone obliquely, microscopic exami-
nation will usually reveal a “bar code” effect, resulting from defects
in the cutting edge as the blade is applied. The same is true when a
serrated blade strikes bone at a low angle. These markings may be
matched to a suspect blade using a comparison microscope. As is
the case with soft tissue blade injuries, it is unlikely that the defects
will yield information about the dimensions of the offending blade.
When the tip of a blade is forced into a bone, it is sometimes pos-
sible to determine whether it is backed or sharp on two edges (as in
a dagger). Cases involving postmortem dismemberment will usu-
ally present several kinds of blade injuries, from knives, manual and
power saws, cleavers, and even axes.^57 These must be distinguished
from perimortem blade assault. Careful microscopic examination
will usually differentiate knives from saw blades, and manual saws
from circular and reciprocating saws. Further differentiation between
various types of saw blades may also be made microscopically.^58
On a few occasions, the author has observed vital reaction in the
periosteum adjacent to the site of dismemberment of an extremity.
This finding, far more common in soft tissue, indicates active circu-
lation, though hopefully not consciousness, during the removal of
the limb. When multiple blade injuries are present, some investiga-
tors will create a cut map, i.e., a three-dimensional representation of
the skeleton and all of the injuries. This reporting format is useful in
the context of possible witness accounts, and may help in differen-
tiating fatal, nonfatal, and defensive injuries. Finally, in the case of
remains outdoors, it is important to distinguish between blade inju-
ries and pseudotrauma caused by animals with scissoid mouth parts,
e.g., turtles and carrion birds, gnawing by scavengers with carnacil
dentition, and trampling by animals.^59 Animal chewing will usually
produce markings on opposite sides of a bone as the jaws occlude,
whereas true blade marks will appear on only one surface. As in the
case of all penetrating injuries, blade or ballistic, it is important to