Lecture slides on Mechanical injuries Forensic Medicine

2.  Mechanical injuries are the most commonly encountered
type of wounds having varied appearance. There are many
factors, which control their shapes and these factors may be
in the weapon or the part struck.

3. Weapon Tissue
Type of weapon Architectural design of the
tissue
Execution of mechanical
force
Resistance of the tissue
Weight and velocity of
weapon
Movement of the part struck.

5.  Type and shape of weapon directly control the shape of the
wound. Examples are injuries produced with sharp, blunt and
fire arm weapons.
 Execution of mechanical force is an important factor in the
interaction between weapon and a part of the body to
determine the outcome. There are two manners of
application of force to a part of the body direct and indirect.

6.  Direct application of force produces wound at the point of
application proportionate to the extent of the force and such
injuries at the site of impact are called impact injuries.
Examples are injuries produced with a club, kick or brick at
the site of impact.

8.  Indirect application of force results in injury at a place away
from the site of impact. Stretch laceration and deceleration
injuries of the chest and cranium are examples of indirect
application of force.
 Weight and velocity of the agent determine the wounding
power of any moving object, which is its kinetic energy calculated
by the formula KE = l/2 m v. A brick, club and bullet, all have
kinetic energy chiefly proportionate to their weight and velocity. A
bullet has much higher velocity and shall proportionally produce
greater effect.

9.  Human body is composed of different types of tissues, which
are either soft and elastic like skin, fat, muscle and internal
organ or relatively rigid and less elastic like ligament and
cartilage or hard having limited elasticity like bones. Elasticity
of the bones depends upon age of the person and extent of
calcification.

10.  . Bones of infants are relatively elastic than those of adults
and old persons, which become brittle and thus, break more
easily. Shape of bone may be long like those of limbs and
ribs, or plate like vault of skull and crest of the ileum or short
having irregular or peculiar shapes like small bones of hands
and feet. These shapes along with size and density of bone
have relation to the outcome.

11.  Based upon the design, a part of the body may be compact as in limbs
or a cavity as in abdomen, chest and cranium. These cavities have
organs in them, which are of different shapes and consistency being
composed of different types of tissue. Because of the design of these
organs, they have different character;
 Liver, spleen and kidney are solid
 Lungs are spongy and contain air in them
 Stomach, intestine, heart, gall and urinary bladder are hollow sacs
having fluid or semi-solids of different density in them like blood in the
heart, bile in gall bladder, water mixed food in stomach and intestine
and urine in the urinary bladder.

12.  An impact with a club having same force and same direction
on different parts of the body having different architectural
designs shall produce injuries of different shape. Impact on
the forehead produces a laceration, whereas similar impact
on the buttock shall produce a bruise. This difference in the
shape of wound is due to the difference in architectural
design, forehead has scalp stretched over a bone whereas
buttock comprises mostly of soft tissues of skin, fat and
muscles. Hip bones within are deeply buried.

13.  Resistance of the tissue controls the outcome, which
depends upon the extent of surface area involved and ability
of the part to absorb the force without damage. Soft and
elastic tissues like skin and muscle absorb the striking force
effectively without being injured, whereas hard and inelastic
ones like bone fracture with same force.

14.  Effect of movement of the part struck can be appreciated
by noting the differences in wound produced when the part is
stationary or in motion. Difference is best manifested when a
cavity of the body like head or chest is involved. A strike on a
stationary head produces injury of the scalp at the site of
impact and damage may extend even to deeper structures
including bone and brain, but no where else

16.  Types of mechanical injuries most commonly met in
medico-legal practice, resultant from physical assaults and
accidental trauma occurring on the road, rail and in the
industry are discussed one by one.
 Abrasion is an extremely trivial form of damage and is
restricted to most exterior part of the skin. It is important from
the point of view of its causation. When a hard and rough
object is pressed against the body surface and moved, an
abrasion is produced. There are three subtypes: moving,
imprint and friction abrasion.

18.  Moving abrasion indicates direction of the abrasive force
showing heaping or piling up of the epidermis an the far end.
Appearance is characteristic. Example of this variety is a
scratch produced with a fingernail, pin or thorn. Another
example is irregular removal of the epidermis occurring
during dragging of the body surface against the rough object
such as road as seen in vehicular accidents. This abrasion is
called a graze.

19. A. Scratches on the forearm. B. Graze on the
arm.

20.  Imprint abrasion is one, which indicates the pattern of the
object causing it. Examples of this variety are imprint
produced by boot heel, rough stick and teeth. Pattern of
these abrasions generally provides good corroborative
evidence about the causative agent.
 Friction abrasion is an injury, which is produced by a
ligature such as a rope on the neck. It indicates both
movement and imprint of the ligature causing both indent and
friction rub and provides good information about the ligature
material.

21.  The removal of epidermis during the postmortem period may
also occur and this postmortem abrasion does not show
seepage of serum or blood. Ante-mortem abrasion can easily
be differentiated from post-mortem abrasion by the presence
of vital reaction. Post-mortem abrasion is fainter in color and
with passage of time acquires parchment appearance.

23.  Age of abrasion is difficult to estimate especially when it is
superficial and dry. Abrasion heals rapidly leaving no
permanent mark. Estimation of age would depend upon
changes taking place in the effused serum, which may also
occasionally, gets mixed with blood. The fluid when dry
varies in color from straw to yellow to brown, depending upon
the amount of blood.

24.  It is followed by formation of a soft scab in about two days,
which hardens in about another three to four days. Hard scab
retracts in another three or four days and finally falls away.
Time relation of these changes through variable, yet is the
indicator for duration.

25.  Bruise or contusion is a closed wound occurring due to
bleeding into the tissue without solution of the continuity of
the skin or covering of an organ. It is more commonly met
with on the body surface, but bruising of internal organs like
liver or kidneys also occurs. Though the skin is not broken,
yet structure of skin, subcutaneous tissue and other
structures beneath it depending upon its depth are damaged.
Extravasations of the blood from the broken blood vessels
spread into the surrounding tissue.

26. A. Indentation of the tissue B. Resultant bruise indicating shape
of the weapon

27. An impact by a blunt weapon produces sudden indentation of
skin and underlying tissues, which after recoil, becomes
swollen, red in color and painful to touch. A bruise may
acquire the shape of the weapon. Severity of the bruise
depends upon:
 Amount of the force applied
 Type of underlying tissue
 Age and state of health of the individual

28.  Blood spreads in the lax tissue more easily as can happen in
area around the eye and lips. Persons with coagulation defects,
disease of blood vessel and liver will bleed more and may give a
false impression about severity of such injury. Children and old
people bruise more easily. Visibility of a bruise is better in fair
people. Blood collected at the site of impact may move along the
tissue line of least resistance under the influence of gravity
changing both its shape and site as happens in production of
black eye following a bruise of the forehead, scalp and
extravasations from injury to the membranes of the brain. It is
valuable to re-examine the victim after about twenty-four hours of
the first inspection.

29. B D
Bruises on the skin and internal organs. A. On the left eye B. On the back C&D. On the surfaces of
liver and kidney

30. Gravity shifting of extravasations

31.  Pseudo-bruising may occur in skin, internal organs, tissue
spaces between organs and their coverings. Development of
pseudo-bruising show up by development of intense
localized postmortem lividity of the skin usually in internal
organs and body coverings. It may also occur as
displacement of internal pools of blood by gas pressure into
areas away from actual hypostasis, To an untrained eye, it
may simulate ante-mortem bruising and should be
differentiated from ante-mortem bruises.

32.  Likewise, internal pooling of blood in tissue spaces and
retroperitoneal tissue with hemolysis of blood cells also
resembles ante-mortem hemorrhage. Differentiation
becomes more difficult in cases of congestion without
inflammation. The areas showing pseudo-bruising lack vital
reaction. Histological examination may advantageous in such
cases. Importance in their distinction lies in the fact that
bruising is an ante-mortem phenomenon, which indicate
violence before death.

33. 1 Lacks vital reaction. Shows vital reaction of swelling and
inflammation.
2 Blood accumulates within the vessels and
when incised,
blood may ooze out of the cut mouths of
the blood vessels
Blood vessels are broken and
blood is present in the surrounding
interstitial. No flow of blood occurs
upon vessels incision.
3 Confined to the skin and the coverings of
the internal organs like mucosa or serosa.
Lies in the interstities below
epidermis or even deeper, as the
epidermis is devoid of blood
vessels.
4 Cuticle of the skin is intact as it is only an
accumulation due to gravity.
Cuticle is damaged and may show
abrasions due to the violence
causing it.
5 Always appears in a dependant part. Occurs at the site of injury,
irrespective of its being dependant.
6 Sustained pressure however slight
prevents appearance of hypostasis.
Independent of pressure.

34.  Age of the bruise can be estimated by the changes in the
color of effused blood, which occur with the passage of time.
These color changes also depend upon ability of the tissue to
absorb it. Capillary blood is dark red in color, therefore, a
recent bruise appear purple in color. After about two days, it
darkens because oxygen in the blood is removed. The
enzymes of the tissue begin to change the hemoglobin into
blood pigments and in about four to five days, the bruise
becomes greenish.

35.  Fading of the bruise occurs because of absorption of pigment
from the site. With further passage of time, about seven to
ten days, color changes to yellow. Complete disappearance
of color occurs in about fifteen days depending upon site,
size and depth of the extravasations.

36.  Laceration is an open wound caused by a breach, tearing of
skin, or covering of an internal organ along with underlying
tissues. It is produced by application of blunt force.
Depending upon the mechanism involved, there are three
subtypes:
 Crush or also called split laceration
 Overstretch laceration
 Grinding compression

37.  Split lacerations most commonly occur on the scalp,
forehead and chin or any other part of the body where skin is
firmly supported by the underlying bone. Sudden
compression of the skin and other tissues between the
weapon and the underlying bone splits it. It may resemble an
incision wound and may be confused with it.

38.  The characteristics of recognition of such a wound are
breach of skin and underlying tissue showing minimal
irregularity and bruising of the edges and surrounding tissue.
Hair if present at the site of tearing is forced into the wound
and bulb of hair is crushed. Denudation of hair in hair bearing
area may occur.

40.  Overstretch laceration is most commonly seen in areas of
the body where skin is supported loosely such as wrist,
forearm, axilla and abdomen. When localized pressure along
with push or pull of increasing force overstretches the skin, it
ruptures and gets separated from the underlying structures.
Such a laceration generally occurs in road traffic accident
and industry.

41.  The parts of the body while get trapped in running belts in
industry also sustain such injury. Rupture of the skin due to
over-stretching may also occurs due to fracture and
deformity of a bone. The characteristics of such lacerations
are breach in the skin and from the underlying tissue showing
flapping in the direction of stretch. External hemorrhage like
other tears is limited.

42. Weapon A stretching soft tissue B to rupture it Arrows indicate direction of pressure and movement.

43.  Grinding compression is usually the result of passing of a
heavy wheel over the limbs of the body causing grinding
compression. The characteristics of such a wound are multiple
perforations in the skin, which is also separated from the
structure under it with crushing of muscles and other underlying
tissues. There are extreme extravasations of blood into potential
spaces of crushed tissue. The wound shows swelling and is
severely painful. When such lacerations occur over wide area,
they may precipitate fat embolism or crush syndrome and death

44. Weapon A grinding tissue B to precipitate compression laceration

45.  Clinical state of victim having such a damage would depend
upon the number of wounds, extent and speed of
hemorrhage from them. External bleeding from these
wounds is generally limited.

46. Lacerated wounds on body surfaces. A. Scalp showing irregular margins, tags and varying depths. B.
Forehead showing regular margins and varying depths. C. Foot showing separation of skin and flapping.

47.  is an open wound resulting from a cut or an incision in the
skin and underlying tissues. The most common instrument
causing it is a knife or a sharp cutting glass. Movements of
the weapon are necessary ingredients for causing a cut in
the tissue. Characteristics of the weapon such as shape, size
and manner of infliction are important factors, which affect
shape and dimensions of the wound. An important feature of
such a wound is involvement of covering clothes.

48.  Wound is generally linear, gaping in the center depending on
to cleavage lines of Langer and becoming spindle shaped
showing clean cut margins, sharp angles and smooth walls.
If the area is hair bearing, it shows cutting of hair including
hair bulbs. External hemorrhage is more than from a
lacerated wound.

49. Knife A causing incised wound in soft tissue B.

50.  Penetrating wound is produced if sharp edged pointed
weapon, which is thrust into any part of the body. When a
body cavity is involved and pierced, wound is called
puncturing wound. Shape and dimensions of length and
depth of the wound would depend upon the shape, breadth
and length of the weapon causing it. Most of the
characteristics of these wounds arc similar to those of incised
wounds, except the depth. In both penetrating as well as
puncturing wounds, depth is the greatest dimension

51. Knife A puncturing abdominal wall B (dotted lines) and indicating
its positions.

52.  Clinical condition of victim of these wounds is generally
serious showing signs of acute hemorrhagic shock due to
extensive internal hemorrhage. In case of penetration of the
chest cavity, additional feature is development of
hemopneumothorax, surgical emphysema in the surrounding
area and hemoptysis.

53.  Both lacerated and incised wounds have some common
features. Both arc open wounds, show external bleeding,
stain clothes of the victims and are produced mechanically.
Differentiating features are shown diagrarnmatically in
diagram and contrasting features are enlisted in

54. A, Incised wound- B. Lacerated wound.

55. Features Incised wound Lacerated wound
Shape Linear or spindle Irregular
Margins Regular Irregular
Angles Sharp and well defined Blurred and ill-defined
Walls Smooth, showing no
bridging or tissue tags
Irregular, showing tissue
tags
Bleeding Profuse Comparatively less
Hair Cut in line of the wound Pushed into the wound
Hair bulbs Cut in line of the wound Crushed
Area around the wound Not bruised May be bruised or
denuded

56.  Age of an open wound whether lacerated or incised depends
upon whether it remains clean or gets infected. Incised wound
comparatively stays cleaner. Clean and non-gaping wound gets
covered over by lymph and blood clot in first twenty four to thirty
six hours. It is followed by adherence of edges in about three to
four days. The process of healing is completed with red linear
scar formation in about seven to ten days. The color of scar
gradually changes to brown. Non-clean and gaping wound
usually become septic and the estimation of its age, depends
upon the extent of inflammation.

57.  There are generally two situations. If the sepsis is slight, the
margins of the wound swell in first twelve to sixteen hours,
followed by appearance of sero-purulent discharge in about three
to four days. It is followed by laying of red-granulation tissue in
the bed of the wound in about five to six days, skin grows over
and healing gets completed in twelve to sixteen days. Fresh scar
in such a case is more prominent and slightly raised over the
surface of the skin. Gross sepsis keeps the wound open
indefinitely and no estimation of age of such a wound is possible.

58.  Fracture of bone occurs by two mechanisms. If the force is
tolerable and of moderate intensity, the bone suffers a limited
local indentation without break and then recoils back to its
original shape like any other tissue of the body. When force is
greater than the limits of its elasticity, it breaks. Fracture
commences at the point of maximum convexity.

59.  Fracture of long bone either occurs at the site of impact or the
bone acts as a lever diverting the force to some remote weaker
point, which fractures. Example of later mechanism is fracture of
clavicle following a fall on an outstretched hand. Long bones of
children being comparatively more elastic show limited damage
to only one side at the convexity of the bend and result in green
stick fractures. Application of twisting force to a long bone of the
child causes fracture having spiral pattern and pull and push
generally separates epiphysis most commonly seen in battered
baby. These are the examples of indirect violence.

60.  Fracture of skull and its pattern depends upon the anatomical
structure of the skull. Strength of skull varies due to thickenings in
both vault and base. In between the thickenings, skull bones are
thin. When direct force is applied, a linear fracture radiating from
the point of impact occurs and in case of indirect application
offeree, fissured fracture distant from site of impact occurs.
Occasionally force from the face like a blow on the mandible,
may be transmitted to the base of the skull, fracturing the
weakest portion namely cribriform plate of the ethmoid.

61.  Another example is transmission of force upward through the
spine after a fall from height on feet or buttocks fracturing
base of the skull.
Rowbotham is of the view that there are two mechanisms of
fracturing of skull bones and they are due to:
 Local deformation of a segment at the site of impact
 General deformation of the whole skull

62.  Fracture due to local deformation of the segment at the site of
impact occurs, if the force applied is sufficient to cause crushing
of outer table into diploe or a bend of the skull bone. Sequence of
events at the site of impact is formation of a shallow cone. Apex
of cone stretches the inner table and compresses the outer table.
At the periphery of the cone convexity of the bend is directed
outwards. If the distortion is beyond the strength of the bone, a
fracture confined to the inner table at the apex of cone results. If
force is greater than the strength of both inner and outer tables of
the skull, both fracture.

63.  Inner table at the apex of the cone fractures before the outer
table, whereas at the periphery the outer table fractures first.
Extension of the break both of inner table at the apex to the
outer table and at the outer table at the periphery to the inner
table completes break in both tables and cause depressed
comminuted fracture. Fracture line in such depressed
comminuted fracture tends to run radially from the central
point at the apex of the cone to the periphery and the fracture
lines also tend to run in a circular manner.

64. Mechanism off fracture by local deformity starting from normal A to localized comminuted
depressed fracture D.

65.  of the whole skull occurs due to compression of the skull.
When the skull is compressed in one plane, it behaves as an
elastic sphere and bulges out in other plane, where fracture
occurs. Examples of this mechanics are compression of skull
of infant by forceps during delivery and head in traffic and
industrial accidents.

66.  Skull when compressed laterally, it elongates in its vertical
and longitudinal plane, producing fractures in these planes.
These fractures are usually fissured ones occurring at parts
of the skull distant from actual site of application of force.
Complication of the fracture of the inner table leads to the
development of adhesions between the duramatter and brain
substance and may precipitate traumatic epilepsy.

67. Arrows indicate compression and general deformation of the whole skull causing fractures.

68.  Moritz claims that if the skull is compressed, spongiosa
between the inner and outer tables being fragile, a
circumscribed segment of the outer table may be driven into
the diploe without disturbing the inner table. This type is an
uncommon finding and generally, it does not occur.

69. Outer table crushed into diploe