This document discusses various types of mechanical injuries including abrasions, contusions, lacerations, and their distinguishing features. It defines abrasions as denudation of superficial skin layers caused by friction against a rough surface. Contusions are characterized by extravasation of blood into subcutaneous tissue due to blunt force trauma. Lacerations are tears or splits of skin/tissue caused by blunt force stretching tissues beyond their limits. The document outlines the classification, appearance, healing process, differential diagnosis and medicolegal importance of each type of mechanical injury.

1. Mechanical Injuries
Dr Nikita Prabhakaran G
Assistant professor

2. Medical definition
• Injury = Wound
• Any breach of natural continuity of skin or mucous membrane

3. Legal Definition- INJURY (44 IPC)
• Any harm
• Whatever illegally caused to any person
• In Body Mind Reputation Property

4. Classification of Injuries
• Based on causative factors
• 1. Mechanical / Physical Injury
• 2. Thermal Injury (Heat and cold)
• 3. Chemical Injury
• 4. Miscellaneous (Electrical, Radiation, Lightning, Blast)

5. Mechanical Injuries
• Caused by blunt force :
• 1. Abrasion
• 2. Bruise/ contusion
• 3. Lacerated wound
• 4. Fracture / dislocation
• Caused by sharp force
•1. Incised wound
•2. stab wounds
• Caused by firearms

6. ABRASION

7. ABRASION
 Characterised by denudation of
superficial layers of skin
 (usually epidermis & papillary dermis)
 Caused due to friction against a
rough surface
 And usually heals without a scar
formation

8. Types of abrasion
• 1. Scratch/ linear
sharp or pointed object
surface layers are collected in front of the object
clean area at the start
heaped up epithelium at the end
Eg: fingernail abrasions, thorn, pin

9. • 2. Graze abrasion (sliding/grinding/scrape abrasion)
• Horizontal or tangential friction
• Between skin and hard rough surface
• Uneven longitudinal parallel lines
• Direction can be appreciated
(heaping up of epithelium at the opposite end)
• Most common
• Particles of glass, gravel or dirt may be found

10. • Brush burn
• wider area rubbing violently ,
• turn firm on drying even without a scab
• Friction burn- wider excoriated area
• redness
• no linear marks
• when covered by clothing

11. 3. Pressure abrasion
• Direct impact or linear pressure of an object over skin (Perpendicular)
• Inward crushing of epithelium
• For longer periods
• Examples:
• Ligature mark
• Nappy rash
• Corneal abrasion – prolonged contact lens use

12. • 4. Imprint abrasion
• When there is a considerable amount of force
• That acts perpendicularly
• But only for a short period of time
• Patterned abrasions
• (when the causing agent can be identified)
• Otherwise called a signature abrasion
• Eg: tyre tread marks

13. Age of abrasion
• Gross and histopathological changes
• Gross:
• (1) Fresh – Bright red
• (2) 1 day – Blood and lymph dries up. Bright red scab forms
• (3) 2-3 days – Reddish brown scab
• (4) 4-7 days – (i) Scab becomes dark brown
• (ii) Epithelium grows under the
• scab and covers defect. Scab becomes ready to fall
• (5) >7days – Scab dries, shrinks and falls

15. Antemortem abrasions/ post-mortem abrasion
Characteristic Antemortem abrasion Postmortem abrasion
1. Site anywhere on the body Only on bony prominences
2. Colour Bright reddish brown Yellow translucent parchment like
3.Exudation More. Scab slightly raised Less. Scab lies low
4. Microscopic Congestion, vital reactions No congestion /vital reaction

16. • Medico Legal Importance of Abrasions
• (1) Direction of force – can be estimated from tissue tags
• (2) Force of impact – can be judged
• (3) Foreign matter sticking over abrasions –
may give an idea of scene of crime
[eg grass, gravel, sand etc]
• (4) Imp and only sign – of internal injury sometimes

17. (5) Manner of production –
• (i) Generally accidental or homicidal in nature
(except Ligature mark in hanging)
• (ii) self-inflicted – false abrasions
(6) Nature –
• (i) Usually simple
because they heal without scarring
• (ii) Do not pose danger to life
(unless multiple and massive,
or involve underlying vital organs)
• ***Grievous abrasions corneal abrasion,
ligature mark
tyre tread mark

18. • (7) Time of assault – can be calculated
• (8) Type of offence – is indicated by site of abrasions
• (i) around anus - homosexuality
• (ii) around breast, cheeks, neck, inner side of thighs
indicate sexual assault
• (iii) over face – indicate struggle
• (iv) over mouth and nose – in smothering
• (v) over neck – indicate throttling
(9) Weapon – can be identified from patterned abrasions.
Sometimes peculiarity of the offender’s nails can be estimated [eg long,
crooked, broken, irregular
etc).

19. Differential diagnosis
• 1. Burns
• 2. Excoriations due to
excreta (Nappy rash)
• 3. Pressure sore
• 4. Ant erosions
• 5. Drying up of skin after
death

20. Contusion/ Bruise

21. Contusion
• Mechanical injury caused by
blunt force
• Characterised by extravasation of
blood into the subcutaneous
tissue
• Due to rupture of subcutaneous
vessels

22. Salient features:
• (1) Situation – the dermis and subcutaneous tissues
(some-times in the fat layer)
• (2) Color – Lighter in the center
(extravasated blood is pushed outward)
• (3) Cause – by blunt force,
• (4) Associated findings –
(a) painful, tender
(b) crushing and tearing of s/c tissues
(c) usually no destruction of skin
(d) may occur in association with abrasions or lacerations.

23. • (5) Size –
(a) Petechial hemorrhages – 0.1-2 mm
(b) Ecchymosis – 2-5 mm
(c) Bruise – more than 5 mm.
***Size of a bruise >>>the surface of the weapon
(as blood continues to ooze)
(d) Hematoma – More than 5 mm
with appreciable swelling.
Forms a fluctuant mass
by large vessel bleed
(6) Margins – blurred
(7) Extent – depends on the force

24. Types:
(1) Intradermal bruise - occurs in dermis (Fig 12.9).
Amount - of extravasated blood is small,
pattern more clear (more superficial)
occurs especially when the impacting object has
alternating ridges and grooves
(2) Subcutaneous bruise - Most common type of bruising (appears soon)
(3) Deep bruise - deep subcutaneous tissue
just above muscle, or between muscular bundles.
apparent after 1-2 days after

26. Factors Modifying Size and Shape
• 1. Age Children and old people bruise
• 2. Sex Women bruise more easily than men [more s/c fat]
• 3. Obesity Fat people bruise more easily [greater amount of s/c fat]
• 4. Color of skin Fair skin- better appreciated visually
• 5. Effect of embalming dark pigment complex with blood
• 6. Condition and type of tissue
(i) Vascular and loose tissue (eg face, vulva, scrotum)
(ii) Good muscle tone (boxers, athletes
(ii) Resilient areas (abdomen, buttocks) bruise less.

27. • 7. Weapon used : yielding weapon (less bruising )
• 8. Associated diseases
(i) Arteriosclerosis –rupture easily
(ii) Blood dyscrasias –even on minor trauma
(iii) Poisonings – Hepatotoxic poisons
Chronic alcoholics
9. Miscellaneous factors
(i) If injured part is thickly clothed, bruising may not be seen
(ii) Persons on anticoagulants, antiplatelet drugs, SSRI"More extensive
bruising. SSRIs

28. Special bruise
• 1. Tram line bruise/ rail road bruise
struck by a pliable instrument broom handle, cane
appears as two parallel lines of bruising
with an undamaged zone in the centre
The intervening pale area = the width of the weapon

30. • 2. Ectopic contusion/ Migratory bruise
• The site of bruise does not necessarily indicate the site of violence
• Extravasated blood tracks along fascial planes
or between muscular layers
• under the influence of gravity
• to reappear at a site below the injured site
• it is known as ectopic, migratory or percolated bruise

31. Examples:
(i) Spectacle hematoma –
(a) Blunt injury to the forehead collects around the eye
(b) Blunt injury to skull / fracture of anterior cranial fossa
known as spectacle hematoma, panda eyes or raccoon eyes
(ii) Battle sign –
Bruise behind the ear [mastoid ecchymosis]
may indicate fracture of posterior cranial fossa

33. (iii) fracture of jaw – “bruise in neck”
(iv) fracture of pelvis – “bruise in thigh”
(v) fracture of femur - lower outer aspect of thigh
(vi) Blunt injury to upper part of thigh- above knee
(vii) Kick on the calf- around ankle.
(viii) Gray Turner’s sign – retroperitoneal hemorrhage, pancreatitis
(ix) Cullen’s sign – retroperitoneal or intra-abdominal haemorrhages

35. Age of bruise
Duration Colour Pigment
1 Initially Red Oxy hemoglobin
2 Few hours- 3days Blue Deoxy hemoglobin
3 4th day Bluish black- brown Hemosiderin
4 5-6 days Green Hematoidin
5 7-12 days Yellow Bilirubin
6 2 weeks Normal Oxyhemoglobin

36. Special situations:
(i) Subconjunctival bruising – color changes do not occur.
They change straight from red to yellow
(ii) CO poisoning – bruise have a cherry red color.

37. Differential diagnosis

38. Postmortem bruise
Antemortem bruise Postmortem bruise
Time of appearance Before life Within 2-3 hours of death
Swelling around Present Absent
Damage to epithetlium Present after
Size Small to large Always small
Extravasation More less
Site anywhere Bony prominences
Tissue underneath Staining +++ Washes off easily with water
Histology Inflammatory reaction + nil
Colour changes + Always dull blue
Histochemistry Enzymes++ ----

40. Artificial bruise
True bruise Artificial bruise
Cause Blunt force Irritant juices
Site Anywhere Exposed accessible parts
Colour Changes with time Dark brown
Shape ovoid irregular
Margins Regular diffuse Distinct irregular
Itching No Yes
Vesicles No Present
Redness and inflammation Seen over the lesion Seen around the lesion
Contents Extravasated blood Acrid serum
Chemical tests ------ +++++

42. Postmortem staining vs contusion
Postmortem staining Contusion
Dependent portions anywhere
Postmortem change Caused by Blunt force
Confined to the vessels Infiltration in deep tissues
Margins- defined Blurred margins
Blanch test +++ Does not blanch
Incision- blood in vessels Incision- blood infiltration
Area not elevated Area elevated
Enzyme histochemistry – enzymes++ No enzymatic activity

43. Mongolian spot

44. Medicolegal importance
1) Age of bruise –Can confirm or refute the story of victim
2) Alcoholics – are more prone to bruising
3) Decomposition – can alter the appearance of contusions
4) Distribution of bruises –indicate the character and manner of injury
(i) Child abuse – of different ages all over the body
(ii) Manual strangulation – 6 penny bruises
(iii) Pinning on the ground -bruising of shoulder blades
(iv) Restraint signs- wrists
(v) Sexual assault – bruising of inner aspect of thighs

46. 5) Manner of production:
(i) Self inflicted – Very rare because painful.
May be seen in hysteria and mentally ill persons.
(ii) Accidental – (a) Very common
(b) Seen on prominences [forehead, nose, elbows, knees]
(iii) Homicidal - (a) On any part of the body
(b) Associated injuries

47. 6) Medicolegal value –
medicolegally less valuable than abrasions
because:
(i) Ectopic bruises - appear away from the site of injury.
(ii) Direction of force – not indicated
(iii) Shape and size - does not correspond to weapon [due to oozing]
(iv) Time of appearance –may be too long after infliction
(v) Visibility - in dark skinned persons
7) Patterned bruises – May indicate the surface features of offending weapon
8) Size – can indicate the degree of violence.

49. LACERATIONS

50. • Lacerations are
tears or splits of skin,
mucus membrane,
muscle or
internal organs,
produced by application of
blunt force to the body,
which stretches tissues beyond
their limits of elasticity.

51. • Salient features:
(1) Also called ruptures
(2) Displacement of tissues is most common – when soft tissues
are crushed against bone, e.g. scalp, facial bones, shoulders and shin.

52. • General Characteristics
• (1) Margins – irregular, ragged, uneven
• (2) Edges:
(i) Angular impact
(a) side opposite to the direction of motion - torn free and undermined.
(b) side from which blow was delivered -abraded and bevelled
(ii) Perpendicular impact - Equal undermining on all sides.
• (3) Depth – depends on
(i) degree of force
(ii) depth of soft parts at the site of injury.

53. • (4) Shape and size:
• (i) May not correspond - with the weapon
• (ii) Linear –long, thin objects eg crowbars, pipes.
• (iii) Irregular, ragged or Y-shaped –objects with flat surfaces
• (iv) if curved - convexity of curvature points towards the direction of force
• (v) Stellate [star shaped] – blunt round object
• (vi) Crescentic–blunt object with an edge, eg hammer head
• (vii) Semicircular –head against wall or other hard surface (convexity of head)
• (viii) Patterned lacerations

55. (ix) Swallow tails at one end –
seen sometimes due to tearing at angles of lacerations

56. (5) Gaping –
present due to pull of elastic and muscular tissues.
(6) Bruising: in skin or s/c around the wound
(7) Tissue bridges – at the base of wound
Signature of a BLUNT FORCE
deeper tissues [BV, connective tissue, elastic fibres, nerves etc]
are unevenly divided.
(8) Hair bulbs – crushed

58. (9) Hair and epidermal tags – Deeply driven in the wound
(10) Hemorrhage: less in laceration. vessels are crushed and blood
clots readily
(11) Foreign matter – usually present in the wound.

59. TYPES
(1) Tear- the most general
having sufficient amount of underlying fat and muscle (eg thigh).
(2) Split laceration
skin direclty overlying a bone,
with minimal amount of underlying fat and muscle.
(eg: scalp, shin of tibia)
mimics an incised wound [called incised looking lacerated wound].

60. Tear laceration Split laceration

61. (3) Stretch laceration
skin is overstretched, resulting in a large flap.
Ex. a glancing kick by foot.
(4) Cut laceration
• by heavy cutting weapons
• between a true laceration and a true incised wound.
• The edges of the weapon do cut the skin
but since the edges are heavy, they crush and bruise the margins of
the wounds too.
Also called chop wounds (usually + fracture)

63. • (5) Avulsion
if grinding compression is applied,
causing avulsion (separation)
of large areas of skin from its underlying attachments
***also known as flaying

64. Incised wound Lacerated wound
Edges Clean cut Ragged
Margins Bruised Not bruised
Injuries to underlying tissues
(TISSUE BRIDGES+++)
Clean cut Crushed
Hair bulbs Clean cut crushed
Bleeding More Less

65. Incised wound Incised looking lacerated
wound
Margins (under hand
lens)
Clean cut Ragged
Edges Minimally bruised Heavily bruised
Blood vessels at the base Cleanly cut crushed
Subcutaneous tissue Cleanly cut Tissue bridges+++
Hair around the wound Cleanly cut Crushed

66. MLI
(1) Age of lacerations – (very much irregular)
(i) Fight - indicates time of struggle
(ii) Disputed pregnancy - age of perineal lacerations
(2) Extent of force
(3) Extraneous material –may connect the injuries -place of occurrence

67. (4) Manner of production –
(i) Accidental - falls etc
(ii) Suicidal lacerations – are very rare, (painful and rarely effective)
May be seen in suicidal jumping from high buildings.
(iii) Homicidal –
(a) Lacerations on the vertex generally indicate homicide.
Bagh Nakh [tiger claws]
designed to lacerate skin and muscle.

70. (5) Shape of lacerations –
rarely indicate the weapon. (patterned lacerations).
Exceptions- Eg : chains
(6) Tendons and muscle lacerations
• without corresponding lacerations on skin
• Can indicate violent muscular contractions and spasm
(convulsants)
• lacerations in hollow viscera may also be seen.

71. INCISED WOUND

72. • It is a clean cut wound through the tissues
• caused by a sharp-edged instrument
• where length is its maximum dimension

73. • Salient features:
(1) Force
delivered over a very narrow area
corresponding with the cutting edge of the instrument
(2) Skips in pattern
(i) when there are bony ridges
(ii) tendons or
(iii) over areas of loose wrinkled skin

74. Characteristics
1. Length (1) Greatest dimension
(2) No relation to the cutting edge of the weapon
(may be drawn to any distance)
2. Width  may be greater than the edge of weapon
due to retraction of divided tissues
3. Margins
(1) Clean-cut, well-defined
(2) if knife is serrated – may produce a saw-toothed cut
(3) Edges - usually everted (sometimes inverted – eg: scrotum)

75. 4. Abrasions and contusions – only if it is perfectly sharp
5. Shape
(1) usually spindle shaped – retraction of edges
(2) Crescentic – if blade is curved or struck surface is convex
(3) Zigzag – if skin folds are loose
6. Gaping –
is greater if muscle fibres are cut transversely or obliquely
[due to retraction].

76. 5. Direction
(1) deeper at the beginning
because more pressure is applied on the knife at this point. (head)
(2) become increasingly shallow towards the tail
The portion where the epithelium alone is cut is known
as tailing of the wound.

79. • 6. Beveling cut
• refers to a cut which is not perpendicular to the skin surface, but at an angle
• Direction of weapon:
• (1) Vertical –edges of wound would make a nearly 90° angle with the skin surface
• (2) Oblique
one edge - an angle >90° with the skin surface (beveled edge)
The other edge -makes an angle <90° with the skin ((under mined edge)
• (3) Nearly horizontal –a wound with a flap is produced.
• usually indicates homicide,
• and may indicate relative position of the assailant and victim.

81. • 7. Hemorrhage
• (1) Hemorrhage is more as the vessels are cut cleanly.
• (2) Spurting will occur if an artery has been cut.

82. SUICIDAL CUT THROAT HOMICIDAL CUT THROAT
Left side of neck (in right handed)
Rarely crosses to opposite side
Usually on both sides
High above thyroid cartilage Low below thyroid cartilage
Ragged edges Sharply cut edges
Hesitant cuts +++ Single deep wound
Tailing present Absent
Less severe Severe
Jugular vein injured >> Carotid CAROTID +++ JUGULAR

83. SUICIDAL CUT THROAT HOMICIDAL CUT THROAT
Weapon – Present at the scene Weapon – always absent
Clothes- not damaged Clothes- torn
Hands- cadaveric spasm holding weapon ---
Defence wounds- absent Defence wounds + palms, wrists
Circumstantial evidence– depressed,
room locked from inside

84. Age of Incised Wounds
1. Gross (1) Fresh – Hematoma formation
(2) 12 h – (i) Edges red, swollen, adherent with blood and lymph
(ii) Leukocytic infiltration
(3) 24 h – Dried clot in the form of crust or scab.
2. Histopathology
(1) Few min Dilatation of capillaries ,Margination and emigration of neutrophils
(2) 12 h to 24h–fibroblasts + Monocytes appear in exudate
(3) 72 h – Formation of vascularized granulation tissue
(4) 4-5 d – New fibrils are formed
(5) 1 wk – scar formation if wound is small

85. MLI of Incised Wounds
(1) Reconstruction of crime
(a) the nature of the weapon – sharp edged
(b) Age of injury and
(c) Direction of force
(2) Body with incised wounds immersed in water soon after death - Blood
is lysed by water. It is difficult to make out if the wounds were AM or PM.
(3) Manner of injury –may be accidental, suicidal or homicidal.

86. STAB Wounds

87. • A stab wound is one which has depth as its maximum dimension
• It is produced when force is delivered
• along the long axis of a narrow or pointed object
• into the depths of the body.

88. • Punctured wound
• is a stab wound caused by a circular
pointed smaller shaped object.
• Insertion of pins, needles
• Snake bite
• Drug addiction
• Needle punctures are a common method
of infanticide
(through anterior or posterior fontanelles).

89. • Penetrating wound
• enters into a body cavity without coming out.
• Should be described in a sequential order,
i.e. entrance wound,
depth and direction of track
specific location of termination
Ex - (i) Stab wound to the chest or abdomen [having no exit]
(ii) Gunshot wound to the head [having no exit

91. • Perforating wound
• has both an entry and exit wound
• and firearm wounds;
• in a sequential order as above,
• i.e. entrance wound, path of wound, exit wound

92. Characteristics
• 1. Length stab wound ‘l’ is normally less than width ‘w’ of weapon.
• 2. Width may not indicate the true thickness of blade, because of retraction of
wound edges,
• 3. Margins
• (1) If weapon has sharp edges Margins are clean cut [incised stab wound]
• (2) If weapon has rounded edges Margins are contused and lacerated
[lacerated stab wound].
• 4. Depth (1) Greatest dimension - Depth is the greatest dimension in stab
wounds.
• 5. Shape
• which runs across the lines of Langer wound causes gaping;
• a parallel /an oblique cut - a crescentic or semicircular wound

94. Shape of the entry
wound-
depends on the
weapon

95. • Complications
• (1) Air embolism – especially in stabs of neck vessels
• (2) Choking due to inhalation of blood
• (3) Hemorrhage
• (4) Infection
• (5) Pneumothorax.

96. MLI of Stab Wounds
• (1) Concealed puncture wounds – used homicidally.
• (2) Depth of wound – indicates force used
• (3) Direction and dimension of wounds – Indicate relative positions of
assailant and victim
• (4) Manner of production
• (5) Multiplicity of wounds - revenge murders
• (6) Shape of wound – Indicates weapon
• (7) Time of attack –the age of stab wound

97. DEFENCE WOUNDS OFFENCE WOUNDS

98. SELF-INFLICTED INJURIES Therapeutic wounds

99. THANK YOU