Mechanical Injuries: Abrasions, Bruises, Incised and Stab Wounds

Indian forensic medicine uses a classification that has been stable in Modi's, Reddy's, and Parikh's textbooks for decades. The five categories are blunt force, sharp force, firearm, thermal and chemical. Within blunt force you get abrasion, contusion and laceration. Within sharp force you get incised, stab and chop wounds. The categories are not airtight; a stick studded with nails produces both blunt and sharp injuries on the same blow, and a half-blunt half-sharp instrument like a kukri produces a wound with characteristics of both incision and laceration. The classification is a starting point, not a destination.

The Indian anchor here is the historical Modi classification, which Parikh's later editions preserved and which Indian courts treat as authoritative. When the defence cross-examines a surgeon on whether a particular injury is an incised wound or a laceration, the surgeon's answer is expected to track Parikh chapter and verse. Improvising on classification is one of the fastest ways to lose credibility on the stand.

An abrasion is confined to the epidermis: skin scraped away, dermis exposed, no involvement of deeper tissue. It heals without scarring, and an abrasion older than two weeks is nearly invisible to the naked eye. Despite their superficiality, abrasions preserve the geometry of the offending surface. A tyre-tread imprint on the chest records the wheel profile. Crescentic abrasions on the neck indicate fingernails, including the side and orientation of the grip. A ligature abrasion records the material, width, and direction of pull.

Indian forensic surgeons recognise four types of abrasion that the standard textbooks all carry:

• Scratch (linear) abrasion. Produced by a pointed object drawn across the skin. Tip and tail of the scratch reveal direction: skin tags pile up at the tail and the scratch is broader and deeper at the head. A common Indian context is the fingernail scratch in sexual assault cases.
• Graze (sliding or brush) abrasion. Produced by sliding contact with a rough surface, with the body moving relative to the surface or vice versa. Road rash from motorcycle crashes is the classical example. The leading edge is shallower; skin tags pile up at the trailing edge, indicating direction of movement.
• Impact (imprint or patterned) abrasion. Produced by perpendicular force where the offending surface stamps its pattern onto the skin. Tyre-tread marks, fabric weave, the muzzle imprint of a contact gunshot, the patterned grip of a hammer head. These are the most useful abrasions because the pattern itself identifies the weapon or vehicle.
• Pressure abrasion. Produced by prolonged compression rather than a single impact. Ligature marks (hanging, strangulation), bite marks in their abrasive component, fingernail crescents on the neck in throttling. Pressure abrasions are often parchmentised post-mortem (dried, leathery, yellow-brown).

Ageing an abrasion is approximate but defensible. A fresh abrasion is bright red and weeping serum. Within 12 to 24 hours the surface dries to a reddish-brown scab. By day three the scab is dark brown and harder. By day seven it is a thin scab beginning to lift at the edges. By two weeks the scab has fallen off and the skin underneath is paler than surrounding skin but otherwise healed. The differentiation between ante-mortem and post-mortem abrasion is the same point covered in Forensic Medicine and Inquest: an ante-mortem abrasion shows vital reaction (capillary congestion, fresh haemorrhage at base, leukocyte infiltration on histology), a post-mortem one does not.

A contusion (or bruise) is extravasated blood under intact skin. The blood comes from blunt-force rupture of small vessels in the dermis or deeper tissue. Three layers of bruise are recognised: subcutaneous (visible immediately or within hours), intramuscular (visible only after the muscle is sectioned at autopsy), and deep tissue or occult (visible only with imaging or sectioning). A defence counsel who argues "no bruise on the surface, so no assault" is exploiting the surgeon who only looked at the surface.

The colour timeline of a bruise is the most-tested ageing tool in Indian forensic medicine. The classical sequence is red (fresh) progressing through blue and purple over the first 48 hours, then green by day three to seven, then yellow by week two, then resolved by week three. The colour change is the breakdown of haemoglobin to bilirubin and biliverdin. Three caveats every candidate needs to remember: the colour change is not metronomic, deep bruises become visible at the surface late and look "older" than they are at first appearance, and senile bruises (on the back of the hands and forearms in elderly people) develop spontaneously without trauma and do not follow the timeline at all.

The patterned bruise gives contusions their investigative value. A linear stick blow produces what is called a "railway-track" or "tramline" bruise: two parallel haemorrhagic lines with a pale central strip. The blood is pushed laterally by the stick at impact, ruptures the vessels at the edges, and leaves the centre comparatively pale. The width between the rails equals the diameter of the stick. A buckle of a belt prints its shape. A patterned bruise from a hand grip on the upper arm shows four oval bruises medial and one lateral, in the geometry of the assailant's grip.

A laceration is a full-thickness tear of skin produced by blunt force, typically where soft tissue is crushed against underlying bone (scalp, eyebrow, shin, elbow). An incised wound is a clean cut from a sharp-edged weapon. Defence counsel routinely argue that a laceration is an incised wound, or vice versa, because the distinction carries different sentencing implications. The surgeon who cannot articulate the difference concedes ground on the stand.

The presence of tissue bridges across the depth of the wound is the single most reliable distinguishing feature. Tissue bridges are tougher structures (vessels, nerves, connective tissue) that resist the tearing force of blunt impact and remain stretched across the gap. A sharp blade divides them along with everything else. If the surgeon photographs the wound with the edges drawn apart and tissue bridges are visible, it is a laceration. If the edges separate cleanly with nothing between, it is an incised wound.

Incised wounds are further analysed for direction and intent. A suicidal incised wound on the wrist or neck typically shows hesitation marks: shallow tentative cuts adjacent to the main wound, representing the suicide victim's preliminary attempts before the committed cut. Suicidal wrist cuts are usually on the non-dominant wrist, shallow, parallel, and at the level of the radial pulse. Suicidal neck cuts are usually on the left side of the neck (right-handed victim), pass from above-left to below-right, and are deepest at the start of the cut. Homicidal incised wounds rarely show hesitation marks, may be at multiple non-classical sites, and are commonly accompanied by defensive wounds. The scene reconstruction in Processing Physical Evidence at the Scene often supports or contradicts the autopsy's suicidal-versus-homicidal opinion.

A stab wound is deeper than it is long. Its surface dimensions tell you about the blade; its depth tells you about the thrust. A single-edged blade (kitchen knife, kukri tip, dagger) produces a stab wound with one acute angle (the blade edge) and one squared or rounded angle (the spine of the blade). A double-edged blade (dagger proper) produces a wound with both angles acute. The width of the wound, measured at the surface with the wound margins approximated rather than gaping, gives the maximum blade width; the depth of the tract gives at least the length of blade inserted (recognising that compressible structures like abdomen can yield, so tract depth may exceed the blade length).

1. Step 1
   Photograph the stab wound in situ before dissection, with a scale and a north-arrow.
2. Step 2
   Approximate the wound edges using forceps; measure surface length with the edges closed.
3. Step 3
   Note both angles of the wound: one acute and one squared / rounded indicates single-edged blade; both acute indicates double-edged blade.
4. Step 4
   Dissect the wound tract layer by layer in the plane of the wound; record direction (anteroposterior, lateral, superior-inferior) and depth.
5. Step 5
   Identify each organ traversed; record the path through each in the same axis system.
6. Step 6
   Compare tract depth with the length of any recovered suspect weapon; note that tract may exceed blade length if abdominal wall yielded under the thrust.
7. Step 7
   Sample the wound margins for trace (textile, paint, tip-of-blade fragment) before suturing for body release.

Defensive wounds are the autopsy's record of the victim fighting back. Classical sites are the palmar surface of the hand (incised wound from grabbing the blade), the medial side of the forearm (incised wound from a raised arm warding off a blow), and the fingertips (incised or stab wounds where the victim tried to disarm the attacker). The presence of defensive wounds is among the strongest single arguments against a suicide claim. The absence of defensive wounds in a stab-homicide case is itself a finding: the victim was incapacitated, restrained, or attacked from behind.

Ante-mortem versus post-mortem differentiation runs through every injury described above and is the question the trial court will ask most often. The vital reaction is the macroscopic and histological signature of an injury sustained during life. Macroscopically: haemorrhage at the wound base, swelling of the margins, retraction of edges (the gap of an incised wound widens because living skin is under tension). Histologically: leukocyte infiltration begins within minutes (earliest PMN appearance reported from 10 to 30 minutes) but is not reliably established on standard histology until 4 to 6 hours after injury; fibrin deposition follows; granulation tissue appears at day three. Post-mortem injuries show none of these. A bruise inflicted after death produces no extravasation because the heart has stopped. An incised wound inflicted after death does not gape because the skin tension has resolved. The differentiation is one of the cornerstones of Indian forensic medicine and a near-certain question in every contested injury case.

Every injury in a medico-legal autopsy is described using six elements, in a fixed order, on the body diagram and in the report text. The structure is what makes the report defensible under cross-examination. The structure is taught in the same form in Modi, Reddy and Parikh, and is the working template every Indian forensic-medicine practitioner is expected to reproduce.

• Type. Abrasion, contusion, laceration, incised wound, stab wound, chop wound, or combination.
• Site. Anatomical region named precisely, with distance from a fixed reference (e.g., "4 cm below the right clavicle, 6 cm right of the midline").
• Size. Length × breadth × depth in centimetres. Surface dimensions only for abrasions and contusions; depth recorded for lacerations and sharp-force injuries.
• Shape. Linear, curvilinear, oval, irregular, V-shaped, U-shaped, stellate. Drawn on the body diagram and photographed.
• Edges (and margins). Clean and everted (incised), ragged and abraded (laceration), inverted (entry of low-velocity penetrating injury).
• Age. Estimated by colour for bruises, by scab progression for abrasions, by healing stage for incised and lacerated wounds.
• Direction. Where applicable, the line of force or the line of the cut. For stab wounds, the tract direction in three axes.

A body diagram accompanies the description, with each injury numbered and the number reproduced in the report text. Photography follows the rules in Forensic Photography: two shots per injury (one with scale, one without), in a colour-managed file format, with a case-identifier slate. Scaled photography of injuries is increasingly the source of evidence the court actually trusts; the body diagram and the report text are corroborative.