Mechanical injuries

Mechanical injuries 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.

Factors effecting appearance of wound.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.

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.

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.

Site and distribution of force by blunt impact.

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.

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.

. 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.

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.

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.

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.

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

Impact injury to the stationery head.

Types of mechanical injuries 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.

Moving abrasion

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.

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

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.

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.

Postmortem abrasion

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.

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.

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.

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

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

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.

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

Gravity shifting of extravasations

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.

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.

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.

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.

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.

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

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.

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.

Weapon A causing impact on scalp B producing split laceration.

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.

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.

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

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

Weapon A grinding tissue B to precipitate compression laceration

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.

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.

Incised wound 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.

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.

Knife A causing incised wound in soft tissue B.

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

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

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.

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

A, Incised wound- B. Lacerated wound.

Features Incised wound Lacerated woundShape 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 lessHair 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

Clothes Show corresponding cuts

No such effect

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.

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.

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.

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.

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.

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

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.

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.

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

Fracture due to general deformation

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.

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.

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

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.

Outer table crushed into diploe

Thank You