An abrasion is the most superficial of injuries and, in the most restrictive of definitions, is one that does not pene- trate the full thickness of the epidermis. Thus the pure abrasion does not bleed, as blood vessels are confined to the dermis. Because of the corrugated nature of the dermal papillae, however, many abrasions enter the corium and bleeding commonly occurs.
Another definition (all of which are arbitrary) would describe an abrasion as a superficial injury to ‘the skin’, which would allow penetration of the upper dermis rather than only the epidermis, so that bleeding would fall within the definition.
Abrasions are known in lay terms as ‘scratches’ or
‘grazes’, though the former usually indicates a linear mark and the latter a ‘brush’ abrasion caused by wider tangential impact. Where these brush abrasions are the result of scraping contact with the ground, the lay term is a ‘gravel rash’. There are many causes of abrasions, which are common every- day lesions, especially in children whose legs are rarely free from some scratches and bruises. Any contact that rubs across the epidermis and removes the keratinized layer and under- lying cells will cause that area to become discoloured and moistened by exuded tissue fluid, even if bleeding does not occur from abraded dermal papillae.
When death ensues soon afterwards, the abrasion becomes stiff, leathery and of a parchment-like brown colour as a result of the drying of the moist exposed sur- face. This is classically seen, for example, in the ligature mark of hanging or strangulation. It is impossible to tell whether a superficial abrasion occurred immediately before or after
Epidermis
Dermis
Subcutaneous tissue
Deep fascia Muscle FIGURE4.2 General structure of skin.
FIGURE4.3 Simple abrasion of the skin caused by an almost perpendicular impact of the head against the ground. There is only slight tangential scuffing though most abrasions have some element of sideways contact that damages the epidermis.
Abrasions
death if there was insufficient time for any inflammatory reaction to occur at the margins. Post-mortem abrasions are common, especially after autopsy when the body is re-examined, because mortuary instruments and the mov- ing of bodies into refrigerators and coffins can often make marks. These abrasions commonly appear yellow and translucent, and are absolutely devoid of any colour change at the edge.
Tangential or brush abrasions
Most abrasions are caused by a lateral rubbing action rather than vertical pressure. Where this tangential component is marked, the direction of the force can often be determined by tags of epidermis dragged to the terminal end of the abrasion. For example, in the ‘brush abrasion’, which is common in childhood falls and pedestrian accidents, the skidding of the body across a rough surface scrapes linear furrows across the skin. Strands and tags of epidermis may
be peeled along these furrows to the further end where con- tact ceased. Visual examination, using a lens if necessary, can indicate the direction of movement of the body. Similarly, if a victim is struck a glancing blow with a rough object such as a stone or brick, similar epidermal tags may indicate the direction of the blow.
The same type of grooved abrasions can be caused when a victim is dragged along the ground, either in a vehicular accident or by an assailant. It may be important, though dif- ficult, to attempt to differentiate such drag marks as being ante-mortem or post-mortem, a problem which is discussed in another chapter.
Crushing abrasions
Where the impact is vertical to the skin surface, no scraping or tangential marks occur. Instead the epidermis is crushed and an imprint of the impacting object is stamped on the sur- face. If the impact is substantial and the area of contact small,
FIGURE4.4 A linear abrasion or ‘graze’, confined to the upper layers of the skin. The tangential direction of impact of the weapon was from above downwards (along the longitudinal axis of the upper arm), as can be determined by the shreds of epidermis peeled towards the lower end.
Direction
of impact Tags Terminal epidermal tag
FIGURE4.5 Determination of the direction of impact in an abrasion caused by a tangential force. The epidermal tags raised by the impact tend to pile up at the distal end.
a punctured wound will be made, but otherwise a crushed abrasion will occur. The lesion is slightly depressed below the surface unless an underlying bruise or local oedema bulges the tissues. These abrasions are the ones that most clearly reproduce the pattern of the injuring object. An example FIGURE4.7 Brush abrasion from skidding contact with the road surface during a drunken scuffle. The lesion is partly abraded and partly bruised. The direction of movement can be discerned, as the scratches begin more abruptly and deeply near the ruler, and tail off superficially at the opposite edge.
FIGURE4.8 Drag marks on the back of a murder victim. Death was caused by a stab wound of the front of the chest – the body was pulled along the ground for a short distance, obviously in the direction of the feet, as the scratch near the waist is deeper near the feet end and tails off at the opposite end.
FIGURE4.6 ‘Brush abrasion’ or ‘grazes’
caused by tangential contact of a moving body with a rough surface. Although most are seen in traffic accidents from contact with the road surface, this example is from a murdered woman dropped down a mine shaft. There are grazes running in two directions at right angles, indicating that she must have struck the wall twice, in different postures.
would be the marks of a vehicle radiator on a pedestrian victim or the pattern of a floor grid on to which a person has fallen. If the impact is forcible, then the dermis may also be injured: an area of bruising may underlie the abrasion.
Fingernail abrasions
These are important because of their frequency in assaults – especially child abuse, sexual attacks and strangulation.
Often associated with focal bruises, fingernail abrasions are most often seen on the neck, the face, the upper arms and the forearms. They may be linear scratches if the fingers are dragged down the skin, or short, straight or curved marks when the skin is gripped in a static fashion. As women tend to have longer, sharper fingernails than men, they are natur- ally more often associated with causing such abrasions.
A victim resisting a sexual or other attack may rake her nails down her assailant’s face, causing linear, parallel scratches that may be several millimetres wide and placed a centi- metre or two apart. The expected pattern may be fragmentary, however, as is often seen on the neck when a victim of either manual or ligature strangulation attempts to tear away the attacking fingers or cord. These marks are usually vertical, as opposed to the more random marks that may be inflicted by the nails of the assailant in manual strangulation.
The upper arms are a frequent site for gripping and restraint, both in adult assaults and child abuse. Bruising is most common, but fingernail marks may be superimposed.
Static fingernail abrasions may be straight or curved, often
about half to one centimetre long. The direction of curvature must be interpreted with care if one wishes to decide which way the hand was held at the time of infliction.
Although it is natural to assume that the concavity of the mark indicates the orientation of the fingertip, experiments by Shapiro et al.(1962) have shown that this is often not the case. Because the skin is put under lateral tension when it is indented by the nails, it may distort, so that when the tension is released the elasticity of the skin causes it to return to its original position, carrying the nail mark with it. The curve may then reverse to form either a straight line or a convexity. The shape of the free edge of the fingernail also affects the mark, as pointed nails are more likely than those with straight edges to give these paradoxical results.
Once again, the pathologist has to be wary of incorrect interpretation when, for instance, deciding if nail marks on a neck were made by hands approaching from the front or passing around the back of the neck. However, personal experiments with the Shapiro et al.contention have shown that it by no means always applies.
Patterned abrasions
Formerly it was often claimed that abrasions retained the pattern of the impacting object more accurately than other injuries such as bruises and lacerations. Though abrasions undoubtedly do preserve such patterns well, many of the examples were not in fact true abrasions, but were intra- dermal bruises, mentioned in the next section.
Abrasions
FIGURE4.9 Abrasions in manual strangulation. The area is more extensive than is usually seen in such circumstances.
The large area of superficial damage to the epidermis is caused by sliding movements of the assailant’s hands, the area having become dried and leathery during the post- mortem interval. The smaller marks are fingernail scratches.
Patterned injuries occur when the force is applied at or near a right angle to the skin surface, rather than with the skidding impact of a graze. If a weapon with a patterned surface strikes the skin – or the body falls against a pat- terned surface – the abrasion of the epidermis follows the ridges of the object if it has a profile of varying height. Not only may the epidermis be damaged, but the skin may be compressed into the cavities of the pattern, with consequent capillary damage leading to an intradermal bruise. Probably the best example of this is seen when a motor tyre passes over
the skin, leaving a pattern where the skin has been squeezed into the grooves of the rubber tread.
There is little point in trying to list all the possible patterns that can be distinguished in abrasions on a body, but a few
FIGURE4.10 Extensive abrasion of the knees and shins, in a drunk who stumbled amongst furniture before dying of a head injury. The damaged skin has exuded tissue fluid, which has dried post-mortem to produce the dark, leathery appearance.
FIGURE4.11 Patterned abrasion of the forehead. The victim was struck on the head in a public house with a heavy glass ashtray, the bottom of which had embossed concentric circles moulded into the glass.
FIGURE4.12 Abrasions and intradermal bruising on the forehead of a swimming bath attendant. He was found drowned when there were no witnesses, but the spacing of the marks exactly matched the ridged tiles at the edge of the bath, so it was presumed that he had slipped and struck his head before falling unconscious into the water.
have particular medico-legal significance. In former years the honeycomb grid of a motor-vehicle radiator provided many examples of patterned abrasions, but changes in vehicle design have relegated these to historical interest. There may still be projections on vehicles that cause damage, but these are more likely to inflict bruises and lacerations. The muzzle of a firearm can imprint an abrasion on the skin, which is of importance in that it confirms that the discharge was contact in nature. Impact against ribbed ceramic tiles in a bathroom or swimming bath may assist in reconstructing unwitnessed events. Blows from a weapon with a recognizable surface may
help to identify that weapon, such as a plaited rope or leather whip, or a solid object with an embossed pattern. Abrasions from objects with a recurring pattern, such as bicycle chain used in gang fights, or a serrated knife, can readily provide a clue to the nature of the weapon.
Post-mortem abrasions
Unlike post-mortem bruises, artefactual abrasions are com- mon. They may have been inflicted after death from a variety of causes, including dragging a corpse or buffeting in moving water. Some post-mortem animal injuries also resemble abra- sions such as insect bites, especially by ants.
Other damage may be caused following autopsy. As the post-mortem interval increases, so the skin becomes more fragile. Even the normal procedures of post-autopsy recon- struction and handling in the mortuary may cause dermal damage, especially after washing with hot water. If the path- ologist returns for a later examination, or if he is retained to perform a second autopsy for the defence, the appearances should be checked with the original description or photo- graphs, if some injuries suggest a post-mortem origin.