The third major type of blunt injury is the laceration, in which the full thickness of the skin is penetrated.
Lacerations differ from incised wounds in that the con- tinuity of the tissues is disrupted by tearing rather than clean slicing, but the distinction is often blurred because some lacerations are caused by jagged projections ripping into the skin in much the same manner as a blunt knife or axe.
Unless great force is used, most lacerations require a firm base to act as an anvil for the skin and underlying tissue to be pinned against. It is unusual for a blunt impact to lacer- ate the abdomen or buttock, but the scalp, shins, shoulder, face and – to a lesser extent – the thorax, are all prone to lac- erated injury. Where a soft area such as buttock, thigh, calf or forearm is lacerated, the lacerating agent is either a pro- jecting point or edge, or a completely blunt object is pulled obliquely against the tension of the skin until it tears.
Because of the crushing and tearing components of a lacera- tion, there is usually associated abrasion and bruising,
FIGURE4.24 A footmark imprinted in superficial bruising on the back. There is another partial mark at waist level, both being made by stamping with the flat of a foot through thin clothing, rather than by swinging kicks.
FIGURE4.25 Bruising of the interior of the lip from a blow in the mouth. The lip has been impacted on the underlying teeth, but not sufficiently hard to cause a laceration.
L acerations
though these may be minimal if the lacerating force acts at right angles to the surface.
The scalp offers the best example of a laceration, as the skin and subcutaneous tissue lie over the bony platform of the skull and are crushed against it when the force impacts.
In fact, scalp lacerations can resemble incised wounds, because this ‘sandwich effect’ is so pronounced that a blow from a blunt instrument can cleanly split the tissues against the skull, leaving a linear wound that appears to the inexperi- enced to be a knife or chopper cut.
A laceration can be distinguished from an incised wound by:
■ the bruising and crushing of the margins, though this may be a very narrow zone, requiring inspection through a lens
■ the persistence of tissue strands across the interior of the wound, including fascial bands, vessels and nerves.
In a wound from a sharp weapon these are divided
■ the absence of a sharply linear injury in the underlying bone, especially if it is the skull. A knife or axe is likely to chip or score the base of the wound
■ if the area is covered with hair, as on the scalp, intact hairs will survive to cross the wound; an incised injury would divide them.
A flat impact may cause a laceration, especially on the scalp. If the head falls to the ground or is hit by a wide, flat weapon, the skin and subcutaneous tissues are compressed
FIGURE4.26 Laceration of the eyebrow with surrounding bruising. The wound is stellate as a result of crushing against the underlying bone. The victim fell from a low cliff on to rocks. The sea has washed away the original bleeding.
FIGURE4.27 Multiple homicidal lacerations of the scalp. The unusual shape is difficult to interpret, but they were caused by a claw hammer. Two are triangular, the upper and lower show tissue bridges because of the gap between the two claws.
on the anvil of the skull and may split sideways, often with a zone of surrounding bruising.
Other lacerations are caused by the impact of an edged object, be this a rod, a brick, the edge of a kerbstone or the wing mirror of a vehicle. Though the impact may be virtu- ally perpendicular to the skin surface, there is usually some tangential element and this can cause one edge of the wound to differ from the other. Where there is a glancing element, one edge will be relatively clean-cut, whereas the other will be ripped away from the first, suffering more tearing of the margin and often showing undercutting of the edge. If the impact is significantly asymmetrical, then this undercutting may be pronounced enough to form a flap of skin and underlying tissue, which is peeled off the underlying bone or deep fascia.
In extreme forms, this produces a ‘flaying injury’, where a large area of skin and subcutaneous tissue is rolled off a limb, almost always by the rotary action of a revolving motor wheel. A similar injury can occur on the scalp again from a rotating wheel – though a similar ‘scalping’ lesion can be caused by traction from hair being trapped in machinery. This was formerly a common industrial acci- dent and was the reason for the ‘snood’ hairnet being worn by women factory workers during the last war.
Patterned lacerations
Lacerations do not reproduce the shape of the injuring agent nearly as well as do abrasions and intradermal bruises. As with
FIGURE4.28 Laceration of the scalp from a 30 cm long heavy torch (insert). The skin over the shoulders is reddish due to first- and second-degree burns. The victim was hit on the head while sleeping in bed, after which the husband poured petrol over the body and set it on fire.
FIGURE4.29 Homicidal lacerations of the scalp penetrating the skull.
Although some of the injuries resemble incised wounds, their margins are crushed, and hairs and tissue strands cross the injuries. The damage was probably inflicted with a metal rod with sharp edges.
skull fractures, the magnitude of the force needed to cause a blunt tearing of skin leads to blurring of the impact shape, often with radiating or totally irregular tearing. Sometimes the shape is recognizable and probably the best example is a
hammer blow to the head. A circular face may punch out a circle or an arc of a circle, which may also be reproduced in an underlying depressed skull fracture. The exact size of the hammer face may not be accurately reproduced in the lacer- ation, which may be slightly larger than the hammer.
Kicks may cause lacerations, especially if a heavy boot with a hard toecap is used. These tend to be tangential and may peel up a flange of tissue. They can be clean-cut and are sometimes mistaken for knife wounds. Stamping injuries are more likely to cause abrasions and bruises than lacerations, unless the violence is extreme. A heavy focal blow may cause a linear or a stellate laceration, the latter radiating out from the focus of impact. The surface may be abraded and the sur- rounding tissue deeply bruised, so the final lesion is complex.
Firearm wounds are a special form of laceration and will be dealt with separately.