6 Wounds and Injuries

Introduction

A wound is generally considered to be a skin injury, caused by some external force, that may extend to deeper tissues. However, external forces may injure (or wound) deeper tissues without necessarily breaching the skin. Such injuries fall within the definition of ‘blunt force injuries’. The common denominator in both types of injury is the ‘external force’.

In the initial stages of an investigation the immediate concern of the pathologist is to describe the nature and location of the injuries. How the injuries were inflicted, and whether they were accidental or deliberate, can be considered later. This two-stage process encourages a balanced assessment of the injuries and reduces the likelihood of ‘jumping to conclusions’ early in the investigation.

Skin injuries can be divided into:

• Blunt force injuries – abrasions, bruises (contusions), lacerations (split wounds)

• Sharp force injuries – incised wounds (cuts or slashes), stab wounds (puncture or penetrating wounds).

Blunt force injuries to deeper tissues include bruising and laceration of muscles, damage to internal organs, and fractures. Stab wounds, in addition to the skin damage, may also injure deeper organs.

Certain terms are commonly used in human forensic medicine and are understood by lawyers and judges. These include: abrasion, laceration, incised wound, puncture wound and perforating wound. Their correct use in veterinary cases simplifies reports (and verbal explanations in Courts) and makes ‘animal’ cases more understandable to the legal profession and to juries.

Blunt force injuries

General

Blunt force injuries are more commonly encountered in veterinary medicine than wounding by sharp implements. Feet, fists, hammers, sticks, baseball bats, billiard cues and bricks are some of the many implements used to injure animals. The resulting damage may occasionally reflect the type of object used, but for the most part the injuries identify where the blows struck but not the weapon. Although single blows are encountered, most animals have more than one injury, often widely distributed over the head, body and limbs.

Abrasions

Abrasions are the most superficial of wounds to the skin. When the skin collides tangentially with a rough surface, the outer layers (the keratinised parts) are rubbed off, exposing the more sensitive layers (Fig. 6.1). Remnants of the abraded layers may be found piled up at the edge of the wound.

Fig. 6.1 Domestic hen. Abrasion of the wing showing areas of denudation of the outer layer of skin. The deeper layer of the skin (dermis) is intact.

Frequently, abrasions do not bleed but merely leak tissue fluid. This causes the injury to appear wet at first and then to become darker and drier with time. When the slightly deeper layers of the skin are involved, blood may ooze from damaged dermal papillae and a dark scab may form.

In motor vehicle accidents and falls on to rough surfaces, small fragments of grit may be embedded in the abraded surface. Hair protects the skin from many minor blows that would otherwise cause abrasion of bare skin. In domestic animals it is therefore relatively rare to find the patterned or crush abrasions that in human forensic pathology are valuable because they provide clues to the type of object that struck the skin (e.g. the sole of a shoe).

Bruises (contusions)

Bruises (also known as contusions) result from blunt trauma. Blood leaks from vessels within the skin or from deeper tissues. The size and appearance of bruises can depend on factors such as tissue density and the fragility of blood vessels. Tight fibrous tissue discourages the collection of blood, whereas loose, soft, well vascularised tissues allow blood to pool. When the tissues are stretched or crushed against underlying bone, the extent of the bleeding may be increased. Conversely, the malleable abdominal wall frequently shows little or no evidence of bruising even after an impact sufficient to cause extensive damage to internal organs such as liver or spleen.

Not all bruises are immediately obvious. Hair and skin colour commonly obscure intradermal and subcutaneous bleeding. When it is feasible, clipping/shaving or plucking areas of suspected bruising may be helpful in the live animal (Fig. 6.2), even in very dark-coloured animals such as black Labradors (Fig. 6.3). Clipping/shaving can also be done at the start of the post-mortem examination. In many cases, however, severe bruising may not be discovered until the skin is reflected at post-mortem examination.

Fig. 6.2 Domestic hen. Subcutaneous bruising is often obscured by feathers. Plucking of the leg of this hen revealed the extent of the bruising.

Fig. 6.3 Labrador. Bruising is less obvious in dark-haired animals than in light-skinned ones. However, clipping the side of the chest of this dog greatly assisted in diagnosing bleeding in the axilla.

It is good practice to photograph areas of bruising that are found after reflection of the skin as soon as practicable. Delay results in the exposed bruise fading, spreading and becoming less clearly defined. There is also a danger that leakage of blood from severed vessels or from body cavities may contaminate the area and confuse the picture.

The margins of bruises spread and blur with time, making the shape of a bruise an unreliable guide to the outline of the object that struck the body. However, blows by sticks, broom handles or similar narrow objects to relatively hairless skin may leave characteristic ‘tramline bruises’.¹ The skin along the line of impact is depressed and compressed by the force of the weapon, whereas the skin at the margins of this area is stretched. This action results in the blood vessels at the centre of the injury being compressed whilst those along the margins are torn. As blood flows back into the area, leakage from the torn vessels results in two linear bruises at the margins of the area of contact by the stick.

Stick marks and other bruising related to transport are common in livestock sent for slaughter.² They may be recognised in light-skinned pigs before slaughter, but in cattle are more commonly found after skinning. In the subcutis and superficial muscles, the bruises do not usually develop a ‘tramline’ appearance.

Extensive bruising of livestock, found at slaughter, can be the first direct evidence that a significant husbandry problem exists on a farm (Fig. 6.4) or that there are major deficiencies in the transport arrangements. The veterinarian’s report will be a key element in the subsequent investigation.

Fig. 6.4 Deer. A group of abattoir-slaughtered farmed deer showed extensive bruising over their bodies and head. Investigation revealed major problems with on-farm handling of the deer.

(By kind permission of Leonard ‘Sam’ Mansley.)

Age of bruising

As the bruise ages, red cells rupture and haemoglobin degrades. This causes the sequence of colour changes readily seen in animals and birds with light-coloured skin that survive the injury by several days. Observations of poultry ³ record bruises changing from red at 2 minutes post-trauma through dark red–purple at 12 hours, light green–purple at 24 hours, yellow–green–purple by 36 hours, becoming yellow–green at 48 hours and yellow–orange at 72 hours, reducing to be ‘slightly yellow’ at 96 hours and normal by 120 hours post-injury.

Because of economic losses related to trimming of bruised meat from slaughtered animals, there has been considerable interest in establishing when these bruises occurred. The approximate age of bruises in cattle and sheep, as judged by their macroscopic appearance, ranges from red and haemorrhagic between 0 and 10 hours after injury, dark coloured when approximately 24 hours old, watery in consistency by 24–38 hours, and having a rusty orange colour and a soapy texture when more than 3 days.⁴

Research conducted in Australia on lambs and calves ⁵ has provided a guide to histological ageing of bruising over the 0–48-hour period after trauma in these animals. This research showed that trauma occurring immediately before death can lead to haemorrhage in subcutaneous tissues, in the muscle septa, and between muscle fibres. Small numbers of neutrophils and macrophages are present in the extravasated blood. At 8 hours after trauma, the extent of the bleeding is greater and fibrin strands are recognisable. Many neutrophils and few macrophages are present in the extravasated blood, the damaged muscle and the subcutis. The amount of haemorrhage changes little between 8 and 24 hours after injury, but the ratio of neutrophils and macrophages alters so that they are found in approximately similar numbers at 24 hours. This change in cell population continues over the subsequent 24-hour period, resulting in macrophages greatly outnumbering neutrophils by 48 hours after trauma. At this time, capillaries with plump endothelium can also be seen invading the damaged tissues.

There is a paucity of information on the ageing of bruises in other species. Perhaps the guidelines for lamb and calf bruising are relevant to a range of other animals, but present knowledge is limited and caution is advised when interpreting tissue injury based on observations made in substantially different species.

Haemosiderin deposits are readily identified by the Prussian Blue reaction in macrophages 48 hours after injury. Haemosiderin deposited or trapped in scar tissue may be demonstrated many weeks after injury and may provide convincing evidence of previous bruising in suspected cases of repetitive injury.

Testing for the formation of bilirubin (as haemoglobin is broken down in the area of the bruise) has also been used to estimate the time elapsed since injury. This method is based on the colour change seen in samples of bruised muscle after being soaked in a mixture of trichloroacetic acid and ferric chloride.⁴

Force required to cause bruising

‘How much force is required to cause a bruise?’ is a frequently asked question to which there is no precise answer. It is often assumed that small bruises correlate with limited force and that larger ones signify impacts of greater force. However, because of the variables noted in the section on bruising (e.g. tissue density and vessel fragility) and other unknown factors, including the bleeding time and the protection offered by coat hair, such assumptions can be misleading. Nevertheless, it is reasonable to conclude that bruising in deeper tissues may have required greater force than that resulting in only subcutaneous bruising at a similar site.

Lacerations

Lacerations are caused by blunt trauma that results in tearing or splitting of the tissues. They can be accidental, as in motor vehicle accidents (Fig. 6.5), or can be caused by heavy blows from a blunt weapon, or by violent shaking and tearing, during which the skin and deeper tissues are stretched until they tear.

Fig. 6.5 Dog. Laceration of the skin over the back and on to the flank of a dog killed in a road accident.

Lacerations frequently do not conform to the shape of the object that inflicted the damage, and severely lacerated muscle may be present underneath intact skin (e.g. see Bite wounds).

The margins of lacerated skin wounds are usually irregular and may show abrasion and bruising. Strands of tougher tissue, such as blood vessels, may be seen extending from side to side across the deeper parts of the wound. Bleeding commonly accompanies laceration but the stretching and crushing action of the injury can cause blood vessels to retract, so that the extent of haemorrhage is commonly less than might be expected for the severity of the damage.

Head, face and neck injuries

Head injuries

The head is a common target for blows to dogs and cats. A hammer, stick or spade may be used to club dogs and foxes, whilst hammer blows can also cause fatal head injuries to calves. Whenever possible, the suspect weapon should be examined in order to gauge whether, because of its shape, size and weight, it could have caused the injuries. Equally importantly, it may be found that the flimsiness of the putative weapon raises doubts that it was used to fracture a mature skull. The weapon should be examined for blood traces and adherent hairs (Fig. 6.6).

Fig. 6.6 Hammer used in a sustained attack on an elderly dog. Note blood and hairs on shaft and head of hammer.

Small creatures, such as kittens, may suffer major head injury as a result of being held by the hind limbs and swung against a wall or floor. The injuries in these cases are frequently disproportionately severe and cast doubt on the veracity of histories that claim the injuries were the consequence of a ‘fall’.

Depending on the type of object striking the head, superficial soft tissue injury might consist of abrasions, lacerations or incised wounds. Subcutaneous bruising usually accompanies blunt trauma to the head and can be valuable in establishing the nature and direction of the blow(s) (Case study 6.1, Fig. 6.7). Extensive or marked intramuscular haemorrhage in the temporalis muscles of dogs suggests high-energy trauma.

Case study 6.1

Clinical history:

A 4-month-old mongrel puppy was recovered from a rubbish pile following a domestic dispute during which the female partner fled in fear of her life.

Post-mortem examination:

The only external sign of injury was a small bruise on the left side of the head, at the base of the ear. Internally, severe bruising was present over the right dorsal and lateral aspect of the head but the skull was not fractured in this area (Fig. 6.7). On the left side of the face and head, bruising overlay part of the upper jaw and cheekbone, and extended into the adjacent muscles. The cheekbone was fractured in two places and a depressed fracture involved much of the side of the skull. A large haemorrhage was present within the left side of the brain.

The issues:

1 How many blows were struck?

The areas of injury were well defined in this case and guidance on the number of times that the puppy was struck was important. The nature and distribution of the bruising and fractures suggested one or more blows to the left side of the head with a further heavy blow to the top of the right side of the head.

2 What type of object or weapon was used?

Nothing could be stated with certainty about the object or weapon that caused the damage in this particular case, but kicking or punching can result in this type of injury in puppies or kittens.

3 Was suffering caused?

Death resulted from haemorrhage within the brain. However, such haemorrhage takes time to develop and there was no basis to suppose that death was instantaneous or that the puppy was insensible throughout the period when blood was leaking into the brain. It was considered highly likely, therefore, that the puppy suffered (a) during the actual assault when the cheekbone and skull were fractured and (b) during the subsequent period of bleeding into the brain.

Fig. 6.7 Puppy. Extensive haemorrhage over the back of the head on the right side. The skull was not fractured at this site. Note the line of haemorrhage along back of skull from base of left ear, probably caused by sudden over-flexion of neck when head was struck.

Absence of bruising over the head in cases where there is a history (or witness evidence) of the animal having been beaten on the head, suggests that either the history is wrong (Case study 6.2) or the beating occurred after death.

Case study 6.2

Clinical history:

A bull terrier-type dog was exhumed from a flowerbed after information was received that she had been beaten to death. The owner said that the dog had died from a ‘heart attack’. Later he changed the story, claiming that he had hit her, lightly, with a baseball bat after she had defaecated on the furniture and the children’s clothes. The owner claimed that he hit her on the head and that she lay down in the living room. He found her dead in that room some time afterwards.

Post-mortem examination:

The dog, which had been buried for approximately 4 weeks, showed advanced post-mortem change but was in reasonable bodily condition. There were no skeletal fractures and no evidence of head injury. However, extensive bruising affected the back, chest (both sides) and the left side of the abdominal wall. Semi-solid material, which was considered to have leaked from the stomach or small bowel, was free within the abdominal cavity. No other significant injuries were present.

The issues:

1 Was the degree of post-mortem change an impediment to the investigation?

Advancing post-mortem decomposition obscures the finer details of changes that occurred before death – small bruises, for example, become less distinct. In addition, post-mortem leakage of blood pigments from blood vessels may mimic small bruises. However, in this case, there was obvious bruising on the body related to significant blunt trauma to the chest and abdomen.

Post-mortem changes introduced some uncertainty with regard to the final cause of death inasmuch as rupture of the stomach/intestines could have occurred after death. It was absence of other significant pathological changes to account for the death of this dog that suggested that leakage of gut contents into the abdominal cavity was an ante-mortem event. Lack of immediate veterinary attention for such a catastrophic event would have resulted in shock and death.

2 Was there evidence of diarrhoea to account for the history of inappropriate elimination in the house?

Forming faeces in the colon were of normal consistency and colour, suggesting that the explanation given by the owner for his outburst of rage was false.

3 Was there evidence of head injury that might have rendered the dog insensible?

No head injuries were present and this finding, again, cast doubt on the owner’s story.

Interpretation of bilaterally symmetrical areas of ‘bruising’ on the skull needs to be approached with caution. Usually these marks are normal anatomical features that are generally overlooked in diagnostic necropsies or they are post-mortem artefacts.

Skull fractures and specific injuries

Radiological interpretation

The radiological classification used for skull fractures in abused children ⁶ is equally appropriate for abused pets and livestock. Skull fractures are divided into simple or complex categories. Simple fractures are single lines that extend in a straight, jagged or curved manner. These fractures do not cross sutures. In complex fractures there is more than one fracture line. Further useful descriptors are comminuted, depressed and elevated.