Physical injuries 

These are mainly classified in to four groups: injuries due to mechanical forces, changes in temperature, changes in atmospheric presence, and electromagnetic energy.

A-Injuries due to mechanical forces

Injuries due to mechanical forces are (1) soft tissue injuries, (2) bone injuries, (3) head injuries.  Injuries to the bones & head are considered elsewhere. Here we deal with soft tissue injuries, which are divided accordingly to their depth. Abrasion: this type of injury represents the most superficial type of skin injury, which involves the epidermal layer.  It occurs when superficial epidermal cells are turnoff by friction or a glancing blow.  There is no perforation of the skin & hence regeneration occurs with out scarring.

Laceration versus incision

Laceration is an injury over the skin which is an irregular tear produced by overstretching.  Depending on the tearing force it can be linear or satellite. The margins of a laceration are frequently hemorrhagic & traumatized and there will be bridging stands of tissues like blood vessels or fibrous tissues at the base. An incision is made by a sharp cutting object like knife. The margins are relatively clean and there are no bridging fibrous strands or tissues. An incision, in contrast to laceration, will be approximated by sutures to heal leaving no or little scar. laceration can take place to deeper tissues or organs without apparent superficial injury for example when a fast moving vehicle collides with and object the liver of a driver, not using safety belts, can lacerate when his body impacts on the steering wheel.

Contusion

This is an injury that is cause by a blunt force that injurs small blood vessels & causes intestinal bleeding usually with out a breach on the superficial tissue the bleeding will be evident if the contusion is on a superficial tissue but if it is in deeper structures like skeletal  muscles the bleeding will be evident after several hours or may remain obscured excepts the swelling & pain that is felt at the area over the contusion. 

Gunshot wounds 

Looking at the gunshot wounds give a very detailed story as to whether the shot is from a distance or, nearby, or from a rifle or a handgun.  It also tells the direction from which the bullets came & other important information for a forensic pathologist.  The character of a gunshot wound at entry & exit and the extent of injury depend on the type of gun used, caliber of bullet, the type of ammunition, the distance of the firearm from the body, etc. Entry wounds in general are smaller than exit wounds. With a shot from close range, the entry wound has a gray – black discoloration produced by the heat, smoke and unburned powder. There are also peripheral stippling of  discrete, larger particles formed by the unburned powder, When the shot distance increases a beat only the stippling are present and at greater distances no gray black discoloration or stippling are present rather a wound smaller in size from the bullet and with narrow enclosing rim of abrasion is present. Cutaneous exit wounds are generally more irregular than the entry wounds due to the wobbling or trajectory motion of the bullet. In high velocity riffle bullets the exit wounds are larger and there are no stippling or dark discolorations. Large caliber, light velocity bullets cause extensive injury around the traversing wound due to the mass, velocity and motion of the bullet. Small caliber low velocity bullets cause a limited amount of injury to surrounding tissue.  In general, it suffices to say that gun shot wounds tell a story to the experienced   individual.

B-Injuries related to changes in temperature

Human beings are homoeothermic and their internal temperature must be maintained between 30 ⁰C and 43 ⁰C. Even these limits can be tolerated for a brief time. Abnormally high and low temperatures are injurious to the body and their damage is different and have to be discussed separately.

A. Injuries due to abnormally high temperature

These can be brought by flame, boiled water or steam, electricity and etc. It involves mainly children and young adults and is very common in our society.

Cutaneous Burns

The severity of the burn effect depends on:  

-  % Of total body surface involved 

-  Depth of the burn

-  Possible presence of internal injuries form inhalation of hot gases & fumes

-  Promptness and efficacy of the post burn therapy

Burn can involve the most superficial part of the skin or it can go even deeper to internal organs. Terms like ‘partial thickness’ and ‘full- thickness’ burns are applied to describe the degree of burn injury. In partial thickness, the dermis with its skin appendages is preserved. Epidermis can be fully or partially devitalized and it continues to provide a cover to the burned area. Such burns are characterized by blistering, proteinacious fluid exudation from dilated and injured small blood vessels. Inflammatory reaction and regeneration of the epidermis from preserved appendages of dermis are also common features. The epidermal

cells may exhibit deranged membrane permeability, with nuclear and cellular swelling or may show clean pyknosis and granular coagulation of cytoplasm. Full thickness burn implies total distraction of the entire epidermis extending into the dermis and even more deeply at times. Regeneration from dermal appendages is scarce and hence healing will result in scarring unless skin grafting is performed. With the epidermis burnt out the dermal collagen may take the appearance of a homogenous gel. The cytologic changes described in partial thickness burn may be seen in deeper structures and the inflammatory reaction seen in the partial thickness burn is greater here. The systemic effects are feared more than the  local injury. Neurogenic shock can prevail due to the pain and this can be followed by hypovolemic shock when the individual looses fluid from the burned area. Dreadful infection can develop because of a wide area, which is open to infection and due to a media favorable for proliferation of microorganism. The wound infections can progress to regional thrombophllbitis, infective endocarditis, pneumonia, cellulitis, and sepsis.

B. Injuries due to abnormally low temperature

The effects of hypothermia depended on whether there is whole body exposure or exposure only of parts. Death may result when the whole body is exposed, without inducing apparent necrosis of cells or tissues. This is because of the slowing of metabolic process, particularly in the brain and medullary centers, when parts of the body are exposed, local changes result depending on the types of exposure to low temperature 

Local reactions

Injury to cells and tissues occur in two ways

1.  Direct effect of low temperature on the cells

2.  Indirect effects due to circulatory changes

Circulatory changes will be in two ways: slow temperature drop that will result in vasoconstriction and increased permeability leading to edematous changes as in ‘trench foot’, sudden sharp drop that will result in vasoconstriction and increased viscosity of the blood leading to ischemia and degenerative changes. Edematous changes in trench foot could be followed later by atrophy and fibrosis.

C. Injuries related to changes in atmospheric pressure

1. High altitude illness

This is encountered in mountain climbers in  atmospheres encountered at altitudes above 4000m. The lower oxygen tension produces progressive mental obtundation and may be accompanied by poorly understood increased capillary permeability with systemic and, in particular pulmonary edema.

2. Air or Gas Embolism

This may occur as a complication of scuba diving, mechanical positive- pressure ventilatory support, and hyperbaric oxygen therapy. In all these occasions there is an abnormal increase in intra-alveolar air or gas pressure, leading to tearing of tissue with entrance of air into the interstitium and small blood vessels. Pulmonary, mediastinal, and subcutaneous emphysema may result. The coalescence of numerous small air or gas emboli that gain access to the arterial circulation may lead acutely to stroke- like syndrome or a myocardial ischemic episode.

D-Electrical Injuries

The passage of an electric current through the body:-

•  May pass without effect

•  May cause sudden death by disruption of neural regulatory impulse producing, for example, cardiac arrest

•  Or may cause thermal injury to organs exposed to electric current

Although all tissues of the body are conductors, their resistance to flow varies inversely to their water content. Dry skin is particularly resistant, but when skin is wet or immersed in water resistance is greatly decreased. Thus, an electric current may cause only a surface burn of dry skin but, when transmitted through wet skin, may cause death by disruption of regulatory pathways.

References

Bezabeh ,M. ; Tesfaye,A.; Ergicho, B.; Erke, M.; Mengistu, S. and Bedane,A.; Desta, A.(2004). General Pathology. Jimma University, Gondar University Haramaya University, Dedub University.