Forensic Medicine:Sharp Force Injuries

 

                                          

                                                      TOPIC: Sharp Force Injuries

Sub-topics:

·         Types of sharp force injuries and the mechanism of their production

·         The differentiation of sharp force and blunt force injuries

·         Sharp force injuries of the neck and trunk

·         Sharp force injuries of the limbs

Notes for the topic:  Stab wounds are incised wounds where the length of injury on the surface is less than the depth of penetration into the body. Most stab wounds are homicidal, rarely accidental. Most suicidal stab wounds involve the left chest and sometimes the abdomen. Most often the wounds are multiple with many "hesitation" stabs –wounds that barely penetrate the skin or are very superficial. The differentiation between sharp force and blunt force injuries can be done by examining the wound considering following topics such as cause, edges  bruising/abrasions, depth ,presence of tissue bridging, position, presence of foreign bodies,  hairs , bony injury , healing intention. Stab wounds to the chest resulting in fatalities usually involve the aorta or the heart. Hemopericardium and cardiac tamponade are common. Fatal abdominal stab wounds can occur from wounds to the lower chest as well as directly and usually involve the liver or some major blood vessel. Stab wounds of the neck can result in rapid death due to exsanguination or from air embolism. A stab wound of an extremity is not usually fatal. The femoral artery is most often involved in that type of injury.

 

 

 

 

 

 

 

Types of sharp force injuries and the mechanism of their production

• Incised wounds - caused by any implement/ object having a sharp edge. This can include knives and broken glass, for example.
• Stab wounds - which are incised wounds where the length of injury on the surface is less than the depth of penetration into the body. Most stab wounds are homicidal, rarely accidental. Suicidal stab wounds are uncommon but often have somewhat characteristic findings. Most suicidal stab wounds involve the left chest and sometimes the abdomen. Most often the wounds are multiple with many "hesitation" stabs –wounds that barely penetrate the skin or are very superficial. The real clue that the wounds are of suicidal often is the fact that in the majority of cases the individual has unbuttoned or pulled aside the clothing so that it is not involved. Persons with homicidal intent are extremely seldom or never quite so considerate. The size, depth, shape, and appearance of a stab wound are dependent upon several factors: the nature of the weapon, the direction of entry of the weapon into the body , the influence of the lines of Langer ,any movement of the blade or the victim while blade is in the wound, the sharpness or dullness of the weapon, the state of tension or relaxation of the skin , the length of the weapon that enters the wound , etc .

 Stab wounds are of 3 types :

• Punctured wound – Here the weapon just enters into the part of the body without entering into any of the body cavity. Technically it is a typical stab wound as its depth is greater than width. Example: Knife entering into the gluteus muscle in the buttocks
• Penetrating wound – Here the weapon just enters into the body cavity producing only one wound, i.e. wound of entry. Example: Knife entering into the abdominal cavity, without coming out of the abdomen. Thus it penetrates a body cavity. Major body cavities are chest, abdomen and skull . Other body cavities, upon entering which the wound would qualify as a penetrating wound are eye balls, major joints such as knee joint, hip joint, shoulder joint etc
• Perforating wound (through and through punctured wound) – Here the weapon after entering into one side of the body will come out through the other side, producing two wounds , a)wound of entry – through which the weapon enters the body. It is larger and with inverted edges. B)Wound of exit – through which the tip of the weapon emerges out of the body. It is usually smaller with everted edge.
• Slash wounds - which are incised wounds that are longer than they are deep.
• Chop wounds – Chop wounds are injury produced by a blow with the sharp cutting edge of a fairly heavy weapon like an axe, hatchet, saber, etc They are often severe in nature, and can include extensive soft tissue and bone damage. They represent a combination of sharp and blunt force trauma; the sharpness of the cutting edge influences how clean the wound edges are.

The differentiation of sharp force and blunt force injuries

		Blunt force injury wound
Cause		Blunt force trauma	Sharp force trauma
Edges		Ragged/ irregular	Cleanly divided
Bruising/abrasions?		Yes	No
Depth		Variable	Can be uniform
Presence of tissue bridging?		Yes	No
Position		Particularly bony prominences	Any location
Presence of foreign bodies?		Often contaminated wounds	Usually clean (unless caused by glass)
Hairs		Intact hairs may cross the wound	Hairs are cleanly divided
Bony injury		May have associated fractures	Scoring or chipping of bone may occur
Healing		2° intention (with extensive scarring)	1° intention  – good if wound edges apposed. Generally leaves fine scarring

 

Sharp force injuries of the neck and trunk:

Fatal abdominal stab wounds can occur from wounds to the lower chest as well as directly and usually involve the liver or some major blood vessel (aorta, vena cava, or iliac or mesenteric vessel). Survival may be prolonged in cases in which the mechanism of death is peritonitis resulting from wounds of the gastrointestinal tract.

Stab wounds to the chest resulting in fatalities usually involve the aorta or the heart. Hemopericardium and cardiac tamponade are common, but death usually results from a combination of the hemopericardium and additional blood lost externally and within the thoracic cavities. Death can occur from the presence of as little as 150 cc of blood in the pericardial sac. Death usually occurs more rapidly with wounds of the atria rather than the ventricles since the contraction of the ventricles can produce slowing or stoppage of the bleeding.

Stab wounds of the neck can result in rapid death due to exsanguination or from air embolism. Radiograph of the chest is suggested in stab wounds of the neck to detect air embolism. Asphyxia may also result from involvement of the trachea with consequent massive accumulation of blood in the tracheobronchial tree or from massive soft tissue hemorrhage that produces compression of the trachea and vessels in the neck. Delayed death can result from secondary thrombosis of the cerebral vessels with resultant cerebral embolism or infarction.

Cerebral stab wounds are not usually immediately fatal, and a wide range of volitional activities may follow these injuries.

Sharp force injuries of the limbs: A stab wound of an extremity is not usually fatal. The femoral artery is most often involved, and almost without exception the victim is intoxicated and does not appreciate the seriousness of his injury. One may have combinations of stab and incised wounds. An incised-stab wound either begins as a stab wound that becomes an incised wound as the knite is withdrawn or as an incised wound that ends as a stab wound produced by the thrust of the blade into the body.

 

 

 

 

 

 

 

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