Pathophysiology

Gunshot and stab wounds account for the largest percentage of penetrating extremity injuries. Gunshot and blast injuries often present a diagnostic and management dilemma. A basic understanding of wound ballistics will enable astute clinicians to better plan the clinical management of patients who sustain a gunshot wound to the extremity. Diagnostic and treatment modalities as well as outcome differ with the type and severity of the injury. Although the damage from a stab wound can be relatively predictable with a good knowledge of clinical anatomy, the tissue damage inflicted by a missile or blast depends on a variety of factors (see Chap, 256,

"Wound Ballistics"). The notion that projectile velocity alone determines the extent of damage is false. Wound profiles depend on variables that include the projectile's shape, construction, composition, angle of impact, flight characteristics in tissue (yawing, or turning sideways in relation to line of flight), velocity, and mass. 3 An example would be a shotgun blast. At close range, a shotgun creates a more severe wound than a high-velocity M-16 assault rifle would at the same range because of the increased total mass and fragmentation of the shotgun load. The impact of a missile on tissue also creates indirect damage due to pressure waves accelerating radially away from the point of penetration, thereby displacing tissue. This phenomenon, termed temporary cavity, can cause significant additional damage.4 The severity of injury due to the temporary cavity varies inversely with the elasticity and density of the surrounding tissue. As an example, muscle and fat are relatively more elastic and therefore far less susceptible than bone or liver to this type of indirect damage. A third proposed mechanism of damage is termed shock wave: a sound wave traveling in front of the bullet is generated by the missile impact onto tissue. This theory has not been proven in multiple studies, and the nature of the subsequent damage is not well defined. Overall, tissue damage is usually proportional to the amount of fracture comminution and displacement, blood loss within the limb, and nerve or vascular injury. The wide variety of handguns available on the market and the availability of military-surplus weapons, as well as the inaccuracy of the information given to treating physicians about weapon and bullet type by the injured and their associates, make clinical findings and diagnostic modalities the best guides in determining management.

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