BLUNT FORCE INJURIES
A contusion occurs when blunt force trauma causes disruption of small blood vessels in the subcutaneous tissues. The injured vessels lead red blood cells into the surrounding soft tissue. The overlying skin is intact. The bleeding into the soft tissue is seen as blue, red or sometimes purple in the fresh contusions. Over time (days to weeks) the blood pigment (hemoglobin) breaks down, resulting in color changes. In approximately a week, the bruise or contusion appears brown due to conversion of hemoglobin to bilirubin. As the pigment is converted to biliverdin, the contusion turns green-yellow. This occurs in approximately two weeks. Finally, the contusion fades away in about two to four weeks. It is important to note that these times are just broad generalizations. Variables affecting the healing of contusions include size, depth of the injury, age of the subject and health of the location circulation.
Microscopic sections can be used to help age a contusion. Within a few hours of injury, acute inflammatory cells (neutrophils) will appear. In two to four days, early scar tissue formation is seen. However, exact aging of contusions is impossible. The time interval between injury and death can only be estimated.
Lacerations are skin splits caused by blunt force blows. They can be quite irregular or linear depending on the configuration of the blunt instrument used. They are readily distinguished from incised wounds by examination. Lacerations have tissue bridges which are slender strands of tissue extending from side to side at the base and edges of the injury. Injuries caused by knives have sharp edges and margins. Tissue bridging is not present in incised injuries. Lacerations are often surrounded by abrasions and/or contusions.
Abrasions are skin scrapes. Friction against the skin results in scraping away the superficial portions of the epidermis or there may be destruction of the superficial layers of the skin by compression. Antemortem (before death) abrasions are red-brown in color. Postmortem (after death) abrasions are often yellow or parchment-like in appearance.
When examining any of the blunt force types of injuries, it is important to recognize and to carefully note any patterned injury. This helps investigators identify blunt force instruments used in assaults or aid in reconstruction of the fatal accident.