The largest percentage of physical child abuse occurs in the age range of birth to 5 years. Children of these ages are particularly vulnerable due to their age and undeveloped skill levels. Although only skilled medical professionals can fully substantiate the presence of skeletal injury, the field investigator should watch for several signs. Skeletal damage should be suspected if a joint or limb is red, raw, or swollen or if pain, local tenderness, irritability, or unwillingness to move the limb are present. Skeletal system damage can be serious, but it is usually not life threatening. However, head and abdominal injuries are both life-threatening and the most frequently encountered forms of injuries leading directly to death in children. Head injuries may include concussions, contusions, or lacerations. Shaking of children is often responsible for subdural hematomas, which can produce death or disabling permanent damage such as visual loss, blindness, motor deficits, seizures, developmental delays, and cerebral palsy. Abdominal injuries are usually caused by an adult's punch or kick and have a 50-percent mortality rate. 20 footnotes.