Two types of health problems—infectious disease and injury—have been the most important causes of lost years of productive life for Americans. Improvements in sanitation and housing and other public health measures in the nineteenth century made it possible to reduce the prevalence of infectious disease. In the early twentieth century, infectious disease ceased to be a major cause of lost years of life before age 65, leaving injury alone in that position in the United States, exceeding cancer and heart disease combined. This report deals with injury that is severe enough to cause one to seek medical care or to be unable to perform usual activity for a day or longer. Such injury strikes almost one-third of Americans in a given year.¹²³

Consider some of the primary facts concerning injury in the United States:

• Injury caused 143,000 deaths in 1983.¹²⁴
• Injury is the fourth leading cause of death among all Americans, accounting for 61 deaths per 100,000 population in 1983, compared with 328 for heart disease, 188 for cancer, and 67 for stroke.¹²⁴
• Injury causes almost half the deaths of children aged 1-4, more than half the deaths of children aged 5-14, and nearly four-fifths of the deaths of persons aged 15-24. Thus, injury is the leading cause of death among children and young adults (Figure 1-1).

Figure 1-1

Percentages of deaths from injury and other causes in the United States in 1980, by age. Modified from Baker et al.

Among young children, the largest numbers of injury deaths are caused by motor-vehicle crashes, drowning, and fire; pedestrian deaths constitute a major problem in urban areas.¹² Especially high death rates among teenagers and young adults ate associated with motor-vehicle crashes, firearms, and drowning.

Up to age 44, injury deaths continue to outnumber deaths from any other cause. Only after age 45 do other health problems—notably heart disease and cancer—cause more deaths than injuries. Even among the elderly, however, injury is an important cause of death; in fact, the death rate from injury (the number of injury deaths per 100,000 of population) is higher among the elderly than among younger people.

Injury is the leading cause of physician contacts—in 1980, there were 99 million such contacts, compared with 72 million for heart disease, the second leading cause of such visits, and 64 million for respiratory disease, the third leading cause.¹²⁵ And more than 25 percent of hospital emergency-room visits are for the treatment of injuries.¹²⁵

Injury is also a leading cause of short- and long-term disability. In 1981, people spent 144 million days in bed because of injuries.^{1 2 3} With respect to long-term disability, more than 75,000 Americans each year sustain brain injuries that result in long-term disability, including 2,000 who remain in persistent vegetative states.^{98 99} In addition, over 6,000 persons who were injured are discharged from hospitals with paraplegia or quadriplegia.¹⁰⁰ Each year, over 4 million years of future worklife are lost to injury, compared with 2.1 million to heart disease and 1.7 million to cancer³² (Figure 1-2).

Figure 1-2

Percentages of years of potential life lost to injury, cancer, heart disease, and other diseases before age 65. Modified from Centers for Disease Control.

The importance of health problems to society can be seen by measuring the dollar costs of their effects, such as lost productivity (indirect costs to society) and the use of medical and other resources (direct costs to society). The societal costs of all injuries occurring in a given year have not been computed, but the costs of the largest class of severe injuries—those resulting from motor-vehicle crashes—have been estimated:

• Motor-vehicle crash injuries in 1980 were estimated to cost society over $36 billion.¹¹⁰
• Injuries resulting from motor-vehicle crashes cost the federal government about $7.5 billion and state governments about $3.5 billion in direct payments and revenue loss in 1980.¹³⁰
• The societal costs of motor-vehicle crash injuries are second only to those of cancer, among the other leading causes of death.⁷⁹
• The direct costs resulting from motor-vehicle crash injuries are approximately twice those resulting from heart disease.⁷⁹
• The indirect costs of motor-vehicle crash injuries are especially high, because the average age at which injuries occur is much lower than the average ages at initial onset of the other leading causes of death.⁷⁹

Motor-vehicle crashes are the leading cause of severe injury and death and have been studied in more detail than most other injury causes. Although police reports generally understate the magnitude of the problem,¹⁵ consider the following statistics on motor-vehicle crashes: Approximately 3.2 million people were injured in motor-vehicle crashes in 1982.¹³² Of these, approximately 1.4 million were treated in emergency rooms and 350,000 were hospitalized.¹³² In 1982, over 50,000 person-years of work (not counting housewives, students, and others who are not classified as part of the work force) were lost by injured persons.¹³²

Given that the total number of injury-related deaths per year is about 3 times the number resulting from motor-vehicle crashes, and that the total number of nonfatal injuries is more than 10 times the number resulting from motor-vehicle crashes, a conservative estimate of the societal costs of all injuries in 1980 is approximately $75-$100 billion (in 1980 dollars).

The dollar costs of injury, as large as they are, account for only a portion of the total costs. Additional, less easily measured costs include pain, grief, family and social disruption, and the social and psychologic effects of disfigurement and long-term disability, such as those caused by severe burns, epilepsy from head injury, limitations of mobility from spinal cord injury, amputations, traumatic arthritis, and severe reduction in mental function from head injury.

Injury and death result not only from unintentional events, such as motor-vehicle crashes and falls, but also from deliberate events, such as assault and suicide. It is Common to think of injuries as different from disease because they occur suddenly—in a few milliseconds or a few minutes—but that is not always the case. The cause of injury to the human body is excessive exposure to energy (kinetic, thermal, and chemical energy, electricity, and radiation) or the absence of essentials, such as oxygen and heat. The five forms of energy that cause injuries are termed agents of injury. Typically, injuries result from short-term exposure to large amounts of energy (e.g., involvement in a car crash, contact with a hot stove, or ingestion of an overdose of aspirin). However, injuries can also result from repeated exposure to smaller amounts of energy (e.g., deafness resulting from prolonged exposure to excessive noise or back pain or arthritis in a worker exposed to repeated vibration) or from a combination of acute and chronic exposure (as in the greater sensitivity to head injury in a football player or boxer who has previously had head injury or to acute back injury in a worker who has had back trouble).

Kinetic or mechanical energy (e.g., from motor vehicles and firearms and in falls, jumps, and cutting) is by far the leading cause of injury-related death in the United States and accounts for more than 95,000 deaths a year (Table 1-1). Asphyxiation (drowning, suffocation, hanging, and strangulation) causes over 13,000 deaths, chemical energy (poisoning by solids, liquids, and motor-vehicle carbon monoxide) approximately 10,000, and fires and burns about 6,000. Deaths from electricity make up only a small percentage of all injury deaths (about 1,000 a year). Deaths from radiation are extremely rare. Mechanical energy is also the leading cause of nonfatal injuries, although the relative importance of specific causes differs somewhat from the relative importance of causes of fatal injuries. For example, falls are the second leading cause of death from unintentional injury, but the leading cause of injuries treated in hospital emergency rooms.

TABLE 1-1

Major Categories of Injury Deaths in 1982 in the United Stares.

Even though they are important, with many of the characteristics of injuries, health problems resulting from chronic exposure to injury agents will not be addressed in this report. Rather, it focuses on acute injuries and death associated with transportation, the workplace, the home, and recreational and public environments and on assaultive and self-inflicted injuries.

There are many misconceptions about the causes and control of injury. An event that produces injury is often thought of as an isolated occurrence with a single cause, and prevention of that single cause as the only, or best, solution to the problem. Note, for example, the common oversimplification in a report that someone died in a highway crash because the driver was drunk. The associated perception often is of a fatal injury attributable to a single cause—in this case, the misuse of alcoholic beverages. That leads to the misperception that such deaths could be prevented by eliminating excessive alcoholic beverage consumption by drivers or by separating such drinkers from their vehicles. In fact, many ways of preventing or limiting such deaths are possible.

Over the last 2 decades, useful ways have been developed for systematically considering the potential to produce injury, and those ways lead to options for preventing or reducing injuries. In one such approach, presented by Haddon,⁷³ an event that could result in injury is considered to have three phases—the pre-event, event, and post-event phases. The pre-event phase covers the period during which people use or are otherwise exposed to a source of energy before a potentially injurious event occurs. The event phase begins once the energy source is out of control. The post-event phase begins after acute exposure to the energy. Each phase presents opportunities for intervention to reduce the likelihood or severity of injury, if one systematically considers interactions of each of the three phases with various entities, such as vehicles, humans, and the environment. This report examines the status of and needs for research in all three phases of injury-producing events that will permit development of effective injury-control measures.

The medical treatment of injury has a long history. Descriptions of treatments of 48 cases of head and foot injuries appear on papyrus dating to approximately 1600 B.C. In approximately 500 B.C., Hippocrates studied wounds and fractures and suggested mechanisms of injury and methods of treatment. Most early physicians spent much time managing wounds that occurred in civilian life and in warfare. Although treating injuries and wounds has occupied the primary attention of physicians since the beginnings of scientific medicine, coordinated research in the treatment of injury has been generally lacking.

Injury control, encompassing activities from prevention through treatment and rehabilitation, is relatively young—in many ways still in its infancy. Newtonian laws of motion have been known for some 300 years, but biomechanical concepts of injury were not developed until this century, and it was not until World War II that biomechanics research was systematized. There is now a growing body of scientific literature and research on injury control, but substantially more needed research can be identified than can be supported by the limited resources available today.