Research Analyzes Level of Protection Provided by Children’s Bicycle Helmets

Bicycle accidents are a common cause of traumatic injury in the United States. The most recent statistics indicate that there were an estimated 500,000 bicycle-related injuries treated in U.S. hospital emergency rooms in 2004. Of those, 69,500 were head injuries, and of the 600 bicycle-related deaths, about two thirds were attributed to traumatic brain injury (TBI).

Between 1984 and 1988, 557,936 visits to emergency rooms were related to bicycle accidents. About 6 percent (33,500) of these were serious enough to require hospital admission. In those same years, an average of 962 deaths annually resulted from these injuries. TBI caused 62 percent of all deaths resulting from bicycle accidents. Forty percent of deaths occurred in children age 15 and younger. Clearly, children are at the greatest risk of sustaining these injuries. Boys age 10 to 14 are at the highest risk. It is estimated that bicycle-related injury and death cost society $8 billion annually. Bicycle helmets are widely touted as a protective step against head injury. However, the degree of protection that they provide has not been widely investigated.

Researchers recently assessed the level of protection provided by children’s bike helmets. The results of this study, Quantification of the Protection Granted by Children’s Bicycle Helmets Using Engineering Tools and Experimental Design, will be presented by Chris A. Sloffer, MD, MBA, 4:30 to 4:40 p.m. on Tuesday, April 25, 2006, during the 74th Annual Meeting of the American Association of Neurological Surgeons in San Francisco. The co-author of this study is Julian J. Lin, MD.

Four human skulls were utilized for this study. Skulls were soaked in water and filled to weigh four pounds to correspond to the approximate weight of a child’s skull. An accelerometer was mounted to each skull to facilitate measurement of the forces sustained by the skulls during testing. Identical, commercially available bicycle helmets were obtained for use in each step of testing.

Current industry testing standards require helmets to be placed on a head form and dropped from various heights onto a metal anvil. The helmets pass if they do not sustain injury. In this study, each helmeted skull was dropped from progressively greater heights of two to four feet. Impact decelerations experienced by the skulls were recorded. Skulls without helmets were dropped beginning at two feet and increased until failure (fracture). Decelerations experienced by these skulls were also recorded. As an additional method of testing, compressive force was applied to skulls, both with and without helmets, as well as to helmets without skulls inside. Forces tolerated were recorded in each of these categories, and digital video records were taken of all testing. The results of the testing were as follows:

•Forces measured remained below the maximum allowed by commercial helmet design standards in falls up to three feet. •Skulls without helmets experienced a deceleration between 4.2 and 7.7 times that of helmeted skulls in the heights tested. •Helmeted skulls were unable to be crushed in compression testing at loads up to 470 pounds, whereas both the skull and helmet alone failed (fractured) in testing.

Children’s bicycle helmets provide measurable protection in terms of both reducing the deceleration experienced by the child’s head and protecting against direct compressive force. “By quantifying those two measurements through experimental engineering design, an assessment of the protection levels of each type of helmet can be made, and this information has potential for enabling improvements in future helmet design,” remarked Dr. Sloffer.

Comparing the protection levels of different types of currently available commercial helmets would be a logical further topic to study. Additional studies should also assess the relationship of the deceleration forces on the skull to the brain injury itself. “The results of this study lend evidence to the theory that helmets reduce head injury significantly, and consequently, the use of properly fitting helmets should be strongly encouraged as a public health initiative,” concluded Dr. Sloffer.