Neck Injury in Forward-Facing Child Restraints
Facing a child forward for travel is not without risks, but too often it is seen by parents as a goal to be achieved as soon as possible. This goal is inappropriate, but misinformation and lack of understanding about the crash environment and child physiology have been difficult to overcome, even within the medical community. There has long been a concern in bioengineering literature that a child?s cervical spine could be pulled apart from the force on the head in a crash when the shoulders are held back.15 One popular misconception, however, is that muscle strength can overcome this force, and that a child who can hold up its head and sit erect is ?strong? enough to face a frontal crash.
In a 50 km/h (30 mph) crash with a 25-g passenger compartment deceleration, for instance, the head of a forward-facing adult or child may experience as much as 60 or 70 g, because the occupant?s head stops later and more abruptly than the vehicle?s floor pan. Even the strong neck muscles of military volunteers make little difference in such an environment. Rather it is the hardness of the vertebrae, in combination with the tightness of the connecting ligaments, that determines whether the spine will hold together and the spinal cord will remain intact within the confines of the vertebral column.42,107
Adult cervical spines can withstand severe tensile forces associated with decelerations up to 100g,76 and failure is nearly always associated with
fracture. On the other hand, the immature vertebrae of young children consist of both bony segments and cartilage, and the ligaments are loose
to accommodate growth.63,84 This combination allows the soft vertebral elements to deform and separate under crash conditions, leaving the spinal cord as the last link between the head and the torso. According to Huelke et al.,42 ?In autopsy specimens the elastic infantile vertebral bodies and
ligaments allow for column elongation of up to two inches, but the spinal cord ruptures if stretched more than 1/4 inch.? Mathematical models of pediatric spines (age 1, 3, and 6) subjected to various types of loading indicate that, compared to adult spines, the anatomical and material properties of immature spinal elements make them much more flexible than would be predicted by relative size alone.62 Stalnaker notes that the risk of spinal cord injury in children increases with crash severity and decreases with age.107
Accident experience has shown that a young child?s skull can be separated from its spine by the force of a crash,27 the spinal cord can be severed,41 or the child may live but suffer paraplegia or tetraplegia due to the stretched and damaged cord.67,113,122 Eleven cases studied in depth were included in the two 1993 reports. All children with severe injuries were 12 months old or younger, whereas others who suffered less severe injuries, such as C2 odontoid fractures, were over 18 months. All crashes were frontal (10 to 2 o?clock), with velocity changes ranging between 24 and 60 km/h (15 to 37 mph). It must be emphasized that these injuries appear to be rare, although there has been no recent attempt to estimate the risk of occurrence. Because of the potentially severe consequences, however, and the relatively simple countermeasure to such injury among the youngest children, it makes sense to keep them restrained rear-facing as long as possible (figure 12).
From www.carseat.org/Resources/Weber_CPCP.pdf page 12