Transporting infants in bicycle trailers

Abstract

Inflicted Head Injury by Shaking Trauma (IHI-ST) is a form of abusive trauma caused by violent shaking, which children under the age of one are particularly vulnerable to. Because the exact injury mechanisms of IHI-ST remain unclear and direct evidence such as eyewitnesses is often lacking, legal cases concerning suspected IHI-ST often debate the actual cause of the diagnosed head trauma: Was it shaking, or was it an alternative “accidental” scenario raised by the defendant? One scenario that is sometimes raised is that of a rough trailer ride over bumpy terrain, where the transported infant was exposed to repeated shaking for the duration of minutes to hours. However, the validity of this alternative scenario has not been studied, yet. Therefore, the aim of this study was to evaluate the plausibility of the trailer scenario as a cause for IHI-ST. To get insight in the plausibility of this scenario without performing ethically questionable experiments, we recorded the complete head and torso kinematics of an infant dummy during controlled bicycle trailer rides over bumps with different heights, slopes, and at different trailer speeds. Due to limited biofidelity of the surrogate and the absence of valid thresholds it is currently impossible to know exactly which linear and angular accelerations and which degree of rotational nature of head motion would lead to injury. Therefore, we compared the recorded kinematics of the trailer scenario with recently reported values in the same instrumented dummy under violent shaking circumstances, assuming that the shaking scenario leads to injury. We found that the head motion during rough trailer rides in worst-case conditions (minimized impact damping and the absence of a head rest) was, even at the highest speeds and steepest and largest bumps, less rotational than violent shaking, and while the torso reached similar peak linear accelerations, the head angular accelerations barely reached half of those during violent shaking. However, although the head angular accelerations were lower, a low injury risk for head and neck injuries due to trailer rides can not be concluded yet, because the duration of the infant’s exposure to these accelerations is much longer (minutes to hours) than during violent shaking (a few seconds).