An improved method to calculate paediatric skull fracture threshold

There is a need to better understand the threshold for paediatric skull fracture. Historically, drop tests of cadaver heads have been used to estimate thresholds. However, societal and ethical considerations prevent tests with child cadavers. Therefore, researchers have attempted to estimate the threshold by scaling adult tolerance data. Recent work suggests that mass and material scaling of adult tolerance data is insufficient to develop robust estimates of paediatric skull fracture tolerance. Researchers have also attempted to develop finite element models to estimate skull fracture tolerance. These models require that both geometry and material properties of the skull and brain be known, but, while detailed geometry is known, lack of experimental material test data prevents development of reliable finite element models. This paper describes development of a method to estimate skull fracture tolerance using fall data collected in emergency room. The method depends on the observation that width of force versus time pulse recorded in head drop tests onto a given surface does not vary with height of fall or the mass of head. This observation is supported by analyzing data from adult cadaver head drop tests onto 50mm thick 90 Shore D, and 40 Shore D rubber pads. Next, data from neonatal head drop tests are used to estimate pulse width when an infant head is dropped onto a steel plate. This pulse width is used together with child fall data collected at the Children’s Hospital, Milwaukee to estimate forces needed to cause a simple linear fracture in an infant head. This paper describes the procedures used to obtain anthropometric data and fall data such as height of fall and type of surface that the head contacted. This physics based method can be used to analyse child fall data relatively easily to obtain robust estimates of child skull fracture. INTRODUCTION Paediatric skull fracture threshold is an important variable needed to design a number of child protective devices such as helmets, child seats and children’s playground surfaces. Historically, skull fracture thresholds are estimated from drop tests of Post Mortem Human Subjects [PMHS] heads. Drop tests were the used to estimate adult skull fracture threshold levels. However, societal and ethical considerations prevent testing with child PMHS. Therefore, researchers have attempted to use scaling laws to estimate paediatric skull fracture tolerance levels from adult skull fracture tolerance levels [Irwin and Mertz, 1997, Melvin, 1995]. Initially, mass scaling was used but it was soon realized that differences in structure of the adult and child skull, and material properties would require that material properties also be scaled in the estimation of threshold [Thibault and Margulies, 1999]. Paediatric skull fracture threshold is also of interest to clinicians and in the field of forensic medicine. In many instances, physicians and law enforcement personnel are required to determine whether head injury is a result of an accident or abuse. Tarrantino et al [1999] reported that unintentional falls were the leading cause of nonfatal injury in infants less than a year old. Linear skull fractures are seen 58% of the time in accident cases [Reece and Sege, 2000] found that linear fractures were much more common than complex fractures in accident cases and occurred in 54% of the cases. Prange, et al [2004] conducted head drop tests using 3 neonate heads. The heads were dropped from 15 and 30 cm heights and the objective of the tests were not to cause fracture. Weber [1984, 1985] conducted whole body child PMHS drop