Biomechanics of the toddler head during low-height falls: an anthropomorphic dummy analysis

Laboratory investigation

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Object

Falls are the most common environmental setting for closed head injuries in children between 2 and 4 years of age. The authors previously found that toddlers had fewer skull fractures and scalp/facial soft-tissue injuries, and more frequent altered mental status than infants for the same low-height falls (≤3 ft).

Methods

To identify potential age-dependent mechanical load factors that may be responsible for these clinical findings, the authors created an instrumented dummy representing an 18-month-old child using published toddler anthropometry and mechanical properties of the skull and neck, and they measured peak angular acceleration during low-height falls (1, 2, and 3 ft) onto carpet pad and concrete. They compared these results from occiput-first impacts to previously obtained values measured in a 6-week-old infant dummy.

Results

Peak angular acceleration of the toddler dummy head was largest in the sagittal and horizontal directions and increased significantly (around 2-fold) with fall height between 1 and 2 ft. Impacts onto concrete produced larger peak angular accelerations and smaller impact durations than those onto carpet pad. When compared with previously measured infant drops, toddler head accelerations were more than double those of the infant from the same height onto the same surface, likely contributing to the higher incidence of loss of consciousness reported in toddlers. Furthermore, the toddler impact forces were larger than those in the infant, but because of the thicker toddler skull, the risk of skull fracture from low-height falls is likely lower in toddlers compared with infants.

Conclusions

If similar fracture limits and brain tissue injury thresholds between infants and toddlers are assumed, it is expected that for impact events, the toddler is likely less vulnerable to skull fracture but more vulnerable to neurological impairment compared with the infant.

Abbreviations used in this paper: CRABI = child restraint air bag interaction; HIC = head injury criterion; HIC15 = HIC with a maximum time interval of 15 msec; HIC36 = HIC with a maximum time interval of 36 msec.

Article Information

Address correspondence to: Susan S. Margulies, Ph.D., Department of Bioengineering, The University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd Street, Philadelphia, Pennsylvania 19104-6321. email: margulie@seas.upenn.edu.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Photographs. Skull casing (A) and scalp (B) of the 18-monthold surrogate. The total body is shown (C).

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    Graph showing the representative head acceleration trace. Example of angular head acceleration in the sagittal, coronal, and horizontal directions in a drop onto concrete from 1 ft.

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    Peak angular acceleration of the toddler surrogate head. Representative directional differences for concrete drops from 2 ft (upper) and height/surface differences in the sagittal direction (lower). Brackets indicate groups that are significantly different (p < 0.05).

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    Peak-to-peak change in angular velocity of the toddler surrogate head. Representative directional differences for concrete drops from 2 ft (upper) and height/surface differences in the sagittal direction (lower). Brackets indicate groups that are significantly different (p < 0.05).

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    Estimated impact force of the toddler surrogate head for 3 heights and 2 surfaces using a center of rotation in the middle of the neck. Brackets indicate groups that are significantly different (p < 0.05).

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    Toddler versus infant peak angular acceleration. Peak angular acceleration was significantly higher in the toddler compared with the infant (p < 0.05). This was more pronounced in drops onto concrete drops (closed symbols) than in drops onto carpet (open symbols). Black, dark gray, and light gray represent drops from 1, 2, and 3 ft, respectively. Diamonds, rectangles, and triangles represent the mean peak sagittal, coronal, and horizontal accelerations, respectively.

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    Toddler versus infant impact force. Impact force was significantly higher in the toddler than in the infant at all heights onto all surfaces except 1 ft onto carpet pad (p < 0.05). Black, dark gray, and light gray represent drops from 1, 2, and 3 ft, respectively. Closed and open shapes represent concrete and carpet pad drops, respectively.

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    Angular velocity traces in the sagittal direction from toddler (upper) and infant (lower) drops. Angular acceleration in the toddler consisted of a single peak, whereas in the infant a cyclic pattern was observed due to repetitive head rebound.

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    Resultant acceleration/velocity data from toddler drops compared with mass scaled concussion data from boxers and football players.

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