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Research Papers

Age Dependent Mechanical Properties of the Infant Porcine Parietal Bone and a Correlation to the Human

[+] Author and Article Information
Timothy G. Baumer, Brian J. Powell

Orthopaedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, East Lansing, MI 48824

Todd W. Fenton

Department of Anthropology, College of Social Sciences, Michigan State University, East Lansing, MI 48824

Roger C. Haut

Orthopaedic Biomechanics Laboratories, College of Osteopathic Medicine, Michigan State University, A407 East Fee Hall, East Lansing, MI 48824haut@msu.edu

J Biomech Eng 131(11), 111006 (Oct 21, 2009) (6 pages) doi:10.1115/1.4000081 History: Received January 21, 2009; Revised May 14, 2009; Posted September 01, 2009; Published October 21, 2009

An infant less than 18 months of age with a skull fracture has a one in three chance of abuse. Injury biomechanics are often used in the investigation of these cases. In addition to case-based investigations, computer modeling, and test dummies, animal model studies can aid in these investigations. This study documents age effects on the mechanical properties of parietal bone and coronal suture in porcine infants and correlates the bending properties of the bone to existing human infant data. Three beam specimens were cut from porcine specimens aged 3 days, 7 days, 10 days, 14 days, 18 days, and 21 days: one across the coronal suture and two from the parietal bone, one parallel to and one perpendicular to the coronal suture. An actuator-mounted probe applied four-point bending in displacement control at 25 mm/s until failure. Bending stiffness of bone specimens increased with age; bone-suture-bone specimens showed no change up to 14 days but increased from 14 days to 18 days. All three specimen types showed decreases in ultimate stress with age. Ultimate strain for the bone-suture-bone specimens was significantly higher than that for the bone specimens up to 14 days with no differences thereafter. There was no change in the bending modulus with age for any specimen type. Bone-suture-bone bending modulus was lower than that of the bone specimens up to 14 days with no differences thereafter. There was no change in strain energy to failure with age for the bone specimens; bone-suture-bone specimens showed no change up to 14 days but decreased from 14 days to 18 days. There was an increase in specimen porosity with age. Correlation analysis revealed a weak (0.39) but significant and negative correlation between ultimate stress and porosity. While the mechanical properties of parietal bone and coronal suture did not change significantly with age, bone specimens showed an increase in bending stiffness with age. Bone-suture-bone specimens showed an increase in bending stiffness only between 14 days and 18 days of age. Correlation analyses using existing and new data to compute the bending rigidity of infant parietal bone specimens suggested that days of pig age may correlate with months of human age during the most common time frame of childhood abuse cases.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Top view of cranium with locations of the beam specimens

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Figure 2

Diagram of testing fixture

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Figure 3

Representative stained cross section of a beam from a 14 day specimen showing separation of compact and porous layers: The voids in the bone matrix were colored black and the box represents the analyzed area of a test specimen

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Figure 4

Recorded values of stiffness for (a) both orientations of bone and (b) bone-suture-bone specimens from 3 days to 21 days. *Significantly different means.

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Figure 5

Linear regressions of ultimate stress for bone and bone-suture-bone specimens against age

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Figure 6

Ultimate strain for bone and bone-suture-bone specimens. *Significantly different means.

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Figure 7

Bending modulus for bone and bone-suture-bone specimens versus age. *Significantly different means.

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Figure 8

Strain energy of bone and bone-suture bone specimens versus age. *Significantly different means.

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Figure 9

Linear regression analyses of both orientations of infant porcine bone specimens against age. Both orientations displayed significant dependencies on age.

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Figure 10

Bending rigidity of human and porcine specimens versus age (human in months; porcine in days): The human data were based on the data from Coats and Margulies (13) and the unpublished data from Li (14)

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