Progressive changes in the properties of bone during soft tissue decomposition
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Abstract
Changes in bone characteristics during soft tissue putrefaction were investigated over 140
days, equating to between 638 and 1450 cumulative cooling degree days (CCDD)
depending on ambient temperature using a porcine experimental model in surface and
burial depositions. The hypothesis that changes observed in bone characteristics during
soft tissue putrefaction could be utilised for possible forensic applications was proved.
Human bones were tested for comparison. The techniques used were colorimetric
analysis of staining, measurement of micro-crack lengths (in the order of 0.1 to 1.0 mm)
on fractured bone surfaces under scanning electron microscopy, inductively coupled
plasma optical emission spectroscopy elemental profiling, thermogravimetric analysis
(TGA), zoological mass spectrometry profiling non-collagenous peptide content, and
Vickers hardness testing. The findings pertaining to the experimental porcine bone
samples were as follows. Stain colour did not equalise between periosteal and fractured
cortical bone surfaces. The fracture is widely considered perimortem if said surfaces are
homogeneous in colour and postmortem if different. Observed inconsistences in colour
change limit the potential of this technique as a potential forensic test of postmortem
interval (PMI). After 28 CCDD, shorter intersecting micro-cracks changed to longer
linear micro-cracks tracking lamellae. A longitudinal to tangential Vickers hardness (HV)
ratio of 1.5 to 1 associated with minimal decomposition indicated 250 CCDD or less
elapsed. The same ratio associated with marked decomposition indicated 1450 CCDD or
more elapsed. A ratio of less than 1:1 indicated 250 to 1450 CCDD. Decreases in iron,
sodium and potassium concentrations associated with tissue fluids can determine if bone
is in the early stages of decomposition. TGA correlation of water loss between 22 and
100˚C with observed changes in micro-crack lengths, HV, and elemental profiles
suggested progressive dehydration as the underlying common factor. These techniques
demonstrated some potential to be developed as forensic tests of PMI. As no correlation
with PMI was evident with proteomic profiling of non-collagenous peptides, no such
potential was demonstrated