Postmortem change in bone biomechanical properties: Loss of plasticity.

Bone is a hierarchical composite material composed primarily of collagen molecules, mineral crystals, and water. The mineral phase confers strength and stiffness while the organic matrix provides toughness. As a result, living bone is very capable of absorbing energy and resisting fracture. After death, the bone often becomes dehydrated and the collagen degrades causing greater stiffness and reduced toughness. These changes in mechanical properties are augmented due to the combined effects of water loss and collagen degradation. As a result, bone becomes more brittle postmortem, which causes the changes in fracture characteristics that are commonly used to estimate the timing of the fracture. However, because the loss of moisture and collagen degradation are influenced by taphonomic conditions, anthropologist must use caution when interpreting the timing of fractures based solely on fracture characteristics. As part of this special volume on hard tissue alterations associated with trauma, the aim of this article is to provide an overview of the mechanical changes that occur in bone postmortem and summarize major works in bone biology and anthropology examining the cause and timing of plasticity loss in bone after death.