A new Baylor University study looking at the different fracture properties of bones at various stages of degradation has found that bones degrade and fracture differently under certain environmental conditions like sun, shade or in water. The Baylor study also found that some postmortem fractures look like they occurred perimortem - at or near the time of death - under some specific environmental conditions.
"Forensic anthropologists see a lot of damage on bones from animals or people and we have to determine whether it happened perimortem or postmortem," said Dr. Lori Baker, associate professor of anthropology, archeology and forensic science at Baylor who helped lead the study. "This study gives insight into when changes to bones are expected to occur because that helps us pinpoint time since death."
The Baylor study tested dozens of sheep long bones under a variety of environmental conditions like full sun, shade and in water. The Baylor researchers left the bones, which were the humerus, radius and ulna, in the different environmental conditions for times ranging from one week to four months. The researchers then applied blunt force trauma to the midshaft of each bone using a custom-designed test jig, which could apply a repeatable and controlled force that simulated the bone being hit by crowbar or pipe.
The results showed:
All the bones degraded over time, however the rate at which the bones degrade greatly varies depending under which environmental condition they are exposed. The bones left in the sun degraded faster than bones left in shade or in water. The bones left in water maintained their strength the longest because they were less dehydrated.
The biggest degradation change to the fracture properties of the bones happened in the first two weeks since death regardless of environmental condition.
Forensic anthropologists know that if a bone break occurs postmortem, there will not be any fracture lines. If there are facture lines, the break occurred perimortem. However, the study found that at four weeks, if the bones were left in the sun or shade, the breaks had facture lines. This conclusion shows that even though the researchers knew the break happened postmortem, it appeared to have occurred perimortem.
The bones would facture into a few large pieces up to four weeks. After four weeks, the bones would break into many, much smaller pieces.
"As the bone becomes more brittle and flaws start to appear, the bone would break into tiny pieces along the fracture lines," said Dr. Carolyn Skurla, associate professor of mechanical engineering at Baylor who helped lead the study. "Forensic anthropologists have speculated and have anecdotal evidence that these findings are true but nobody has ever tested them. This study confirms some of things we thought were accurate."