The Shapes of Bones

When a body turns up, forensic scientists have to be creative. Dental records, finger prints, tattoos, implants and DNA are all routinely used to identify a corpse. Now a graduate student at the University of Toronto claims that the shape of thoracic vertebrae − captured inadvertently in routine chest X-rays − may yield useful clues as well.

Lelia Watamaniuk, a master’s student in the department of anthropology at U of T Mississauga, looked at 100 chest X-rays of males living in Toronto. She carefully examined the 12 thoracic vertebrae, and noticed that they seemed to have about seven characteristic shapes. For instance, when she looked at the midline of the vertebrae from a side view, some were clearly straight, some pinched and some angled.

Watamaniuk worked out how often each shape was likely to occur, then checked to see if those frequencies held up in a second set of 100 chest X-rays. They did.

Then she decided to test vertebral shape as a tool for identification. An assistant presented her with 24 X-rays, plus a reference set of another 100. Watamaniuk’s job was to figure out which two X-rays came from the same man, even though they were taken at separate times. Doing a point-to-point comparison, she was able to accurately match 21 of the 24 X-rays.

Since 40 per cent of people will get a chest X-ray in their lifetime − more than any other type of radiograph − and since this part of the spinal column is often well preserved after death, Watamaniuk argues in the September issue of the Journal of Forensic Sciences that chest X-rays may provide a useful extra avenue for identification of the dead. “It’s another piece of the toolkit,” she says.