Whitney Palmer

There are currently many methods forensic scientists use to figure out the biological

Kristen Rectenwald, an N.C. State grad student who works with professor Troy Case, measures a talus - an ankle bone - on a mini-osteometric board. Case's team learned the sex of a person can be determined due to the differences between men's and women's ankle bones.

sex of almost any complete set of skeletal remains. But in instances where skeletal remains are scant, these findings prove accurate identification of sex is possible in 80 percent of cases.

“The tarsals are good candidates to determine biological sex because they are weight-bearing bones located at the bottom of a big column of body weight,” said Troy Case, Ph.D., associate professor of anthropology at NCSU and lead study author. “This is important when you consider there are two ways to measures body size – height and weight.”

The tarsals are often reliable indicators of biological sex because they are particularly dense bones and are frequently protected by shoes.

Specifically, the talus bone is the best predictor of biological sex because its length, breadth and height vary the most the between the sexes. The talus is the bone that works like a hinge between the foot and leg. Researchers measured the other bones, as well, including the heel bone, the calcaneus.

According to Case, modern men and women vary in height by roughly 5 percent to 10 percent. On average, men stand 7 percent to 8 percent taller. The weight difference is greater: Men typically weigh 15 percent more than women. Heavier mass in men almost always equates to bigger bones that can withstand the added stress.

Using skeletons housed at the University of Tennessee in Knoxville, Case and his colleagues gathered 18 measurements each of length, width, and height from 160 male and female tarsal bones. The bones came from men and women of European-American descent.

The researchers found talus measurements to be the most reliable indicator. In women, the talus is, on average, 53.75 mm (2.11 inches). But in men, it is, on average, 61.05 mm (2.4 inches). The actual size of the bones might be small, Case said, but the 13 percent difference in length is significant enough to identify biological sex.

By combining talus measurements with other tarsal bones, the researchers achieved an even greater indication of biological sex. For example, coupling talus height with the length of one of the cuneiform bones that runs along the center of the foot, the team pinpointed sex with 93.6 percent accuracy.

Other findings

Case and his team also discovered talus length from the right side of the body is often more accurate than length measured from the left. In fact, the talus from the right foot correctly identified biological sex 90 percent of the time.

“It was kind of interesting to find that the right side was better at predicting biological sex,” Case said. “In the legs, there’s a much smaller difference between both sides in length, but most people tend to kick with the right foot and spend more time with all their weight on just the left side.”

The left leg is the “plant leg” – the one that remains somewhat stationary and bears the burden of body mass. Due to that extra stress, Case said he would have expected the left side talus to be a bit bigger or more reactive to weight bearing.

While these findings and methods can only be used to correctly identify the biological sex of the bones from someone of European-American heritage, Case anticipated other researchers will now build upon this work and develop similar measurements for other racial and ethnic groups.

Although most cases that come to the N.C. Office of the Chief Medical Examiner, based at UNC Chapel Hill, involve relatively complete skeletons, knowing how to use the tarsals to determine biological sex would be a useful arrow in the quiver, said Dr. Sam Simmons, associate chief medical examiner and associate professor of pathology at Chapel Hill.

“The utility rate of using these bones would be low. But if there were even one case where it was useful, then it would certainly be of benefit,” Simmons said. “Even though it won’t help you figure out race, age, or any other characteristics, it’s an important tool to have in the toolbox.”

Ultimately, Case said, he hopes these findings will be most substantially useful in forensic anthropology by aiding in determining the biological sex skeletons that have been substantially decayed.