This tiny knee bone had almost disappeared as humans evolved. It comes back

A tiny bone hidden in the knee tendon began to disappear during the evolution of man … or at least thought scientists.

Now, a new study finds that this so-called fabella (Latin for "little bean") is making a comeback. The bone, which is a sesamoid bone, or which is embedded in the tendons, is three times more prevalent in humans today than it was there was a century, scientists reported Wednesday, April 17 in the Journal of Anatomy.

A group of researchers from Imperial College London reviewed records (such as x-rays, MRI scans, and dissections) from more than 27 countries and more than 21,000 knees. They combined their data to create a statistical model estimating the prevalence of this bone elusive over time.

In early records dating back to 1875, they discovered that fabella was found in 17.9% of the population. In 1918, it was present in 11.2% of the inhabitants and in 2018, it was hidden in the tendons of 39% of the population. [The 7 Biggest Mysteries of the Human Body]

According to a statement from Imperial College London, the bone has already been associated with arthritis or inflammation of the joints, pain and other knee problems. Indeed, people with osteoarthritis of the knee are twice as likely to suffer from this bone as people who do not have one, he writes.

A long time ago, the fabella had a purpose similar to that of a knee brace for monkeys of the Old World, according to the statement. "As we move towards great apes and humans, we seem to have lost the need for fabella," said lead author Michael Berthaume, an anthropology engineering engineer at Imperial College London. "Now it only causes us problems, but the interesting question is why is he making such a comeback."

Sesamoid bones like Fabella are known to develop in response to mechanical forces, according to the release. Because humans are now more nourished than their ancestors, making them bigger and heavier, the body is putting more pressure on the knee, Berthaume said. "This could explain why fabellae are more common now than they once were."

Originally published on Science live.