The fabella bone found in our primate ancestors was once rare in humans and scientists believed that we might have lost this primordial knee bone during evolution. However, a recent study from Imperial College of London found an increasing occurrence - this bone is now three times more common in humans than it was a hundred years ago.
The fabella bone is a small bone behind the knee and up until now nobody knows its function.
"We don't know what the fabella's function is – nobody has ever looked into it," says one of the team, Michael Berthaume.
"The fabella may behave like other sesamoid bones to help reduce friction within tendons, redirecting muscle forces, or, as in the case of the kneecap, increasing the mechanical force of that muscle. Or it could be doing nothing at all."
What we do know is that the fabella is linked to knee pain and arthritis, though it doesn't necessarily cause it – people with osteoarthritis of the knee are twice as likely to have a fabella than people without osteoarthritis, for example.
It seems like our scientists will be busy in studying the relation between fabella and osteoarthritis.
(Image Credit: Imperial College London)