‘Pointless’ rare knee bone makes evolutionary comeback in humans | Science & Tech News

A small knee bone with “no apparent function”, which evolution appeared to have discarded, has made a surprising comeback.

The fabella, described as the “appendix of the skeleton”, is buried in a tendon behind the knee and acted as a kneecap in Old World monkeys.

It can cause pain and discomfort and was once rare in humans – but a new study has shown it is becoming more common.

Scientists from Imperial College London (ICL) examined 21,000 knee studies from 27 countries spanning 150 years.

Between 1918 and 2018, the number of people with a fabella increased more than threefold. In 1918, just 11.2% of the world population had one, but by 2018 the percentage had risen to 39%.

In the earliest records studied, dating from 1875, a fabella was found in 17.9% of the population.

Dr Michael Berthaume, from ICL’s bioengineering department, said improving nutrition may have been behind the fabella’s resurgence, because that is “one of the few environmental changes that have affected most countries in the world”.

There is also thought to be a genetic component in the development of a fabella.

In terms of evolution, however, it is a mystery.

“As we evolved into great apes and humans, we appear to have lost the need for the fabella,” Dr Berthaume said.

“Now, it just causes us problems – but the interesting question is why it’s making such a comeback.”

He added: “The fabella is a bone that has no apparent function and causes pain and discomfort to some and might require removal if it causes problems.

“Perhaps the fabella will soon be known as the appendix of the skeleton.”

He added, however, that the bone may “help reduce friction within tendons, redirecting muscle forces”.

The study authors say their findings could have implications for how patients with knee pain are treated.

Their work has been published in the Journal of Anatomy.

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