By Joe Pinkstone For Mailonline
Published: 13:07 BST, 19 April 2019 | Updated: 19:33 BST, 19 April 2019
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A tiny bone in the human knee, which was thought to be on the way to evolutionary extinction, is making a comeback and has been linked to osteoarthritis.
The fabella is found in a tendon at the back of the knee and scientists are currently unaware of any actual function and say it may be pointless.
Researchers say it has experienced a resurgence in the last century - going from being found in 11.2 per cent of the global population in 1918 to 39 per cent in 2018.
This 3.5-fold increase has baffled scientists who say further studies are needed to find out if it serves any purpose or if it will join the list of useless, vestigial human organs along with the coccyx and the appendix.
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The fabella (pictured) is found in a tendon at the back of the knee and scientists are currently unaware of any actual function and say it may be pointless
Lead author Dr Michael Berthaume, from Imperial College London, said: 'We don't know what the fabella's function is – nobody has ever looked into it!'
Dr Berthaume added: '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.'
'We are taught the human skeleton contains 206 bones, but our study challenges this. 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.'
Osteoarthritis - sometimes called 'wear and tear' - is a condition that occurs when the surfaces within joints become damaged.
Cartilage covering the ends of bones gradually thin over time, and the bone thickens, according to Arthritis Research UK.
Around a third of people aged 45 years and over in the UK suffer from the condition. This equates to roughly 8.75 million people. At least 20 million are known to suffer in the US.
It is different to rheumatoid arthritis, a long-term illness in which the immune system causes the body to attack itself,
