Humans have grown an extra bone: Scientists discover a pointless knee bone called the fabella that may be causing osteoarthritis
- Found in 39 per cent of people around the world in 2018 but has no known use
- May be a vestigial organ which has become redundant over time as we evolved
- Was only present in 11.2 per cent of people around the world in 1918
- Improvements in nutrition made humans bigger which meant the bone – which is embedded in a tendon behind the knee – has been growing
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.’
The study, published in the Journal of Anatomy, the authors detail how they reviewed 21,676 individual knees from 27 countries dating back to 1875.
Data stemmed from a variety of sources, including X-rays, MRI scans and anatomical dissection.
The fabella is known as a sesamoid bone, which means it grows in the tendon of a muscle.
A kneecap is the largest sesamoid bone in the human body.
The study found that there is a link between osteoarthritis and the presence of the mysterious bone.
People with osteoarthritis of the knee are twice as likely to have a fabella than people without osteoarthritis.
But, the researchers say, it can not be said yet that the presence of the bone causes the ailment.
It is also believed the nuisance bone affects knee replacement surgeries and can cause discomfort itself.
Its use in modern humans is widely debated, but thought to be negligible or non-existent.
However it is thought that in our evolution it had larger role to play before becoming irrelevant.
It may have acted as a kneecap to these animals before evolution made it redundant in our ancient human ancestors.
Three knees with three different sizes of fabella (small bone to the right of each image). Researchers from London 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
Its resurgence over the past 150 years is thought to be a result of improved nutrition in the wake of the man wars that beleaguered the 20th century.
Better nutrition means humans are now taller, stronger and heavier than ever in our history and this is increasing the strain on our frames.
Knees are therefore under much greater pressure and the bone develops as the tendon is exercised, which may have led to the resurgence.
Dr Berthaume explained: ‘The average human, today, is better nourished, meaning we are taller and heavier.
‘This came with longer shinbones and larger calf muscles – changes which both put the knee under increasing pressure.
‘This could explain why fabellae are more common now than they once were.’