Return of the rare bone linked to arthritis
‘Pointless’ fabella was once lost to human evolution but has made a surprising comeback, study reveals
A Once-rare bone that increases the risk of arthritis is becoming increasingly common in humans, scientists have found, and better nutrition is possibly to blame.
The fabella, a small bone in the knee that was once lost to human evolution, has made a surprising resurgence over the past century.
The bone – thought of as pointless by doctors – is buried in a tendon behind the knee and those who have it seem to be more likely to suffer from arthritis.
Researchers from Imperial College London have found that fabellae are becoming more common in humans.
Their results, which spanned more than 21,000 knee studies conducted in 27 countries over 150 years, showed that between 1918 and 2018, the rate of fabellae occurrence in humans rose more than threefold. In 1918, fabellae were estimated to be present in 11 per cent of the world population. By 2018, they were found in 39 per cent of examinations according to analysis published in the Journal of Anatomy.
Dr Michael Berthaume, from Imperial’s department of bioengineering and the report’s lead author, said: “We don’t know what the fabella’s function is – nobody has ever looked into it.
“[It] is a sesamoid bone, meaning it grows in the tendon of a muscle; the kneecap, for instance, is the largest sesamoid bone in the human body ... 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.”
The earliest records analysed, from 1875, showed that fabellae were found in 17.9 per cent of cases. The researchers then created a statistical model to predict its prevalence rate.
People with osteoarthritis of the knee are twice as likely to have a fabella than non-sufferers but it is not known whether the fabella causes knee osteoarthritis, and if so, how. It can also cause pain and discomfort on its own and can complicate knee replacement surgery.
Dr Berthaume said: “We are taught that 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,” he added.
As humans evolved from great apes and monkeys, the fabella appeared to have been lost. However, researchers believe it could be making a comeback as a result of healthier diets.
“We found evidence of fabella resurgence across the world, and one of the few environmental changes that have affected most countries in the world is better nutrition,” Dr Berthaume said.
“The average human today is better nourished, meaning we are taller and heavier. This came with longer shinbones and larger calf muscles [putting] the knee under increasing pressure. This could explain why fabellae are more common now.”