Mystery arthritis-linked knee bone three times more common than 100 years ago

The fabella, a small bone in the knee once lost to human evolution, has made a surprising resurgence over the last century.

The new findings could help clinicians treating patients with knee issues and provide insight into human evolution over the past 100 years.

The bone, linked to knee problems and pain, is buried in a tendon behind the knee, and was once rare in humans.

Now, a new study by Imperial College London researchers has found that fabellae are becoming more common in humans.

The results, which spanned over 21,000 knee studies over 150 years, showed that between 1918 and 2018, the rate of fabellae occurrence in humans increased more than threefold.

Through the analysis, published today in the Journal of Anatomy, they reviewed 21,676 individual knees over 27 countries.

The earliest records they looked at, which were from 1875, showed that fabellae were found in 17.9 per cent of the population. From this, the researchers created a statistical model which predicted prevalence rate while controlling for country of study and method of data collection – such as X-rays, anatomical dissection, and MRI scanning.

Their analysis showed that in 1918, fabellae were present in 11.2 per cent of the world population, and by 2018, they were present in 39 per cent – a 3.5-fold increase.

Lead author Dr Michael Berthaume, from Imperial’s Department of Bioengineering, said: “We don’t know what the fabella’s function is – nobody has ever looked into it!”

The fabella 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.

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.”

Full article: Imperial College London

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