Evolution sees small bone make comeback

It was small, pointless, often painful, and seemingly on the way out. And now it is having a revival.

An insignificant bone in the knee that once looked as though it was being lost to evolution has made a surprising comeback during the past century, according to scientists.

The fabella – which means little bean – is a small bone buried in a tendon behind the knee. It is a sesamoid bone, meaning a small bone or bony nodule.

Linked to arthritis, it was once rare in humans. However, a study by researchers from Imperial College London has found that it is becoming more common.

Between 1918 and 2018, its prevalence rose by more than three times, from among 11.2 per cent of the world population to 39 per cent.

The study’s lead author, Michael Berthaume, from Imperial College’s Department of Bioengineering, said the comeback could be down to better nutrition.

‘‘We don’t know what the fabella’s function is,’’ he said. ‘‘[It] 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.’’

People with osteoarthritis are twice as likely to have a fabella as those without the condition. However, scientists do not know if it causes osteoarthritis, and if so, how. It can also cause pain and discomfort on its own, and can get in the way of knee replacement surgery.

The Imperial College study looked at medical literature on knees over 150 years in 27 countries, including Britain.

‘‘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,’’ Berthaume said.

‘‘The average human today is better nourished, meaning we are taller and heavier. This came with longer shin bones and larger calf muscles, changes which both put the knee under increasing pressure.’’ – The Times