"Fabella" by Jmarchn / CC BY-SA 3.0

This Tiny Knee Bone Had Nearly Vanished As Humans Evolved. It’s Coming Back

Apr 19, 2019

By Yasemin Saplakoglu

A tiny bone hidden in the tendon of the knee started to disappear over the course of human evolution … or so scientists thought.

Now, a new study finds that this so-called fabella (Latin for “little bean”) is making a comeback. The bone, which is a sesamoid bone, or one that’s embedded in tendons, is three times more common in humans now than it was a century ago, scientists reported Wednesday (April 17) in the Journal of Anatomy.

A group of Imperial College London researchers reviewed records — such as results from X-rays, MRI scanning and dissections — from over 27 countries and over 21,000 knees. They combined their data to create a statistical model estimating the prevalence of this elusive bone across time.

In the earliest records that dated back to 1875, they found that the fabella was found in 17.9 percent of the population. In 1918, it was present in 11.2 percent of people, and by 2018, it hid within the tendons of 39 percent of the population.

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