Fabella, a tiny bone in the knee thought lost to human evolution, is making a comeback. Researchers said that the bone is becoming more common in humans and they do not know why.

Fabella: Appendix Of The Skeleton.

The fabella can be found buried in tendon behind the knees. The bone, which is associated with knee problems and pain, does not seem to have any important function.

Michael Berthaume, from Imperial College London's Department of Bioengineering, said fabella may soon be known as the appendix of the skeleton.

"We don't know what the fabella's function is — nobody has ever looked into it," he said. "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."

Fabella Becoming More Common

Fabella was once rare to humans, but there appears to be a resurgence of this tiny bone over the last century.

In a study published in the Journal of Anatomy, Berthaume and colleagues reviewed 21,676 individual knee studies in over 27 countries that were conducted over a period of 150 years.

The earliest records used in the analysis were from 1875 and they showed that the knee bone was present in only 17.9 percent of the population. However, between 1918 and 2018, the occurrence of fabella has increased more than threefold.

The researchers then created a statistical model to predict the prevalence rate of the fabella. They found that in 1918, fabellae were present in 11.2 percent of the world's population, but by 2018, 39 percent of the population likely have fabella, marking a 3.5-fold increase.

More Common In People With Arthritis

The researchers said the bone is most common among Asians and Australian. The bone is also more prevalent in people with arthritis. People with osteoarthritis of the knee are two times more likely to have fabella.

Despite that fabella is more common in people who suffer from knee problems, it isn't clear if it causes arthritis. Researchers also said that the bone can get in the way of knee replacement surgery.

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