A small bone behind the knee that scientists previously thought had been selected out by evolution a century ago is now three times more prevalent - and possibly linked to arthritis, according to a new study.

Experts at Imperial College London say scientists don’t know what the fabella does, but patients with osteoarthritis are twice as likely to have a one, the study published this week in the Journal of Anatomy reported.

TEEN'S FOOT ATTACHED BACKWARD TO FORM NEW KNEE AFTER CANCER SURGERY

The fabella may help reduce friction within tendons, Dr. Michael Berthaume, a co-author of the study, said, but it’s unclear because the bone has never been researched.

Study researchers looked at 20,000 knees dating back to 1918 and found fabellae prevalence went from 11 percent in 1918 to 39 percent in 2018.

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The researchers used CT scans and medical journals for the study.