Only some people actually have one, and even less people have two. It is estimated that a third of the population have a fabella bone, and only half of those people have a fabella behind each knee.

Do all people have a fabella?

Not all people have fabellae, however, and there is likely a genetic component controlling the ability to form one – but for those who can form a fabella, this increased mechanical forces might drive their formation.

How common is a fabella?

Epidemiology /Aetiology. The presence of the fabella in humans varies widely and is reported in the literature to range from 20% to 87%. The fabella can be found in 10 to 30 per cent of the population and if it is present there is a 50 per cent chance that it is bilaterally.