It’s not present in all humans and…it does nothing except increase the risk of knee arthritis. A new study sheds some light on the mystery of the fabella, bone calcification whose prevalence has greatly increased in a century, probably linked to better nutrition.
The fabella is a sesamoid (resembling sesame) bone, a remnant of a calcified ligament, located in the tendon of the knee. The formation of these sesamoid bones is different from that of other bones since they are remnants of calcified ligaments that are not considered part of the human skeleton. Meaning “little bean”, the fabella has, at first sight, no use. It is also not present in everyone, without this impacting the health or stability of people who do not have it.
The fabella bone has re-emerged dramatically: Between 1918 and 2018, the number of human knees that appeared to be useless fabellas tripled, says a study published in the Journal of Anatomy. Et this is the first time that the prevalence of fabella has been studied in such detail by region, age and sex because until now it was unclear who was likely to have one or two and why. A new meta-analysis, led by Dr Michael Berthaume, from Imperial College London, finds the mystery bone is more common in older people, Asians and more common in men than women .
A link with geography, age and gender
After further research, the team found out why certain fabellas are formed in some people and not in others, what is the connection with geographical region, age and gender. The researchers, based in Imperial College’s Department of Bioengineering, had previously found that better nutrition is a key factor in the resurgence of fabella.
For this new study, the researchers used the same dataset as the previous research, which included 66 research papers spanning 27 countries and 21,676 individual knees. Since the radiographs did not correctly detect the fabella, the study results were analyzed by dissection.
Nearly half of the knees studied in Asia had a fabella, while one in five knees studied in Africa had one. “Our results show how region-related genetic variation plays an important role in fabella formation. However, regional factors unrelated to genetics may also play an important role,” Dr. Berthaume points out.
Fabellas appeared more frequently in older people, suggesting that Fabella development increases with age. According to the authors, this could be explained by the fact that the elderly are more likely to have undergone the mechanical stimuli necessary for the ossification of the fabellas, ossification which can occur at any age. “Among bones, fabellas are unique because they can appear at any age. They are more common in older people because they can appear as individuals grow,” says Dr. Berthaume.
A link to muscle strength and shin length
Men are slightly more likely than women to have fabellas. The authors explain this by the difference between average muscle strength and tibia length between the sexes. As Michaël Berthaume points out, “The fabella is a sesamoid bone, a tendon-related bone that grows in response to mechanical forces such as friction, tension, pressure and stress. In men, the largest muscles and longer shins produce more mechanical force, which is why men are more likely than women to develop fabellas.”
Just over one in three knees worldwide have a fabella, and seven out of ten people with a fabella on one knee have a fabella on the other knee. The authors indicate that this symmetry supports the role of genetics in fabella ossification. People with only one fabella are likely to have one in either the right or left knee. This lack of preference for one or the other knee supports the role of environmental factors in the development of fabella.
Genetic and environmental influences
According to the research team, these findings provide even more insight into genetic and environmental influences on human evolution over the past 150 years, with fabella formation likely due to a combination of the two. Differences in fabella rates by sex and age suggest that they are due to mechanical stress, while the likelihood of fabella occurrence in both knees, with differences in ethnicity, lean towards a genetic factor.
In this sense, the expert adds that “ethnicity, age and gender play a role in the development or not of a fabella. These new findings add to our previous sense that better nutrition likely drove the resurgence of the fabella, but that genetics and other factors, which we still have to deal with, also play a role.”
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