Fabella prevalence rate increases over 150 years, andrates of other sesamoid bones remain constant: a systematicreview

Fabella prevalence rate increases over 150 years, and
rates of other sesamoid bones remain constant: a systematic
review:

Abstract

The fabella
is a sesamoid bone located behind the lateral femoral condyle. It
is common in non‐human mammals, but the prevalence rates in humans
vary from 3 to 87%. Here, we calculate the prevalence of the
fabella in a Korean population and investigate possible temporal
shifts in prevalence rate. A total of 52.83% of our individuals and
44.34% of our knees had fabellae detectable by computed tomography
scanning. Men and women were equally likely to have a fabella, and
bilateral cases (67.86%) were more common than unilateral ones
(32.14%). Fabella presence was not correlated with height or age,
although our sample did not include skeletally immature
individuals. Our systematic review yielded 58 studies on fabella
prevalence rate from 1875–2018 which met our inclusion criteria,
one of which was an outlier. Intriguingly, a Bayesian mixed effects
generalized linear model revealed a temporal shift in prevalence
rates, with the median prevalence rate in 2000 (31.00%) being
~ 3.5 times higher than that in 1900 (7.64%). In all four
countries with studies before and after 1960, higher rates were
always found after 1960. Using data from two other systematic
reviews, we found no increase in prevalence rates of 10 other
sesamoid bones in the human body, indicating that the increase in
fabella prevalence rate is unique. Fabella presence/absence is due
to a combination of genetic and environmental factors: as the
prevalence rates of other sesamoid bones have not changed in the
last 100 years, we postulate the increase in fabella
prevalence rate is due to an environmental factor. Namely, the
global increase in human height and weight (due to improved
nutrition) may have increased human tibial length and muscle mass.
Increases in tibial length could lead to a larger moment arm acting
on the knee and on the tendons crossing it. Coupled with the
increased force from a larger gastrocnemius, this could produce the
mechanical stimuli necessary to initiate fabella formation and/or
ossification.