Background: Football, as the most popular sport worldwide, has long been under suspicion
of causing varus knee alignment as early as adolescence. However, no causal relationship has yet
been found. The first step to do so would be to determine the prevalence of lower leg malalignment
among male junior football players depending on age, performance level and the number of active
seasons played. Methods: Leg axis alignment in frontal plane was determined in male junior football
players of different age levels between 7 and 18 years by measuring the intercondylar/intermalleolar
distance (ICD/IMD) in an upright position. In addition to anthropometric data, multiple sportspecific
data such as the start of their football career or training time per week were collected by
means of questionnaires (clinical trial registration number: DRKS00020446). Results: 207 male junior
football players were included in this survey. The mean age was 12.8 years. Within the group of
15 to 18 year olds, the prevalence of varus knee malalignment was highest at just under a third
(32.1%). In the subpopulation that played actively for more than ten seasons, 28.9% showed varus
leg axis. Regarding performance level, the highest IMD/ICD values and highest prevalence of
varus alignment were found among football players who play on a semi-professional level (16.7%),
compared to amateur (11.4%) and high-performance levels (2.8%). Conclusions: Further research is
necessary to investigate if this high prevalence of varus knee in children of a higher age and higher
playing levels is due to the selection bias of football players with varus knee or a real development of
varus knee in individuals.