Blount's disease (tibia vara) occurs in young children and adolescents. The cause is unknown but is thought to be due to the effects of weight on the growth plate. The inner part of the shin bone, just below the knee, fails to develop normally.

Unlike bowlegs, which tend to straighten as the child develops, Blount's disease slowly gets worse. It can cause severe bowing of one or both legs.

This condition is more common among African-American children. It is also associated with obesity and early walking.