What can cause people to become bow legged?

Genetic, degenerativ: As a child, bow leg is commonly a self limited condition resolving by age 3. A rare condition, known as blounts disease, will not self correct and needs treatment. As an adult, arthritis affecting the inside or medial part of the knee will cause the joint to narrow and result in the knee becoming "bow legged".

See below: It is usually a problem at birth but lack of vitamins could in time create the deformity.