Knock knees, also known as genu valgum, is a condition in which the knees angle in and touch each other when the legs are straightened. It is common in children aged 3 to 6 and usually gets better on its own as they grow without causing any problems. However, sometimes older children or adults can have it. The condition is slightly more common in girls.

Symptoms of knock knees include a gap between the ankles when standing with the knees together. Most people will not have any other symptoms, but sometimes, if knock knees are severe or caused by another condition, you may have knee or leg pain, or difficulty walking.

The causes of knock knees can be normal bone growth and development when kids are about 2-4 years old, which can cause the knees to turn inward. Rarely, knock knees that begin or worsen after age 4 can be caused by a health problem. For example, nutritional rickets is an important cause of childhood genu valgum or knock knees in some parts of the world.

Treatment for knock knees is usually not necessary, as the condition usually gets better as children grow and their legs straighten. However, sometimes physiotherapy or treatment from a foot specialist (podiatrist) may be recommended. In rare cases where children have symptoms such as pain or trouble running, doctors might suggest surgery after age 10.