Knock knee 

The term knock knee describes a large distance between the ankles when the knees are touching.

It is common in young children but is not usually anything to worry about. Up to three-quarters of children between the ages of three and five have knock knee. In most cases, it corrects itself by the age of six. Treatment may be necessary if knock knee does not correct itself, or if it is caused by an underlying growth problem or disease.

The medical term for knock knee is genu valgum. Genu is Latin for knee and valgus means in-curving.