Knock-knee – a deformity of the lower limbs in such a direction that when the limbs are straightened, the legs diverge from one another. As a result, in walking, the knees knock against each other. The amount of knock-knee is measured by the distance between the medial malleoli of the ankles, with the inner surfaces of the knee touching and the knee-caps facing forwards. The condition is so common in children between the ages of 2–6 years that it may almost be regarded as a normal phase in childhood. However, it can also be acquired from conditions such as RICKETS, OBESITY or after bony trauma or infection and certain other congenital bony or muscular conditions. If marked, or persisting into later childhood, it can be corrected by surgery (osteotomy).