Your child has been referred to the clinic with either bow-legs or knock-knees. This leaflet has been prepared to help you learn more about these related conditions. Bow-legs means that there is a gap between the knees when the ankle bones are pressed together. Knock-knees are present when there is a gap between the ankle bones with the knees are pressed together.
ARE BOW-LEGS OR KNOCK-KNEES ABNORMAL?
Not in most children. A study in Scandinavia in 1975 found that all children had bow-legs up till age 2 years. After this they became knock-kneed. The degree of knock-knee is most obvious between age 3 and 4. The legs then slowly straighten to the adult shape by age 10 to 12. Heavy children and children with loose ligaments stretch their knee joints and will appear to have a greater deformity. Many babies have big calf muscles, which can make the leg seem quite bent even when the bones are only slightly curved.
We call bow-legs before age 2, and knock-knees between age 2 and 12 years, "physiological" because this is how a human is supposed to develop.
If a child has bow-legs beyond the age of 2, or knock-knees before age 2 or after age 10 to 12, this may indicate a problem. Further investigation may be indicated for these children. Even then the child may be normal since there is a wide range of "normal" which can sometimes overlap with the abnormal.
WHAT CAUSES ABNORMAL BOW-LEGS OR KNOCK-KNEES?
There are a number of causes. Overweight children who walk early (below age 1) may damage their growth plates. This stops the normal correction of the bow-legs to knock-knees so the child is still bow-legged after age 2. They can still correct up to age 3 but sometimes treatment with splints or even surgery may be needed to sort the problem. Your Orthopaedic doctor would keep an eye on this problem with X-rays.
Rickets is another cause, both of abnormal bow-legs or knock knees. Rickets results from lack of vitamin D. This occurs either through poor diet, lack of sunlight (which makes vitamin D in the skin) or because some people's metabolism can't use vitamin D. The diagnosis is made by a blood test. Rickets is treated with medication. Occasionally surgery is needed if the deformity does not get better with medication.
The third most common cause of abnormal bow-legs is genetic. If a close relative has bow-legs as an adult this may suggest that your child's bow-legs are inherited if they are still there after age 2. Treatment, if required, is usually by surgery.