The knee in a child has a natural progression from bow legs as a baby to correcting at about 18 months of age and then developing knock knees at about 4 yrs of age and becoming normal by 7 years of age.
There can be minor deviations to this natural progression and this is completely physiological. Besides sometimes the deviations can be delayed in correcting and this is again physiological.
However there can be pathological conditions that mimic these physiological "normal" knee alignment.
Bow Legs (Genu Varum):
The two common conditions that can cause bow legs as illustrated in the picture above, are Rickets and Blount's disease.
Rickets is most commonly caused due to nutritional Vitamin deficiency (although there are innumerable other causes too). Vitamin D is a hormone that is synthesized in the skin upon exposure to sunlight. This undergoes further transformation to its active form in Liver and then the kidneys. It is a very important hormone to regulate bone metabolism. The only other way to get Vitamin D is via diet and there are limited sources available such as Oily fish, shiitake mushrooms, fortified milk and margarine.
Blount's disease is a developmental disorder that results in an abnormal growing area on the leg bone (proximal tibial physis) which results in a progressive knock knee deformity. This can affect very young children or adolescents.
Knock Knees (Genu Valgum):
The opposite deformity to bow legs is knock knees. This is most commonly developmental and can correct with growth. Occasionally it fails to correct and may need intervention.
The less common causes of knock knee (and bowlegs) are infection in the bone and trauma near the growing areas and rare genetic conditions such skeletal dysplasias.
Some observation is needed in both bow-legs and knock knees as these can correct spontaneously. However if they fail to do so, there is simple surgical treatment available called "Guided growth". This treatment approach uses "8-plates" to stop one side of bone growing and allows the other side to keep growing and corrects the deformity gradually over a period of 12-18 months.
Once the deformity is corrected, the 8 plates can be removed.
Knee deformities in children can be treated easily.
Any asymmetry in the deformity should raise an alarm bell.
Any parental concern regarding knee deformity needs to be evaluated by a doctor, preferably a paediatrician or a paediatric orthopaedic surgeon.
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