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Bow Legs Knock Knees

Normal development of the legs in young children involves the following changes; 

Bow leg (varus) in the infant which aligns to straight legs by 18 months and then into a mild knock knee (valgus) around 3-4 years and then straight legs (adult alignment) by around 7 years.

These changes are mild, should be symmetrical and should not cause limp or discomfort. 

Bow legs (Genu Varum) are common and is considered normal until 2 years of age.

Referral is necessary if: 

  • There are signs of asymmetry.
  • Changes are associated with pain or functional impairment (e.g., prone to falling). 
  • Changes are extreme (the femoral intercondylar distance is >6 cm).
  • Changes worsen or persist beyond age 4 years.

Conditions to consider include:

Rickets - look for other clinical signs and if relevant, check bone chemistry (calcium, phosphorus and alkaline phosphatase) and vitamin D; especially if the child is failing to thrive, has generalised aches and pains, or has other risk factors such as a vegan diet, malabsorption syndromes or an ‘at risk’ ethnicity.

Skeletal Dysplasias and dwarfism syndromes such as Achondroplasia - Consider growth and limb proportions (short limbs compared to trunk).

Photo: Severe Varus in Achondroplasia

 varus in rckets

Knock knees are normal in young children and most resolve by 6 years of age.

Between the ages of 2 and 4 years, a gap of 6 to 7 cm between the medial malleoli (the bone prominences at the ankles) is normal. 

Referral is necessary if there is an ankle gap larger than 6-7 cm, pain, asymmetry or if problems persist beyond 5 years of age.

Conditions to exclude are Rickets, Skeletal Dysplasias or Chronic (untreated) Inflammatory Arthritis (picture below).

 knock knees in JIA

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