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
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).