All babies are born with bow legs, but it is unusual in adults, most of whom are slightly knock-kneed. This is part of the normal development of the lower limbs. Bow-legs gradually change to knock-knees on average around the time a child starts to walk, and knock-knee can become quite extreme from age 18 months to 3 years. Physiological (normal) bow-legs should always be symmetrical, should always improve and should have gone by age 3 years. If not, there may be a pathological process involved. The most well-known cause of pathological bow legs is probably rickets, but despite a lot of concern about Vitamin D deficiency in the UK, bow legs from rickets is still unusual.
Blount’s disease is probably the next biggest cause of pathological bow legs.This is a growth disturbance of the upper tibia that leads to progressive bowing. It requires surgery and can be reversed if treated early. Otherwise it results in repeated procedures throughout childhood and may lead to early arthritis of the knee in adulthood. Other causes of pathological bow legs and knock knee are even more rare, but are seen quite often at the tertiary centres such as Great Ormond Street. These causes include local infections, septicaemia, metabolic conditions, local bone dysplasias (including Blount’s disease) and the general skeletal dysplasias.
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