Approach to Genu Varum
First thing: consider the differential diagnosis
– physiologic bow legs
– infantile or juvenile/adolescent tibia vara (Blount’s)
– hypophosphatemic rickets
– some sort of bony dysplasia – MED, SED, achondroplasia and pseudoachondroplasia, focal fibrocartilaginous dysplasia, metaphyseal chondrodysplasia, Down’s, pseudoachondroplasia
– post-traumatic (easily ruled out)
As always, do a full history.
– What’s the time course of the problem? How old is the patient? – physiologic bow legs should be gone by 2.
– Family history? Hypophosphatemic rickets is an x-linked dominant trait
– Overall health, weight gain, motor milestones, growth and development – short stature (rickets or one of the bony dysplasias); ARE THEY A DWARF?? DO THEY HAVE DYSMORPHIC FEATURES!
– Assess for risk factors of Blount’s – black, fat, female, early walker
Basically, you want have a treatment algorithm for Blount’s, so you want to make sure that the genu varum you are seeing is in fact Blount’s and not something else – the other disorders are treated differently!!!
Do a physical
– measure the deformity and do a knee exam looking for laxity, etc.
– note the height of the patient (rickets patients are short!)
– do a general physical to rule out any dysmorphic features and examine the hips
Get standing AP x-rays, and have low threshold for getting entire femur to see hips and entire tib/fib to see ankles.
– Check the metaphyseal diaphyseal angle
– 16 – Blount’s
– Take a good long look at the physis – Does it look normal? Does it look widened and irregular (rickets or metaphyseal chondrodysplasia)?
– take a look at both the femoral and tibial epiphysis – do they look normal? Look for epiphyseal dysplasias of some form or another.
– look at the surrounding bone – are there any cystic lesions, or signs of old trauma?
If you’re not sure if this is part of a generalize skeletal dysplasia, get a skeletal survey!
Hypophosphatemic Rickets (vitamin D resistant rickets) – X-linked dominant; look for increasing varus deformity, osteopenia, positive family history, short stature (below 5th percentile), and do bloodwork to confirm (low calcium, low phosphorus, high alk phos)
– the management requires optimal medical treatment and the delay of operative correction as long as possible; may require multiple-level osteotomies because of the generalized nature of the deformity.
Bony Dysplasias – similar to hypophosphotemic rickets: the deformities are generalized and recurrence is common if you do surgery early. Whether you should do surgery at all is controversial. Bracing is not appropriate. Try to delay operative treatment until function is affected or growth completed, but they will need osteotomy.
Notice how different the treatment algorithm is for rickets and the bony dysplasias from Blount’s – hence, you MUST seek to make this diagnosis!
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