In 1949, Schmid reported a series of cases of metaphysial dysostosis without skeletal deformity at birth but presenting with bow-leg deformity, waddling with coxa vara, mild limb shortened but may show limited elbow extension, wrist enlargement broad hands and short fingers with limited extension.
The diagnosis is confirmed when other members of the family are found to be similarly affected.
Inheritance is autosomal dominant.
Radiological Appearances
The long bones are short and relatively broad, with flared metaphyses. There are irregular translucencies in the metaphysial region, most easily seen in the lower femoral and upper tibial metaphyses.
The upper femoral metaphyses show similar changes with coxa vara. The appearances closely simulate those of vitamin D resistant rickets but there are not abnormal serum electrolyte levels and no response to vitamin D therapy.
Election microscope studies show dilation of the endoplasmic reticulum of chondrocytes by a granular precipitate thought to result from storage of an undetermined substance.
Treatment
Conservative treatment by bracing is advocated by to the age of 6 years, since there is a possibility of some spontaneous correction.
In later childhood, epiphysial stapling, or, in adolescence, supracondylar femoral osteotomy is indicated.
If coxa vara reaches 90 degrees, a valgus upper femoral osteotomy is indicated and may need to be repeated if the deformity recurs.
In an older child, overgrowth of the greater trochanters may benefit from trochanteric epiphysiodeses and this may also help to diminish the degree of coxa vara.
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