This condition is a developmental abnormality characterized by asymmetrical osteochondromatous growth arising from one side of an epiphysis or from a tarsal or carpal bone.
It was first described by Mouchet & Belot as tarsomegaly, but it was Trevor who drew a attention to the more widespread distribution of the lesions and named the abnormlity as tarsoepiphysial aclasis. Later authors showed that it may affect other epiphyses and Fairbank gave them and dysplasia epiphysialis hemimelica.
It is rare condition and commoner in boys than in girls.
Clinical Features:
The presentation is usually as a swelling or deformity of the inner or outer aspect of the ankle or knee with or without interference with joint function. Involvement is characteristically unilateral and affects one limb.
The commonest sites are the talus, the lower femoral or the distal tibial epiphysis.
The medial side in the lower limb and the radial side in the upper limb are more often affected. At the knee involvement of the medial side of the epiphysis causes genu valgum or of the lateral side, genu varum.
A bony mass on the medial side of the ankle produces severe valgus deformity or, if on the lateral side, causes varus deformity.
The condition usually presents in early childhood after the fourth year of life.
Radiological Appearances:
Except in the smaller tarsal bones, one side of the epiphysis is involved. This portion is enlarged, irregular, discrete from the main epiphysis and accompanied by multiple small centres of ossificantion.
When the lesion affects the lower femoral epiphysis the projection is sideways, downwards and backwards. At the ankle, the body of the talus may be massively enlarged and irregular with an outgrowth extending medially or laterally from it.
It is notable that when the knee and ankle are affected the lesion presents on the same aspect of each joint. The tarsal and carpal bones show premature ossification. The lesions are usually confined to the epiphyses.
Pathology:
Microscopically the appearance are like those of an osteochondroma with a thick zone of hyperblastic cartilage, active normal endochondral ossification and bony centres which are irregular in size and shape.
Treatment:
Part or all of the outgrowth can be removed and, if this is done, the deformity can be improved or corrected.
If it is not possible to correct the deformity sufficiently without causing instability of the joint it may be corrected by osteotomy. Severe ankle deformity may require arthrodeiss in an older child.
Inequality of limb length may require correction in older childhood.
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