RESUMO
The radiological appearances of the infantile form of Blount's disease (tibia vara) are described. These consist of a various deformity of the upper end of the tibia, torsion of the tibial shaft, irregularity and fragmentation of the medial part of the tibial metaphysis and gross thickening of the cortex on the medial side of the tibial shaft. This condition is very common in Jamaica and presents clinically as severe as bow legs. A study of the knees of 75 Jamaican children who presented with severe bow legs was carried out. Radiological examination revealed three different appearances. I. Severe simple (physiological) bow legs. 111. Early Blount's disease, due to a defect in the medial part of the metaphyseal beak, the metaphyseal "tear". III. Typical Blount's disease. Thirty cases showed transition from I to II or III and II to III. Evidence from the present study suggests that the development of the changes of Blount's disease in children with severe but simple bow legs is due to the increased proportion of the body weight which is supported by the medial part of the tibial metaphysis. This is described as eccentric pressure. The Jamaican child walks at an earlier age than the British child which results in the Jamaican child walking on the physiological bow legs. The British child walks on legs which are straight or show physiological knock knees. This is the racial factor. It is suggested that because of the normal plasticity of bone the child who walks on physiological bow legs will develop severe bow legs. This would explain the high incidence of severe bow legs in Jamaican children and hence the fact that Blount's disease may develop. Therefore, the three factors, eccentric pressure (due to severe bow legs), racial factors (early walking) and natural plasticity of bone are thought to be responsible for the persistence of physiological bow legs, the high incidence of severe bow legs and the development of Blount'd disease in the Jamaican child.(AU)
