Avascular necrosis as a complication of septic arthritis of the hip in children.

Seventy-one hip joints in 69 infants and children with pyogenic arthritis were studied. Twenty joints (28%) with the radiographic characteristics of avascular necrosis were identified and the changes classified into 3 groups: Group 1 (infants up to the age of 6 months) had ischaemic changes characterized by the absence or delayed appearance of the epiphyseal ossification centre; Group 2 (children aged between 7 months and 5 years) showed disappearance of this centre whether followed by revascularization or not, with the shape of the cartilaginous femoral head preserved in either case; and in Group 3 (children 6-16 years of age) the femoral epiphysis was either totally or partially involved with increased bone density; collapse of the head may or may not have occurred. At follow-up for between 2 and 15 years, a trend towards more severe deformities was seen in the 11 hip joints of Group 3 when compared to the 9 hip joints in Groups 1 and 2. The opposite was observed in relation to less severe deformities. Early diagnosis and treatment of infection is mandatory in patients with pyogenic arthritis and increased intra-articular hydrostatic pressure, or those with septic thrombosis of the epiphyseal vessels, which could cause avascular necrosis (AVN).