Risk factors of avascular necrosis in the treatment of congenital dislocation of the hip.

We examined the causes of iatrogenic avascular necrosis of the femoral head in 254 hips with congenital dislocation (CDH) treated conservatively. The influence of the age of the child, the height of the displacement of the femoral head, the extent of acetabular dysplasia, and the method of treatment on the frequency and degree of necrosis were estimated. The investigation showed that children are at the highest risk of iatrogenic necrosis in the following cases: (a) age less than 6 months, (b) severe acetabular dysplasia, (c) use of an abduction apparatus such as the Frejka pillow for outpatients, and (d) "frog-leg" position after reduction.