Avascular necrosis of the proximal femur in developmental dislocation of the hip. Incidence, risk factors, sequelae and MR imaging for diagnosis and prognosis.

Avascular necrosis of the proximal femur still remains the major complication of the treatment for developmental dislocation of the hip. In a three part study I reviewed this problem. Part I analyzed incidence, causes, and risk factors of avascular necrosis. In 105 children with 113 hips who developed avascular necrosis out of 636 consecutive patients with 823 hips treated nonoperatively for developmental dislocation of the hip in the years 1972-1976 the risk factors of avascular necrosis were determined. A method of treatment in most cases was Frejka pillow. Conventional radiographs obtained in AP views during the course of treatment and follow-up were analyzed. Avascular necrosis was found in 14 percent of the hips, classified as mild (49%), moderate (14%), and severe (37%). The differences between mild and severe cases were significant as regards age at the onset of treatment (p 0.006); with higher average age in mild forms, and degree of dislocation (p 0.01) with higher values in severe forms. The older the child was at the onset of treatment, the greater the risk of necrosis, notably if treatment was begun after 6 months of age. However, the incidence of the more severe cases was higher in the group up to 6 month of age. In general, avascular necrosis was more likely to occur in cases with high degree of initial dislocation and the differences between groups with low and high degree of dislocation were significant. In the group with highest initial dislocation the number of both mild and severe forms was high. Part II evaluated the growth and remodeling of the hip joint with avascular necrosis after nonoperative treatment of developmental dislocation on the basis of conventional radiography. An attempt was also made to determine the correlation between the severity of necrosis as seen in conventional radiography and the clinical and radiographic appearance of the hip after completion of growth. Finally the prognostic value of conventional radiography in prediction of deformities of the proximal femur due to necrosis was estimated. 68 patients with 98 involved hips treated exclusively nonoperatively for developmental dislocation of the hip in whom avascular necrosis developed were selected for the study. The average age at the time when the final radiograph was made was 25 (18-36) years and the average follow-up period was 23 (18-35) years. 16 patients (27 hips) were examined twice after completion of growth with the time interval of 10 years, the second examination being at an average age of 30 (26-36) years. In this group also progress of signs and symptoms of degenerative changes in clinical and radiographic examination was noted. To achieve sufficient data necessary to establish indications for further operative treatment in 2 patients also CT examinations with three-dimensional surface reconstruction were performed after physeal closure. Physical examinations were performed in all patients after completion of growth. Radiographs made before the onset of treatment for developmental dislocation of the hip, during treatment, at the child's age of 4-6 years, all obtained until the cessation of growth, and at final assessment, were studied. By physical evaluation 77 hips were rated as excellent or good, being pain free or with only occasional mild pain after walking long distances, with a good range of hip motion and negative Trendelenburg sign. The reasons for 21 fair or poor clinical end-results were pain, mostly with activity, and limp due to pain and abductor weakness. By radiographic evaluation in this group there were 50 hips rated as excellent or good, and 48 hips rated as fair or poor. In 29 hips excellent or good clinical findings at final review contrasted with fair or poor radiographic scores. In no case fair or poor clinical end-result coexisted with excellent radiographic ones. In the group examined twice after completion of growth with the time interval of 10 years no difference in clinical score was found in