Background: Avascular necrosis after treatment for late developmental dysplasia of the hip can result in deformity of the femoral head and long-term morbidity. This study aims to analyze the clinical and radiographic factors that are associated with femoral head deformity in the early stage of avascular necrosis.
Methods: Thirty patients with unilateral developmental dysplasia of the hip treated by the same operation before 3 years of age and who developed early signs of avascular necrosis, were studied. Avascular necrosis was diagnosed by either broadening of the femoral neck, fragmentation of the capital epiphysis, or the presence of a metaphyseal growth disturbance line in the first postoperative year. After 10-year follow-up, the hips were classified into spherical head or deformed head by irregularity <2 mm or more to analyze the associated factors.
Results: Sixteen hips had spherical femoral heads and the other 14 hips had deformed femoral heads. Age, sex, side, Tonnis classification, and preoperative or postoperative acetabular index were not associated with the outcome after avascular necrosis. Among the early signs of avascular necrosis, fragmentation of the capital epiphysis was significantly associated with later head deformity. Fragmentation was a sign with high sensitivity (79%) and high specificity (88%) in predicting a deformed head. Broadening of femoral neck had a high sensitivity (93%), but a low specificity (38%) in outcome prediction.
Conclusions: Fragmentation and flattening of the femoral epiphysis are the worst radiographic signs indicating subsequent growth disturbance and deformity of the proximal femur. Broadening of the femoral neck exhibited high sensitivity in predicting later deformity, and physicians should be alerted to subsequent epiphyseal fragmentation. A metaphyseal growth disturbance line is a sign of avascular necrosis, but the predictive value is limited.
Level of evidence: Diagnostic level 3.