Abstract
Background: Developmental dysplasia of the hip (DDH) is the most common deformity of the lower extremity in children, and the etiology remains unclear. The biomechanical change during closed reduction (CR) focused on cartilage contact pressure (CCP) has not been studied. Thereby, we try to provide insight into biomechanical factors potentially responsible for CR treatment success and complications by using finite element analysis (FEA) for the first time.Methods: Finite element models of one patient with DDH were established based on the data of MRI scan on which cartilage contact pressure was measured. During CR, CCP between the femoral head and acetabulum in different abduction and flexion angles were tested to estimate the efficacy and potential risk factors of avascular necrosis (AVN) following CR.Results: A 3D reconstruction by the FEA method was performed on a sixteen-month-old girl with DDH on the right side. The acetabulum of the involved side showed a long, narrow, and "plate-shaped" deformity, whereas the femoral head was smaller and irregular compared with the contralateral side. With increased abduction angle, the stress of the posterior acetabulum increased significantly, and the stress on the lateral part of the femoral head increased as well. The changes of CCP in the superior acetabulum were not apparent during CR. There were no detectable differences in terms of pressure on the femoral head.Conclusions: Severe dislocation (IHDI grade III and IV) in children showed a high mismatch between the femoral head and acetabulum. Increased abduction angle corresponded with high contact pressure, which might relate to avascular necrosis, whereas increased flexion angle was not. Enhanced pressure on the lateral part of the femoral head might increase the risk of AVN.
Interobserver and Intraobserver Reliability in the Salter Classification of Avascular Necrosis of the Femoral Head in Developmental Dysplasia of the Hip
