Analysis of the causes for hip joint re-dislocation after triad-osteotomy in the patients with developmental dislocation of hip joint

Objective To analyze the causes for hip joint redislocation after triad-osteotomy in the patients with developmental dislocation of hip joint(DDH) using three-dimensional computed tomography(3D-CT)technique.Methods Twenty eight hips of 28 children with DDH underwent triad-osteotomy and had hip joint redislocation were recruited in this study as re-dislocation group.Pictures of 3D-CT was gained, and anterior lateral acetabular lip angle(ALAL),posterior lateral acetabular lip angle(PLAL),lateral acatabular incline(LAI),anterior aeetabular index(AAI),posterior acetabular index(PAI),acetabular anteversion(AA),femoral neck anteversion(FNA)and femoral neck shaft angle were measured.The morphology of latero-superior(mid-superior)part of acetabulum and concentric position of acetabulum and femoral head was also studied.Fifty hips of 38 DDH patients(non-redislocation group)who underwent surgery but without hip joint redislocation and normal hips were taken as controls.Results The neck shaft angle was significantly larger in the patients of redislocation group than that of controls.The ineidence of severe defects in latero-superior acetabulum was significantly higher in re-dislocation group than that of the non-redislocation group.In re-dislocation group.all the hips were abnormal in concentric position,while in the non-redislocation group,all the hips appeared normal or nearly normal concentric position.Conclusions The causes for redislocation after triad-osteotomy are associated with abnormal neck shaft angle,the morphology of laterosuperior acetabular rim and the concentric position of acetabulmn and femoral head. Key words: Hip dislocation,congenital; Imaging,three-dimensional; Acetabulum