Pathological Morphology Evaluation Of Developmental Dislocation Of The Hip In Infant By Three-Dimensional Computed Tomography

Developmental dislocation of the hip(DDH) is the most common disease in pediatric orthopedics, acetabular dysplasia, nonconcentric hip-joint articulation and approximate femoral deformity are the main pathologic morphology abnormality. The development of advanced three-dimensional computed tomography (3DCT) methods provides greatly improved, near anatomically detailed images that improve the surgeon's ability to understand hip abnormalities in both children and adults. Because a portion of the acetabular rim consists of growth cartilage, which is not readily demonstrated with 3DCT techniques, the detailed pathologic morphology remains unclearly, particularly in children younger than 3 years. The purpose of this study is to evaluate the morphology of DDH in infant by 3DCT.MethodsBetween January 2000 and October 2003, 44 children under 3 years, with unilateral DDH, were analysed using 3DCT in our department, the hip images were reconstructed in 3DCT workstation. The quantitative measurement parameters included: (1) Anterolateral acetabular lip angle, ALAL, (2) Lateral acetabular inclination, LAI, (3) Transverse rotation of the acetabulum, TRA, (4) Spherical index of ossification center of the femoral head, (5) Diameter of ischium in acetabulum center. The qualitative observation included the acetabular deficiency in superior rim and the location of the femoral head, and according to the deficiency degree in superior acetabular rim, we divided all the abnormal hips into two groups, (1) minimal deficiency group: mild irregularity or loss of smooth concavity in superior acetabular rim, but the original superior acetabular rim could be identified. (2) severe deficiency group: the superior acetabular rim was severely eroded, lost smooth concavity, produced the shape of a gothic arch or produced false acetabulum, original superior acetabular rim could not be identified. According to the degree of the dislocation of femoral head, all abnormal hips was also divided into two groups,group a included degree I and degree II completely dislocated hips, and group b included acetabular dysplasia, subluxated and degree III completely dislocated hips. The data was analysed with software SPSS 11.5.ResultsAll the quantitative measurement parameters in normal hips contrasted to abnormal hips, there were significantly statistical difference, p<0.01. The deficient degree in superior acetabular rim significantly related to the location of the femoral head, the frequency of severely deficient acetabulum was 62.5% in group a (degree I and degree II completely dislocated hips), and 16.7% in group b (acetabular dysplasia, subluxated and degree III completely dislocated hips), p<0.01. the frequency of severely deficient acetabulum changed significantly with age in this study, in group of older than 18 months, the frequency of severely deficient acetabulum was 59.3%, and only 35.3% in group of younger than 18 months, p<0.01.Conclusion1 3DCT reconstruction of hip can demonstrate the pathologic morphology of DDH in children under 3 years clearly, and allows quantitative measurement and qualitative observation.2 Degree I and degree II completely dislocated hips, because of concentrating forces on a narrow area of the superior acetabular margin, the superior acetabular rim is eroded severely, especially after the age of walk.3 Under 3 years old, the increased acetabular anteversion is one component of the anatomic deformity in DDH, furthermore, the longer the hip dislocates, the more evident the acetabular anteversion is.4 The ossification nucleus of femoral head is ellipse in normal, but which is near sphericity in DDH, and ossifies later than normal.