RESUMEN
PURPOSE: This study analysed the incidence and the degree of an acetabular retroversion in a dysplastic hip. MATERIALS AND METHODS: 28 cases of dysplastic hips, in whom the CE angle was <20 degrees, and 20 cases of control group with a normal CE angle were enrolled in this study. Four cuts among the CT images (most superior cut of the femoral head, middle cut of the proximal half, middle portion, and middle cut of the distal half of the femoral head) were used to measure the acetabular anteversion. RESULTS: In the control group, anteversion of four cuts (form the cranial to caudal) were observed with an average of 4.1, 10.3, 16.5, 19.7degrees, and there was one case with a retroversion. In the dysplastic hips, the average anteversion angles were 4.4, 11.0, 17.9, 20.8degrees, and 9 cases with retroversion were discovered. In all cases showing retroversion, an overlapping of the acetabular anterior and posterior wall (cross-over sign) was observed on the simple pelvis AP radiography. CONCLUSION: There was a 32% incidence of acetabular retroversion, which was much higher than the control group (p<0.05). Therefore, in order to prevent an over-correction of the retroversion, which may cause impingement, the presence and the amount of retroversion must be recognized using CT before performing a periacetabular osteotomy.