[Acetabular anteversion in congenital luxation of the hip]

Acetabular anteversion angle (AAA) and orientation angle of the iliac bone (AOOI) determined by use of a CT scan were studied in CDH. 55 children with CDH were selected on hip arthrography for this study. Subluxated hips were excluded (i.e. opposite hip of a unilateral CDH is normal). 10 boys and 45 girls with a mean of age of 2 years 1 month (extremes from 1 to 4 years 3 months) were studied. CT scan was performed before any orthopaedic treatment in 3 cases of bilateral luxation and 14 cases of unilateral. In the other cases, time between the end of orthopaedic treatment and CT scan varied between 4 and 18 months. A group of 23 normal children, 10 boys and 13 girls, (mean age of 2 years 10 months) served as reference group. On the selected CT slide we measured AAA, AOOI, IAA and IAP (anterior acetabular index and posterior acetabular index as proposed by Guggenheim).

We noted that the orientation of the iliac bone was variable in the two groups. This orientation angle could have higher or lower values. AAA: in bilateral luxation, this angle was higher (16 degrees +/- 5 degrees) than in reference group (13 degrees +/- 4 degrees), p < 0.005. In unilateral luxation there was no statistical difference (14 degrees +/- 4 degrees) with reference group, between normal and pathological side and when CT scan was performed before or after orthopaedic reduction. AOOI: there was no significant difference between bilateral, unilateral or reference group. Correlation analysis showed that AAA and AOOI moved in the same direction. IAA: in bilateral luxation this index was higher (p < 0.001); in unilateral luxation only right luxation showed an higher index (p = 0.002). IAP: no significant difference between the different groups.

This study shows that there is any typical CT scan aspects of morphologic abnormality in CDH. The lesions of the anterior or posterior acetabular wedge are variable. The orientation of the iliac bone is also variable; we concluded that acetabular anteversion must be analysed depending on the morphologic aspects of the anterior and posterior extremities of the acetabulum and iliac bone orientation.