Computed tomography measurements of the acetabulum in adult dysplastic hips: which level is appropriate?

A study has been performed to evaluate whether one or several levels are needed with computed tomography (CT) study to provide sufficient information regarding anteversion and acetabular support to the femoral head. A total of 23 hips in 14 adults with uni- or bilateral congenital hip dysplasia (center-edge angle less than 20°) were assessed by obtaining 5-mm contiguous CT slices and performing acetabular measurements at four levels. Both anterior and posterior acetabular supports as quantified by the anterior and posterior acetabular sector angles were significantly lower than normal at all levels. The sector angles increased in the proximal cuts, whereas the acetabular anteversion increased caudally. Because no important additional information was gained by measuring at different levels, we conclude that CT study at one level is sufficient for acetabular measurements and suggest that the slice through the center of the femoral head is the most appropriate one.