Acetabular Development in the Contralateral Hip in Patients with Unilateral Developmental Dysplasia of the Hip

Background: Adult patients may present with acetabular dysplasia without a history of developmental dysplasia of the hip. The purpose of the present study was to clarify the development of primary acetabular dysplasia in patients under the age of eighteen years by evaluating the contralateral hip in those with unilateral developmental dysplasia of the hip. Methods: Radiographs of the contralateral hip of eighty-eight patients with unilateral developmental dysplasia of the hip were reviewed retrospectively. The center-edge angle was measured at the age of eighteen years. The primary acetabular dysplasia group included hips with a center-edge angle of <20 degrees, and the normal group included hips with an angle of >= 20 degrees. The acetabular index at the age of three years, the center-edge angle between the ages of three and eighteen years, and the acetabular angle of Sharp between the ages of six and eighteen years were measured. Results: According to our classification system, twelve hips (13.6%) were assigned to the primary acetabular dysplasia group. At the age of three years, there were no significant differences between the two groups radiographically. A significant difference in the center-edge angle between the two groups was seen at each evaluation period after the age of six years. However, twenty-two patients in the normal group had poor acetabular coverage and three patients in the primary acetabular dysplasia group had good acetabular coverage at the age of nine years. After the age of nine years, improvements in the center-edge angle and the acetabular angle of Sharp were noted in the normal group, whereas no acetabular growth was seen in the primary acetabular dysplasia group. There was no patient with a center-edge angle of <15 degrees at the age of twelve years in the normal group. Conclusions: After the age of six years, a difference in acetabular growth develops between patients with primary acetabular dysplasia and those with normal hips. However a final prognosis for acetabular development appears to be difficult to determine until the age of twelve years.