Purpose: The aim of this prospective controlled study was to assess the natural history of acetabular development in D.D.H. treated under 18 months of age.

Method: For this purpose, patients who were treated using a posteromedial approach soft tissue surgical procedure due to unilateral D.D.H., had intraoperative radiographic anatomic reductions, had neither any type of avascular necrosis of the femoral head nor breakage of the Shenton’s line during the follow-up period, had complete follow-up till at least 10 years of age and had normal center-edge angles at the latest follow-up were selected from a prospective series that started in December 1993. Unaffected contrlateral hips were used as controls. Fourteen hips of 14 patients (13 females and 1 male) met the above mentioned strict criteriae and included the study. Acetabular angle of Sharp (AA) was measured to assess the acetabular slope in the frontal plane preoperatively and during follow-up. A paired t-test was used for the statistical analysis of the data and a P value less than 0.05 was considered significant.

Conclusion: In anatomically reduced and uncomplicated dysplastic hips which have been treated under 18 months of age, acetabular slope in the frontal plane tends to improve continuosly till at least 10 years of age and reaches to similar angular values as in the unaffected hips at nearly 7 years of age. In such hips, it may not be appropriate to make a final decision on whether the acetabular development is sufficient or not before 7 years of age.