Aim: To assess the effectiveness and need for X-rays undertaken at 9 to 12 months of age in cases were children have a strong family history of DDH and have had a normal ultra-sound scan at 6 weeks of age.

Materials and Methods: A retrospective study was undertaken over a five-year period. 122 children were identified as having a positive family history of DDH with a normal ultra-sound scan at 6 weeks. 56% were female and 44% were male. 6 were breech (4.9%). The mean ultra-sound was undertaken at 8.9 weeks. The mean X-ray was undertaken at 11.6 months. Acetabular dysplasia was diagnosed if the acetabular index was over 30 degrees. All X-rays were reviewed by one specialist.

Results: 3 children were noted to have late acetabular dysplasia (2.5%). One case was bilateral and 2 cases were unilateral.

Conclusion: The study showed a sub-group of cases where there was an incidence of acetabular dysplasia where the ultra-sound was normal at 6 weeks in those with a strong family history of DDH. It was felt that the finding of this dysplasia supports the policy to X-ray these cases at one year because of the significantly increased risk of acetabular dysplasia in this group.