Associations between risk factors and developmental dysplasia of the hip and ultrasonographic hip type: a retrospective case control study.

Purpose: We aimed to revisit the correlation between the previously defined risk factors and the occurrence of developmental dysplasia of the hip (DDH) and to assess the influence of these factors on the ultrasonographic type of hip dysplasia according to the Graf's classification in patients with DDH.

Methods: Data of healthy infants (mean age 33 days) who had bilateral mature (normal) hips (Graf type I) were compared with the data of infants (mean age 105 days) who were treated by abduction brace due to unilateral or bilateral DDH (Graf type IIa- and worse hips).

Results: Infants with at least one risk factor had a significantly higher rate of DDH than those with no risk factors (p < 0.001). Likewise, infants with more than one risk factor had a significantly higher rate of DDH than those with only one risk factor (p = 0.008). Family history, breech presentation and swaddling were found to be the three significant risk factors related to the development of DDH. Family history, swaddling and oligohydramnios were found to be the three significant risk factors correlated with a higher rate of unstable/decentred hip(s) (Graf types D/III/IV) in patients with DDH.

Conclusion: The risk of DDH significantly increases in infants who have more than one risk factor for DDH. Positive family history and postnatal traditional swaddling are the two main factors both in the aetiology of DDH and in development of a more severe hip dysplasia in patients with DDH. Besides, breech presentation increases the risk of development of DDH and oligohydramnios leads to development of a more severe hip dysplasia in patients with DDH. By introducing these four variables as 'absolute risk factors for DDH' to the selective newborn hip screening programmes, the sensitivity and specificity of these programmes may be optimized and the risk of delayed diagnosis may be lessened.

Level Of Evidence: Level III prognostic study.