Developmental dysplasia of the hip: a new approach to incidence

The controversy over the incidence of developmental dysplasia of the hip (DDH) stems mainly from an ambiguity of criteria for defining a genuinely pathologic neonatal hip. In this study, we evaluate an algorithm we devised for the treatment of DDH, for its ability to identify those neonatal hips which, if left untreated, would develop any kind of dysplasia and, therefore, are to be included in the determination of DDH incidence.

Clinical and ultrasonographic examinations for DDH were performed on 18 060 consecutive neonatal hips at 1 to 3 days of life. Newborns with skeletal deformities, neurologic/muscular disorders, and neural tube defects were excluded. Hips that featured any type of sonographic pathology were reexamined at 2 or 6 weeks, depending on the severity of the findings. Only hips in which the initial pathology was not improved or had deteriorated were treated; all others were examined periodically until the age of 12 months.

Sonographic screening of 18 060 hips detected 1001 instances of deviation from normal, indicating a sonographic DDH incidence of 55.1 per 1000. However, only 90 hips remained abnormal and required treatment, indicating a true DDH incidence of 5 per 1000 hips. All the others evolved into normal hips, and no additional instances of DDH were found on follow-up throughout the 12 months.

The implementation of our protocol enables us to distinguish two categories of neonatal hip pathology: one that eventually develops into a normal hip (essentially sonographic DDH); and another that will deteriorate into a hip with some kind of dysplasia, including full dislocation (true DDH). This approach seems to allow for a better-founded definition of DDH, for an appropriate determination of its incidence, for decision-making regarding treatment, and for assessment of the cost-effectiveness of screening programs for the early detection of DDH.