Background It has been reported that the national incidence of developmental dysplasia of the hip (DDH) has decreased in Japan. This is because of prevention activities after birth since around 1970. However, cases of late-diagnosed DDH have still been noted in some children's hospitals. There has been no recent survey of DDH in Japan. The purpose of this study was to investigate the current epidemiology of DDH using a comprehensive nationwide survey. Methods A questionnaire was sent to orthopedic surgeons in 1987 facilities nationwide, who were asked to complete and return a survey card on each DDH patient treated between April 2011 and March 2013. Results A total of 783 (39%) facilities completed and returned the card. Of these, 79% reported no cases of DDH-related dislocation over the 2-year period, while the remaining facilities reported 1295 cases. The characteristics of children diagnosed with DDH-related dislocation were as follows: girls (89%), left side involvement (69%), bilateral involvement (4%), positive family history (27%), first-born (56%), and pelvic position at birth (15%). Seasonal variation showed an increase in DDH incidence among those born in the winter. Overall, 199 cases (15%) were diagnosed at >1 year of age, and these included 36 cases diagnosed very late, at >3 years of age. The majority of the 199 cases of late diagnosis had received earlier routine screening at <1 year of age. Conclusion The characteristics of the children diagnosed with DDH nationwide were similar to past data from local regions. However, many children were diagnosed late (>1 year of age), particularly in the more populous regions. The findings identify a need for improved early routine screening for DDH in Japan.
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