Congenital dislocation of the hip in Western Australia. A comparison of neonatally and postneonatally diagnosed cases.

Speculation that neonatally diagnosed congenital dislocation of the hip (CDH) may have a different etiology from cases diagnosed in the postneonatal period has not been examined in Australia because insufficient data have been available. A population-based study of CDH in children up to the age of two years who were born in Western Australia (WA) in 1981, 1982, or 1983 is the subject of this report. Study material comprised cases of CDH from the WA Congenital Malformations Register and denominator data (all births in WA for 1981-1983) from the Health Department of WA. From this material, rates of CDH were calculated for each of the study variables of interest. The rate of CDH was low for babies born to aboriginal mothers, and it is postulated that this may have a cultural basis, possibly in infant carrying postures. Overall, the prevalence of CDH for 1981-1983 was 6.4 cases per 1000 births, with 4.2/1000 diagnosed in the neonatal period and 2.2/1000 in the postneonatal period. Epidemiologic differences were noted between infants diagnosed in the neonatal period and those diagnosed postneonatally; rates of neonatally diagnosed CDH were higher in first births, breech presentation, and postmature infants than were rates of postneonatally diagnosed cases. Bilateral dislocation was more common (45.3%) in neonatally diagnosed cases than in postneonatally diagnosed cases (23.3%). These findings tended to support the idea that the time of diagnosis may define two distinct entities in CDH.