[Heredity in congenital dislocation of the hip]

The hereditary pattern of CDH is well known, but the results depend on time of diagnosis, either late or in the immediate postnatal period, the latter having been the basis of the more recent studies. Early screening shows that newborns with an unstable hip are 4 times more frequent than those with late CDH. The etiology includes constitutional and environment factors. This is well demonstrated in twins. In a large series of Idelberger the concordance was 41.4% (12/29) in identical twins in cases of late CDH whereas in fraternal twins, the concordance was 2.8% (3/109). Fraternal twins have the same genetic differences as other siblings. There is also a sexual factor. In Western Europe, the frequency of unstable hips varies between 3 and 5/1000 (except in some specific areas) with 3 to 8 times more cases in girls than in boys, depending on the study and on the period of diagnosis.