Congenital Dislocation of the Hip

Between 1977 and 1982, 19 cases of congenital dislocation of the hip (CDH) were encountered in black infants. Six of these cases were associated with other anomalies (atypical CDH); 13 were typical CDH. The incidence of complete CDH in the white population studied is 1.5/1000, in the black population studied it is 0.46/1000. The increased incidence in comparison to previous studies may possibly reflect genetic heterogeneity in the control population relative to the African black.

The purpose of this study is to report on the experience at the authors' hospital with black children with congenitally dislocated hips who were treated between 1977 and 1982.

MATERIALS AND METHODS
The charts of all the children treated for dislocated hips during the years 1977-1982 were reviewed. All dislocations in children with crebral palsy, myelodysplasia, and other entities that would cause a developmental or paralytic dislocation were excluded from the study. Likewise, patients with a diagnosis of subluxated hips were not included. A number were not initially seen at the authors' institution but were referred at a later date for definitive treatment; those patients with documentation of a congenitally dislocated hip were included in the study. Verification of the dislocated hip was provided by ( I ) direct examination by the physician with a positive Ortolani's sign (Cases 1 and 10) or (2) radiographic evidence of a dislocated hip by either plain roentgenogram (Cases 15,16,and 19) or an arthrogram (11)(12)(13)(14)17,and 18).
Ninety-one children with 105 dislocated hips were treated between 1977 and 1982. Seventy-six were girls and 15 were boys. Fifty-seven of the dislocations were left hips and 48 were right hips. Records indicated that 19 of these children were black and accounted for 24 dislocated hips (Table  I). Thirteen children (12 girls and one boy) with 17 dislocated hips were classified as having a typical dislocation. Six children, four girls and two boys, with seven dislocated hips were classified as having teratologic dislocations. Included in the teratologic group were three patients with multiple congenital anomalies, one with Ehlers-Danlos syndrome, one with trisomy 14, and one with arthrogryposis.   Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Typical  Teratologic  Teratologic  Teratologic  Teratologic  Teratologic   Primary open reduction with femoral shortening (and possible acetabuloplasty).
Ages of patients at initial treatment ranged from one day to 22 months, with a median of six months. All but four were seen in the first 12 months of life.
Treatment was determined with the protocol outlined in Table 2. Following this protocol, 18 of the hips required at least one arthrogram; 1 1 needed adductor tenotomies; and six required an open reduction. An upper femoral osteotomy was performed on three occasions. Two patients (Cases 16 and 19) were untreated because of poor prognosis from other anomalies.

DISCUSSION
No attempt was made to analyze treatment outcome because the follow-up period was too short to allow meaningful analysis of results with reference to other published series. It is the authors' opinion that there is no difference in response to treatment.
Since 1976, there have been 182,484 black births in the state of Louisiana. With the incidence quoted by Trevor'* of one per 30,000, this would equate to six black children with dislocated hips born over the same period of time in the entire state. Since 1977, the authors have treated 24 dislocated hips in black children. This difference is statistically significant (p < .0001). Since the au-thors' institution does not treat all the dislocated hips in the state, the actual incidence is probably considerably higher than one in 30,000.
The population seen at the authors' hospital is representative of the entire state's population and birth rate. Since 1976, 461,898 children have been born in Louisiana, including 279,416 (60.5%) white and 182,484 (39.5%) black. This corresponds well with the yearly census at the authors' hospital over the same period, with whites accounting for 6 1.9% and blacks 36.9% of the census, so the high number of dislocated hips in blacks seen at the authors' institution is not due to the presence of a disproportionate number of blacks.
Only crude estimates of the actual incidence of CDH in the American black are available. The 24 hips in the present study, taken from a group that constituted 36.9% of the total census, accounted for 19.8% of the hips treated. Assuming that the remaining 75 dislocated hips represent an incidence of 1.5/1000, as quoted by Barlow,' then the black population has an estimated incidence of 0.461 1000 for typical dislocations and 0.641 1000 for all congenital dislocations. This number is of the same magnitude as that found by Gross et aL6 who examined 2800 black newborns and found one bilateral CDH, an incidence of 0.36/1000. The African black is virtually free from CDH as shown by many studie~.~.~.'.~-' 1. 13-15.17 Postnatal nursing habits, relative joint laxity,2.20 and acetabular dysplasia" have been thought to play prominent roles in the genesis of CDH in general. Nursing habits and relative joint laxity have been shown not to be of prime importance in the black's relative immunity to this problem.'." Conversely, Skirving showed that black neonates had a deeper acetabulum more frequently than did whites. This "configuration of the acetabulum is an inherited characteristic, probably a multiple gene system,"'6 and accounts for the African black's low incidence of CDH. 192 January-February. 1985 American blacks are markedly different, both culturally and genetically, from the African blacks studied in previous reports. The cultural differences are obvious. Genetically, American blacks are an admixture of various black African populations and an unknown amount of other racial influence^.'^.'^ Reed12 used the frequency of the Fx" gene in the Duffy blood group system as an estimate of Caucasian ancestry in United States black populations. His estimates showed that the southern black gene pool is comprised of 11% nonblack genes. In Northern cities, the estimate is 20%-25%. Presumably, the American black's immunity to CDH is significantly altered by this admixture.

Number
A review of the literature revealed only 14 reported cases of congenital dislocation of the hip in blacks. The present series of 19 patients with 24 dislocated hips represents an estimated incidence of 0.46/1000 live births in black infants. Throughout the state of Louisiana, it would appear that congenital dislocation of the hip in blacks is much more common than was previously thought.