Letter: Rising rates of congenital dislocation of the hip

Seasonal variation in children with developmental dysplasia of the hip

BACKGROUND

It has been postulated that developmental dysplasia of the hip (DDH) is more frequent in infants born in the winter months. It was the purpose of this study to ascertain if there was any seasonal variation in DDH at the author's institution and compare/contrast our results with those in the literature using rigorous mathematical fitting.

METHODS

All children with DDH treated at the author's institution from 1993 to 2012 were identified. The month of birth was recorded and temporal variation was analyzed using cosinor analysis. Similar data from the literature was analyzed.

RESULTS

There were 424 children (363 girls, 61 boys). An additional 22,936 children were added from the literature for a total of 23,360. Pearson's Chi-square test demonstrated a non-uniform distribution in the month of birth for both our 424 children as well as the combined literature series in both the Northern and Southern hemispheres. Cosinor analysis of the 424 children demonstrated double peaks in mid-March and mid-October. For the entire 23,360 children, no seasonal variation was observed in 2,205 (9.4 %), a single winter peak in 16,425 (70.3 %), a single summer peak in 1,280 (5.5 %), and double peaks in the spring and autumn in 3,450 (14.8 %).

CONCLUSIONS

This study partly supports the hypothesis of tight clothing/cold temperature as one factor in the etiology of DDH with the tighter clothing/swaddling increasing the risk of DDH. However ~20 % of the DDH births demonstrated a non-winter peak. The single summer and double spring/autumn peaks, as well as in those series where no seasonal variation was noted, refutes the cold winter clothing hypothesis. Perhaps these different patterns in seasonal variation represent the heterogeneity of the genetic factors in DDH interacting with external factors (temperature and clothing) and internal factors (metabolic). Further study will be required to understand these different patterns in DDH seasonal variation.

LEVEL OF EVIDENCE

IV-case series.

The epidemiology and demographics of hip dysplasia

The etiology of developmental dysplasia of the hip (DDH) is unknown. There are many insights, however, from epidemiologic/demographic information. A systematic medical literature review regarding DDH was performed. There is a predominance of left-sided (64.0%) and unilateral disease (63.4%). The incidence per 1000 live births ranges from 0.06 in Africans in Africa to 76.1 in Native Americans. There is significant variability in incidence within each racial group by geographic location. The incidence of clinical neonatal hip instability at birth ranges from 0.4 in Africans to 61.7 in Polish Caucasians. Predictors of DDH are breech presentation, positive family history, and gender (female). Children born premature, with low birth weights, or to multifetal pregnancies are somewhat protected from DDH. Certain HLA A, B, and D types demonstrate an increase in DDH. Chromosome 17q21 is strongly associated with DDH. Ligamentous laxity and abnormalities in collagen metabolism, estrogen metabolism, and pregnancy-associated pelvic instability are well-described associations with DDH. Many studies demonstrate an increase of DDH in the winter, both in the northern and southern hemispheres. Swaddling is strongly associated with DDH. Amniocentesis, premature labor, and massive radiation exposure may increase the risk of DDH. Associated conditions are congenital muscular torticollis and congenital foot deformities. The opposite hip is frequently abnormal when using rigorous radiographic assessments. The role of acetabular dysplasia and adult hip osteoarthritis is complex. Archeological studies demonstrate that the epidemiology of DDH may be changing.

Risk factors for developmental dysplasia of the hip: ultrasonographic findings in the neonatal period

The relationship between ultrasonographic findings at birth and risk factors for developmental dysplasia of the hip have not been prospectively evaluated. Since implementing a routine screening programme for all new-born babies in 1989 we have collected 48 000 sets of data, including family history, birth presentation, mode of delivery and birth weight. Of the 92 babies (three per 1000 live births) with persistent ultrasonographic abnormality at 6 weeks only 20% displayed evidence of clinical instability at the original examination. Female babies without the additional risks of breech birth or positive family history were quantitatively the most significant group, accounting for 75% of cases treated. The majority of babies requiring intervention would not have been identified utilizing present criteria for selective ultrasound screening.

Congenital dislocation of the hip: a prospective study comparing ultrasound and clinical examination

Screening for congenital dislocation of the hip by standard clinical methods and ultrasound was compared prospectively in 1503 newborns (1291 girls and 212 boys). A total of 82.8% of the hips (78.8% of the infants) had well developed acetabulae, 14.5% (17.2% of the infants) were shallow (immature) and 2.7% (4.1% of the infants) were dysplastic. Within 1-3 months 96.7% of the infants with clinically stable, but immature hips normalized, while 3.3% did not improve or worsened, and therapy was therefore initiated. Indications for treatment included dysplastic and/or clinically unstable hips, and a higher number of newborns were treated during the study period than in 1982-85 (31.2 vs 19.7 per 1000, p = 0.0002). Thirty-seven percent of the patients had both clinical and ultrasound findings compatible with congenital dislocation of the hip, while the decision to treat was based on clinical findings alone in 25.0% and on ultrasound findings in 38.0%. Infants born during the study period of nine months had a low incidence of late congenital dislocation of the hip compared with our earlier reported results from 1982-85 (0.9 vs 3.5 per 1000, p = 0.012). The study demonstrated major discrepancies between clinical and ultrasound evaluation of hips in the newborn, and the role of ultrasound in the screening for congenital dislocation of the hip requires further evaluation.

Effectiveness of screening for congenital dislocation of the hip

The incidence of congenital dislocation of the hip (CDH) in Birmingham was measured in the period 1942-52 and again in 1950-54; it is measured now in 1974-83. Despite the introduction of neonatal screening for CDH in November 1966, between the times of the earlier and the present measurements there was no indication that CDH requiring prolonged treatment had declined. The performance of the procedure itself was poor. It detected only a third of genuine cases, and the false positives outnumbered the true positives by 10:1. The incidence of 'definite' cases varied markedly from year to year in a manner suggesting diagnostic idiosyncracies rather than genuine fluctuations. There was no evidence in particular maternity units that high levels of early detection led to low levels of late diagnosis. Indeed, maternity units with the worst results--the highest rates of late diagnosis and of prolonged treatment--had the highest rates of early detection and early treatment. Current theories of natural history, aetiology, and treatment should be reappraised.

Congenital hip dislocation: an increasing and still uncontrolled disability?

A study of 178 cases of congenital dislocation of the hip in babies born between 1965 and 1978 in Southampton health district showed that the incidence had virtually doubled over this period. Established cases (persisting beyond the first birthday) had risen to around two cases per 1000 per live births. One-third of these were first diagnosed after the age of 1 year and one-fifth after 18 months. The findings are particularly disappointing as there were opportunities after the neonatal period for earlier diagnosis. Thus, neonatal screening appears to have failed to make a substantial impact on the morbidity of the disease, probably because of a combination of inherent difficulties in the neonatal screening test as well as failure in its proper application. Much greater vigilance is needed during the first year of life if congenital dislocation of the hip is to be detected and treated as early as possible. Perhaps this could be achieved if all health professionals were more aware of the problem and were encouraged to examine hips at every opportunity and health authorities periodically audited their results.