Neonatal hip instability. The anterior-dynamic ultrasound method. Population screening and re-evaluation of some aetiological factors

Abstract

To evaluate neonatal hip instability, the values for the physiologically normal movement of the femoral head by provocation were determined by an anterior-dynamic ultrasound method. The maximal movement of the femoral head with the acetabulum at provocation was 6.0, 6.6 and 6.8 mm for the birth weights 2,000, 3,000 and 4,000 g. The femoral head diameter was found to be 16.08 ± 1.49 mm and 15.56 ± 1.43 mm. Five infants had four consecutive examinations performed. No significant difference was found between degree of movement after the first and the fourth examination. By using the ultrasound method as the only diagnostic the frequency of treatment fell from 1.7% to 0.18% and no late cases were diagnosed before walking age.The sensitivity for the clinical examination was low: for paediatricians 24% and for trained technicians 53%. The breech malposition was confirmed to predispose to neonatal hip instability. The instability was manifest before delivery and was surely not a result of delivery forces. Vaginal delivery after an external version to vertex presentation and caesarean section without an attempted version represents the same risk for neonatal hip instability. Breech malposition and vertex presentation after an external or spontaneous version should both be considered risk factors for neonatal hip instability.Blood samples from the umbilical cord were saved from all neonates born during one year to evaluate whether intrauterine exposure to high levels of the maternal hormones could be an aetiological factor in neonatal hip instability. The hormone relaxin could not be detected except in three samples from three neonates in the control group. In infants without hip instability S-17 b-oestradiol concentrations were higher in male newborns compared to females, depending on the fact, that most girls with high oestradiol levels were cases. A trend to inverse relationship between oestradiol and parity was demonstrated. Using logistic regression analysis with adjustment for the associations to breech presentation, parity and gender, a significant association between S-oestradiol and neonatal hip instability was demonstrated in male newborns with low serum concentrations. S-oestradiol (<10 nmol/l) gave an increased risk of hip instability. In contrast, high S-oestradiol (>15) tended to be associated with an increased risk of hip instability in female newborns.From this study we conclude that:Population screening is necessary if both the dislocatable and the dislocated hip joints are to be identified.The anterior-dynamic ultrasound method is well suited to the screening situation and is shown to be reliable and reproducible.The anterior-dynamic ultrasound method can identify all neonatal hip dislocations within the first two days of life.The normal values for the physiological movement of the femoral head are a reliable standard dividing the population into two groups: those in need of medical attention and those with normal hip joints.Breech malposition is a risk factor for neonatal hip instability. The instability is present before delivery and is unaffected by delivery by caesarean section and/or attempted external version.An increased serum concentration in cord blood of the maternal hormone relaxin is not a cause of neonatal hip instability.S-17 ß-oestradiol in the umbilical cord blood is associated with gender as well as parity, but no firm conclusion on the association between 17 ß-oestradiol and neonatal hip instability can be made from this limited study.