[Ultrasonography of the borderline between normal and pathological state of the hip in newborn infants (borderline hip)].

Infant hips are classified, according to Graf, in 4 US types on the basis of the morphologic changes in both the cartilaginous and the bony roofs (type I, II, III, IV). Out of 6,000 examined hips, 170 (2.8%) were considered, which could be classified neither as type I (mature) nor as type II (delayed/immature ossification). These hips were called borderline hips. They exhibited some characteristic US features: good bone modeling, rounded cotyle, and alpha angle 60 degrees +/- 2. They were always observed during the first month of the patients' life. Anamnestic data were not specific (27.5% breech delivery, and 13% oligohydramnios); clinics sometimes overestimated the actual anatomic development (64/170 cases with positivity of Ortolani's sign and/or restricted abduction; 25% of patients presented with no suspicious signs). Dynamic hip examination showed only physiological cranial deflection of the cartilaginous roof. Finally, borderline hips developed into type I hips in 99% of cases, within the third month of the patients' life.