Introduction and Aims: In the management of newborn’s hips, ultrasonography (US) has proven to be a useful tool. However, the progression of measurements at different ages in normal hips has not been thoroughly investigated. This prospective study assessed the longitudinal development of clinically stable hips from birth to the age of 12 weeks.

Method: Forty newborn children (80 hips) with clinically stable hips were assessed by ultrasound at three points in time – namely within the first few days of life, at six weeks of age and finally at 12 weeks of age. Femoral Head Coverage (FHC) as well as Graf’s alpha and beta angles were measured.

Results: A significant change in all values occurred between the three points in time (p< 0.001). The mean FHC progressed from 58% at birth, to 65% and 69% at six weeks and at 12 weeks respectively. The mean alpha angle improved from 70 degrees to 77 degrees and then 80 degrees at birth, six weeks and at 12 weeks, respectively. The mean beta angle progressed from 52 degrees to 46 degrees and then 43 degrees at birth, at six weeks and at 12 weeks, respectively.

Conclusion: In clinically stable hips, the FHC, alpha and beta angles change significantly over time. It is important, therefore, to consider the baby’s age when interpreting US images, especially when making management decisions regarding splintage. This has important implications if ultrasound is used as a screening tool.