Neonatal hip stability and the Barlow test. A study in stillborn babies.

Ten normal neonatal hips were examined in stillborn babies. At first, forcible Barlow manoeuvres did not produce subluxation or dislocation, but by repeated examination a previously stable joint could be rendered unstable. Dissection of the hips showed that the vacuum fit between the femur and the acetabulum was an important factor in neonatal hip stability. The posterior capsule was not a strong or, in itself, an important structure. It is postulated that the capsule and the labrum act together as 'O' rings to maintain the vacuum fit; it is possible that repeated examinations, by producing an effusion, could break the seal and allow instability.