[The phenomenon of a permanent spontaneous articular vacuum (or anti-vacuum effect) in neonatology].

Natural permanent pneumarthrography (NPP) is due to entrance of gases in-to the joint spaces following a sudden increase in intra articular volume and lowering of intra articular pressure by sudden stresses. A case of N.P.P. of the hip occurred in one of two stillborn twins (breech delivery); the causes of death were some amniotic bridles of the cord with consequent stop in the blood flow.