Second order elasticity at hypersonic frequencies of reactive polyurethanes as seen by generalized Cauchy relations.

The non-equilibrium process of polymerization of reactive polymers can be accompanied by transition phenomena like gelation or the chemical glass transition. The sensitivity of the mechanical properties at hypersonic frequencies-including the generalized Cauchy relation-to these transition phenomena is studied for three different polyurethanes using Brillouin spectroscopy. As for epoxies, the generalized Cauchy relation surprisingly holds true for the non-equilibrium polymerization process and for the temperature dependence of polyurethanes. Neither the sol-gel transition nor the chemical and thermal glass transitions are visible in the representation of the generalized Cauchy relation. Taking into account the new results and combining them with general considerations about the elastic properties of the isotropic state, an improved physical foundation of the generalized Cauchy relation is proposed.

[X-ray computed tomographic aspects of spinal aneurysmal cysts in children]. / Aspect tomodensitométrique d'un kyste anévrysmal rachidien chez l'enfant.

The interest of CT imaging in a case of aneurysmal bone cyst of the posterior arch of the 6th cervical vertebra in a 10 y.o. child is underlined. The value of intra tumoral densities which are relatively low, inferior to 100 Hounsfield unit is stressed but the most contributory feature in this case was the presence of a fluid level inside the cyst due to different densities of fluid components into the cyst.

[Medial acetabular displacement and other pelvic displacements after Chiari osteotomy (author's transl)]. / La médialisation du cotyle et les déplacements parasites dans l'ostéotomie pelvienne de Chiari.

The authors have made a study of displacement after Chiari osteotomy in cadavers and in patients. In most of the cases, following osteotomy, there is movement not only at the pubic symphysis but also in the two sacro-iliac joints. Movement in the ipsilateral sacro-iliac joint is associated with upward and lateral displacement of the iliac crest giving an improved cover of the femoral head even though the acetabulum is not medially displaced. Movement in the controlateral sacro-iliac joint does result in medial displacement of the acetabulum but the whole of the opposite hemi-pelvis is also displaced so that the opposite acetabulum is displaced laterally and becomes more vertical. The authors attempt to draw conclusions on the biomechanical action of Chiari osteotomy on the opposite acetabulum.

[Angular synthesis in upper tibial valgus osteotomy in osteoarthritis. Apropos of a series of 544 cases]. / Synthèse angulaire dans l'ostéotomie tibiale haute de valgisation pour arthrose. A propos d'une série de 544 cas.

Five hundred and forty-four valgus osteotomies for medial compartment osteoarthritis of the knee have been performed by two teams working separately over a period of twenty years between 1964 and 1984. From this series the results of a technique which aims to combine precision of correction with stability of fixation have been assessed. The clinical results in the short and medium term are encouraging. Above all, it seems that improvement in the osteoarthritis can be maintained for ten years or more, that is to say greater than the mean expectation of life of the patients.