[Survival charts. Examples]. / Courbes de survie. Exemples.

Subject to the correct choice of the criterium one want to study, drawing survival curves is an interesting statistical means. This enables to manage information closer to the time passed and reduces to the best the loss in patients we have lost sight of. The present article tends to enable the attentive reader not only to understand its principles, but also to provide him with all practical elements for drawing them and comparing them together.

[Development of the gravity vector in normal walking. Muscular and kinetic correlations]. / Evolution du vecteur gravitaire au cours de la marche normale. Corrélations musculaires et cinétiques.

The vertical vector P which represents the body weight in a standing subject undergoes variations in the course of walking which merits study. This is the subject of this article. It is based on the numerical findings derived from work published on walking and is concerned with its displacement, the ground contact forces, muscular activity and expenditure of energy. A study using pressure transducers makes it possible to trace the progressive area of the gravity vector in the horizontal plane in the course of walking. At the same time, the progressive position of the centre of gravity in space can be registered and timed. The resulting trace is analogous to that obtained by a study of plantar pressures. The gravity vector is displaced in the course of walking like the clapper of a clock, suspended at the centre of gravity and passing successively in diagonal form in the four sectors of the horizontal plane defined by the axis of the walking and the frontal plane. In this displacement, its value varies steadily and cyclically. The trunk muscles, whose contraction has been studied clinically and by electromyography at the time of the different phases of walking are exactly those which can provide the mechanical compensation necessary for the displacement of the body weight vector. As to the time factor, it seems to show that, for a given subject, there exists, in relation to his weight and the height of the centre of gravity a speed of walking that corresponds to the minimum expenditure of energy.

[Constraints on the knee caused by meniscal and ligament derangement. Study of the internal condylotibial joint. Experimental cinematic method]. / Contraintes du genou par dérangement ménisco-ligamentaire. Etude de l'articulation condylo-tibiale interne. Méthode cinématique expérimentale.

In a previous paper the authors have demonstrated that the polycentric curve of the surface of the medial condyle of the femur is a logarithmic spiral arch whose centre is the point of attachment of the medial ligament. In the present study, the totality of the menisco-ligamentous system was considered and studied on cadavers following a geometric model. It is shown that the ligament system controls combined or successive movements of gliding or rotation of the condyle on the tibial plateau in such a way as to avoid any cam effect or additional strain. Division of ligaments or excision of a meniscus leads to an increase in strain which varies in relation to the type of lesion. The increase is moderate after division of the anterior cruciate ligament, greater after division of the posterior cruciate ligament and severe after meniscectomy especially when associated with ligamentous division.

[How to perform oblique-plane osteotomy]. / Comment réaliser une ostéotomie plane oblique.

Oblique plane osteotomy allows correction of associated angular and rotational deformity by a single bony section and also allows modification of the existing angle at the cervico-diaphyseal level in the femur. Exact assessment of the direction of the osteotomy and of extent of rotation are essential to success. This paper proposes a simple method by use of a table and performance is facilitated by the of Kirschner wires.

[The normal and prosthetic hip. A comparison of different surfaces]. / Hanche normale et prothétique. Un comportement de surfaces différent.

The authors made a study of the biomechanical features of the normal and the prosthetic hip with a special reference to the distribution of forces and the characteristics of low friction. In his conclusion, he points out that the normal hip constitutes a remarkable system for the distribution of pressure in that the bearing surfaces are increased in direct relation to the load. This mechanism only functions because of the absence of friction and for the same reason, the size of the femoral head does not have any particular mechanical importance. In contrast, in the prosthetic articulation, even the smallest load is localised to the polar region on a surface which becomes more limited the greater the modulus of elasticity of the two composing parts. Excessive pressure is not harmful as it may be in a normal hip. Friction constitutes one of the features of an artificial hip and may be a friction of rotation or a friction of leverage. To limit these phenomena to their maximum, the coefficient of friction should be made as low as possible and, as far as possible the diameter of the prosthetic head should be limited.

[Mechanical effects of femoral anteversion of the hip. Assessment of the validity of Pauwels' theory (author's transl)]. / Action mécanique de l'antéversion fémorale sur la hanche. Degré de validité de la théorie de Pauwels.

Continuing the study of the mechanical forces acting on the hip in the line of Pauwels work, the author makes an important criticism of this author's theory--that the system is limited to a single plane. By using a vectorial presentation and with a mathematical model corresponding to the true situation of three dimensions, he shows that anteversion puts the point of contact the femoral head in a different plane from the line of gravity and the summit of the greater trochanter. This brings into play a group of muscles other than the gluteus medius, and in particular the ilio-psoas and the flexors of the hip. Calculations based on the mathematical model show that Pauwels schema is valid for the position of equilibrium when the patient is standing on one leg, and when the gluteus medius is close to the plane of gravity. When anteversion is marked, the anterior muscles play a much greater role in the maintenance of equilibrium compared with the gluteus medius. Anteversion, in conditions of the average cervico-diaphyseal angle will have a tendency to increase pressures on the hip. If the cervico-diaphyseal angle tends to be in valgus, anteversion diminishes the stress due to the gluteus medius. In varus, the situation is opposite; anteversion increases the stress caused by the gluteus medius and thus the diminution in pressure obtained by varisation is greater when anteversion is less.