[The normal and prosthetic hip. A comparison of different surfaces].

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.