[Mechanical effects of femoral anteversion of the hip. Assessment of the validity of Pauwels' theory (author's transl)].

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.