Importance de la position du grand trochanter.

: The position of the greater trochanter influences the mechanical stress of the hip joint, the extent of contraction of the gluteus medius and minimus muscles, and the mechanical stress of the femoral neck. A normal neck-shaft angle appears to achieve a compromise between a maximum lever arm of the abductor muscles and a maximum possibility of contraction. For the same length of the femoral neck, in a varus hip the articular pressure is lower and the bending stress of the femoral neck is greater than in a normal hip; in a valgus hip the articular pressure is higher and the bending stress of the femoral neck is less. In exaggerated anteversion of the femoral neck the articular pressure is greater than normal. An appropriate derotation has the same effects as a varus osteotomy. However, these rules apply only to hips of approximately normal configuration. A very high position of the greater trochanter (exaggerated coxa vara) can result in shortening of the lever arm of the abductor muscles and, by changing the direction of these muscles, in a decrease in the articular weight-bearing surface. Moreover the extent of contraction of the abductor muscles is then very small. In such instances, lowering the greater trochanter reduces the mechanical stress of the joint and improves the extent of contraction of the muscles. Too much distal displacement of the greater trochanter increases the articular pressure. Lateral displacement of the greater trochanter decreases the pressure in the joint. In certain hips very deformed by hypertrophic osteoarthritis, however, an appropriate valgus osteotomy, although lowering the greater trochanter, considerably enlarges the articular weight-bearing surface and can lengthen the lever arm of the abductor muscles, thus reducing articular pressure sufficiently to permit very significant regeneration of the joint tissues.