[Radiologic evaluation of the rotation center of the hip].

We studied 98 normal hips in 54 patients in order to assess precise settlement of the theorical hip center using the U landmark as reference i.e. determine A distance (vertical settlement) and C distance (horizontal settlement)) A being the vertical distance between U landmark and the femoral head center, C the horizontal distance between U landmark and the femoral head center. We found two indexes (A/E = 0.2 and C/D = 0.3) which allowed us to fix that center in vertical (A/E) and in horizontal (C/D) direction even in case of bilateral hip dysplasia, and which can be used either in pre-operative planning or in post-operative evaluation. D being the horizontal distance between the U landmarks, and E the vertical one between the U landmark and the sacroiliac joint.