[Radiology and measurement in adolescent slipped capital femoral epiphysis].
Two X-rays taken in two planes perpendicular to each other secure the early diagnosis of adolescent slipped capital femoral epiphysis (SCFE). In imminent SCFE, two radiographic features are considered the most important signs: the broadening and the irregular demarcation of the upper femoral epiphyseal plate. In the beginning of SCFE, the process of dislocation is much better visible in the second radiographic plane (the lateral tangent of the femoral neck builds a smaller secant of the lateral femoral head). In chronic SCFE, the aforementioned radiographic signs including the epiphyseal dislocation are more marked. An additional feature can be various deformities of the femoral neck and duplicate contours of the medial demarcation of the femoral neck. In acute SCFE, there is a complete disruption of continuity between the metaphysis and epiphysis. Beside the marked gap in the epiphyseal plate, there is a severe dislocation between the femoral neck and the epiphysis. There are also partly patchy, partly cystic changes in the metaphyseal part of the femoral neck. The so-called acute on chronic slip, a sudden slip of the upper epiphysis after prolonged chronic slipping, is considered a specific case of SCFE. The long-term result of treated as well as untreated SCFE can be the gradual increase of coxarthrosis, which is typically more marked in the medial direction of the joint. The direction and the degree of the epiphyseal slip play an important role in the development of "epiphyseal" coxarthrosis. The planning of corrective operations as well as the quantitative evaluation of the prearthrotic deformity require the conversion of angles of dislocation that are projected on X-rays into anatomically correct angles. This conversion is done with tables that were created with the aid of computers and requires that the positioning of the femur for taking the X-rays is always done under standardized conditions.Mostly, in minor dislocations in the usual direction (medially and dorsally), the difference between the projected and the real angles is relatively small. Therefore, in these cases of SCFE it might not be necessary for practical and operative needs to convert these angles into real angles. However, this simplification is only then acceptable if the prescribed positioning of the femur for taking the X-rays is strictly adhered to so that additional errors of projection are excluded.