[Calculation of the true angle in malposition of the skeletal system using electronic data processing. Retrospective study of 53 axis deviations in healed femoral fractures].

Under standard conditions deformations in the skeletal system are diagnosed by two X-ray photographs whose planes of projection form a right angle. The degree of deviation from the axis is measured directly on the X-ray photograph with a protractor. The analysis of the position of the axis of a tabular bone is carried out by determining the varus/valgus or ante/recurvation deformities resp. in the a.-p. and lateral rays. The degree of deformation is expressed through the supplementary angle. We asked ourselves whether a diagnostic procedure using X-rays taken in two planes is suitable for substantiating the evidence of a deformation of the axis. Example: If a fracture of the lower leg shows a varus deformity of 20 degrees in the a.-p. and a normal position of the axis in the lateral photograph, the actual angle is 20 degrees. This situation is an expection in that most cases the defect of the axis is a so-called combined defect (dislocation from the axis in both planes). In this case it can maintained that the measurable angle of deviation in the a. -p. and lateral X-ray photographs is smaller than the angle that is actually included by both fragments. We call this angle true angle. If you think of a fractured tubular bone as a cylinder it can be shown in a diagram that its deformation can only occur in one plane (Figure 1). Only from the perspective of a ray falling vertically on the curve k we would be able to determine the true angle directly from the photograph with a protractor.(ABSTRACT TRUNCATED AT 250 WORDS)