Three-dimensional analysis of the skeleton of the lower extremities with 3D-precision radiography

Abstract

A tool is presented to assess the lower extremities using linear and angular measurements under full weight-bearing in three dimensions. While the patient is standing on both legs in a frame representing a calibrated three-dimensional (3D) space, standard radiographs of the hips (anteroposterior view, AP) as well as of the knees (AP and lateral views) are taken. The coordinates for localisation of the malleoli are determined clinically in respect to the coordinate system of the 3D space. Characteristic landmarks are digitized on the calibrated radiographic films, and the so determined coordinates of the malleoli are fed into the computer together with the femoral anteversion, which is ascertained from an additional Dunn-Rippstein II view. All angles of the lower extremities in the frontal or sagittal planes as well as torsions are measured with an error of less than ± 5° and the lengths, with an error of less than 5 mm. The data are presented in a stick figure diagram and listed in a table. With this device, it is possible to determine simultaneously the angular values and bone lengths under full weight-bearing. The method has proved its value for planning corrective surgery of complex bony deformities of the lower extremities. An accuracy evaluation is reported which includes intra- and interobserver reliability of results.