Resemblance of Valgus Malalignment of the Distal Tibia in 15-Degree Craniocaudal Radiographs

Purpose. To describe and quantify a radiological phenomenon where the distal tibial plafond appears in valgus malalignment in intra-operative fluoroscopy owing to 15° craniocaudal angulation of the X-ray beam. Methods. The lateral distal tibial angle (LDTA) of 14 male and 9 female skeletally mature patients was measured by a single reviewer using 2 types of anteroposterior radiographs, in which the X-ray beam was projected at 0° (orthogonal to the ankle) and then at 15° (in a craniocaudal direction). The LDTA was the angle between the long axis of the tibia and a line drawn across the most radiodense part of the tibial plafond. The paired t-test was used to compare the LDTA of the 2 measurements. Results. The mean LDTA on the 0° orthogonal radiographs was 89° (range, 87°-92°), whereas the mean LDTA on the 15° craniocaudal radiographs was 79° (range, 77°–81°). The mean difference was 10° (range, 9°-12°; p