Inaccuracy of Forefoot Axial Radiographs in Determining the Coronal Plane Angle of Sesamoid Rotation in Adult Hallux Valgus Deformity: A Study Using Weightbearing Computed Tomography.

Abstract

Hallux abducto valgus is a triplane deformity with recent attention given to the significance of correcting the coronal plane component. This study explored the accuracy of the forefoot axial (FFA) study as a standard radiographic assessment method compared with weightbearing computed tomography (CT). Twelve feet with hallux abducto valgus from 12 individuals were included in this study. Three images of the affected foot were taken: FFA radiograph and weightbearing CT with the foot in maximum pronation (pronated CT) and maximum supination (supinated CT). Five investigators determined the sesamoid rotation angles (SRAs) from each of the images. The measurements from a single investigator were used to compare the SRA means from each of the image types, and those from all five investigators were used to determine reliability. The mean ± SD SRA was 22.1° ± 7.6° for pronated CT, 10.5° ± 5.0° for supinated CT, and 12.2° ± 9.4° for FFA images. The mean SRA from the pronated CT was significantly greater than the supinated CT (P < .001) and FFA (P < .005) SRAs. There were no significant differences in mean SRA between the FFA and supinated CT images (P > .99). Results indicated high reliability in measurements among investigators. Using weightbearing CT, these findings indicate that the sesamoids significantly alter their position in the coronal plane, as determined by the SRA, with changes in weightbearing subtalar joint position. Moreover, the affected foot positioning required for determining the SRA from the FFA radiograph seems to significantly underestimate the true SRA. Thus, use of this image in surgical hallux abducto valgus planning is called into question.