Artificial intelligence-based diagnosis of hallux valgus interphalangeus using anteroposterior foot radiographs

Figure 4 Automated determination of proximal and distal phalanx bone axes. A: Input X-ray and post-processed bone segmentation results; B: The bones are approximated using ellipses, from which the ellipse axes are extracted. The axes within the bones are indicated by pink lines, with their proportions determined experimentally: (1) 0.25: 0.25 for the proximal phalanx; and (2) 0.40: 0.25 for the distal phalanx; C: The central points of the ellipse subaxes are represented by light blue lines; D: Lines perpendicular to the ellipse subaxes are drawn at their endpoints and illustrated in purple; E: The midpoints of these purple lines are marked with light blue dots, serving as key points for defining the bone axis, which is depicted as blue and red lines; F: The final axes, shown as yellow lines, for interphalangeal angle estimation are computed as a weighted average of the ellipse axis and the bone axis. IPA: Interphalangeal angle.