  The aim of this study was to develop a new method for generating reproducible
3D measurements for the quantification of the distal radioulnar joint
morphology. We hypothesized that automated 3D measurement of the ulnar variance
and the sigmoid notch angle are comparable to those of the gold standard, while
overcoming some of the drawbacks of conventional 2D measurements. Radiological
data of healthy forearm bones of 53 adult subjects were included in the study.
Automated measurements for the assessment of the sigmoid-notch morphology based
on 3D landmarks were developed incorporating the subject-specific estimation of
the cartilage surface orientation. A common anatomical reference was defined
among the different imaging modalities and a comparison between the sigmoid
notch angle and UV measurements was performed in radiographs, CT scans and 3D
models. Finally, the developed UV measurements in 3D were compared to the
method by radiographs in an experimental setup with 3D printed bone models. The
proposed automated 3D analysis of notch subtype showed a significantly larger
notch radius for negative notch angle compared to positive sigmoid notch angle
subjects. Similar UV measurements were obtained in healthy joint morphologies
with a high correlation between the radiographs and 3D measurements, for
sigmoid notch angle and UV . In the experimental setup with a modified radial
inclination, the UV was on average 1.13 mm larger in the radiographs compared
to the 3D measurements, and 1.30 mm larger in the cases with a modified palmar
tilt. The developed 3D measurements allowed to reliably quantify differences in
the sigmoid notch subtypes.
