Rotational behaviour and morphological associations of the CT-based distal ulnar centering and eccentricity (DUCE) method in cadaveric specimens

Non-invasive assessment of distal radioulnar joint (DRUJ) stability remains challenging because CT-based measurements, such as the radioulnar ratio (RR), depend on forearm rotation and notch anatomy. The CT-based Distal Ulnar Centering and Eccentricity (DUCE) method describes DRUJ articulation relative to individual notch geometry, separating rotational translation into direction and magnitude. Thirty cadaveric upper limbs underwent cone-beam CT in pronation and supination, 11 also in neutral rotation. Centering (ulnar head centre to a notch-derived reference axis) and Eccentricity (to the deepest notch point) were compared with RR. RR varied with rotation (28.7 ± 8.5% vs. 70.8 ± 13.6%; P < 0.001) and with notch morphology (R 2 up to 0.31); no such association was detected for DUCE. Signed Centering reversed systematically (+ 3.11 vs. − 3.10 mm; P < 0.001), while its magnitude remained equivalent. Averaged across both end positions, Centering was equivalent to zero (exploratory ± 0.6 mm equivalence margin; TOST P < 0.001), placing the notch-derived axis at the centre of the rotational arc at group level, though not in individual limbs. Eccentricity did not differ with rotation. Interrater reliability was good to excellent. DUCE provides an anatomically referenced description of rotational DRUJ behaviour. Clinical studies must show whether it improves assessment of pathological instability.