Measurement of Radiological Parameters of Distal Radius Fracture Using the Ulnar Axis Compared with the Radial Axis

Background: The long axis of the radius is a standard reference for measuring radiological parameters in distal radius fractures. However, in patients with severe comminution and anatomical variation with distal radius bowing, it is challenging to assess using the long axis of the radius. The long axis of the ulna can be used as an alternative reference. The aim of this study is to assess the reliability and level of agreement using the long axis of the ulna as an alternative reference in comparison to the long axis of the radius. Methods: Posteroanterior (PA) radiography of the wrist in patients with acute distal radius fractures was evaluated in two rounds by four observers. Radial height, radial inclination and ulnar variance were measured using radial and ulnar long axis as references. The intraobserver and interobserver reliability of the measurements with two reference axes was assessed using intraclass correlation coefficient (ICC). The level of agreement was determined using the Bland-Altman plot. Results: In total, 59 patients who underwent PA radiography of the wrist were included in this study. All parameters exhibited good agreement between the two methods, with a mean difference of nearly zero (radial height = -0.03 mm, radial inclination = -0.14° and ulnar variance = 0.03 mm). The limits of agreement in radial height (-2.87, 2.82 mm) and ulnar variance (-0.81, 0.87 mm) were narrow. However, for the radial inclination, it was wider (-6.21, 5.94°). Intraobserver reliability between the long axis of radius and ulna (ICC = 0.85-0.99 and 0.84-0.98, respectively) was good to excellent. The interobserver reliability of each parameter was excellent (ICC = 0.94-0.97). Conclusions: The ulnar long axis can be used as an alternative reference for measuring radial height, radial inclination and ulnar variance in PA radiography of the wrist in acute distal radius fracture, particularly if the radial long axis is distorted. Level of Evidence: Level III (Diagnostic).