Dorsal Tilt of the Distal Radius Fracture Changes With Forearm Rotation When Measured on Radiographs

Abstract

Purpose: This study examined the impact of pronation and supination on the reliability of the radiographically measured values of dorsal tilt, radial inclination (RI), and ulnar variance (UV) in cadaveric forearms with artificially created distal radius fractures.

Methods: We prepared 21 human cadaveric forearms (11 right and 10 left) for radiostereometric analysis (RSA) by insertion of tantalum markers. Distal radius fractures were created midway between the marker segments. Radiographs and RSA images were taken at different degrees of supination and pronation. The precise degree of forearm rotation was calculated using RSA software. Two observers (H.B.T. and T.T.) independently measured tilt, RI, and UV on all radiographs in a blinded and randomized fashion. Univariate linear regression analyses were used to determine the relationship between forearm rotation and the measured radiographic values.

Results: The radiographically measured value of tilt was significantly impacted by forearm rotation. Supinating or pronating the forearm by 10° decreased and increased, respectively, the radiographic value of dorsal tilt by approximately 3°.

Conclusions: This study showed that the positioning of the fractured forearm during the radiographic procedure significantly impacted subsequent radiographic measurements of tilt. Dorsal tilt measurements increased (ie, fracture displacement measured more dorsal) with pronation and decreased (ie, fracture displacement measured more toward neutral, with less dorsal tilt) with supination of the forearm. However, measurements of RI (p = 0.12 and p = 0.55 for observer 1 and 2) and UV (p = 0.34 and p = 0.17, observer 1 and 2) were not significantly impacted by rotation.

Clinical relevance: Treatment of a distal radius fracture is, at least to some extent, based on radiographic quantification of fracture deformity. Therefore, unreliable measurements may adversely influence clinical decision making.

Keywords: Accuracy; Distal radius fracture; Dorsal tilt; RSA; Radiostereometric analyses.

Figure 1

Lateral wrist radiograph. Rotation around the y axis is supination (−) and pronation (+) for right arms. Signed values are reverted for left arms.

Figure 2

Line A indicates the longitudinal axis of the radius in each panel. Line B is perpendicular to line A, drawn from the distal ulnar palmar corner of the radial articular surface. Line C connects the distal ulnar palmar corner of the radial articular surface to the distal part of the radial styloid tip. Line D is parallel to line B. It is positioned up against the most distal point of the articular surface of the ulna. Line E is perpendicular to line A and can be drawn at a convenient level. Line F connects the distal palmar and dorsal margins of the radial articular surface. Tilt is defined as the angulation of the distal radial articular surface in the sagittal plane. It is measured as the angle between lines E and F. Radial inclination is defined as the angulation of the distal radial articular surface in the coronal plane. It is expressed as the angle between lines B and C. Ulnar variance is defined as the length of the ulna relative to the radius. It is quantified as the distance between lines B and D.

Figure 3

Scatter plots depicting point clouds forming around the regression lines for tilt measurements.

Figure 4

Bland-Altman inter-rater plots with 95% LoA including all measurements (n = 119; left column) and reference image measurements isolated (n = 17; right column). The solid black lines represent upper and lower LoA, with the shaded blue areas depicting the 95% CIs. The dotted black lines signify the mean measured difference between observers, and the shaded green areas depict the 95% CIs.

Figure 5

Bland-Altman plots depicting intra-rater agreement (n = 61; images) for observer 1 and observer 2. The solid black lines represent upper and lower LoA, with the shaded blue areas depicting the 95% CIs. The dotted black lines signify the mean measured difference between the first and second measurements, and the shaded green areas illustrate the respective 95% CIs.