Accuracy of radiographic measurements of fracture-induced deformity in the distal radius

Abstract

Background: Management of the distal radius fracture (DRF) is to some extent based on radiographic characterization of fracture displacement. It remains unclear, however, if the measurements used to quantify displacement are accurate.

Purpose: To quantify accuracy of two radiographic measurements: dorsal/volar tilt and fracture compression, measured indirectly as ulnar variance (UV), using radiostereometric analyses (RSA) as reference standard.

Material and methods: Twenty-one fresh frozen non-fractured human cadaveric forearms (right = 11, left = 10) were thawed and eligible for inclusion. The forearms were mounted on a custom made platform that allowed for controlled forearm rotation, and they underwent two rounds of imaging (both rounds consisted of RSA and radiographs). In round one, the non-fractured forearms were radiographed. In round two, artificial DRF´s with compression and dorsal angulation were created and imaging procedures repeated. Change in tilt and UV between the non-fractured and later fractured forearms was defined as fracture-induced deformity. Deformity was measured radiographically and additionally calculated using RSA. Bland Altman analyses were used to estimate agreement between radiographically measured, and RSA calculated, fracture-induced deformity.

Results: Our results indicated that radiographs underestimate the amount of fracture-induced deformity. Mean measured differences (bias) in dorsal tilt deformity between radiographs and RSA were -2.5° for both observers. The corresponding values for UV were -1.4 mm and -1.5 mm.

Conclusion: Quantifying fracture-induced deformity on radiographs underestimated the actual deformity when compared to RSA calculated deformity. These findings suggest that clinicians, at least in part, base fracture management and potentially corrective surgery on inaccurate measurements.

Keywords: distal radius fracture; dorsal tilt; measurements accuracy; radial inclination; ulnar variance.

Figure 1.

Forearm secured to wooden platform with K-wires through the distal portion of the forearm and the olecranon.

Figure 2.

Radiographic measurements. Ulnar variance is measured as the difference i axial length between two lines perpendicular to the longitudinal axes of the radius. The two lines are placed against the most distal points of the ulnar and radial articular surfaces, respectively. Dorsal/volar tilt of the radial articular surface is measurend as the angle between two lines, one line connecting the palmar and dorsal surfaces of the distal radius and a line perpendicular to the longitudinal axes of the radius.

Figure 3.

Bland-Altman plots displaying differences between RSA and radiographically measured fracture induced deformity for both observers. Differences are found by deducting the RSA value from the radiographically measured value. The solid black lines indicate upper and lower 95% limits of agreement, shaded blue areas depict respective confidence intervals. The dotted line represents the estimated bias, that is, the mean measured difference between RSA and radiographs; shaded green areas show respective confidence intervals. The bias line is below zero in all cases, indicating that radiographic measurements underestimated the measured values when compared to RSA.