Computed tomography (CT) has been used to understand the deformity of scaphoid nonunion, but no standard protocol for the reformatting of scaphoid CT imaging exists. The purpose of this study was to compare the reliability of measurements of the deformity of scaphoid waist nonunion between CT-scans reformatted in line with the scaphoid long axis and CT-scans reformatted in line with the wrist axis.

We hypothesized that CT-scan which was reformatted along the scaphoid long axis is more reliable for understanding the deformity of scaphoid waist nonunion.

CT-scans of 28 wrists with a scaphoid waist nonunion were reformatted along both the long axis of the scaphoid and of the wrist. For each set of CT-scans, the nonunion gap in axial, coronal and sagittal series, the intrascaphoid angle, and the height to length ratio were measured. All scans were reviewed twice by three observers and intraclass correlation coefficients (ICCs) for inter- and intraobserver reliability were assessed.

For the measurement of nonunion gaps and height to length ratio, neither inter- nor intraobserver reliability showed significant differences between the two reformatting scans. However, for the intrascaphoid angle, both inter- (ICC: 0.202 vs. 0.419, p<0.001) and intraobserver (ICC: 0.614 vs. 0.790, p<0.001) reliability were significantly higher on scaphoid axis CT-scan than on wrist axis CT-scan.

In the assessment of deformity in patients with scaphoid waist nonunion, scaphoid axis reformatting CT-scans showed superior reliability for the measurement of intrascaphoid angle than did wrist axis reformatting CT-scans. Although there are several limitations for the correct assessment of all three-dimensional deformity, scaphoid axis reformatting CT-scans could help in assessing the extent of humpback deformity in patients with scaphoid waist nonunion.

IV; diagnostic.