Objective/Hypothesis: The objective of this study is to radiographically assess scaphoid dorsal translation in patients with scapholunate instability. We hypothesized that (1) there is a significant difference in scaphoid dorsal translation in lateral plain radiographs in patients with scapholunate instability when compared with controls, (2) magnetic resonance imaging (MRI) will correlate with radiographic dorsal scaphoid translation measurements in patients with scapholunate instability. Materials and Methods: This was a retrospective case-controlled study of 24 patients with scapholunate ligament (SLIL) injury. Five carpal alignment indices were assessed on radiographs: scapholunate gap in clenched pencil view, scapholunate angle, radiolunate angle, scaphoradial angle, and scaphoid dorsal translation. Scaphoid dorsal translation was defined as the distance (mm) between the centers of the best fit circles for (1) the scaphoid proximal articular surface and (2) the scaphoid fossa, using the external palmar cortex of the radius as the orientation axis. Two examiners measured these radiographic indices, and interobserver reliabilities were determined and expressed as intraclass correlation coefficient (ICC). For convergent validity testing, the correlation between the radiograph dorsal translation and dorsal translation in MRI was assessed. Independent sample t test was used to compare the alignment indices between cases and controls. Results: Significant differences were found between the cohorts in the following measurements: scapholunate angle (P = .001), scaphoradial angle (P = .04), and scaphoid dorsal translation (mm) (P ≤ .001). However, no difference was found between groups for the radiolunate angle measurement (P = .665). Interobserver reliability for scaphoid dorsal translation in radiographs and MRI was excellent with ICCs of .82 and .92, respectively (95% confidence interval [CI], 0.565-0.925, and 0.111-0.914, respectively). The correlation between radiographs and MRI scaphoid dorsal translation was moderate for reader 1 with ICCs of .505 (95% CI, 0.021-0.161) and excellent for reader 2 with ICCs of .908 (95% CI, 0.135-0.968). Conclusions: This study introduces a new radiographic parameter, scaphoid dorsal translation, in patients with diagnoses of scapholunate instability. This parameter is, theoretically, the most correlative to symptoms as it shows whether the joint is statically subluxated. Radiographic scaphoid dorsal translation is correlated with MRI findings and might represent a lower cost option for early detection of the radioscaphoid joint eccentric wear seen in some stages of scapholunate instability.
