Bilateral Dynamic CT for Scapholunate Instability: Toward Personalized, Protocol-Standardized Kinematic Diagnosis.

BACKGROUND: Dynamic CT imaging enables three-dimensional assessment of wrist motion, is increasingly being used to diagnose scapholunate (SL) ligament injuries. However, protocol variability across institutions limits comparability and standardization. A key consideration is whether to use unilateral or bilateral scanning, since unilateral scanning often requires reference sets for diagnosis. This study evaluates whether contralateral referencing in bilateral dynamic CT scanning supports SL injury diagnosis by assessing (1) the influence of scan protocol variation; (2) similarity between wrists of healthy individuals and contralateral wrists of patients; (3) wrist motion symmetry in healthy individuals; and (4) contralateral referencing in patients with a unilateral SL injury. METHODS: This retrospective multicenter study combined dynamic CT data from three cohorts: healthy individuals scanned unilaterally, bilaterally, and patients with arthroscopically confirmed unilateral SL lesions scanned bilaterally. Scapholunate distance (SLD) at five points was automatically extracted during flexion-extension and radial-ulnar deviation and compared. RESULTS: Differences in scan protocols led to measurable offsets in SLD of 0.5 mm, particularly during radial-ulnar deviation. Contralateral healthy wrists of patients showed similar motion to that of healthy volunteers. Minimal asymmetry was found between dominant and non-dominant wrists. In patients with total SL injuries, an increased SLD up to 2.0 mm was observed in the injured wrist compared to the contralateral side. Partial SL lesions showed smaller, localized asymmetries (~0.3-0.4 mm). CONCLUSIONS: Contralateral referencing in bilateral dynamic CT scanning is both possible and justified for supporting the diagnosis of unilateral total SL injuries. This approach removes the need for reference datasets and should therefore be considered.Level of Evidence: Diagnostic study, Level III.