Measuring external rotation of the fibula and fibular length in bilateral CT scans: how reliable is this method?

Abstract

Objective. During ankle fracture surgery, goals include accurate reduction and fixation of the tibiofibular joint and fibular length. Bilateral postoperative computed tomography (CT) can be performed to assess syndesmotic reduction, the talar dome angle and fibular length.. The study aim is to compare side-to-side differences of the fibular rotation and fibular length using bilateral CT’s of uninjured ankles. Methods. We included patients with bilateral CT scans of uninjured ankles and measured external rotation using the Nault talar dome method and fibular length using the coronal method of Prior et al. The average, difference, and ratio (injured side/healthy side) and inter-observer variability were calculated. Results. There were 83 patients included (166 ankles, mean age 47 years, 77.1% male). A random set of 66 ankles (33 CT scans) were used to measure inter-observer variability. The mean degrees of external rotation ranged from 6.6 to 7.7, mean difference from 1.4 to 3.4 degrees, mean ratio from 1.1 to 1.5, inter-observer variability from 0.27 to 0.65. For fibular length, the mean ranged from 24.6 to 25.8 mm, mean difference in fibular length ranged from 0.5 to 2.1 mm, mean ratio ranged from 1.0 to 1.1 mm and inter-observer variability ranged from 0.45 to 0.73. Conclusion. Using bilateral ankle CTs, mean differences in fibular rotation using the Nault talar dome method were 1.4 to 3.4 degrees. The distal fibular length had a mean difference between both sides of 0.5 to 2.1mm. Even though the ICC’s were low, the inter-leg differences between patients were small, making them useful for clinical practice. Level of evidence. Diagnostic level III. See Instructions for Authors for a complete description of levels of evidence.