Introduction/Purpose: Accurate diagnosis of syndesmotic disruption remains a challenge, as conventional radiographs and CT demonstrate limited sensitivity, detecting subtle instability in only up to 67% of cases. Missed injuries can lead to chronic pain, loss of function, and post-traumatic arthritis, highlighting the need for more reliable diagnostic methods. Weightbearing CT (WBCT) enables three-dimensional assessment of the ankle under physiologic load, with the potential to quantify fibular and talar displacement relative to the tibia. However, objective criteria for classifying syndesmotic injury on WBCT have not been established. This study aimed to evaluate whether referencing the contralateral ankle as an internal control during standard-of-care WBCT evaluation can improve diagnostic accuracy by quantifying translational and rotational differences of the fibula and talus relative to the tibia.
Methods: This IRB-approved study evaluated 36 fresh-frozen through-the-knee cadaveric specimens (22 male, 14 female), each scanned bilaterally with WBCT under a 356N axial load. Scans were obtained in the intact state and again following sectioning of all syndesmotic ligaments (AITFL, interosseous ligament, distal 3 cm of interosseous membrane, PITFL) while preserving the deltoid complex, lateral ligaments, and superior peroneal retinaculum. Three-dimensional bone models were analyzed using an automated tibial coordinate system pipeline with point-cloud registration to generate fibular and talar translations and rotations relative to the tibia. Six kinematic parameters were quantified, comprising mediolateral, anteroposterior, and superoinferior translations, together with rotations about the same axes. As these parameters are correlated and do not occur in isolation, dimensionality reduction was performed with principal component analysis prior to predictive modeling. Matched-pair conditional logistic regression then compared each specimen’s intact and destabilized ankles, and model discrimination was assessed using receiver operating characteristic analysis.
Results: Syndesmotic disruption produced distinct displacement patterns compared with controls (Figure 1). The fibula showed the most consistent differences, with greater lateral translation (0.51 vs 0.16 mm, p=0.007), posterior translation (–0.86 vs 0.01 mm, p<0.001), inferior displacement (–0.44 vs –0.12 mm, p=0.015), and external rotation (2.42° vs 0.03°, p<0.001). These changes defined a injury pattern of fibular posterolateral translation with external rotation, consistent with rotational instability. Principal component analysis explained 83.2% of total variance across five components. A matched-pair logistic regression model classified injured versus intact ankles with high accuracy (AUC 0.889, p<0.0001). The primary displacement component was strongly associated with injury (OR 0.05, 95% CI 0.003–0.75, p=0.030), indicating that displacement in the injury direction increased odds nearly 20-fold.
Conclusion: This study demonstrates that computational analysis of contralateral ankle differences can accurately predict syndesmotic injury with high discrimination in a cadaveric model. Characteristic displacement patterns were identified, with fibular lateral–posterior translation and external rotation emerging as key discriminators of disruption. Automated analysis within clinical WBCT platforms could provide orthopedic surgeons with immediate, objective assessment of syndesmotic integrity during routine imaging. Quantitative thresholds derived from these measurements may also guide surgeons with specific anatomical targets for reduction during fixation. Future studies should validate these findings in patient populations and establish optimal diagnostic thresholds for clinical use.
