The Effects of Syndesmotic Malalignment on Radiographic Sagittal Tibiotalar Alignment: Is Anterior/Posterior Talar Subluxation a Reliable Indicator of Syndesmotic Malreduction?

Research Type: Level 5 - Case report, Expert opinion, Personal observation Introduction/Purpose: Achieving accurate syndesmotic reduction is essential for outcomes. Traditional parameters such as tibiofibular overlap/clear space have demonstrated inconsistent reliability. Sagittal tibiofibular overlap has increased in popularity but may be effected by rotation. While intraoperative CT scan/arthroscopy provide enhanced accuracy, their invasiveness and limited availability highlight the need for a practical, fluoroscopy-based intraoperative tool. Talar subluxation following syndesmotic fixation is a commonly seen phenomena and may suggest syndesmotic malalignment. Despite this, no studies have yet elucidated the specific modes of malreduction and their impact on sagittal plane talar displacement. The purpose of this cadaveric study was to investigate whether anterior/posterior talar subluxation can reliably indicate syndesmosis malreduction and to identify which simulated malreduction conditions are most closely associated with this radiographic finding. Methods: Twelve fresh frozen cadaveric trans-knee amputated specimens were subjected to six controlled fibular malreduction conditions: · Anterior displacement (5 mm) +/- overcompression · Posterior displacement (5 mm) +/-overcompression · External rotation (15°) +/- overcompression Each condition was tested with and without overcompression using a custom-designed displacement block. After the initial trials, each malreduction condition was repeated after complete transection of the deltoid ligament. For each malalignment condition, perfect lateral fluoroscopic images and weightbearing computed tomography (WBCT) scans were obtained. Tibiotalar Distance (TTD) was measured across both imaging modalities to assess anterior/posterior talar subluxation. Kruskal-Wallis tests were conducted to assess significant factors, and paired Wilcoxon rank-sum tests were used to evaluate potential outliers. Results: Fluoroscopic Tibiotalar Distance (TTD) measurements demonstrated variable responses to syndesmotic malalignment, with notable trends despite statistical variability. Fluoroscopic analysis identified significant cadaver variability (p < 10⁻⁹, Kruskal-Wallis), but no definitive association was found between TTD and specific malalignment conditions (p = 0.57). However, a significant effect was observed for translation and rotation (p = 0.04), suggesting a possible correlation. However, external rotation (15°) demonstrated a significant increase in TTD (p = 0.05), highlighting a potential relationship with sagittal plane displacement. WBCT findings mirrored fluoroscopic trends, confirming that TTD variations were observed across malalignment conditions, although without reaching statistical significance (p > 0.2). Importantly, WBCT emphasized the influence of patient-to-patient variability, suggesting that TTD’s utility may depend on individual anatomical differences. Conclusion: Talar subluxation following syndesmotic fixation is a commonly seen phenomena and may suggest syndesmotic malalignment. In our investigation fluoroscopic and WBCT findings demonstrated trends of increased TTD in these malalignment conditions demonstrating talar subluxation is evident with syndesmotic malreduction states. While these displacement patterns suggest some utility of TTD as an adjunctive marker in intraoperative syndesmotic assessment, the modest trends observed highlight the need for additional means of assessment. Future work should focus on developing more precise radiographic parameters and integrating complementary assessment techniques to enhance the accuracy of syndesmotic reduction evaluation.