The Effects of Multiplanar Limb Rotational and Translational Alignment on Sagittal Tibiofibular Overlap and its Effects on Apparent Syndesmotic Malalignment

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: Accurate radiographic assessment of syndesmotic reduction is critical in managing ankle injuries. Given limitations in tibiofibular overlap/clear space and poor availability/utilization of intraoperative computed tomography or arthroscopy, there has been an increasing reliance on sagittal tibiofibular alignment to assess syndesmotic reduction. However, the reliability of various sagittal tibiofibular alignment radiographic parameters may be influenced by limb positioning, rotational malalignment, and translational shifts, which may result in apparent syndesmotic malreduction. However, the effect of these variables has not been assessed in the current literature. This study aims to determine if internal, external rotation, or translational leg repositioning may change the tibiofibular overlap (TFO) seen in acceptable lateral views via fluoroscopy in a cadaveric model with intact syndesmotic structures. Methods: Twelve trans-knee amputated cadavers with intact syndesmotic/collateral ligaments were utilized. Each specimen was mounted in a custom-designed jig that allowed for controlled application of various degrees of internal rotation (IR), external rotation (ER), abduction, and adduction. For each tested position, fluoroscopic lateral radiographs were obtained. After obtaining a true lateral view in neutral position, lateral images were obtained for each of the experimental positions (incremental increases in IR, ER, abduction, adduction). A true lateral view was identified by utilizing the talar dome double shadow (TDDS) superimposed method. Three foot and ankle surgeons evaluated each image to determine acceptability/accuracy as a true lateral view with level of agreement assessed. Sagittal TFO was measured by anterior tibiofibular ratio (ATFR) to assess changes in sagittal tibiofibular alignment corresponding with apparent syndesmotic malreduction on images deemed a true lateral radiograph. Statistical analysis included ANOVA to assess the effect of limb positioning on TFO. Results: Sagittal TFO was significantly affected by internal and external rotation (R = -0.7792, p = 0.000138), with increasing external rotation leading to decreased overlap and internal rotation increasing overlap. ANOVA confirmed that rotation had a statistically significant effect on TFO (p = 0.000138). However, fibular displacement (anterior-posterior shift) was not significantly correlated with rotation (p = 0.2054), indicating that rotation alone does not cause substantial anterior or posterior fibular translation. Similarly, tibial plafond coverage did not show a significant correlation with rotation (p = 0.9227), further suggesting that rotation does not contribute to apparent syndesmotic malalignment. These results confirm that sagittal TFO is highly sensitive to limb positioning and should be interpreted with caution in malpositioned views, even when an acceptable lateral is obtained. Conclusion: This study highlights significant variability in sagittal TFO across different limb rotational and translational alignments resulting in apparent syndesmotic malreduction in a ligamentously intact cadaver model. Even with acceptable lateral ankle views (as deemed by consensus of three orthopaedic surgeons), substantial changes in TFO were observed, particularly with external rotation. These findings suggest that while TFO may provide useful information, it should not be solely relied upon for assessing syndesmotic reduction in the presence of subtle limb malpositioning, as improper positioning can mimic displacement. Given this variability, reliance on TFO alone may lead to diagnostic inaccuracies and apparent syndesmotic malreduction.