Application of external torque enhances the detection of subtle syndesmotic ankle instability in a weight-bearing CT

PurposeAcute syndesmotic ankle injuries continue to impose a diagnostic dilemma and it remains unclear whether weightbearing and/or external rotation should be added during the imaging process. Therefore, the aim of this study was to assess if combined weightbearing and external rotation increases the diagnostic sensitivity of syndesmotic ankle instability using weightbearing CT (WBCT) imaging, compared to isolated weightbearing.MethodsIn this retrospective study, patients with an acute syndesmotic ankle injury were analysed using a WBCT (N = 21; Age = 31.6 & PLUSMN; 14.1 years old). Inclusion criteria were an MRI confirmed syndesmotic ligament injury imaged by a WBCT of the ankle during weightbearing and combined weightbearing-external rotation. Exclusion criteria consisted of fracture associated syndesmotic injuries. Three-dimensional (3D) models were generated from the CT slices. Tibiofibular displacement and talar rotation were quantified using automated 3D measurements (anterior tibiofibular distance (ATFD), Alpha angle, posterior Tibiofibular distance (PTFD) and Talar rotation (TR) angle in comparison to the contralateral non-injured ankle.ResultsThe difference in neutral-stressed Alpha angle and ATFD showed a significant difference between patients with a syndesmotic ankle lesion and contralateral control (P = 0.046 and P = 0.039, respectively). The difference in neutral-stressed PTFD and TR angle did not show a significant difference between patients with a syndesmotic ankle lesion and healthy ankles (n.s.).ConclusionApplication of combined weightbearing-external rotation reveals an increased ATFD in patients with syndesmotic ligament injuries. This study provides the first insights based on 3D measurements to support the potential relevance of applying external rotation during WBCT imaging. In clinical practice, this could enhance the current diagnostic accuracy of subtle syndesmotic instability in a non-invasive manner. However, to what extent certain displacement patterns require operative treatment strategies has yet to be determined in future studies.