Diagnostic Accuracy of Comparative Computed Tomography with Stress Maneuvers for Diagnosing Isolated Syndesmotic Instability in an Acute Ankle Sprain
Authors: Rodrigues João C. , Godoy-Santos Alexandre L. , Prado Marcelo P. , Alloza José Felipe Marion , Masagao Renato do Amaral , Rosemberg Laercio , Santos Durval D. , Castro Adham , Demange Marco K. 
Published: March 2021

Category: Ankle; Sports; Trauma Introduction/Purpose: Although there are several imaging options for diagnosing the syndesmotic injury, a fundamental question that guides treatment remains unanswered. Syndesmotic instability is still challenging to diagnose correctly, and syndesmotic disruption and true syndesmotic instability should be differentiated. Currently, imaging tests quickly diagnose severe syndesmotic instability but have difficulty in diagnosing mild and moderate cases. Recently, weight-bearing CT (WB-CT) has emerged as a new modality for the examination of syndesmosis; however, studies have shown that WB-CT is not superior to conventional computed tomography (CT), and axial loading has no benefit for the diagnosis of instability. This study aims to investigate which index test between a CT in a neutral position (CTNP) and a new CT test with stress maneuvers (CTSM) can more accurately diagnose syndesmotic instability. Methods: This diagnostic accuracy-test study consecutively selected individuals older than 18 years with an orthopedic evaluation suspected for acute syndesmotic injury. The accuracy of the index tests (CTNP and CTSM) were examined using magnetic resonance imaging (MRI) as the reference standard. The external rotation and dorsiflexion of the ankle guided the stress maneuvers. Comparison measurements between the injured syndesmosis and the uninjured contralateral side of the same individual investigated syndesmotic instability regarding the translational and rotational relationship between the fibula and tibia. Sensitivity, specificity, positive likelihood ratio (+LR), and negative likelihood ratio (-LR) value analyzed the diagnostic accuracies of the index tests. Results:: The population included in this study consisted of 64 patients (34 men, 30 women; age range 18-69 years; mean age 35 years). The CTNP exam showed a sensitivity of 18.7% (95% CI, 8 to 35), a specificity of 97% (95% CI, 85 to 99), a +LR of 6.3 (95% CI, 0.8 to 50), and a -LR of 0.8 (95% CI, 0.7 to 0.9). The CTSM exam showed a sensitivity of 91% (95% CI, 76 to 99), a specificity of 94% (95% CI, 80 to 98), a +LR of 15.4 (95% CI, 4 to 59), and a -LR of 0.09 (95% CI, 0.03 to 0.28). The CTSM reflected superior accuracy because the +LR was higher than that of the CTNP, and the confidence interval (CI) for the +LR does not contain 1. Conclusion:: Nevertheless, CTNP is used routinely, this study showed that the test was insufficient for the correct diagnosis, as it presented low sensitivity result. A CTNP with a normal result was not able to exclude syndesmotic instability. The use of the stress maneuver with external rotation and dorsiflexion was a decisive factor for the correct diagnosis, considering that the CTSM exhibited high sensitivity and captured a significantly greater number of true positive cases than the CTNP. This study confirmed CTSM as an accurate method for diagnosing syndesmotic instability and opened a new approach to investigate mild and moderate challenging cases.