Using Dynamic Portable Ultrasonography for the Diagnosis of Lateral Ankle Instability

Abstract

Category: Sports; Ankle Introduction/Purpose: Destabilizing injuries to the lateral ligament have relied on physical examination and radiographic stress test for diagnosis, with a focus on anterior translation and tilting of the talus relative to the tibial bone. Portable ultrasonography (PUS) has increasingly been used in the clinical setting, allowing dynamic and non-invasive evaluation. The primary aim of this study was to assess the anterior translation and tilting of the talus with PUS in various stages of lateral ankle ligamentous injury. Secondary, we compared the instability values measured with PUS with those measured on fluoroscopy. Third, we aimed to determine the optimal cutoff values of the PUS that distinguish stable from unstable state. Methods: 8 fresh-frozen cadaveric specimens underwent PUS and fluoroscopic evaluation for lateral ankle stability. The assessment was done with all ligaments intact and later with sequential transection of the anterior-talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior-talofibular ligament (PTFL). In all scenarios, 2 loading conditions were considered; 1) Performing the anterior drawer test under 50N and 80N of force, anterior translation was measured with PUS and fluoroscopy; 2) Performing the talar tilt test under 1.7Nm of torque, the lateral clear space (the distance between the fibular tip and lateral process of the talus) was measured with PUS, and the talar tilt angle was measured with fluoroscopy (Figure1). Pearson’s and Spearman’s rank correlation was used to determine the correlation. Youden’s J statistic was used to determine the optimal cutoff values for the PUS to distinguish intact or ATFL injury versus ATFL-CFL or ATFL-CFL-PTFL injuries under various loading conditions. Results: Strong positive correlations were found between PUS and fluoroscopic measurements (Pearson correlation:r=0.78- 0.85). PUS and fluoroscopic measurements during anterior translation and talar tilt test increased as additional ligaments were transected (Spearman’s rank correlation: anterior translation; r=0.74, p =0.8). The optimal PUS cutoff values for distinguishing intact or ATFL injury from ATFL-CFL or ATFL-CFL-PTFL injuries were >=3.40mm (sensitivity 87.5%, specificity 81.25%) and >=4.78mm (sensitivity 87.5%, specificity 81.25%) of anterior talar translation under 50N and 80N of force respectively, as well as >=3.09mm (sensitivity 75%, specificity 93.75%) of the lateral clear space under 1.7Nm of torque. Conclusion: Portable ultrasonography for the diagnosis of lateral ankle instability was strongly correlated with fluoroscopic findings, and thus, can be a valuable diagnostic tool at the point of care. We recommend future in vivo research to investigate the accuracy of this new ultrasound application in a clinical setting.