Portable Dynamic Ultrasonography Versus Fluoroscopy for the Evaluation of Syndesmotic Instability: A Cadaveric Study

CATEGORY: Ankle; Trauma INTRODUCTION/PURPOSE: Syndesmotic instability, when subtle, is challenging to diagnose and often requires visualization of the syndesmosis during applied stress. The purpose of this study was to determine the association between tibiofibular clear space (TFCS) values measured with 1) a portable ultrasound (US) device and 2) fluoroscopy during applied external roation stress for the evaluation of syndesmotic instability. METHODS: Eight fresh lower leg cadaveric specimen amputated above the proximal tibiofibular joint were used in this study. Portable US device (Butterfly iQ, Butterfly Network Inc) images and fluoroscopic images taken by a mini C-arm were used to evaluate the ankle syndesmosis in the intact stage, and after sequentially sectioning of the anterior-inferior tibiofibular ligament (AITFL), interosseous ligament (IOL), and posterior-inferior tibiofibular ligament (PITFL) at 7.5Nm torque. A Pearson’s correlation was performed to investigate the correlation between the TFCS among the two modalities. A paired t-test was used to compare TFCS values measured with US or fluoroscopy. Three cadavers were measured by two independent observers to assess reliability of the measurements for each diagnostic modality and analyzed using intraclass correlation coefficients (ICC). P-values of < 0.05 were considered significant. RESULTS: The mean TFCS (+- SD mm) values measured with the US and fluoroscopy are presented in Table 1. TFCS values obtained with the US and fluoroscopy correlated (rho 0.60). Between the imaging modalities similar TFCS values were found in the intact state (difference 0.81+-1.0, p-value 0.061). Compared with fluoroscopy, the TFCS values measured using US increased significantly after sequential transection of the AITFL (0.039), IOL (p=0.004) and PITFL (p<0.001). The ICC for measuring the TFCS with US was 0.86 and 0.84 with fluoroscopy indicating excellent agreement. CONCLUSION: During application of an external rotation force to the ankle, US and fluoroscopic TFCS measurements among different stages of syndesmotic ligamentous injury correlate. However, compared with fluoroscopy, a portable US ultrasound device seems to be a more sensitive diagnostic technique to evaluate subtle syndesmotic instability.