Portable Dynamic Ultrasonography is a Useful Tool for the Evaluation of Suspected Syndesmotic Instability

CATEGORY: Ankle INTRODUCTION/PURPOSE: Portable ultrasonography (P-US) is increasingly used to diagnose syndesmotic instability. The aim of this study was to evaluate syndesmotic instability by measuring the distal tibiofibular clear space (TFCS) in a cadaveric model using P- US with progressive stages of syndesmotic ligamentous transection. METHODS: Ten fresh lower leg cadaveric specimens amputated above the proximal tibiofibular joint were used. Using P-US, the TFCS was evaluated in the intact stage and after progressive sectioning of the 1) anterior-inferior tibiofibular ligament (AITFL), 2) interosseous ligament (IOL), and 3) posterior-inferior tibiofibular ligament (PITFL). The TFCS was measured in both the unstressed (0 Nm) state and with 4.5 Nm, 6.0 Nm, 7.5 Nm, and 9.0 Nm of external rotation stress at each stage of ligamentous transection stage using both P-US and fluoroscopy. RESULTS: When assessed with P-US, partial syndesmotic injury encompassing the AITFL and IOL resulted in significant TFCS widening at 4.5 Nm of external rotation torque when compared to intact state with a TFCS-opening of 2.6 +- 2 mm, p = 0.01. In contrast, no significant differences in TFCS were detected using fluoroscopy. Only a moderate correlation was found between P- US and fluoroscopy. CONCLUSION: P-US is much more sensitive than fluoroscopy in diagnosing syndesmotic instability during external rotation stress examination. Extrapolated to the clinical setting, 4.5 Nm of force can be used when comparing to the stressed, uninjured side, and may be better tolerated by patients than higher torque values. When using P-US, a TFCS-opening of 2.6 mm is likely to correlate with syndesmotic instability. While absolute threshold values may vary between individuals, the ready availability of the contralateral, uninjured side overcomes this constraint.