Portable Dynamic Ultrasonography is a Useful Tool for the Evaluation of Suspect Syndesmotic Instability: A Cadaveric Study

CATEGORY: Ankle; Sports; Trauma INTRODUCTION/PURPOSE: To evaluate syndesmotic instability by measuring the tibiofibular clear space (TFCS) opening using a portable ultrasound device. In addition, we assessed the optimal amount of external rotation torque required to detect syndesmotic instability. METHODS: Eight fresh lower leg cadaveric specimen amputated above the proximal tibiofibular joint were used. Using a portable ultrasound device (Butterfly iQ, Butterfly Network Inc) the ankle syndesmosis was evaluated in the intact stage, and after sequentially sectioning of the anterior-inferior tibiofibular ligament (AITFL), interosseous ligament (IOL), and posterior-inferior tibiofibular ligament (PITFL)(Figure 1). In each ligamentous sectioning stage TFCS in millimeter (mm) was measured with ultrasound while consecutively 0N, 45N, 60N, 75N, and 90N external rotation directed torque was applied to the ankle. To evaluate which amount of torque would be sufficient to detect syndesmotic instability the delta increase of TFCS opening at different states of torque compared to the unstressed state was calculated. One-way repeated measures ANOVA was used to detect whether an increase in delta-TFCS opening could be detected between the intact state and consecutive syndesmotic ligament transection stages. Correction for multiple comparisons was performed using the Bonferroni-Holm correction. RESULTS: Under all torque-loading conditions TFCS (mean+-SDmm) opening increased as additional syndesmosis ligaments were transected (p-values<0.001). With all ligaments intact an increase of TFCS opening was detected during torque increment, ranging from 4.50+-1.2mm at 0N to 5.7+-1.00mm at 90N. After AITFL transection this amount increased from 5.2+-1.4mm at 0N to 6.5+-1.8mm at 90N. After AITFL+IOL transaction from 6.2+-1.3mm at 0N to 10.6+-6.2mm increase at 90N, and after AITFL+IOL+PITFL transection the TFCS opening increased from 6.8+-1.2mm at 0N to 11.1+-2.8mm at 90N. Significant difference from intact was seen after transection of the IOL, already from the unstressed (0N) state on (difference 3.0+-1.4mm, p-value 0.036). Additionally, the AITF+IOL could also be differentiated from AITFL transection stage at 45N with a difference in TFCS opening of 2.06+-1.2mm (p-value 0.006). CONCLUSION: Portable dynamic ultrasonography is a useful tool to evaluate suspect syndesmotic instability. TFCS opening increased as additional ligaments of the syndesmosis were transected and application of 45N torque seems to be sufficient to detect syndesmotic instability.