Intraoperative Syndesmotic Instability Test

Abstract

Category: Ankle, Trauma Introduction/Purpose: Precise diagnosis of distal tibiofibular syndesmotic injury is challenging and a gold standard diagnostic test has still not been established. Tibiofibular clear space identified on radiographic imaging is considered the most reliable indicator of the injury. The Cotton test is the most widely used intraoperative technique to evaluate the syndesmotic integrity although it has its limitations. We advocate for a novel intra operative test using a 3.5 mm cortical tap. Methods: Tibiofibular clear space was assessed in nine cadaveric specimens using three sequential fluoroscopic images. The first image was taken prior to the application of the tap test representing the intact and non-stressed state. Then, a 2.5 mm hole was drilled distally on the lateral fibula, and a 3.5 mm cortical tap was then threaded in the hole. The tap test involved gradually advancing the blunt tip against the lateral tibia, providing a tibiofibular separation force (intact, stressed). This same stress was then applied after all syndesmotic ligaments were released (injured, stressed). Measurements were compared by one-way ANOVA and paired Student’s t-test. Intra and inter-observer agreements were evaluated by intraclass correlation coefficient (ICC). P-values 6 mm as diagnostic for syndesmotic instability, the tap test demonstrated a 96.3% sensitivity and specificity, a 96.3% PPV and NPV and a 96.3% accuracy in diagnosing syndesmotic instability. Conclusion: Our cadaveric study showed that this novel syndesmotic instability test using a 3.5 mm blunt cortical tap is a simple, accurate and reliable technique able to demonstrate significant differences in the tibiofibular clear space when injury was present. It could represent a more controlled and stable low-cost alternative to the most used Cotton test.