Unveiling Syndesmotic Malreduction: A Proof-of-Concept towards Portable Ultrasound Detection.

Objectives: To evaluate the utility and diagnostic performance of portable handheld ultrasound for evaluating fibular rotation at the distal tibiofibular articulation after syndesmotic disruption.

Methods: Four above-the-knee cadaveric specimens were included. Syndesmotic disruption was precipitated by transecting the Anterior Inferior Tibiofibular Ligament, Interosseous Ligament, and Posterior Inferior Tibiofibular Ligament. Thereafter, a proximal fibular osteotomy was performed, and three conditions were modeled at the distal syndesmosis: 1) reduced, 2) 5 degree internal rotation malreduction, and 3) 5 degree external rotation malreduction. Two blinded observers performed separate ultrasonographic examinations for each condition at the level of both the anterior and posterior distal tibiofibular articular surfaces. Syndesmotic gap penetrance, defined as the ability of the P-US to generate signal between the distal fibula and tibia at the level of the incisura, was graded positive if the sonographic waves penetrated between the distal tibiofibular joint and negative if no penetrating waves were detected. The accuracy measures of the anterior and posterior gap penetrance were evaluated individually.

Results: Our preliminary results showed that posterior gap penetrance showed good performance when detecting either internal or external rotational malreduction of the fibula with very good specificity (87.5%) and PPV (90.0%). On the other hand, the anterior gap penetrance showed limited performance when detecting either form of rotational malreduction.

Conclusion: We introduced a novel sign, the "gap penetrance sign", best measured from the posterior ankle, which can accurately detect syndesmotic malreduction using P-US in a manner that does not require specific quantitative measurements and is readily accessible to early P-US users.