SLR - July 2021 - Tyler Rodericks

Arthroscopic Characterization of Syndesmotic Instability in the Coronal Plane: Exactly What Measurement Matters?

Reference: Elghazy MA, Massri-Pugin J, Lubberts B, Vopat BG, Guss D, Johnson AH, DiGiovanni CW. Arthroscopic Characterization of Syndesmotic Instability in the Coronal Plane: Exactly What Measurement Matters? Injury. 2021 Apr 9:S0020-1383(21):00339-9.

Level of Evidence: Level V

Scientific Literature Review

Reviewed By: Tyler Rodericks, DPM
Residency Program: Mount Auburn Hospital – Cambridge, MA

Podiatric Relevance: Evaluation of syndesmotic stability as well as anatomic reduction of the syndesmosis is a crucial component in the management of ankle fractures and ligamentous injuries. Very mild displacement of the talus within the mortise secondary to syndesmotic instability causes a significant increase in contact forces on the talus and can potentially lead to the development of debilitating post-traumatic ankle arthritis. Arthroscopy has been used with increasing prevalence in the diagnostic and therapeutic management of ankle injuries and provides the benefit of direct visualization of tibia-fibular space at the incisura through a minimally invasive approach.

Methods: This is a cadaveric study in which 22 fresh frozen above knee cadaver specimens underwent syndesmotic evaluation via arthroscopy using an anteromedial portal for visualization and a probe through an anterolateral portal for measurement. The anterior one third and posterior one third of the incisura were probed with sequentially sized probes in 0.1 millimeter increments to measure the tibia-fibular space both unstressed and subsequently stressed with a lateral hook test through an incision 5cm proximal to the ankle joint and the tibial-fibular space. The limbs were then split into three groups in which the anterior-inferior tibio-fibular ligament (AiTFL), interosseus ligament, posterior-inferior tibio-fibular ligament (PiTFL) and deltoid were sequentially sectioned in differing combinations with repeat unstressed and stressed measurements taken after each. Statistical analysis was utilized to determine correlation between syndesmotic instability (defined as transection of all three syndesmotic ligaments, or two syndesmotic ligaments and the deltoid) as it related to anterior and posterior measurements as well as to determine an ideal cutoff measurement for identifying syndesmotic instability. Sensitivity and specificity was calculated at various cutoff measurements.

Results: No significant correlation existed between the anterior incisura measurements and syndesmotic instability with or without the hook test. There was significant correlation between posterior incisura measurements and syndesmotic instability both with and without the hook test. Low sensitivity and specificity was present for stressed and unstressed anterior incisura measurements, whereas they were higher for the posterior measurements. A 2-millimeter cut off value for instability determined by the posterior incisura measurement had an 86 percent sensitivity and 29 percent specificity whereas a 3 millimeters cut off value had a 55 percent sensitivity and 83 percentspecificity. A 2.7 millimeters cutoff resulted in about a 70 percent sensitivity and specificity.

Conclusions: The authors concluded that coronal plane syndesmotic instability is best diagnosed arthroscopically when measuring the posterior third of the incisura. They suggest 2.7 millimeters to be an ideal single value cutoff to assess syndesmotic stability. They suggest that based on these results a stressed syndesmosis with a posterior tibiofibular space <2 millimeters is likely to be stable whereas >3 millimeters is likely unstable. This study did not assess instability in the setting of ankle fractures and utilized probes that may not be readily available at many centers, making functional utility of the technique a bit challenging and limited at the present time. Further studies are needed to relate the cadaveric findings to the clinical relevance before significant changes to clinical practice could be made based on the findings in this study.

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