A New and More Sensitive View for the Detection of Syndesmotic Instability

We hypothesize that a single syndesmotic view, capturing both sagittal and coronal tibiofibular displacement, will be more sensitive than a mortise view to detect syndesmotic instability.

Ten fresh frozen human lower limbs were used to test the new syndesmotic view with simulated syndesmosis injury. The anteroinferior tibiofibular ligament, interosseous membrane, and posteroinferior tibiofibular ligament were sectioned sequentially. At each stage, the syndesmosis was tested using the external rotation stress (ERS) test and lateral stress test (LST). For each stress condition, a true mortise view and the new syndesmotic view were performed. Medial clear space and tibiofibular clear space (TFCS) were measured on a mortise view, and TFCS was measured on a syndesmotic view (TFCS-s). Wilcoxon signed-rank tests were used to compare measurements.

Syndesmotic view enabled instability detection with a 2-ligament dissection at a mean increase in TFCS-s of 2.37 mm (P = 0.021) and 1.98 mm (P = 0.011), using the ERS and LST, respectively. TFCS on the mortise view was significantly different only with a complete injury. Medial clear space did not vary significantly with injury increments. Sensitivity was 66% and 61% using ERS and LST, respectively, for the TFCS-s, compared with 27% and 33%, respectively, for the TFCS. Specificity was similar for TFCS and TFCS-s.

This study was able to demonstrate that the syndesmotic view is more sensitive than the mortise view in detecting syndesmotic instability in a cadaveric model. It is particularly helpful to uncover instability secondary to an incomplete syndesmosis injury requiring fixation.