Abstract
Objectives:
The syndesmotic ligaments are crucial in resisting diastatic forces between the distal tibia and fibula while the deltoid ligament is primarily responsible for stabilizing ankle during eversion and external rotation. Numerous biomechanics studies have evaluated surgical treatment options for deltoid ligament and syndesmosis injuries in isolation. However, there remains a paucity of studies analyzing surgical treatments for a combined deltoid and syndesmosis injury pattern which is commonly seen in clinical practice. The goal of this study is to analyze three surgical treatments: trans-syndesmotic repair, deltoid repair and anterior inferior tibiofibular ligament (AITFL) augmentation. We hypothesized that that the deltoid and syndesmosis injury pattern would significantly increase eversion, external rotation, and lateral translation. We further hypothesized that trans-syndesmotic repair and deltoid repair with AITFL augmentation would each reduce laxity, with the combination of all repairs providing the greatest reduction in laxity.
Methods:
Ten cadaveric specimens were acquired for this study, and four have been tested as of the submission of this abstract. Each specimen was mounted to a 6-degrees-of-freedom robotic and tested in 7 consecutive states: 1) Native, 2) Anterior Deltoid Cut: tibio-navicular, tibio-spring, and deep anterior deltoid ligaments, 3) Syndesmosis Cut: anterior-inferior tibiofemoral ligament (AITFL), posterior-inferior tibiofemoral ligament (PITFL), inter-osseous membrane, 4) Trans-syndesmotic repair of the syndesmosis using a tightrope (TR), 5) Addition of deltoid repair; 6) Addition of AITFL augmentation with suture tape; 7) Removal of Deltoid repair. Biomechanical testing consisted of three tests: External Rotation (5 Nm), Eversion (5 Nm), Lateral Drawer (88 N), each run at neutral and 25 degrees of plantarflexion. To match the repeated measures design of the study, a 1-factor linear mixed effects model will be run for each test, and all post-hoc pairwise comparisons between ankle states will be made, using Tukey’s method to adjust for multiple comparisons. In the present abstract, means and standard deviations from the first 4 specimens are presented.
Results:
The study results at neutral plantarflexion are displayed on figures 13. In external rotation, the anterior deltoid cut caused a small increase (+2.0°), while the syndesmosis cut caused a large increase (+8.2°). The trans-syndesmotic repair partially stabilized ER (-4.1°), and the Deltoid repair further stabilized ER (-4.8°) with no benefit seen from the AITFL augmentation. In eversion, the anterior deltoid cut caused an increase (+2.9°), while the syndesmosis cut caused a smaller increase (+0.5°). The tightrope did not provide any stabilization, while the deltoid repair did provide some stabilization (-1.4°), with no benefit seen from the AITFL augmentation. In lateral translation, the anterior deltoid cut caused a small increase (+0.9 mm) and the syndesmosis cut caused a larger increase (+1.5 mm). The tightrope provided some stabilization (-1.6 mm), with no further benefit of the AITFL or Deltoid repair.
Conclusions:
The data collected so far suggests that the optimal repair in the setting of a combined syndesmosis + anterior deltoid injury is a trans-syndesmotic fixation and a deltoid repair, with no benefit seen from the AITFL suture tape augmentation. The anterior deltoid was found to be a primary stabilizer of eversion, while the syndesmosis was a primary stabilizer of external rotation and lateral translation of the ankle. The data from this study can help inform clinical decision-making in the context of combined deltoid and syndesmosis injuries.
