Deltoid Ligament Insufficiency Results in Greater Anterior Translation and Medial Clear Space

Abstract

Category: Ankle; Other Introduction/Purpose: The arthroscopic drive-through sign (aDTS) aids in diagnosing intra-operative deltoid complex deficiencies by measuring the ankle’s medial clear space (MCS). However, there is some debate regarding the validity of aDTS. The study's primary objective was to determine if the medial aDTS is a viable and reproducible technique to diagnose deltoid instability, simulated by sequential sectioning of the lateral and medial stabilizing ligaments. A secondary objective was to determine how a combined medial and lateral ligament dual-sided repair (DSR) affects aDTS and anterior translation (AT) compared to the following testing phases: intact, chronic instability, and isolated lateral ligament repair. Methods: Five tibia-to-toe cadaveric specimens were assessed (57±14 years). Specimens were mounted to an electromechanical testing system on a custom fixture with a single degree of freedom in the anterior-posterior direction (~60mm). The proximal tibia/fibula was fixed at the crosshead in 20° of plantar flexion. An anterior drawer test was simulated by loading specimens anteriorly with 2kg/3kg/4kg at each arthroscopic sequential ligament sectioning and repair phase in the following order: intact, lateral instability (ATFL/CFL cut (A/C-C)), chronic instability (CI) (A/C-C + anterior deltoid cut), dual-sided repair (DSR), and lateral repair alone (LRA). A 3D-digitizer was used to measure AT. aDTS was executed with bulleted probes (2.0mm – 5.0mm diameter, 0.5mm increments) in an unloaded state before each phase. A positive aDTS was defined as probe passage into the MCS without excessive force. AT mean±standard deviation (mm), [95% confidence interval], and the largest probe diameter (mm) that yielded positive aDTS were reported. Results: 4/5 intact specimens resulted in a positive aDTS with a 2.0mm probe and 1/5 with a 2.5mm probe. In the simulated CI model, the minimum probe size to achieve a positive aDTS was 3.5mm (1specimen), and the maximum was 4.5mm (3specimens). The remaining passed with a 4.0mm probe. DSR restored aDTS to the intact MCS. The LRA reduced the MCS, indicated by a 3.5mm probe for 3/5 specimens; however, it did not restore MCS to intact. No differences in AT were observed between the three load weights (P=0.981). The maximum loading (4kg) was used for analysis. AT in the CI model was significantly greater than intact (14.3mm±1.9mm [12.6-16.0] vs. 7.4mm±1.5mm [6.1-8.7], P< 0.001). DSR and LRA restored intact AT values (4.8mm±0.8mm [4.1-5.5], P=0.637; 7.0mm±1.1mm [6.0-8.0], P=0.958). Conclusion: The aDTS was successfully executed for all samples, and intact MCS values ranged between 2.0 and 2.5mm. A probe size of 3.5mm proved acceptable to detect deltoid incompetence in the instance of simulated chronic instability. Likewise, a 3.0mm probe diameter or larger was shown to diagnose deltoid insufficiency after lateral ligament repair. Instability in the anterior direction was most reduced when both medial and lateral deficiencies were addressed in the DSR phase. A key observation was that the addition of a medial deltoid repair contributed to a 23.2% reduction in AT, compared to LRA, in the simulated CI model.