The Role of the Individual Bundles of the Deltoid Ligament in Multidirectional Stability and Articular Contact Pressure of the Ankle Joint: A Finite Element Analysis.

The deltoid ligament (DL) is the primary stabilizer of the medial ankle; however, a limited understanding of the functional roles of its various bundles hinders rational surgical decision-making. This study aims to investigate the roles of individual DL bundles in maintaining ankle stability and articular contact pressure and thus seeks to guide decisions on whether reconstruction is required for specific injuries. A validated finite element foot model was used to simulate isolated and multiple deficiencies in the DL bundle. The articular displacements, rotations, and peak talar cartilage contact pressure were evaluated under anterior drawer force and under internal-external rotation, eversion, and plantarflexion-dorsiflexion moments. Compared with the intact model, anterior tibiotalar ligament (ATTL) deficiency resulted in the greatest anterior drawer displacement (increase: 29%). Talonavicular ligament (TNL) deficiency caused the largest internal-external rotation and plantarflexion (increases in external rotation: 69%; in internal rotation: 10%; in plantarflexion: 32%). Tibiocalcaneal ligament (TCL) deficiency caused the largest eversion (increase: 93%). Deep posterior tibiotalar ligament (dPTTL) deficiency caused the largest dorsiflexion (increase: 68%). The maximum talar cartilage contact pressure occurred in the TNL-deficient model under the plantarflexion condition. In conclusion, individual DL bundles exhibit specific functions in terms of controlling multidirectional ankle stability-the ATTL, TNL, TCL, and dPTTL are the primary stabilizers for anterior translation, rotation/plantarflexion, eversion, and dorsiflexion, respectively. These findings provide a biomechanical rationale for personalized surgical strategies. When comprehensive DL reconstruction is not feasible, clinicians can prioritize the reconstruction of specific bundles according to the patient's instability severity and functional demands across degrees of freedom.