BIOMECHANICAL ANALYSIS OF ANKLE STABILITY FOLLOWING DELTOID LIGAMENT REPAIR AND RECONSTRUCTION

The deltoid ligament has been shown to contribute to the stability of the ankle mortise, preventing valgus talar tilt, external rotation, and translation. Research to date assessing the appropriateness of deltoid repair as a means to reintroduce medial stability to a fractured ankle remains unclear. Deltoid ligament reconstruction using autograft or allograft has been proposed in cases of chronic deltoid insufficiency. This biomechanical study sought to assess the stability offered by deltoid repair and reconstruction compared to the native deltoid ligament in its intact, and de-functioned states. Twelve (six pairs) fresh frozen cadaveric lower extremities with intact deltoid ligaments were assessed in a custom-made multi-axial testing apparatus. Each specimen was tested in plantarflexion/dorsiflexion (PF/DF), inversion/eversion (IV/EV), and internal/external rotation (IR/ER). Each specimen was analyzed for angular range of motion (ROM), normalized ROM, and stiffness. The specimens were tested with an intact deltoid ligament, and following disruption via sharp dissection. Subsequently, each pair was either randomized to deltoid repair, or reconstruction. A single double-loaded suture anchor was used to repair the deep and superficial deltoid ligaments. The tibialis anterior tendon was used as graft in the reconstruction group. The tendon was inserted through interosseous tunnels created in the distal tibia to the talus and calcaneus, and secured with an endobutton and interference screws thereby reconstructing both superficial and deep deltoid ligaments. For each phase of testing, three cycles were conducted and data from the last cycle was collected. Angular ROM was significantly greater in deficient specimens compared to intact, repair, and reconstruction groups during PF/DF (p=0.0002, 0.0184, and 0.0036 respectively). For IV/EV, deficient specimen ROM was significantly greater than the intact (p=0.0037) and repair (p=0.0029) groups, but not from the reconstruction (p=0.36). During IR/ER, the deficient ankle was only significantly different from the intact state (p=0.014). Normalized ROM was not significantly different between intact, repair, or reconstruction in any of the motions tested. Stiffness in the deficient ankle was significantly lower in DF/PF compared to intact (p=0.00014) and reconstruction (0.0023) groups but not compared to the repair group. In IV/EV, deficient ankles demonstrated stiffness which was significantly less when compared to intact (p-0.0013) and repair (p=0.000016) groups, but not the reconstruction group. The repair group was significantly stiffer in IV/EV compared to the reconstruction (p=0.016) group. No significant difference in stiffness was observed in IR/ER between any of the groups. Deltoid repair and reconstruction utilizing the techniques described in this study were comparable in returning the ankles to intact state normalized ROM, and confer stability specifically in PF/DF, and IV/EV. These results would suggest that deltoid ligament reconstruction may be used as a reliable alternative to repair in chronic deltoid ligament insufficiency, and in instability cases where repair is not possible.