Load sharing and stability of deltoid ligament during ankle motion loading-A cadaveric biomechanical study

The deltoid ligament stabilizes the medial ankle through multiple fiber bundles that resist eversion and external rotation. Although its overall biomechanical function is well established, the specific contributions of individual bundles during complex motions such as pronation remain unclear. This study aimed to replicate previous findings using a modified ligament transection sequence and investigate load-sharing among deltoid ligament bundles.

Eight fresh-frozen cadaveric lower limbs (mean age, 85.1 ± 5.8 years) were examined using a six-degree-of-freedom robotic system. Talocrural joint motion was measured under eversion (1.7 Nm) and external rotation (1.7 Nm) at various flexion angles. Pronation was defined as a combination of eversion and external rotation at 15-degree dorsiflexion. Tests were performed in the intact ankle and after deep to superficial sequential transection. In situ forces of individual ligament bundles were calculated using a robotic replay method based on the principle of superposition.

The tibiocalcaneonavicular ligament exhibited the highest in situ force during eversion in plantarflexion and during external rotation from neutral to plantarflexion. Under pronation, it also exhibited significantly greater force than the deep bundles. These findings remained consistent despite reversal of the transection sequence.

Load-sharing distribution among deltoid ligament bundles remained consistent despite reversal of the transection sequence, supporting the robustness of the findings. The tibiocalcaneonavicular ligament plays a major role in resisting eversion, external rotation in plantarflexion, and pronation under non-weight-bearing conditions.