Finite Element Analysis of the Effect of Talar Osteochondral Defects of Different Depths on Ankle Joint Stability.

BACKGROUND Talus cartilage injury leads to changes in biomechanics of the ankle joint and ultimately affects ankle joint function, but which talus cartilage defects require surgery is still uncertain. This research used a finite element method to simulate the effect of different depth of talus cartilage defects on the stress and stability of the ankle joint in a certain area. MATERIAL AND METHODS A three-dimensional finite element model with different depths of osteochondral defects was created to simulate and calculate joint stress and displacement of the articular surface of the distal tibia and the proximal talus while the ankle joint was in the push-off, midstance, and heel-strike phases. RESULTS The equivalent stress of the proximal talus did not change significantly at a defect depth of 1 mm, whereas the equivalent stress of the upper talus increased significantly at a defect depth of ≥3 mm or more, reaching a maximum value at a defect depth of 10 mm. The equivalent stress of the tibial cartilage and the equivalent stress and displacement in the corresponding forces in the midstance phase and heel-strike phase were significantly different from those in the normal group, but the difference in stress in each defect group was not obvious. CONCLUSIONS The effect of cartilage defects of the talus on biomechanics of the ankle is clear, especially in the midstance and push-off phases. When the defect reaches the subchondral bone (at a depth of 3 mm), the most obvious change in ankle joint stability occurs, and it does not increase linearly with the increase in depth of the defect.