Deltoid ligament strain after correction of acquired flatfoot deformity by triple arthrodesis

Deltoid insufficiency represents a difficult surgical challenge. We have witnessed patients who have developed a valgus tibiotalar deformity following a properly positioned triple arthrodesis. To investigate whether the triple arthrodesis itself, by creating a rigid triple joint complex below the ankle, leads to increased strain of the deltoid complex, a flatfoot model was created in 8 fresh-frozen below-knee amputation specimens. Each specimen was loaded in three gait cycle (GC) positions: Heel strike (0% GC), midstance (10% GC), and heel rise (40% GC). The three components of the ground reaction force (GRF) and the tendon forces consistent with those respective positions were applied. To simulate a posterior tibial tendon insufficient state the posterior tibial tendon was not loaded. Strain at the tibiocalcaneal fibers of the superficial deltoid ligament complex was determined at each of the three foot positions. A triple arthrodesis was performed and the deltoid strains were again recorded for each position. A significant increase in the strain of the deltoid ligament was observed for only the heel rise position (p=0.007) in our cadaver model following triple arthrodesis. The results favor medializing the calcaneus following arthrodesis to protect the deltoid complex.