BACKGROUND: Triple arthrodesis and combined talonavicular/subtalar arthrodesis are procedures for hindfoot disorders. Achieving talonavicular joint fusion can be problematic. We hypothesized that talonavicular joint fixation bending stiffness could be increased by adding a fully-threaded screw inserted through the lateral navicular into the calcaneus. MATERIALS AND METHODS: We used ten fresh-frozen cadaver hindfeet. The calcaneus and talus were immobilized, and talonavicular joint stripped of cartilage. Two partially-threaded 4.5-mm cannulated screws were placed across the talonavicular joint, one traversing the central third of the navicular and a second through the medial third of the navicular. We quantified talonavicular fixation bending stiffness and angulation in response to 4N-m bending moments applied to the navicular in four directions: plantar-to-dorsal (P-D), medial-to-lateral (M-L), dorsal-to-plantar (D-P), and lateral-to-medial (L-M). An augmenting fully-threaded 4.5 mm cannulated screw was then placed through the lateral third of the navicular into the calcaneus and the specimens retested. RESULTS: The mean bending stiffness in each direction increased significantly after addition of the third screw. The stiffness increase in each direction was: P-D 92%, D-P 39%, L-M 108%, and M-L 56%. Correspondingly, mean talonavicular angulation significantly decreased in each direction: P-D 43%, D-P 28%, L-M 47%, and M-L 34%. CONCLUSION: A third, fully-threaded screw from the lateral navicular into the calcaneus significantly increases talonavicular bending stiffness and decreases angulation. CLINICAL RELEVANCE: The increased resistance to arthrodesis site motion afforded by the addition of a naviculocalcaneal screw may improve the likelihood of achieving successful talonavicular fusion in combined talonavicular/subtalar arthrodesis.