Talonavicular joint fixation using augmenting naviculocalcaneal screw in modified double hindfoot arthrodesis.

Abstract

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. 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. 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%. A third, fully-threaded screw from the lateral navicular into the calcaneus significantly increases talonavicular bending stiffness and decreases angulation. 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.