Fixation Strength of Anteriorly Inserted Headless Screws for Talar Neck Fractures

Abstract

For noncomminuted talar neck fractures, traditional fixation is with small fragment screws or cannulated screws. Newer screw systems on the market allow placement of cannulated headless screws, which provide compression by virtue of a variable-pitch thread. The headless construct has an inherent advantage, particularly for the talus, when the screws must be countersunk to prevent wear of the joint articular surfaces. This study tested the biomechanical fixation strength of cannulated headless variable-pitch screws compared with conventional cannulated screws, both placed in an anterior to posterior direction. A reproducible talar neck fracture was created in nine paired, preserved, cadaver talar necks using a materials testing machine. Talar head fixation was then performed with two cannulated headless variable-pitch 4/5 screws or two 4.0-mm conventional cannulated screws. The specimens were tested to failure and the fixations were normalized to their intact pairs and compared. The headless variable-pitch screw fixation had significantly lower failure displacement than the conventional screw fixation. No significant differences were found between the two fixations for failure stiffness, load at failure or energy absorbed. Cannulated headless variable-pitch screws significantly improved failure displacement when compared to conventional cannulated screws in a cadaveric model, and may be a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screws have inherent advantages over conventional screws in that they may be less damaging to the articular surface and can compress the fracture for improved reduction. This study demonstrates these screws are also biomechanically similar to conventional screws.