Fully Threaded Versus Partially Threaded Intramedullary Headless Compression Screw Fixation for Proximal Third Fractures of the Proximal Phalanx: A Biomechanical Study.

Purpose: The purpose of this study was to compare the maximal elastic force and deformation resistance of two commonly used headless compression screw systems, a fully threaded 2.5 mm screw and a partially threaded screw of the same dimensions, in a cadaveric model of a human transverse proximal third fracture of the proximal phalanx.

Methods: Six fresh frozen cadavers were used, and the proximal phalanges of the index, long, and ring fingers of both hands were dissected. A proximal third transverse osteotomy was created, and screws were inserted in an antegrade direction. The three-point bending load-to-failure test measured the maximal elastic force and deformation resistance of each bone-screw construct.

Results: The fully threaded screw demonstrated a maximal elastic force of 121 N and a deformation resistance of 134 N/mm. The partially threaded screw showed superior performance with a maximal elastic force of 165 N and deformation resistance of 166 N/mm. The bone-screw construct with the fully threaded screw had a mean maximal elastic force of 155.2 N compared to 101.8 N in the construct with the partially threaded screw. Deformation resistance was 145.2 N/mm for fully threaded screws and 98.6 N/mm for partially threaded screws.

Conclusions: Fully threaded intramedullary headless compression screw fixation provides superior maximal elastic force and deformation resistance compared to partially threaded intramedullary headless compression screw fixation in transverse proximal third fractures of the proximal phalanx.

Clinical Relevance: The findings indicate that fully threaded intramedullary headless compression screw fixation may offer enhanced stability for treating proximal third fractures of the proximal phalanx, potentially leading to better patient outcomes through earlier mobilization and reduced complications compared to partially threaded screws.