Biomechanical Evaluation of a Biodegradable Magnesium-Based Screw for Fixation of Fifth Metatarsal Base Fractures: A Cadaveric Study

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: Fifth metatarsal base fractures are common foot injuries, particularly in athletes and individuals involved in high-impact activities. Effective fixation is critical for ensuring proper healing, restoring biomechanical function. Common fixation methods often involve titanium or stainless-steel screws that inserted intramedullary or hocked-plate fixation which may require subsequent removal surgeries due to hardware complications, soft tissue irritation, patient discomfort, and second surgery for removal. Purpose of this study is to biomechanically evaluate the fixation strength of a 4.5-mm magnesium-based bioabsorbable partially threaded screw when used intramedullary for fifth metatarsal base fracture fixation. Methods: Twelve fresh-frozen human cadaveric feet were used to assess the fixation strength of a single intramedullary 4.5 mm magnesium-based bioabsorbable screw (Bioretec, Finland) with a force testing mechanical device (Mark10, NY, USA). A two-phase biomechanical testing protocol was implemented. Cyclic-loading test in which the cadavers were subjected to 75 loading cycles of up to 175 N (preload: 10N) at 0.5 Hz frequency. The cadavers were then tested in a single-cycle load-to-failure assessment (up to 700 N) to determine maximum yield load. The primary outcome measures were fracture site gap and screw pull-out. Results: In neutral and slightly inverted foot position, no significant displacement was observed during cyclic loading. In the single-cycle load-to-failure test, the mean yield load was 566 ± 184 N, which exceeded the physiological tension exerted by the peroneus brevis tendon. The failure mode was screw pull-out, with no screw breakage observed. Conclusion: The biodegradable magnesium-based 4.5-mm partially threaded screws provided strong fixation for fifth metatarsal base fractures in a cadaveric foot model. Our outcomes are comparable with those of metal screws in the literature. Given that the yield load exceeded the maximum physiological pull of the peroneus brevis tendon, this fixation method appears to offer clinically sufficient strength for fracture stabilization. Magnesium screws seem to provide a superior strength to the so called PLLA and PDLA formulas used in the majority of the currently available biodegradable screws. Further in vivo studies are recommended to evaluate the short- and long-term outcomes.