Intramedullary Threaded Nail Versus Dorsal Plate and Screw Fixation of Comminuted Metacarpal Shaft Fractures: A Cadaveric Biomechanical Study

Purpose: Indications are expanding for the use of intramedullary threaded nail (IMTN) fixation in metacarpal fractures. We hypothesized that IMTN fixation would have superior bending stiffness compared to dorsal plate and screw fixation and provide sufficient stability to withstand cyclic loading comparable with early range of motion. Methods: Index, long, ring, and small finger metacarpals were harvested from matched pair cadaveric hands. A midshaft 1.75 mm transverse gap was created to simulate a comminuted fracture. Specimens were randomized into two groups for fixation with either a retrograde IMTN or dorsal plate and screws. Specimens underwent three-point bend testing with an Instron. Each specimen was cyclically loaded at 70 N for 2,000 cycles (composite grasp), followed by 120 N for 2,000 cycles (tip pinch). Specimens were then loaded to failure. Outcomes included cycles to failure, bending stiffness, peak load to failure, and location of failure. Results: Bending stiffness was significantly greater in the IMTN group compared to the plate group (136.71 ± 24.19 N/mm vs 39.89 ± 14.08 N/mm). Peak load to failure was greater in the plate group, but this difference was not statistically significant (365.33 ± 79.85 N vs 598.11 ± 372.76 N). During the cyclic loading phases, all specimens in the IMTN group completed the 70 N and 120 N loading phases without failure. In the plate group, two of nine specimens progressed to catastrophic failure during the 120 N cyclic loading phase. Conclusions: In a comminuted metacarpal shaft fracture model, IMTN fixation had significantly greater bending stiffness and more consistent load to failure characteristics compared to dorsal plate and screw fixation. Clinical relevance: IMTN fixation provided sufficient stability in comminuted metacarpal shaft fractures to withstand cyclic forces consistent with early range of motion, whereas dorsal plate and screw fixation demonstrated more variable results.