A Biomechanical Analysis of Intramedullary Threaded Nail Fixation and Dorsal Plate and Screw Fixation for Metacarpal Base Fractures.

Purpose: The biomechanics of surgically treated metacarpal base fractures are poorly described. We hypothesized that intramedullary threaded nail (IMTN) fixation and dorsal plate and screw (DPS) fixation would perform similarly in multiple fracture locations approaching the metacarpal base. Methods: Sixty-four metacarpals from eight matched pair cadaveric hands were stripped. Matched pairs were randomly divided into four cohorts based on fracture distance from the metacarpal base. Transverse osteotomies were created at 50%, 35%, 25%, and 15% of the total metacarpal length, measured from the metacarpal base. The 50% cohort served as a control. For each cohort, paired metacarpals were randomized to either DPS or IMTN fixation groups. All specimens were cyclically loaded in 3-point bending for 2,000 cycles at 70 N, 2,000 cycles at 120 N, and then loaded to failure. Bending stiffness, cycles to failure, and peak load to failure (LTF) were collected. Results: Peak bending stiffness and peak LTF were not significantly different in the 15%, 25%, or 35% groups compared to the 50% control for both IMTN and DPS fixation. Direct comparison of IMTN and DPS fixation at each osteotomy level yielded no significant differences in LTF or bending stiffness. There was a nonsignificant trend toward higher LTF and bending stiffness with DPS fixation in more proximal fractures. Conclusions: Peak LTF and bending stiffness were not significantly different for IMTN or DPS fixation in fractures located as proximally as 15% from the metacarpal base. Furthermore, both IMTN and DPS fixation had no significant differences in peak bending stiffness and LTF for metacarpal fractures as proximal as 15% from the base compared to a 50% control. Clinical relevance: When managing proximal metacarpal fractures surgeons can expect no significant difference in stiffness or LTF using either DPS or IMTN fixation with values comparable to those seen when treating a midshaft metacarpal fracture.