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Crossed K-Wires Versus Intramedullary Headless Screw Fixation of Unstable Metacarpal Neck Fractures: A Biomechanical Study.

Background
Intramedullary headless screw (IMHS) has shown promise as an alternative to other fixation devices for metacarpal neck fractures. The purpose of this study was to assess the biomechanical performance of IMHS versus the commonly-used crossed K-wire technique. We hypothesized that IMHS fixation provides superior stability to K-wires.


Methods
A metacarpal neck fracture model in 23 human cadaveric metacarpals was created. The specimens were divided into two groups based upon fixation method: Group 1, 3 mm intramedullary headless screw; and Group 2, 0.045 inch crossed K-wires. A cantilever bending model was used to assess load-to-failure (LTF), maximum displacement, energy absorption, and stiffness.


Results
The mean LTF was 70.6 ± 30.1 N for IMHS and 97.5 ± 34.7 N for crossed K-wires. Mean stiffness was 11.3 ± 3.4 N/mm and 17.7 ± 7.8 N/mm for IMHS and crossed K-wires, respectively. The mean maximum displacement was 20.2 ± 4.6 mm for IMHS and 24.1 ± 3.7 mm for crossed K-wires. Moreover, mean energy absorption was 778.3 ± 528.9 Nmm and 1095.9 ± 454.4 Nmm, respectively, for IMHS and crossed K-wires. Crossed K-wires demonstrated significantly higher stiffness and maximum displacement than IMHS (p < 0.05).


Conclusions
IMHS fixation of unstable metacarpal neck fractures offers less stability compared to crossed K-wires when loaded in bending.


Clinical Relevance
Crossed K-wires offer superior stability for the treatment of metacarpal neck fractures. These results reveal that IMHS fixation is less favorable biomechanically and should be cautiously selected with regards to fracture stability.