Biomechanical evaluation of metacarpal fracture fixation: application of a 90° internal fixation model

Complications in metacarpal fracture treatment increase in proportion to the severity of the initial injury and the invasiveness of the surgical fixation technique. This manuscript evaluates the feasibility of minimizing internal fixation construct size and soft tissue dissection, while preserving the advantages of stable internal fixation in a biomechanical model. We hypothesized that comparable construct stability could be achieved with mini-plates in an orthogonal (90/90) configuration compared with a standard dorsal plating technique.

This hypothesis was evaluated in a transverse metacarpal fracture model. Twelve metacarpals were subject to either placement of a 2.0-mm six-hole dorsal plate or two 1.5-mm four-hole mini-plates in a 90/90 configuration. These constructs were tested to failure in a three-point bending apparatus, attaining failure force, displacement, and stiffness.

Mean failure force was 353.5 ± 121.1 N for the dorsal plating construct and 358.8 ± 77.1 N for the orthogonal construct. Mean failure displacement was 3.3 ± 1.2 mm for the dorsal plating construct and 4.1 ± 0.9 mm for the orthogonal construct. Mean stiffness was 161.3 ± 50.0 N/mm for the dorsal plating construct and 122.1 ± 46.6 N/mm for the orthogonal construct. Mean failure moment was 3.09 ± 1.06 Nm for the dorsal plating construct and 3.14 ± 0.67 Nm for the orthogonal construct. The dorsal plating group failed via screw pullout, whereas the orthogonal failed either by screw pullout or breakage of the plate.

When subject to apex dorsal bending, the orthogonal construct and the standard dorsal plate construct behaved comparably. These data suggest that despite its shorter length, lower profile, and less substantial screws, the orthogonal construct provides sufficient rigidity.

This study represents a "proof of concept" regarding the applicability of orthogonal plating in the metacarpal and provides the foundation for minimizing construct size and profile.