Fixation for metacarpal neck fracture: a biomechanical study

Abstract

Background: There is no robust evidence of the best operative treatment for displaced unstable metacarpal neck fractures. Numerous constructs are used in the fixation of metacarpal neck fractures. Currently, two common methods are dorsal locking plate and K-wire fixation. A new metacarpal sled fixation system for metacarpal neck fracture was designed to provide fracture stability but limit dissection and avoid exposed hardware. The purpose of this study was to compare the biomechanical integrity of the metacarpal sled versus standard locking plate fixation and retrograde K-wire fixation in a simulated porcine metacarpal fracture model.

Methods: Transverse metacarpal neck fractures were created in 30 porcine second metacarpals. The specimens were randomly fixed with locking plates, metacarpal sleds, or retrograde K-wires. Constructs were then loaded to failure in three-point bending. Stiffness and peak load were measured from the load-to-failure deflection curve. Data were analyzed via ANOVA, followed by Tukey-Kramer's post hoc pairwise comparison.

Results: The K-wire group had the highest initial stiffness followed by the sled group and then the plate group. Statistical difference was only found between K-wires and plate. Peak load for the K-wire group was lowest, followed by sled, and then by plate. A statistically significant difference was observed between the peak loads of the K-wires and plate, as well as the sled and plate. However, a difference in peak load was not detected between the K-wires and sled.

Conclusions: For transverse metacarpal neck fractures, a metacarpal sled construct provides similar fixation to K-wires with limited dissection and without exposed hardware or the potential for soft tissue tethering. The new low profile construct using a minimally invasive technique would be suitable for unstable metacarpal neck fractures.

Keywords: Biomechanics; Hand; Internal fixation; Metacarpal fractures.

Fig. 1

Lateral fluoroscopic images of fixation methods for porcine metacarpal neck fractures repaired via a K-wires, b locking plate, and c sled (left); AP fluoroscopic images (center); specimens mounted on testing apparatus (right). T transverse pin, R loading rod, V vertical support, arrow direction of loading

Fig. 2

Failure mechanisms of the three fixation techniques: a K-wires, b locking plate, and c sled

Fig. 3

Stiffness from 20 to 60 N of load of the three fixation methods for the metacarpal neck fracture model

Fig. 4

Peak load of the three fixation methods for the metacarpal neck fracture model