Biomechanical Modeling of Connecting Intermetacarpal K-Wires in the Treatment of Metacarpal Shaft Fractures.

Abstract

Clinical series have been published using the configuration of 2 intercarpal Kirschner wires (K-wires) adjacent to the fracture being connected, but biomechanical analysis is lacking. The objective of this pilot biomechanical study was to model and compare the effects of externally connecting 2 intermetacarpal K-wires for the stabilization of transverse metacarpal shaft fractures. Our research hypothesis was that the connected constructs would be stiffer than the unconnected K-wires. A 3-dimensional computer-based model of small finger transverse metacarpal fracture stabilization was designed with 3 transverse 1.1 mm K-wires being anchored to the adjacent metacarpal. Three arrangements were tested: all 3 K-wires in parallel, the middle K-wire angled toward the proximal wire, and the middle angled K-wire being rigidly fixed to the proximal K-wire. The proximal wire was proximal to the fracture. A finite element analysis was performed by applying a cantilever force of 100 N at the head of the metacarpal. The metacarpal was considered to be uniform in composition with parameters typical for human bone. Kirschner wire parameters for stainless steel were used. Force (N) versus displacement was measured. The configuration with the middle angled K-wire being rigidly fixed to the proximal K-wire showed greater stiffness (12 N/mm) than nonattached constructs. The connected construct was 2.3 times more stiff than the unattached parallel construct and 2.5 times more stiff than angling the middle K-wire without attachment. In a computer model simulation, our results show that attaching 2 K-wires adjacent to the fracture provides more than twice the stiffness of unconnected K-wires.