Fixation of Metacarpal Shaft Fractures: Biomechanical Comparison of Intramedullary Nail Crossed K-Wires and...

Metacarpal (MC) fractures are very common, accounting for 18% of all fractures distal to the elbow. Many MC fractures can be treated non-operatively; however, some are treated most effectively with surgical stabilization, for which there are multiple methods. It was postulated that plates would have a significantly higher (P < 0.05) load to failure than crossed K(XK)-wires and that intramedullary metacarpal nails (IMNs) and XK-wires would have equivalent load to failure.

Mid-diaphyseal transverse fractures were created in 36 synthetic metacarpals and stabilized using nails, XK-wires or non-locking plates. Three-point bending was performed with continuous recording of load and displacement. Statistical analysis was performed using single factor ANOVA and Scheffe's test. Statistical significance was defined as P < 0.05.

Biomechanical testing revealed significant differences between groups in load-to-failure. Average load to failure was significantly greater in the plate (1669 ± 322 N) than the XK-wire (146 ± 56 N) or IMN (110 ± 43 N) groups. The loads to failure of the K-wires and nails were equivalent. Plates were 11 and 15 times stronger in three-point bending than the K-wires and nails, respectively. There was no statistically significant difference between strengths of the K-wires and nails.

Although plates are the most stable means of fixation of midshaft metacarpal fractures, if minimally-invasive techniques are indicated, intramedullary nails may provide equivalent stability as commonly-used XK-wires. Although some studies have shown favorable clinical outcomes with IMNs, additional clinical correlation of these biomechanical results to fracture healing and outcomes is needed.