Mechanical characteristics of eight femoral intramedullary nailing systems.

Abstract

There are few nonproprietary papers addressing the mechanical strength of intramedullary nails; none address the characteristics of the proximal and distal ends of these devices. Our objective was to provide such data. Independent testing of eight femoral intramedullary nail systems at the proximal, middle, and distal regions was undertaken to evaluate strength and flexural rigidity (stiffness). Each device, usually a reconstruction nail, was forty-two to forty-six centimeters in length. Four or five nails of each available size (range 9 to 13 millimeters in diameter) were tested for each system. The nails were cut into proximal, middle, and distal thirds. Each nail section was loaded to failure using a four-point bend test on a custom fixture (modification of the American Society of Testing Materials standard test). Significant variations (p < 0.05) were found in strength and stiffness between the middle and the proximal or distal aspects of some rods. A significant difference (p < 0.05) was observed when comparing the properties of earlier designs with the properties of more recent designs. Newer rod designs all performed in a similar manner with regard to strength. Strength and rigidity increased with increasing rod diameter in some but not all systems. Although none of the newer designs appeared to have superior static strength, the individual systems had significant variations in their mechanical properties (bending rigidity), particularly in the proximal and distal sections. It is important that the surgeon become familiar with the individual characteristics of strength and rigidity for the particular devices available and how these might impact fracture healing. Consideration of this information could alter the decision to select one system over another in a complex fracture situation.