Are stainless steel elastic nails the solution to heavier children with femoral shaft fractures?

Abstract

Background: The use of titanium elastic intramedullary nails for the treatment of femoral shaft fractures, in children weighing 45 kg, has been questioned due to the increased rates of malunion. Our aim was to see if the mechanical properties of stainless steel elastic nails provided enough fracture stability to justify their use in heavier children. Materials and Methods: Twenty pediatric femoral Sawbones®, fixed with titanium or stainless steel elastic nails, were tested. The bending stiffness and moments of the constructs were calculated at increasing loads, along with the angle of fracture deformation. From these estimates of maximum permitted body weight for each nail type were extrapolated. Results: Steel nails created significantly stiffer constructs than titanium in both the coronal and sagittal planes (P < 0.0001). Steel nails allowed bigger sagittal bending moments before losing acceptable alignment, compared to titanium (P < 0.0001). However, in the coronal plane, the difference was not statistically significant (P = 0.457). The estimated body weights extrapolated in the sagittal plane were 45 and 61 kg, in titanium and steel, respectively. In the coronal plane, they were 42 and 44 kg. Discussion: As steel has nearly twice the Young's modulus of titanium, it seems logical that fractures fixed with steel nails would be stiffer and fail at higher loads. However, it is unclear why steel did not outperform titanium in the coronal plane. A theory was proposed that unequal nail slip from the insertion sites might be a contributing factor to these findings. Conclusion: Pediatric femoral shaft fractures fixed with elastic steel nails provide significantly stiffer constructs than those fixed with titanium. However, there is an increased risk of malunion in the coronal plane, in children weighing 45 kg, regardless of material used, possibly due to unequal nail slip at the distal entry points.