Abstract
Objective To evaluate the stability of osteotomies created in the subtrochanteric and trochanteric
regions in a pediatric femur model fixed by flexible intramedullary rods.
Method Tomographic sections were obtained from a pediatric femur model with two elastic
titanium rods and converted to a three-dimensional model. This model created a mesh
with tetrahedral elements according to the finite element method. Three virtual models
were obtained, and osteotomies were performed in different regions: mediodiaphyseal,
subtrochanteric, and trochanteric. A vertical load of 85N was applied to the top of
the femoral head, obtaining the displacements, the maximum and minimum main stress,
and the equivalent Von Mises stress on the implant.
Results With the applied load, displacements were observed at the osteotomy site of 0.04 mm
in the diaphyseal group, 0.5 mm in the subtrochanteric group, and 0.06 mm in the trochanteric
group. The maximum stress in the diaphyseal, subtrochanteric, and trochanteric groups
was 10.4 Pa, 7.52 Pa, and 26.4 Pa, respectively. That is around 40% higher in the
trochanteric group in regards to the diaphyseal (control). The minimum stress of the
bone was located in the inner cortical of the femur. The equivalent Von Mises stress
on the implants occurred at osteotomy, with a maximum value of 27.6 Pa in the trochanteric
group.
Conclusion In both trochanteric and subtrochanteric osteotomies, fixation stability was often
lower than in the diaphyseal model, suggesting that flexible intramedullary nails
are not suitable implants for proximal femoral fixations.
Keywords femoral fractures - finite element analysis - fracture fixation, intramedullary
