Flexible Intramedullary Nails for Stabilization of Transverse Femoral Fractures in Cats: Ex Vivo Biomechanical Characterization

Flexible intramedullary nails (FINs) are commonly used in children and adolescents to treat long bone fractures, but few studies exist in animals. This study aimed to evaluate the biomechanical performance of FINS for the stabilization of transverse femoral fractures in cats. Fifteen bones were kept intact, while in another 15 bones, a mid-diaphyseal transverse fracture was induced and stabilized with two steel FINs of equal diameter, advanced divergently toward the greater trochanter and femoral neck, with end caps applied to the free ends. Five constructs and five intact bones were subjected to axial compression, four-point bending, and torsion tests. In axial compression, intact bones showed higher mean maximum force (1090.51 N vs. 608.43 N) and stiffness (845.98 vs. 298.86 N/m) than constructs. In bending, intact bones reached a maximum force of 1384.75 N, whereas a distinct maximum force could not be determined for the constructs; stiffness was also greater (1580.92 vs. 13.32 N/m). In torsion, intact bones demonstrated substantially higher mean maximum force (6.764 vs. 0.166 Nm) and stiffness (32.11 vs. 1.04 Nm/rad) than constructs. In conclusion, FINs with end caps demonstrate low construct stiffness, particularly under torsional loads, when used to stabilize mid-diaphyseal transverse femoral fractures in cats.