Biomechanical comparison of cephalomedullary and reconstruction nails used in the treatment of subtrochanteric femur fractures.

Abstract

There are several studies comparing various implants for treating subtrochanteric femur fractures. However, there is no known comparison of the DePuy Synthes TFN-ADVANCED and the DePuy Synthes FRN-ADVANCED. This study compares the biomechanical characteristics of 2 nail-composite femur models designed to simulate reconstructed subtrochanteric femur fractures. Eight composite femora were osteotomized to produce models of subtrochanteric femur fractures (Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association 32-C3.i). The simulated fractures were fixed using either a DePuy Synthes TFN-ADVANCED (1 Screw) proximal femoral nailing system or the DePuy Synthes FRN-ADVANCED (2 screw) femoral recon nailing system. The reconstructed fractures were subjected to compressive mechanical testing protocol consisting of cyclic loading and destructive ramp-to-failure. Interfragmentary motion of the proximal and distal bone segments was tracked at multiple locations using 3-dimensional motion-capture. The TFN-ADVANCED withstood a significantly higher maximum force (3512.5 N ± 261.1 vs. 3055.22 N ± 174.1, <i>P</i> = 0.027) than the FRN-ADVANCED and difference in energy to failure approached significance (35.6 J ± 12.01 vs. 18.30 J ± 7.50, <i>P</i> = 0.050). The TFN-ADVANCED also exhibited higher magnitudes of proximal segment displacement at the greater trochanter (7.65 mm vs. 4.72 mm, <i>P</i> = 0.045) but not at the distal segment (3.52 mm vs. 2.62 mm, <i>P</i> = 0.205). There were no differences in overall construct stiffness (506.81 N/mm ± 81.7 vs. 409.74 N/mm ± 112.3, <i>P</i> = 0.212). In all models, the implant underwent plastic deformation as the mode of failure. In simulated subtrochanteric femur fractures, the TFN-ADVANCEDTM implant is stronger and allows more proximal segment motion before failure compared with the FRN-ADVANCEDTM. In addition to strength and deformation, the nails exhibited different failure mechanisms with the TFNA failing proximally and the FRNA failing distally. Osteotomy site motion was the same, which is clinically relevant when considering strain at a healing fracture. III Biomechanical Study.