A new femur intramedullary nail with tube and coil spring for maximum interfragmentary rotational and axial stability after fracture site resorption.

ABSTRACT

OBJECTIVE: This study aimed to biomechanically compare the maximum rotational, axial movements, and compression forces between fracture fragments before and after 1-4 mm fracture site resorption among interlocking nails, compression nails, and newly designed compressive anti-resorption (CARES) nails compressed with tube and coil spring. METHODS: We determined the maximum axial/rotational movements and interfragmentary compression loads between fragments on 10 interlocking nails, 10 compression nails, and 10 CARES nails with 30 composite femurs. Using a compression-distraction testing device, 6 N·m external and internal torques were applied, and we evaluated the maximum rotational and axial displacement between fragments after 1-4 mm fracture site resorption. RESULTS: When 6 N·m of internal-external rotation torque was applied after 2 mm fracture site resorption, the maximum rotational displacement between fragments in the CARES nail was 3 ± 0.52 mm, 101% less than the 6.03 ± 0.83 value in the compression nail and 100% less than the 6 ± 1 mm value measured in the interlocking nail (P=.000). The compression between fragments was 298 ± 72 N in the CARES nail after 1 mm of resorption, while this value was measured as 0 in the other nails. There was a significant difference in rotational, axial stability, and interfragment compression among the different femoral nails after 1-4 mm fracture site resorption. CONCLUSION: The CARES nail having additional coil springs seems significantly biomechanically superior to compression nails and interlocking nails, providing maximum rotational, axial stability, and interfragment compression after fracture site resorption.