MECHANICAL CHARACTERIZATION OF A TOTALLY INTRAMEDULLARY GRADUAL ELONGATION NAIL

An intramedullary gradual elongation nail (Albizzia) capable of fulfil ling the function of traditional intramedullary nails while providing the gradual, controlled distraction of an external fixator was designe d for progressive lengthening of lower limbs, In this study, the biome chanics of the gradual elongation nail were compared with several intr amedullary nails: Grosse & Kempf, Russell-Taylor, AO, and Laffay. Bend ing stiffness, torsional stiffness, ultimate bending strength, and tor sional strength were determined using the American Society for Testing and Materials standard F383-73 as a guide, The results show that in u nextended and elongated conditions, the gradual elongation nail has to rsional stiffness (1-5 Nm(2)) comparable with the AO nail (2 Nm(2)) an d bending stiffness (41-89 Nm(2)), ultimate bending (246 Nm), and tors ional (28-37 Nm) strengths within the ranges obtained for other intram edullary nails (27-105 Nm(2), 167-298 Nm, and 2-100 Nm, respectively), Additionally, the low torque required to lengthen the device under a 500 N load (3 Nm) and the low longitudinal stiffness because of the ac tive dynamization system with bimodal load deformation characteristics (80-120 N/mm initial, 600-800 N/mm secondary) produce a device with a lmost no torsional and longitudinal stress shielding, From a biomechan ical point of view, this single, completely implantable device is a sa fe, viable, and efficacious alternative to external fixation for progr essive lengthening of lower limbs.