Experimental Study for the Treatment of Long Bone Shaft Fracture with Non-reamed Flexible Intramedullary Nail

Woo, Young Kyun

Abstract

Intramedullary rodding has been the treatment of choice for long bone shaft fracture when operative fixation is necessary. The present technology on rodding has been the use of a single, rigid intramedullary rod. However, an undesirable consequence of the use of such a rigid rodding is the post-union osteopenia along the rod, which is believed to be secondary to the over-protection of the surrounding bone from normal stresses, the so called "stress bypass effect". Another disadvantage of the rodding procedure is interruption of intramedullary vascularity by reaming which may contribute to non-union. To evalvate these parameters, experiments were performed on mature dogs, using flexible multiple rods which can be inserted without reaming. The fracture healing was studied biomechanically by measuring the nondestructive bending and torsion stiffness, maximum torque and energy absorption to failure. Using two expermental dogs a zero time test of the osteotomized femur in which one bone was fixed with multiple rods and the contralateral bone fixed with a Kiintscher rod, showed that the bending stiffness was higher in the Kuntscher rod than in the multiple rods fixed bone. This fact means the flexible multiple rods fixation gives more elastic fixation than Kiintscher rod. The bending and torsion stiffness of the femur as expressed by repair per control percentage showed the multiple rods were significantly higher than Kuntscher rod at 6 weeks study but not in 9 weeks study. In the six month study, the repaired femur of the multiple-rods had significantly high bending and torsion stiff-ness, maximum torque and energy. Through these results, it was found that there was some advantage to the multiple rods in terms of early fracture healing at the 6 weeks study but no significant difference between two rod systems at the 9 weeks study. And there was significant advantage in the late remodelling phase of fracture healing in flexible rod.