Biomechancis of biological fixation utilizing a plate with and without an intramedullary rod

Abstract

A wide range of prosthetic devices for internal fixation of the skeleton exist. Each aims to lend support to the injured limb, so as to restore the traumatized osseous and associated soft tissue to pre-fracture strength and functionality. These internal fixation devices act as mechanical fasteners which transfer the physiological loads acting on the bone from one end of the fracture to the other, while maintaining the bone fragments in varying degrees of anatomical Juxtaposition. The ultimate aim of fracture fixation using these devices is to achieve appropriate stability, while allowing the fractured bone to bear loads at some fraction of that of the unbroken bone. This research reported here involved developing a new concept of biological internal fixation using both a bone plate and an intrameduhary rod for fracture reduction. The combined system aims at reduction of the incidence of failure of the fixation device, preserving the biological environment and maintaining low levels of interfragmentary strain. The primary aim of this research was to compare the strains on the surface of the bone plate alone with that of a bone plate and an intramedunary rod during simulated bioloical fracture fixation. Mathematical analysis for the same situations was performed to confirm the experimental results, and to extend the results to predict the improvement in the fatigue life of the bone plate. The results indicate that a stress reduction in the plate of at least a factor of two is achieved when using a plate and a rod together. This yields a ten fold increase in the fatigue life of a bone plate made of 316 L stainless steel. Hence, the results indicate that this is a beneficial technique which provides a marked improvement in internal fracture fixation.