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

Abstract

The goal of internal fixation procedures is the restoration of normal structure and function to the injured bone. Internal fixation devices are utilized to increase the stability of fracture segments, transfer loads across the fracture site, and maintain anatomical alignment. This facilitates the healing process, allowing the union of bone segments. The continuing search for improved internal fixation of fractures has led to a new technique that employs a bone plate with an intramedullary rod. This biological fixation technique combines the advantages of a plate with those of an intramedullary rod, while minimizing their respective disadvantages. The addition of an intramedullary rod is also thought to decrease the susceptibility of the plate to fatigue failure. The research reported here analyzed this biological fixation technique during torsional loading. The strain values on the surface of the plate alone were compared to those of a plate with an intramedullary rod during simulated fracture fixation. The effects of interlocking the rod to the bone were also analyzed. The results indicated that to reduce the strain on the plate the intramedullary rod needed to be interlocked to the bone. When the rod was not interlocked it provided no torsional support for the plate, it served only as an axis of rotation for the bone segments. However the interlocked rod was able to decrease the strains on the plate by one third. The interlocked system was also found to be significantly stronger than the plate alone. This new biological fixation technique is a definite improvement and has great clinical value.