Spinal-Pelvic Fixation Assemblies

Spinal-pelvic fixation assemblies are used by orthopedic surgeons to correct the curvature of a patient’s spine or to stabilize a patient’s spine following injury or surgery.  Currently, the assemblies consist primarily of metal rods and pedicle screws and are made of either stainless steel or titanium.  Stainless steel has been used successfully by orthopedic surgeons for many years, while new titanium alloys have recently become more popular.  The titanium alloys are attractive in part because they do not interfere with MRI or CT scans used during postoperative patient evaluation.  The purpose of this study is to compare the performance of the titanium assemblies with the stainless steel assemblies.

The biomechanical behavior of spinal-pelvic fixation assemblies of stainless steel and titanium are being evaluated experimentally.  The spinal-pelvic fixation implant assembly model is composed of two rods and two pedicle screws.  The constructs simulate fixation between the L-4 vertebra and the pelvis in a vertebrectomy model.  Both the vertebra and the pelvis are simulated with ultra high molecular weight polyethylene.  The rods are secured to the vertebra with the pedicle screws and are secured to the pelvis using the Galveston technique.    The constructs simulate a vertebrectomy by providing a large gap between the simulated vertebra and pelvis.  Using UHMWPE to simulate the vertebra and pelvis eliminates variations in cadaver bone properties and geometry.  The assemblies will be tested in a universal test machine to failure to determine the failure mode (fracture, gross yielding, gross deformation of one or more of the parts of the construct, or by slipping within the construct) and characteristics.  The results of these tests will provide a comparison of the biomechanical behavior of stainless steel assemblies with titanium assemblies used for spinal-pelvic fixation.

Contact:  Anthony Paris, PhD, PE, aparis@boisestate.edu

Last Updated 3/28/2005