A comparison of magnetic and radiographic imaging artifact after using three types of metal rods: stainless steel, titanium, and vitallium

Abstract

Background context After spinal fusion surgery, postoperative management often includes imaging with either computed tomography (CT) or magnetic resonance imaging (MRI) to assess the spinal canal and nerve roots. The metallic implants used in the fusion can cause artifact that interferes with this imaging, reducing their diagnostic value. Stainless steel is known to produce large amounts of artifact, whereas titanium is known to produce significantly less. Other alloys such as vitallium are now being used in spinal implants, but their comparison to titanium and stainless steel has not been well documented in the orthopedic literature. Titanium is a desirable metal because of its light weight and lower production of artifact on imaging, although it is not as stiff as stainless steel. Vitallium is proposed as a replacement for titanium because it has stiffness similar to stainless steel, while still being as light as titanium. Purpose The purpose of this study was to compare the amount of artifact produced on MRI and CT by three types of spinal implants: stainless steel, titanium, and vitallium. Study design A prospective experimental design was used to compare three types of spinal implants used in posterior spinal fusion surgery. Outcome measures The resulting images were evaluated by a radiologist to measure the amount of artifact (in millimeters) and by an orthopedic surgeon to assess the diagnostic quality (on a Likert scale). Methods A porcine torso was used for repeated MRI and CT scans before and after implantation with pedicle screws and rods made of the three metals being studied. Results Images produced after the insertion of vitallium rods and titanium screws as well as those with titanium rods and screws were found to have less artifact and a better overall diagnostic quality than those produced with stainless steel implants. Overall, there was not a difference between the amount of artifact in the spinal images with vitallium and titanium rods, with the exception of a few trials that showed small but statistically significant differences between the two metals, where titanium had slightly better images. Conclusions If vitallium rods are used in posterior spinal surgery in place of implants made of titanium or stainless steel, any postoperative imaging of the spine using MRI or CT should have amounts of artifact that are similar to titanium and better than stainless steel.