Increased medial pedicle angulation of the lumbar spine as a function of the posterior osseous defect in patients with myelomeningocele.

PURPOSE: Bony anatomy in patients with immature spines has been previously characterized. Alterations in lumbosacral morphology in patients with myelodysplasia, demonstrating increasing medial pedicle angulation (MPA) from L1-S1, have been examined; however, MPA related to size of the defect in myelomeningocele patients has not been defined. We aimed to establish that magnitude of posterior vertebral arch defects determines the extent of MPA in the lumbar spine, with larger posterior defects associated with increased MPA. METHODS: This retrospective case-control study compared lumbar morphometric measurements of patients with and without myelomeningocele. Eighteen patients with myelomeningocele underwent computed tomography with three-dimensional reconstruction; there was no concurrent pathology. Advanced imaging software was utilized to manipulate the axial, sagittal, and coronal axes at each lumbar level, and obtain accurate measurements of pedicle width, height, length, MPA, and posterior laminar defect. RESULTS: In lumbar vertebrae with a posterior arch defect (PAD), increased magnitude was associated with a concurrent increase in MPA between 16.2° (43.4%) and 28.1° (299.4%) depending on lumbar level. At levels without a PAD, increases in MPA were between 0.8° (4.3%) and 5.7° (60.6%) depending on lumbar level. Although the actual degree of medial angulation increases from cephalad to caudal levels, the percentage of deviation from normal is higher at the more cephalad levels compared with controls. CONCLUSION: In patients with myelomeningocele, larger posterior vertebral arch defects were associated with increased MPA in the lumbar spine. Lumbar levels without a PAD also demonstrated increases in MPA compared with normal values.

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

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.