Magnification Error in Digital Radiographs of the Cervical Spine Against Magnetic Resonance Imaging Measurements

STUDY DESIGN: Prospective study. PURPOSE: The main purpose of this study was to clarify the range of magnification errors on digital plain radiographs and to determine if there is a correlation between the body mass index (BMI) of a patient and the magnification error. OVERVIEW OF LITERATURE: Most clinicians currently use digital plain radiography. This new method allows one to access images and measure lengths and angles more easily than with the past technologies. In addition, conventional plain radiography has magnification errors. Although few articles mention magnification errors in regards to digital radiographs, they are known to have the same errors. METHODS: We used plain digital radiography and magnetic resonance imaging (MRI) to acquire images of the cervical spine with the goal of evaluating magnification errors by measuring the anteroposterior vertebral body lengths of C2 and C5. The magnification error (ME) was then calculated: ME=(length on radiograph-length on MRI)/length on MRI x100 (%). The correlation coefficient between the magnification error and BMI was obtained using Pearson's correlation analysis. RESULTS: Average magnification errors in C2 and C5 were approximately 18.5%+/-5.4% (range, 0%-30%) and 20.7%+/-6.3% (range, 1%-32%). There was no positive correlation between BMI and the magnification error. CONCLUSIONS: There were magnification errors on the digital plain radiographs, and they were different in each case. Maximum magnification error differences were 30% (C2) and 31% (C5). Based on these finding, clinicians must pay attention to magnification errors when measuring lengths using digital plain radiography.

Posterior Fixation of a Cervical Fracture Using the RRS Loop Spine System and Polyethylene Tape in an Elderly Ankylosing Spondylitis Patient: A Case Report

An 80-year-old woman presented with neck pain and paraparesis of Frankel C in her upper and lower extremities after falling. Imaging revealed an ankylosing cervical spine and a fracture line running obliquely from the anterior C3-4 to the posterior C4-5 level. Posterior fixation from the occi pit to T3 was performed using the RRS Loop Spine System and concomitant polyethylene tape fixation. This system is characterized by the uniqueness of how it screws to the occi pit and its use of a fixation rod with a larger diameter than in other instrumentation devices for use in the cervical region. Sublaminar banding using polyethylene tape was used to secure fixation. Her postoperative course was unremarkable, and her neck pain was relieved, although neurological improvement was minor. To our knowledge, this is the first report of an application of the RRS Loop Spine System to an ankylosing spondylitis patient with a cervical fracture.