The following is the summary of “Dynamic Radiographs Are Unreliable to Assess Arthrodesis Following Cervical Fusion: A Modeled Radiostereometric Analysis of Cervical Motion” published in the January 2023 issue of Spine by Pinter, et al.
The study aimed to use an idealized cervical spine model to investigate whether intervertebral motion parameters on dynamic cervical spine radiographs are affected by the parallax effect or changes in the spine’s position relative to the x-ray source. However, due to the unreliability of the parameters used to assess motion, the clinical use of flexion-extension radiographs still needs to be determined. Therefore, interspinous process distance (IPD) was evaluated using plain radiographs of a cervical spine model with tantalum beads injected into the apex of each spinous process. After adjusting the generator angle and distance in the model, the IPD was calculated.
Differences in these characteristics were evaluated, as were their combined effects on IPD. A multivariate analysis was conducted to determine what factors contribute to the observed heterogeneity in IPD measures. Significant variations in the observed IPD at each intervertebral level in neutral, flexion, and extension resulted from changes in the generator distance and angle alone and in combination with one another, often exceeding an absolute change of more than 1 mm or more than 2 mm. According to the results of the multivariate study, the generator’s distance and the generator’s angle both have a significant impact on IPD measurements.
Absolute changes in IPD measures sometimes surpassed established cutoffs for establishing the presence of pathologic mobility across a fused segment when using an idealized cervical spine model with minor clinically realistic changes in spine position relative to the x-ray generator. This research supports previous findings that motion evaluation on dynamic radiographs is not a viable tool for detecting the existence of an arthrodesis unless these potential causes of variability are consistently addressed.