The Assessment of Cervical Foramina With Oblique Radiographs: The Effect of Film Angle on Foraminal Area

Andrew K. Simpson, Jennifer Sabino, Peter Whang, John W. Emerson, Jonathan N. Grauer
2009 Journal of Spinal Disorders & Techniques  
Study Design: Radiographic evaluation of cadaveric cervical spine specimens. Objective: Assess reliability and reproducibility of foraminal dimensions obtained from cervical radiographs of varying obliquity and determine optimal angles for visualizing foramina at each cervical spine level. Summary of Background Data: Oblique radiographs may be considered to assess cervical foraminal dimensions and are generally obtained 45 degrees from the anteroposterior (AP) orientation. Previous reports have
more » ... evious reports have suggested that foraminal area observed on these radiographs may be influenced by changes in obliquity so that certain film angles may be better suited for accurately assessing foramen size, depending on which level is being evaluated. Methods: Radiographs of 4 human cadaveric cervical spines were obtained at 5-degree increments from 20 to 70 degrees relative to AP orientation, using both left and right sides of each specimen. Foraminal area was estimated by measuring height and width of each foramen and also with a freehand area measurement tool. Reliabilities of both methods were calculated. At each level, foraminal area was plotted against film angle and quadratic best-fit curves were used to determine the maximum area observed and the optimal angle of obliquity for assessment. Results: Assessment of foraminal area using the height and width values was associated with good interobserver reliability, whereas the freehand method exhibited excellent reliability. The optimal film angles for calculating foraminal area increased from 46.3 degrees for C2-C3 to 56.1 degrees for C7-T1. The ideal film angle that minimized the overall error of measurement across the entire cervical spine was estimated to be 52.4 degrees. Conclusions: Optimal angles for visualizing lower cervical foramina are larger than those for upper cervical spine. To minimize overall loss of foraminal area throughout the entire cervical spine, oblique cervical radiographs should be obtained at an angle of approximately 52 degrees from the AP orientation. Key Words: cervical spine, intervertebral foramen, cervical radiographs, cadaver study (J Spinal Disord Tech 2009;22:21-25) P lain radiographs remain the most commonly used diagnostic imaging modality for evaluating patients with spinal complaints and may be useful for identifying fractures, tumors, or degenerative pathologies. In addition to standard anteroposterior (AP) and lateral x-rays, supplementary views such as dynamic lateral, odontoid, and oblique studies may be considered in certain situations. Oblique views of the cervical spine are used to assess the patency of the intervertebral foramina and detect potential sites of nerve compression in individuals with suspected radiculopathy. In fact, a recent study demonstrated that as many as 8% of spine specialists routinely include cervical oblique x-rays as part of the initial battery of radiographic series when working up patients with degenerative cervical spine complaints. 1 Moreover, 16% obtained oblique views in the preoperative evaluation of these patients. Cervical foramina are bordered by the uncovertebral joints anteromedially, the facet joints posterolaterally, and the pedicles of cephalad and caudad vertebrae superiorly and inferiorly. Degenerative changes involving any of these structures may result in compression of the cervical roots as they exit the foramen. 2, 3 As cervical foramina are 3-dimensional structures with an intrinsic angle of orientation, that angle must be reproduced by an oblique radiograph to view the foramen en face and to accurately estimate its dimensions. Any deviation from this specific orientation will result in an apparent foraminal opening that is smaller than the actual foraminal area. Although cervical oblique x-rays are generally obtained with the film positioned 45 degrees relative to the AP orientation, it has not been definitively established that this angle optimizes the view of the cervical foramina. Abel 4 compared oblique radiographs taken at 45 and 60 degrees using both cadaveric specimens and human subjects. They demonstrated that the 60-degree
doi:10.1097/bsd.0b013e3181639b62 pmid:19190430 fatcat:qpcdxbpgxffj7eymrq4umawziq