Determining the sagittal dimensions of the canal of the cervical spine - The reliability of ratios of anatomical measurements

The ratio of the sagittal diameter of the cervical I canal to the correspon ding diameter of the vertebral body has been described as a reliable means for assessing stenosis of the canal and detecting those at risk of cervical neuropraxia. The use of ratio techniques has the advantage of avoiding var iation in magnification when direct measurements are made from plain radiog raphs. We examined the reliability of this method using plain lateral radio graphs of unknown magnification and CT scans. We also assessed other possib le ratios of anatomical measurements as a guide to the diameter of the cana l. Our findings showed a poor correlation between the true diameter of the can al and the ratio of its sagittal diameter to that of the vertebral body. No other more reliable ratio was identified. The variability in anatomical mo rphology means that. the use of ratios from anatomical measurements within the cervical spine is not reliable in determining the true diameter of the cervical canal.