The true sagittal diameter of the cervical spinal canal and its diagnostic significance in cercical myelopathy.

A method is presented for measuring the true sagittal diameter of the cervical spinal canal on routine lateral radiograms by the use of a midline perforated ruler. Sagittal measurements were made in 92 normal adults to establish a range of normal values. The lower and upper limits were 10 mm and 17 mm, respectively, at the levels of C-3 to C-7. Comparison of the results with the anatomical measurements of dried specimens showed good agreement. Four cases of cord compression were presented and the diagnostic significance of the method in cervical myelopathy was discussed.