Study design: This study analyzed anatomic parameters between the midpoint of cervical vertebral lateral masses as seen on the superficial, posterior aspect of the mass and cervical nerve roots. Posterior cervical dissection was performed, with the midpoint of the lateral masses kept intact and the nerve roots exposed.
Objective: To quantitatively determine the location of the cervical nerve roots and the transverse foramina, indicating vertebral artery placement relative to the posterior aspect of the cervical spine.
Summary of background data: Posterior plate-screw fixation of the cervical spine has been widely used to treat unstable fractures of the cervical spine. However, injury to the spinal nerve roots during the procedure remains an important concern. No previous anatomic study regarding the location of the cervical nerve roots relative to the posterior aspect of the cervical spine has been reported.
Methods: Fifteen specimens were obtained for study of the cervical spine. Laminectomy and partial removal of the superior and inferior articular facets then were performed on C2-C3 through C7-T1 to expose the nerve roots and dura. Photographs, containing a reference scale, were taken simultaneously perpendicular to the sagittal and transverse planes of the specimen. Using enlarged versions of the photographs, independent measurements by several observers were taken from the superficial, posterior center of each lateral mass to the nerve root superiorly and inferiorly, and to the lateral limits of the dura. Vertebrae from an additional 20 spines were examined to determine the position of the transverse foramina relative to the lateral mass of the vertebrae.
Results: The results showed that for C3-C7, the average distance from the superficial, posterior center of the lateral mass to the nerve root superiorly was 5.7 +/- 1.5 mm. Inferiorly, the average distance was 5.5 +/- 0.8 mm. The average distance from the lateral mass to the spinal cord dura was 9.2 +/- 1.4 mm, and the average medial angle of the nerve root was 76.3 degrees +/- 4.4 degrees. For cervical vertebrae C3-C5, the transverse foramina were situated medial to the posterior center of the lateral mass. At the C6 level, the transverse foramina were situated anterior to the posterior midpoint of the lateral mass.
Conclusion: This study demonstrates that the posterior midpoint of the lateral mass is a safe point for initiating screw insertion.