The anatomic relation of lateral mass screws to the spinal nerves. A comparison of the Magerl, Anderson, and An techniques.

Study Design: Analysis of the anatomic relation of the Magerl, Anderson, and An screws to the spinal nerve.

Objectives: To compare the potential incidence of nerve root (ventral and dorsal ramus) injury caused by the Magerl, Anderson, and An techniques.

Summary Of Background Data: Posterior plating with lateral mass screw fixation is a common procedure for managing an unstable cervical spine. Comparative study of the Roy-Camille and Magerl techniques has been reported. However, the risk of nerve root injury for the Anderson and An techniques is not known.

Methods: Three lateral mass screw insertion techniques were performed in this study: Magerl, Anderson, and An. Each technique involved two specimens and 20 screws inserted from C3 through C7. A 20-mm-long screw was used to overpenetrate the ventral cortex. The anterolateral aspect of the cervical spine was carefully dissected to allow observation of the screw-ramus relationship.

Results: The overall percentage of nerve violation was significantly higher with the Magerl (95%) and Anderson (90%) techniques than with the An (60%) technique (P < 0.05). The largest percentages of nerve violation for the Magerl, Anderson, and An screws were found at the dorsal ramus (50%), the bifurcation of the ventral dorsal ramus (45%), and the ventral ramus (55%), respectively.

Conclusions: The results of this study indicate that the potential risk of nerve root violation is higher with the Magerl and Anderson techniques than with the An technique.