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, an d An screws to the spinal nerve. Objectives. To compare the potential incidence of nerve root (ventral and d orsal ramus) injury caused by the Magerl, Anderson, and An techniques. Summary of Background Data, Posterior plating with lateral-mass screw fixat ion is a common procedure for managing an unstable cervical spine. Comparat ive study of the Roy-Camille and Magerl techniques has been reported. Howev er, 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 th is study: Magerl, Anderson, and An. Each technique involved two specimens a nd 20 screws inserted from C3 through C7. A 20-mm-long screw was used to ov erpenetrate the ventral cortex. The anterolateral aspect of the cervical sp ine was carefully dissected to allow observation of the screw-ramus relatio nship. 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 M agerl, Anderson, and An screws were found at the dorsal ramus (50%), the bi furcation of the ventral dorsal ramus (45%), and the ventral ramus (55%), r espectively. 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.