Lateral Mass Screw Fixation in the Cervical Spine: Introducing a New Technique.

STUDY DESIGN

This was designed as a randomized double blind study to compare the classical Magerl technique of insertion of lateral mass screws with the authors' technique. The observations regarding length, outcome, and radiology was done by a group blinded to the technique used.

PURPOSE

The present study was designed with the objective of identifying the optimal technique for introducing the lateral mass screws that uses the maximum possible dimension of the lateral mass.

OVERVIEW OF LITERATURE

Lateral mass screw fixation is a common surgery that is performed in the cervical spine. Various modifications for the procedure have been described, such as changes in the entry point, angulation of the screws, and modifications in the exit point. These do not allow the insertion of longer screws that can give more purchase on the bone.

METHODS

From January 1, 2009 to December 31, 2018, 176 patients who were scheduled to undergo lateral mass screw fixation were enrolled. They were randomized into two groups; we inserted lateral mass screws using our new technique for one group and by using the classical Magerl technique for the other group. Intraoperative measurements were used to assess the bone-screw interface length. Postoperative radiography and postoperative computed tomography were performed to assess the trajectory of the screws.

RESULTS

Total 88 patients were included in the study group, including 68 men. The control group included 65 men. The most common indication for surgery was cervical spondylotic myelopathy. The average bi-cortical length that was measured intraoperatively was 19.9 mm in the study group and 16.3 mm in the control group. This was significantly different from the average lengths of screws in the control group.

CONCLUSIONS

The trajectory that involves an entry point as close as possible to the posterior inferior medial angle of the lateral mass cuboid and traverses a distance of about 20 mm to obtain a bi-cortical purchase in the diagonally opposite angle may provide a much better and firmer bony purchase in the lateral mass than conventional points of entry and trajectories.