SAFE LATERAL-MASS SCREW LENGTHS IN THE ROY-CAMILLE-AND-MAGERL TECHNIQUES - AN ANATOMIC STUDY

Study Design. Investigation of the mean safe lateral-mass screw length s in the Roy-Camille and Magerl screw techniques in cadaveric cervical specimens. Objectives. to report the mean screw path length and to ev aluate the relation of the screw trajectory to the nerve root in the R oy-Camille and Magerl screw techniques. Summary of Background Data. Po tential injury to the cervical nerve root caused by too long a screw r emains a major concern. Few studies regarding proper screw length and its relation to the adjacent nerve root are available. Methods. Fourte en cervical spines were used for this study. Each lateral mass from C3 to C7 was drilled according to the techniques described by Roy-Camill e (right side) and Magerl (left side). The cervical spines were harves ted from the cadavers, and the anterior aspect of the lateral mass and spinal nerve were exposed. The screw path length between the dorsal a nd ventral cortices of the lateral mass were measured. An additional m easurement was taken from the ventral aspect of the lateral mass to th e nerve root along th screw path. Results. The mean screw path length in the Roy-Camille technique decreased consistently from C3 (15.7 +/- 1.7 mm) to C7 (11.3 +/- 0.8 mm). The mean distance from the ventral co rtex to the nerve root ranged from 1.2 to 2.3 mm, and the smallest val ue was at C7. The mean screw path length in the Magerl technique also decreased from cephalad to caudal, with a range of 15-16 mm at C3-C6 a nd a mean value of 13.8 mm at C7. Conclusions. a safe screw length is 14-15 mm in the Roy-Camille technique and 15-16 mm in the Magerl techn ique at C3-C6. A short screw may be used at C7 if desired.