Biomechanical Stability and Pullout Strength of the Cervical Artificial Pedicle Screw

Introduction: Surgeons risk injury to the central nervous system when excising neoplastic growths from the anterior spinal canal [1]. One method to facilitate access to this region is to combine laminectomy with unilateral facectomy and pediculectomy. For better exposure, however, surgeons may drill from the origin of the pedicle through the posterio-lateral aspect of the vertebral body [1]. This technique can present challenges when tumors extend beyond a single vertebral level, as the removed lateral masses and pedicles are insertion sites for fixation [1-5]. A novel solution involves the placement of bicortical screws (“artificial pedicle screws APS”) that extend from the pedicle origin on the vertebral body, through the midline of anterior cortical and protrude 2mm [1, 2]. This technique has been successful in a number of clinical cases, but remains biomechanically uncharacterized [1,2]. We hypothesize that the use of artificial pedicle screws provide stiffness and pullout strength similar to traditional lateral mass screws in the cervical spine. Materials and Methods: Five fresh-frozen human C2 to C7 cervical specimens were studied (F=1, M=4; 65 ± 5 y.o; occiput-T1). The specimens were cleaned of muscles and connective tissue but care was taken not to disrupt ligaments and intervertebral discs. Specimens with abnormal morphology, e.g., preexisting cervical fractures and low BMD, were excluded from the study (evaluated via DEXA, Hologic QDR-2000, Hologic, Inc., Bedford, MA). The C2 and C7 vertebrae were potted in a cylindrical metal fixture with polymethylmethacrylate (PMMA).