Cortical Bone Trajectory Screw for Lumbar Fixation: A Quantitative Anatomic and Morphometric Evaluation

BackgroundLumbar cortical bone trajectory (CBT) screw constructs provide an alternative method of pedicle screw fixation in minimally invasive spine surgery. In this study, we explored the CBT technique in further anatomic detail. The primary aims were to evaluate variations in anatomy relevant to CBT screw placement and to determine optimal screw location, trajectory, and length using measures obtained from computed tomography (CT) scans.MethodsOne hundred CT scans of the lumbar spine were reviewed, and 14 total measurements of entry points, trajectories, and lengths for placement of CBT screws were evaluated.ResultsAcross all lumbar levels, the mean right pedicle–pars interarticularis junction length ranged from 7.58 ± 1.18 mm to 8.37 ± 1.42 mm, and the mean left pedicle–pars interarticularis junction length ranged from 7.95 ± 1.42 mm to 8.6 ± 1.74 mm. The pedicle–pars interarticularis junction from L1 to L5 was deemed too small for a 5-mm-diameter CBT screw in 35%, 24%, 17%, 17%, and 19%, respectively, on the right, and in 30%, 17%, 17%, 17%, and 20%, respectively, on the left. The average length of a screw placed along the cranial cortical bone of the pedicle ranged from 27 ± 2.5 mm to 30.5 ± 3.4 mm, and the angle of the screw with respect to the vertebral body endplate ranged from 44 ± 4.1° to 48 ± 6.2°.ConclusionsImproved anatomic knowledge relevant to CBT screw placement for lumbar fixation offers the potential for improving outcomes and reducing complications. Moreover, detailed analysis of the anatomy of the pedicle–pars interarticularis junction via preoperative CT can aid in determining the ideal fixation method.