Comparative CT-Based Bone Density of Traditional Pedicle Screw Trajectory, Cortical Bone Trajectory, and Modified Cortical Bone Trajectory — Radiographic Analysis of 3500 Simulated Pedicle-Screw Trajectories in 1750 Lumbar Vertebrae

Study DesignRetrospective study.ObjectiveTo evaluate and compare bone density along the traditional pedicle trajectory(TPT), cortical bone trajectory(CBT), and modified cortical bone trajectory(mCBT) using computed tomography(CT)-derived Hounsfield unit(HU) measurements.MethodsCT scans of the lumbar spine (L1-L5) of adult patients undergoing CT for non-spinal indications (predominantly younger adults) were retrospectively analyzed. Three pedicle screw trajectories were virtually simulated: TPT, CBT, and mCBT. For each trajectory, CTHU values were measured in sagittal section at four anatomical points along the screw path: posterior cortex, mid-pedicle, mid-vertebral body, and anterior vertebral body cortex using multiplanar reconstruction. Mean CTHU values, maximum screw lengths were compared across trajectories, and subgroup analyses were performed for age and sex.ResultsA total of 350 patients (1750 vertebrae) were analyzed. Mean CTHU values differed significantly among trajectories: CBT (538.2 ± 73.1HU) >mCBT (472.6 ± 87.9HU) >TPT (362.8 ± 68.4HU) (<i>P</i> < .001). At the posterior cortex, density was highest for CBT (1128.9 ± 147.6 HU), followed by mCBT (962.4 ± 192.7 HU) and TPT (582.1 ± 162.3HU). Across mid-pedicle, mid-body, and anterior cortex, CBT and mCBT showed comparable values, both significantly greater than TPT. mCBT showed significantly increased length of screw compared to CBT and TPT(<i>P</i> < .001). Age negatively correlated with CTHU across all trajectories, most pronounced in TPT (r = -0.36,R² = 0.13). Gender differences were significant only for TPT (<i>P</i> < .05).ConclusionIn this radiographic anatomical study of predominantly young adults, CBT and mCBT trajectories traversed higher CT-HU than the traditional pedicle path. These observations are hypothesis-generating and require validation in DEXA-verified osteoporotic cohorts and biomechanical and clinical studies before clinical recommendations can be made.