Background Safely performing instrumented spinal fusion requires an intimate knowledge of anatomy and variations. Pedicle screw position and size have implications on intraoperative and post-operative complications. While pre-operative planning with Computed Tomography (CT) scan measurements may be the safest way to judge trajectory and maximal screw size, it is not standard practice for many spine surgeons. We investigated how height and weight correlated with PD. We hypothesized that these routinely obtained, non-invasive measurements would provide an easily referenced data point to aid in perioperative estimation of maximum safe pedicle screw diameter (MSPSD).
Methods Coronal cuts of the lumbar spine were assessed to obtain transverse outer cortical PD as measured through the isthmus at lumbar vertebrae one through five. We assessed whether height, weight, and BMI significantly correlated with PD in our diverse population.
Results Height and weight were found to significantly correlate with PD. Height explained roughly 10% of the variance in PD, weight explained only 3-4%, and BMI nearly 0%. There were significant differences in this theoretical safety profiles between the “Taller Height” and “Shorter Height” groups for the majority of pedicle screw sizes at L1 through L3. Significant differences between the populations at L4 and L5 were only seen for 8.0 mm screws at the L4 level. At L5, 100% of the “Taller Height” and “Shorter Height” subjects’ pedicles could safely accommodate pedicle screws up to 8.0 mm in diameter.
Conclusions We previously reported on the significant difference in PD between different races. The results of this study provide yet another variable to be considered when making radiographic assessments of pedicle diameter.