Supplemental Digital Content is available in the text

No abstract

Background Cortical bone trajectory (CBT) has been well-known in spine surgery for obtaining improved fixation while minimizing soft tissue dissection. This study was designed to compare the bone mineral density (BMD) between the CBT and traditional trajectory (TT) by using Hounsfield unit (HU) values and identify the ideal decades of patients and the suitable lumbar segments using this CBT technology from a radiological standpoint. Methods Patients were selected randomly from an institutional database based on age (evenly distributed by a decade of life) and gender. A total of 240 healthy patients had a computed tomography (CT) scan of the chest, abdomen, and pelvis. For each patient, axial slices of every vertebra were cut in two planes: one horizontal to the pedicle representing the plane wherein pedicle screws were inserted using the TT and the other in a caudocranial plane representing the plane wherein pedicle screws were inserted using the CBT. For each trajectory, a region of interest (ROI) was selected within the area wherein the screws were inserted. A CT number (HU values) was then calculated within each ROI to represent bone density. Results HU values measured at the ROI of CBT were significantly greater than those of the traditional pedicle screw in all age groups, and the specific value (ratio of the HU values of CBT/the HU values of TT) between CBT and TT was 1.92. A significant difference was observed between male and female. The HU values of CBT and TT of males were generally higher than those of females (males: CBT/TT 1.89 ± 0.45; Females: CBT/TT 1.95 ± 0.47). The specific value in HU values significantly increased with increasing age ( p = 0.000) and cauda lumbar level ( p = 0.000) in males and females. Conclusion BMD, as measured by HU values for the ROI of the CBT screw, was significantly greater than that of the traditional pedicle screw, especially in old patients and cauda lumbar segments.

No abstract

OBJECTIVETraditional trajectory (TT) screws are widely used in lumbar fixation. However, they may require revision surgery in some instances, especially in patients with osteoporotic spines. Cortical bone trajectory (CBT) screws may potentially be used to rescue a failed TT screw and vice versa in nonosteoporotic spines. This study aimed to investigate whether a CBT screw can salvage a compromised TT screw in osteoporotic lumbar spines and vice versa.METHODSA total of 42 vertebrae from 17 cadaveric lumbar spines were obtained. Bone mineral density was measured, and a CBT screw was randomly inserted into one side of each vertebra. A TT screw was then inserted into the contralateral side. The biomechanical properties of the screws were tested to determine their insertional torque, pullout strength, and fatigue performance. After checking the screws for the failure of each specimen, the failed screw track was salvaged with a screw of the opposite trajectory. The specimen was then subjected to the same mechanical tests, and results were recorded. A repeat pullout test on TT and CBT screws was also performed.RESULTSWhen CBT screws were used to rescue failed TT screws, the original torque increased by 50%, an average of 81% of the pullout strength of the initial TT screws was retained, and the fatigue performance was equal to that of the original screws, which were considerably stronger than the loose TT screws—that is, the TT repeat screws/TT screws were 33% of the pullout strength of the initial TT screws. When the TT screws were used to salvage the compromised CBT screws, the TT screws retained 51% of the original torque and 54% of the original pullout strength, and these screws were still stronger than the loose CBT screws—that is, the loose CBT screws retained 12% pullout strength of the initial CBT screws. Fatigue performance and the ratio of the pullout strength considerably decreased between the CBT rescue screws and the original CBT screws but slightly changed between the TT rescue screws and the original TT screws.CONCLUSIONSCBT and TT screws can be applied in a revision technique to salvage each other in osteoporotic lumbar spines. Additionally, CBT and TT screws each retain adequate insertional torque, pullout strength, and fatigue performance when used for revision in osteoporotic lumbar spines.