The complications associated with the use of spine screw fixation, including screw misplacement, nerve root injury, dural injury, and infection, must be considered.14–16 To reduce these complications, 3D template guide techniques have been introduced, with good results reported.1,3,5,6,17,18 For the pedicle screw in the lumbar and thoracic spine, Lamartina et al18 described 43 of 54 pedicle screws (91%) were placed accurately. Furthermore, these techniques are also expected to reduce hazardous radiation exposure and to shorten the operation time. Intraoperative fluoroscopic confirmation with hazardous radiation is still important in the use of an image-guided navigational system or minimally invasive techniques.19 In this study, fluoroscopy was required only once after the insertion of the screws. Thereby reducing the duration of radiation exposure to the surgical team. The PSDT has the ability to customize both the placement and the size of each screw, based on the unique morphology of each patient’s vertebral lamina, and to preoperatively prepare the surgical plan. Verifying the accuracy of this simple template guide may help alleviate procedural anxiety, especially among less experienced spine surgeons. A suitable position of the template was easily found, because of the specific fit of the postural laminar surface with the template, by pressing gently with the surgeon’s finger. Vibration during drilling or the gap between the lamina and the PSDT can cause errors. In this regard, clean preparation of the laminar surface is essential. Although the PSDT has many advantages over previous fluoroscopy-guided screw-insertion techniques, including less hazardous radiation exposure and less screw misplacement rate,3,7,12 the analysis and progress of this technique will require further study. However, such efforts will ensure safety and accuracy of using these techniques. By using this novel, custom-fit navigational template, the operation time can be considerably reduced.5,13
The cortical trajectory followed a caudocephalad path sagittally and a laterally directed path in the transverse plane, engaging only the cortical bone in the pedicle without the involvement of the vertebral body trabecular space.9 CBT screws are shorter and smaller but potentially more powerful. Theoretically, the advantage associated with this technique is increased cortical bone contact, providing enhanced screw grip and interface strength independent of trabecular bone mineral density.20 Mechanical studies support this theoretical advantage. CBT has been shown to increase the resistance to pullout by 30% compared with the pedicle screw.8,9 Clinically, Takenaka and colleagues reported CBT has less blood loss, less intraoperative muscle injury, and less perioperative pain which led early recovery. However, as it is newly developed and unfamiliar, proper positioning is difficult with CBT. The positioning of CBT screws after decompressive procedures such as a partial or total laminectomy during spinal surgery might be difficult because the landmark of the starting point of the CBT screw is on the posterior surface of a laminar bone, which would be removed during the decompression. PSDT may be especially useful for surgeons who are not familiar with CBT.
Compared with the PSDT, robot-based systems and associated navigational systems require more space for the instruments, and their increased operative time can contribute to infection risk.21 Moreover, such systems may require more time, greater personnel, and higher expense. These demands allow the use of robot systems in only a few hospitals that have sufficient human and financial resources.22,23 With the technique presented in this study, a single programmer, handled the software, and the material was inexpensive. The average cost of material in this study was $10 for each template, and known cost for patient-specific drill template is $8 to $50.7 The time required for manufacturing the PSDT including designing and printing was <1 day. Although we need 1 day for preparation, it will be worth it because it can decrease intraoperative time.7 Our 3D printing machine is over $200,000 and is a multipurpose, multimaterial, high-quality machine. An entry-level 3D printer suitable for printing drill guides may be obtained for only a few thousand US dollars with similar or lower average cost of material.7,24 The reliability and print speeds may differ, and further research is needed to determine best practices for 3D printing templates. Nevertheless, we believe the PSDT is cost-effective, convenient, and demonstrates clear advantage of safe and accurate cortical screw placement in the thoracolumbar spine.
Currently, we do not have the standard methods for measuring the accuracy and safety using statistical methods. We need standard methods for evaluating the accuracy of mirror-imaged template to confirm the adequate placement onto the laminar surface. Our design of the template did not aim the soft tissue preservation, which is the advantage of the cortical screw in a clinical situation. Some drill guide templates are composed of 2 units for 1 spine level for the left side and right side. Such design provides the preservation of more soft tissues including posterior ligament complex.7 Further clinical study of the efficacy and optimal design of template will be beneficial. This study is not a comparative clinical trial, and a further study is comparing with the robot and the navigational system would be more informative to decide optimal guide-aided surgery methods.
The PSDT customizes patient-specific trajectory for CBT screw placement in the thoracolumbar spine, based on the unique morphology of the individual. The use of drill templates in placing thoracolumbar CBT screws is promising due to its accuracy, low cost, and ease of use.
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