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Fabrication Patient-Specific Drill Guide Templates for Cervical Pedicle Screw Placement

Safahieh, Amir Hossein | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56614 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Arjmand, Navid; Parnianpour, Mohammad; Azimi, Parisa
  7. Abstract:
  8. One of the most common spinal surgeries involves spinal fusion or vertebral fixation, which is used to treat various conditions such as intervertebral disc disease, scoliosis (lateral deviation of the spinal column), fractures, infections, or the presence of tumors in the spinal column. In this surgical procedure, the use of pedicle screws and titanium rods prevents motion and friction between two vertebrae. Screws may enter the vertebrae in the wrong position and angle, causing bone weakening, rupture of nerve roots or blood vessels, weakness or lack of sensation in some parts of the body, spinal cord injury, and in severe cases, paralysis of the patient. For this reason, fusion surgery is considered complicated and dangerous. The objective of this project was to design a surgical guidance tool to enhance the accuracy of pedicle screw placement in one or multiple cervical spine vertebrae for each patient. To design these guides, the entry point and trajectory of the screws along the pedicle of the vertebrae had to be determined before the surgery. For this purpose, CT scans of two patients' cervical vertebrae were prepared, and from these images, bone 3D models were created using Mimics software. With 3D models of the vertebrae's structure, the appropriate screw placement within the vertebra could be visualized using 3-matic software and patient-specific guides could be designed. Using the same designed path, a suitable template is designed, which uses three legs corresponding to the surface of the vertebra; So that during screw placement, minimal damage is done to the vertebral bone, blood vessels and nerve networks. Now, using 3D printers, single-level and multi-level drill guides, as well as two copies of the five end vertebrae of the cervical spine of each of the samples, along with two copies of the three multi-level vertebrae of each patient, were produced using ABS and polylactic acid materials. The placement of 64 pedicle screws in the manufactured vertebrae was carried out by a surgeon with 15 years of experience using freehand techniques and two types of single-level and multi-level guidance templates. By re-imaging the drilled vertebrae along with the screws, 3D models were constructed, and the screw entry point and alignment errors were measured relative to the pre-designed model. To compare the screw placement errors between freehand technique and guidance templates technique, the measured error values were examined using a paired sample t-test, with a 95% confidence level, and the efficacy of the guidance templates in reducing screw placement errors was confirmed. The results indicated that for single-level vertebrae, the entry point error was reduced by 91% (from 3.2 mm to 0.3 mm), the three-dimensional alignment error was reduced by 67% (from 19.2 degrees to 6.4 degrees), the axial alignment error was reduced by 72% (from 17.2 degrees to 4.9 degrees), and the sagittal alignment error was reduced by 56% (from 8.0 degrees to 3.5 degrees). For multi-level vertebrae, the entry point error was reduced by 87% (from 5.7 mm to 0.8 mm), the three-dimensional alignment error was reduced by 83% (from 27.1 degrees to 4.5 degrees), the axial alignment error was reduced by 86% (from 19.9 degrees to 2.8 degrees), and the sagittal alignment error was reduced by 78% (from 20.1 degrees to 4.5 degrees). The screws placed were also examined using the Gertzbein criteria, and the utilization of guidance templates resulted in a 90% success rate for single-level vertebrae and a 92% success rate for multi-level vertebrae. Also, by measuring the time required for drilling the vertebrae using the two mentioned methods, the impact of the guidance templates on reducing surgical time was validated. Therefore, the use of patient-specific pedicle screw guides is considered a safe method for screw placement in the vertebrae
  9. Keywords:
  10. Fusion Surgery ; Three Dimensional Printer ; Cervical Vertebra ; Template Guides ; Pedicle Screws Placement Accuracy ; Cervical Spine ; Pedicel Screw ; Patient-Specific Guide Template

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