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Background: Pedicle screw placement is the most common method of fixation in the thoracic spine. Use of the "superior facet rule" allows the operator to locate the borders of the pedicle reliably using posterior landmarks alone. This study investigated the ability of 3-dimensionally (3D)-printed thoracic vertebrae, made from combined thermoplastic polymers, to demonstrate pedicle screw cannulation accurately using the superior facet as a reliable landmark., Methods: An anonymized computed tomography scan of the thoracic spine was obtained. The T1-T12 thoracic vertebrae were anatomically segmented and 3D-printed. The pedicle diameters and distance from the midpoint of the superior facet to the ventral lamina were recorded. A total of 120 thoracic pedicles in 60 thoracic vertebral models were instrumented using a freehand technique based only on posterior landmarks. The vertebral models were then coronally cut and examined for medial or lateral violations of the pedicle after screw placement., Results: A total of 120 pedicle screws were placed successfully within the 3D-printed thoracic vertebral models. Average measurements fell within 1 standard deviation of previous population studies. There were no pedicle wall violations using standard posterior element landmarks for instrumentation. There were 3 lateral violations of the vertebral body wall during screw placement, all attributable to the insertion technique., Conclusions: 3D-printed thoracic vertebral models using combined thermoplastic polymers can accurately demonstrate the anatomical ultrastructure and posterior element relationships of the superior facet rule for safe thoracic pedicle screw placement. This method of vertebral model prototyping could prove useful for surgical education and demonstrating spinal anatomy., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Surgical proficiency is classically acquired through live experience in the operating room. Trainee exposure to cases and complex pathologies is highly variable between training programs. 1 Currently, there is no standard for neurosurgical skill assessment for specific operative techniques for trainees. Cadaveric simulation has been used to demonstrate surgical technique and assess resident skill but often presents a significant financial and facility burden. 2-4 Three-dimensional (3D) printing is an alternative to cadaveric tissue in providing high-quality representation of surgical anatomy; however, this technology has significant limitations in replicating conductive soft tissue structures for the use of cauterization devices and haptic learning for proper tissue manipulation. 5-7 Our team has combined novel synthesis methods of conductive thermoplastic polymerization and 3-dimensional-printed cervical spine models to produce a layered biomimetic simulation that provides cost-effective and anatomically accurate education for neurosurgical trainees (Video 1). This is accomplished through virtual modeling and layered simulator construction methods by placing the individual polymer layers according to anatomic location of the simulated in vivo structures. The consistency of the thermoplastics can be tailored according to the desired soft tissue structures (skin, fat, fascia, muscle) according to the degree of polymerization. This cost-effective simulation was designed to represent the material and biomechanical properties of the cervical spine cortico-cancellous interface, as well as individual soft tissue components with specific anatomic details of muscle tendinous and ligamentous insertion. These features allow for representative start-to-finish surgical simulation that has not yet been made widely available to neurosurgical training programs., (Copyright © 2019 Elsevier Inc. All rights reserved.)

We present a surgical video demonstrating the anatomy and technique of freehand C2 pedicle screw placement using a cadaveric specimen and 3-dimensional simulation software. C2 pedicle screws have been shown to augment cervical constructs and provide increased biomechanical stability compared with pars screws due to the increased length and bony purchase of pedicle screws within the pedicle and vertebral body. 1 The presence of vertebral artery variations within the transverse foramen may preclude pedicle screw placement, and these should be identified on preoperative imaging. The C2 pedicle can be directly palpated at the time of screw placement, which aids screw placement in cases of deformity or trauma. A freehand technique without the use of computed tomography scan guidance or intraoperative fluoroscopy decreases radiation exposure for the operator and patient and has been shown to be safe for patient-related outcomes. 2-5 Complete exposure of the C2 posterior elements is key to identifying the pedicle. The trajectory is based on direct visualization of the medial and superior pedicle borders to avoid lateral or inferior breaches into the transverse foramen. A curved probe is used for access into the vertebral body, respecting the outer cortical walls of the pedicle. The intraosseous position is confirmed with a ball-tipped probe. Fluoroscopy should be performed after screw placement to confirm proper position. By accomplishing proper exposure and understanding the anatomy of the C2 pedicle, the placement of C2 pedicle screws using a freehand technique is a safe and efficient technique for high cervical fixation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: 3D printed models have grown in popularity for resident training. Currently there is a paucity of simulators specifically designed for advanced cervical instrumentation. Our institution created a unique simulator for the instruction of freehand placement of C2 laminar screws using a specific 3-dimensional printing technique to replicate the corticocancellous interface. This study was designed to determine the efficacy of the simulator for teaching neurosurgical residents the freehand technique of C2 laminar screw placement., Methods: Ten participants with different experience levels participated in the study. The participants were separated into 2 groups based on experience level. Primary outcome assessments were breach rates, screw-screw interaction, and the ability to successfully place 2 screws in 1 model. Participants were graded based on a performance scoring system, and the outcomes of the 2 groups were compared., Results: All participants in the novice group showed improved technical ability on repeated use of the simulator and were able to successfully place bilateral screws by the fourth attempt. Statistical analysis indicated an association between operative experience level and successful bilateral screw placement, implying that the simulator accurately represented an in vivo intraoperative scenario., Conclusions: By utilizing our novel 3D printing production method, we have created a unique simulator for the freehand placement of C2 laminar screws. To our knowledge, this is the first report of a study investigating the use of a 3-dimensional printed simulator specifically designed to teach the freehand placement of C2 laminar screws to neurosurgical trainees., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Background: Atlantoaxial fusion often requires C2 nerve transection for complete C1 lateral mass exposure. Nerve transection is made ideally at the preganglionic segment proximal to the dorsal root ganglion to minimize the risk of postoperative dysesthesias. If the nerve is transected too proximally, cerebrospinal fluid leak may be encountered by violation of the dura and arachnoid where the sensory and motor nerve rootlets exit the subarachnoid space. In this study we aimed to quantify the length of the C2 nerve preganglionic segment using cadaveric specimens and develop a method for reliable intraoperative localization for sectioning during C1-2 arthrodesis., Methods: Using microsurgical techniques, 16 C2 nerves from 8 frozen and injected cadaveric cervical spine specimens were dissected. Two key measurements were taken to establish a reliable method of preganglionic segment identification. The "sweet spot" for nerve transection was based on the approximate location of the midpoint of the preganglionic segment., Results: The final determination of the ideal spot for C2 nerve transection using these calculations was 3 mm lateral to the medial border of the lateral mass., Conclusions: This anatomic study found remarkable consistency in the preganglionic segment length. The medial border of the lateral mass appeared to be a consistently reliable landmark for identification of the preganglionic segment of the C2 nerve root. By using relationships between known anatomic structures intraoperatively, safety of atlantoaxial fixation can be optimized to maximize complication avoidance and satisfactory patient outcomes., (Copyright © 2019 Elsevier Inc. All rights reserved.)