摘要：

BACKGROUND CONTEXT Irreducible ventral compression of the brainstem or upper cervical spinal cord can result from several pathologies unique to the craniovertebral junction (CVJ). These include tumors, trauma, rheumatoid arthritis, infection, and congenital anomalies (Chiari 1 malformation, basilar invagination). Symptomatic patients present with lower cranial neuropathies, sensory deficits, and myelopathy, often necessitating ventral decompression. Considerable advancements have been made with respect to endoscopic endonasal approaches to the CVJ—and these are now routinely employed to address a variety of pathologies, including odontoidectomy for basilar invagination and resection of tumors that occupy the CVJ and/or basiocciput. However, a significant proportion of these patients will require supplemental occipitocervical fusion. Currently, this is performed through a separate-stage posterior approach, which is associated with considerable muscle dissection, postoperative pain, blood loss, and risk of injury to the vertebral arteries. To date, no validated method for endonasal fixation of O-C1 exists, and the literature on investigational techniques for endonasal occiptocervical fixation is extremely limited. In this study, we describe our experience with designing and implanting a 3D-printed plate-screw construct for endonasal O-C1 fixation in cadaveric specimens. PURPOSE To evaluate the feasibility of a novel method for ventral fixation and fusion of the occipitocervical junction through an endoscopic endonasal approach. To advance surgeons' ability to treat pathology of the CVJ and offer a minimally-invasive alternative to the current methods of occipitocervical fixation and fusion. STUDY DESIGN/SETTING This is a cadaveric feasibility study which was carried out in our institution's microsurgical laboratory. PATIENT SAMPLE Our sample consists of seven embalmed cadaveric heads. OUTCOME MEASURES Average occipital condyle and C1 lateral mass screw starting points, trajectories, and proximity to critical structures (vertebral arteries, hypoglossal canal, emissary vein foramen). METHODS Methodology consists of designing, 3-D printing, and implantation of our plate-screw construct in seven cadaveric specimens. Thin-cut CT scans are obtained for each specimen and used for 3D segmentation of the O-C complex. Using 3D modeling software, plates are designed to span each O-C1 joint and sit flush onto the bone surface. Screw holes are designed to hold 4.0 x 17mm screws. The model is 3D printed in polylactic acid (PLA) for prototyping. After final modifications, the plates are printed in a Titanium alloy (Ti-6Al-4V). Implantation of the plates is performed in our microsurgical laboratory. Specimens are held in pin-fixation and registered to neuronavigation. Endoscopic endonasal exposure of the occipital condyles (OC) and C1 arch is achieved via an inverted U-shaped nasopharyngeal flap. The plates are then introduced, pilot holes drilled at preplanned entry points, and screws placed under neuronavigation-guidance. The O-C1 articulations are decorticated and autograft is packed into the joint space to facilitate arthrodesis. CT scans are obtained after placement to assess screw placement accuracy and proximity to critical structures. RESULTS Average OC screw starting point was 8.2mm lateral and 4.4mm rostral to the medial O-C1 joint. Average C1 screw starting point was 6.6mm lateral and 8.65mm caudal to the medial O-C1 joint. Average OC screw trajectory in the sagittal and axial plane was 6.12 superior and 8.5 lateral, respectively. Average C1 screw trajectory in the sagittal and axial plane was 13 inferior and 8.1 lateral, respectively. There were no injuries to critical structures. CONCLUSIONS Endonasal instrumented fixation of the occipitocervical junction is both technically and anatomically feasible. Future directions include biomechanical testing. Ultimately, this method of fixation and fusion could serve as an alternative to traditional posterior approaches, and may obviate the need for a separate-staged posterior approach

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