Submandibular approach for single-stage craniovertebral junction ventral decompression and stabilization: a preliminary cadaveric study of technical feasibility

Background The craniovertebral junction (CVJ) may be affected by several diseases. It is an anatomically complex region, involving the osteoligamentous, vascular, and nervous structures, which makes surgery challenging. In a case of ventral compression, an anterior approach is preferable, although posterior fixation is often required. Anterior transmucosal approaches are associated with high rates of complications. However, decompression and fixation by the use of retropharyngeal extramucosal approaches may be challenging. Objective To investigate the feasibility of a single-stage, anterior, extramucosal submandibular (SM) approach modification to the CVJ for simultaneous decompression and stabilization. Introduction The craniovertebral junction (CVJ) is a complex anatomic region where nervous, vascular, and musculoskeletal structures form a unique system. 1 Several pathologic conditions may affect the CVJ, 2-6 resulting in segmental instability and compression of the bulbomedullary junction. Posterior surgical approaches to the CVJ are the most commonly reported because they provide the opportunity to achieve both decompression and fixation. However, in cases of ventral compression, anterior approaches may be more useful, although they usually require specific skills and experience. 7,8 Among the anterior approaches to the CVJ, the transoral (TO) and the endonasal (EN) approaches, with their microsurgical and endoscopic variants, have been widely used. 3,6,9,10 These transmucosal (TM) approaches provide a straightforward surgical corridor along with a wide surgical domain, even though they are related to a higher risk of complications such as infections, cerebrospinal fluid leaks, wound healing problems, perioperative tracheostomy, phonation impairment, and dysphagia. 11 The transcervical retropharyngeal and submandibular (SM) approaches represent extramucosal (EM) alternatives. Since its description by Böhler et al. 12 in 1982, the retropharyngeal approach has been routinely adopted for placement of anterior odontoid screws and anterior atlantoaxial transarticular stabilization. 13 Nonetheless, a contemporary ventral decompression is usually challenging because of the limited working angle, the long distance to the target, the narrow working corridor, and limited surgical exposure. 14,15 By contrast, the SM approach provides wider surgical corridors and working angles, along with a shorter working distance, as reported by Salle et al. 16 The combination of ventral decompression and fixation through an anterior approach has been rarely reported. 14,17,18 In fact, implants positioned through a TM approach could increase the infection rate; thus, a second posterior surgical stage is usually preferred whenever fixation is needed. Ideally, an anterior surgical approach that allows performance of both ventral decompression and stabilization in a single stage, avoiding the complications related to a TM approach and prone position, would be very useful in CVJ surgery. Accordingly, the aim of the present study was to investigate the feasibility of a unilateral modified SM approach for single-stage CVJ anterior decompression and fixation in a cadaveric model. Material and Methods Setting and Instruments The operative sections were conducted at SimLab, Mayo Clinic, Jacksonville, Florida. Two silicon-injected human head specimens were used for this investigation. The institutional review board approved this investigation [IRB00044584]. An operative microscope (Carl Zeiss, Oberkochen, Germany), a high-speed drill (IPC system, Medtronic, Minneapolis, Minnesota, USA), a recording camera with a proper storage device (Karl Storz, Tuttlingen, Germany), a portable fluoroscope (Arcadis, Siemens, Munich, Germany), a computed tomographic service, and standard neurosurgical surgical instruments were available. Surgical Technique: SM Approach to the CVJ The heads were positioned supine in a Mayfield 3-pin holder. To maximize the CVJ visibility during the anteroposterior radiographic projections, a gentle extension was used to improve cervical lordosis, and the mouth was kept open with a radiolucent device.13 Materials and Methods This was a preliminary cadaveric feasibility study on 2 injected specimens. A variation of the SM approach with a short “boomerang” incision, microsurgical decompression of the ventral CVJ, and a new hybrid construct for an anterior atlantoaxial stabilization was investigated. The surgical approach, the decompression, and the instrumentation technique have been described. In addition, intraprocedural images and radiographs and also postprocedural computed tomographic images were collected. Furthermore, surgical exposure, working corridors and angles, and decompression grade were measured. Results The SM approach provided wide exposure of the ventral CVJ and the possibility for instrumentation and decompression by removing the anterior arch of C1 and the odontoid process. Conclusion A single- stage anterior extramucosal SM approach for decompression and stabilization of the CVJ is feasible and could result in shorter surgical duration, avoiding the complications related to both the transmucosal approach and the prone position, although specific related risks exist. Mechanical investigation of this hybrid system and in vivo studies are needed to confirm our results.