This study serves as the first to explicitly describe the anatomy of the esophagus relative to the cervical spine. It illustrates that the least quantity of potential space between the esophagus and the cervical spine occurs in the midline. In terms of laterality, there is significantly more usable space adjacent to the medial edge of the right longus colli. The relationship between the esophagus and spine does not change significantly from the level of the C5 vertebral body to the C7 vertebral body.
Given the relatively high incidence of dysphagia following ACDF any factor which may limit this complication could be potentially beneficial for patients [2
]. Hardware is known to be a contributor to this problem [7
]. Now, with a clear description of the normal anatomy in this region, implants can be designed which will place limited pressure on crucial anterior structures such as the esophagus. With an average distance in the midline of 1.02 to 1.31 mm between the cervical spine and the esophagus, the vast majority of cervical plates available today cause resting pressure on the esophagus. This could potentially contribute to dysphagia. It is anticipated that future hardware designs can incorporate these findings and limit hardware profiles in the midline. By preserving the natural course of the esophagus, it would be anticipated that the incidence of dysphagia could be limited. Much like anterior cervical fusion plates, cervical disc replacements that incorporate anterior flanges or screw fixation may benefit from similar considerations. Given the maintenance of motion with cervical disc replacement and potential frictional effects of hardware on the esophagus, our findings may be even more pertinent to these devices.
The limitations of our study include the fact that we used “normal” patients for analysis. Surgical candidates can often have significant anterior cervical osteophytes and may even present with antero- or retrolisthesis at one or more levels. The osteophytes are typically removed at surgery in order to fully decompress the disc space and to accommodate hardware. These osteophytes are produced over years of the degenerative process, and given that extended time period the surrounding structures have time to accommodate to the mass effect that is created. Hence these osteophytes may not contribute to dysphagia in the un-operated cervical spine. Only after there has been surgical trauma and the edition of a plate do the symptoms of dysphagia manifest. Since osteophyte removal is necessary for plate application, they should not contribute to the ultimate relationship that would be found between the esophagus and the cervical spine following ACDF. Rather our findings, recorded from “normal” patients, would be applicable.
The CT scans were obtained in the supine position. It remains unknown if the position of the esophagus relative to the cervical spine changes in an upright position. This appears unlikely as the supine position via gravity, directs more of a posterior force on the esophagus. Lastly, our study was limited to the levels C5 through C7. Findings at other levels will require further study and cannot be directly extrapolated from this report.
One interesting finding observed in this study, although not specifically measured quantitatively, was the anatomic variability of the esophagus as it descends anterior to the cervical spine. In most cases, the esophagus proper becomes well defined at the level of C6. Above, the cricopharyngeus muscle marks the transition from the hypopharynx to the esophagus. There was some anatomic variance as to the exact level where this transition occurred. This too may contribute to the potential risk or predisposition that any particular patient has in developing dysphagia following ACDF.